Pass the Linux signing key to the release workflow (#2798)

XCLIP and XCLIPFRAME; invert flag as AutoCAD's group 290 (#2354)

.github/workflows/release.yml

@@ -85,3 +85,4 @@ jobs:
       AZURE_SIGNING_ENDPOINT: ${{ secrets.AZURE_SIGNING_ENDPOINT }}
       AZURE_SIGNING_ACCOUNT: ${{ secrets.AZURE_SIGNING_ACCOUNT }}
       AZURE_CERT_PROFILE: ${{ secrets.AZURE_CERT_PROFILE }}
+      LINUX_SIGNING_KEY: ${{ secrets.LINUX_SIGNING_KEY }}

Cargo.lock

@@ -729,6 +729,7 @@ name = "cadcraft-fonts"
 version = "0.17.0"
 dependencies = [
  "cadcraft-geom",
+ "encoding_rs",
  "harfrust 0.14.0",
  "icu_segmenter",
  "skrifa 0.48.0",
@@ -755,6 +756,7 @@ dependencies = [
  "cadcraft-geom",
  "cadcraft-render",
  "craft-pdf",
+ "image",
  "miniz_oxide 0.9.1",
  "quick-xml 0.42.0",
  "serde",
@@ -821,6 +823,7 @@ name = "cadcraft-web"
 version = "0.17.0"
 dependencies = [
  "cadcraft-engine",
+ "cadcraft-fonts",
  "cadcraft-io",
  "cadcraft-ui-egui",
  "eframe",

Cargo.toml

@@ -54,7 +54,7 @@ unicode-bidi = "0.3.18"
 # Line-break opportunities between Thai words for MTEXT word wrap (Thai writes no spaces between
 # words): UAX #14 with ICU4X's compiled-in LSTM word model (not its dictionaries).
 icu_segmenter = { version = "~2.3", default-features = false, features = ["compiled_data", "lstm"] }
-image = { version = "0.25", default-features = false, features = ["png", "jpeg"] }
+image = { version = "0.25", default-features = false, features = ["png", "jpeg", "bmp", "tiff"] }
 encoding_rs = "0.8.35"
 # XML for the SVG reader (streaming parser, no entity expansion beyond the five predefined ones)
 quick-xml = "0.42"

apps/cadcraft-cli/src/lib.rs

@@ -45,6 +45,7 @@ fn install_io() {
         write: |d, name| cadcraft_io::write(d, name).map_err(|e| e.to_string()),
         plot: Some(|d, space, opts| cadcraft_io::plotter::plot(d, space, opts).map_err(|e| e.to_string())),
     });
+    cadcraft_engine::cmd::file::set_image_decoder(|b| cadcraft_io::raster::decode(b).map_err(|e| e.to_string()));
     cadcraft_engine::cmd::file::set_write_as(|d, name, o| {
         cadcraft_io::write_with(d, name, &cadcraft_io::SaveOptions { version: o.version, binary: o.binary }).map_err(|e| e.to_string())
     });

apps/cadcraft-web/Cargo.toml

@@ -18,6 +18,7 @@ path = "src/main.rs"
 cadcraft-engine = { workspace = true }
 cadcraft-ui-egui = { workspace = true }
 cadcraft-io = { workspace = true }
+cadcraft-fonts = { workspace = true }
 egui = { workspace = true }
 log = { workspace = true }
 serde_json = { workspace = true }

apps/cadcraft-web/src/main.rs

@@ -119,6 +119,7 @@ mod web {
             write: |d, name| cadcraft_io::write(d, name).map_err(|e| e.to_string()),
             plot: Some(|d, space, opts| cadcraft_io::plotter::plot(d, space, opts).map_err(|e| e.to_string())),
         });
+        cadcraft_engine::cmd::file::set_image_decoder(|b| cadcraft_io::raster::decode(b).map_err(|e| e.to_string()));
         cadcraft_engine::cmd::file::set_write_as(|d, name, o| {
             cadcraft_io::write_with(d, name, &cadcraft_io::SaveOptions { version: o.version, binary: o.binary }).map_err(|e| e.to_string())
         });

apps/cadcraft-web/src/upload.rs

@@ -2,6 +2,11 @@
 //! a path from, so the picker is a hidden `<input type="file">`; the chosen file (or one dropped on
 //! the page) is read in the background and handed to the app on its next frame, which opens it
 //! with OPEN `{data, name}` ([`CadApp::open_bytes`]).
+//!
+//! SHX fonts (text fonts, big fonts, shape files) chosen or dropped with a drawing are the web
+//! build's font folder: they are registered with the font table
+//! ([`cadcraft_fonts::shx::register`]) under their file name, so the styles and linetypes that
+//! name them draw with them, and the drawings are regenerated.
 
 use std::cell::Cell;
 use std::rc::Rc;
@@ -12,8 +17,14 @@ use web_sys::js_sys;
 
 /// The hidden file input (one at a time; a cancelled pick leaves it until the next one).
 const INPUT_ID: &str = "cadcraft_open_input";
-/// What the picker offers: the formats OPEN reads.
-const ACCEPT: &str = ".dxf,.dwg";
+/// What the picker offers: the formats OPEN reads, and the SHX fonts drawings name.
+const ACCEPT: &str = ".dxf,.dwg,.shx";
+
+/// Most files taken from one pick.
+const MAX_PICKED: u32 = 64;
+/// Most bytes being read at once, all files together: a large pick must not exhaust the page's
+/// memory (each file is copied once more into the app).
+const MAX_READING_BYTES: u64 = 512 << 20;
 
 /// A file read in the browser (name, contents), or why it couldn't be read.
 type Upload = Result<(String, Vec<u8>), String>;
@@ -22,12 +33,14 @@ type Upload = Result<(String, Vec<u8>), String>;
 #[derive(Clone)]
 pub struct Inbox {
     files: Rc<Cell<Vec<Upload>>>,
+    /// Bytes of the files being read now.
+    reading: Rc<Cell<u64>>,
     ctx: egui::Context,
 }
 
 impl Inbox {
     pub fn new(ctx: &egui::Context) -> Self {
-        Inbox { files: Rc::default(), ctx: ctx.clone() }
+        Inbox { files: Rc::default(), reading: Rc::default(), ctx: ctx.clone() }
     }
 
     /// Show the browser's file picker and return at once. A chosen file arrives through
@@ -51,13 +64,23 @@ impl Inbox {
             .map_err(|_| "could not create a file input".to_string())?;
         input.set_type("file");
         input.set_accept(ACCEPT);
+        // A drawing and the fonts it uses can be chosen together.
+        input.set_multiple(true);
         input.set_id(INPUT_ID);
         input.set_attribute("style", "display:none").map_err(js_error)?;
         let (inbox, chosen) = (self.clone(), input.clone());
-        // Called once, when a file was chosen (browsers don't fire `change` on cancel).
+        // Called once, when files were chosen (browsers don't fire `change` on cancel).
         let on_change = wasm_bindgen::closure::Closure::once_into_js(move || {
-            if let Some(file) = chosen.files().and_then(|f| f.get(0)) {
-                inbox.read(file);
+            if let Some(files) = chosen.files() {
+                for i in 0..files.length().min(MAX_PICKED) {
+                    if let Some(file) = files.get(i) {
+                        inbox.read(file);
+                    }
+                }
+                let skipped: Vec<String> = (MAX_PICKED..files.length()).filter_map(|i| files.get(i)).map(|f| f.name()).collect();
+                if !skipped.is_empty() {
+                    inbox.push(Err(format!("Open: at most {MAX_PICKED} files at a time; not opened: {}", skipped.join(", "))));
+                }
             }
             chosen.remove();
         });
@@ -87,12 +110,18 @@ impl Inbox {
         if let Some(e) = CadApp::open_size_error(&name, len) {
             return self.push(Err(e));
         }
+        let reading = self.reading.get();
+        if reading.saturating_add(len) > MAX_READING_BYTES {
+            return self.push(Err(format!("Open: {name} was not read: the files being read together are too large; open it on its own")));
+        }
+        self.reading.set(reading.saturating_add(len));
         let inbox = self.clone();
         wasm_bindgen_futures::spawn_local(async move {
             let r = match wasm_bindgen_futures::JsFuture::from(file.array_buffer()).await {
                 Ok(buf) => Ok((name, js_sys::Uint8Array::new(&buf).to_vec())),
                 Err(e) => Err(format!("Open: could not read {name}: {}", js_error(e))),
             };
+            inbox.reading.set(inbox.reading.get().saturating_sub(len));
             inbox.push(r);
         });
     }
@@ -118,9 +147,21 @@ impl Inbox {
         self.ctx.request_repaint();
     }
 
-    /// Open what arrived since the last frame (or report why it couldn't be read).
+    /// Open what arrived since the last frame (or report why it couldn't be read). Fonts are
+    /// registered first, so drawings opened with them draw with them.
     pub fn drain(&self, app: &mut CadApp) {
-        for upload in self.files.take() {
+        let (fonts, files): (Vec<Upload>, Vec<Upload>) = self.files.take().into_iter().partition(|u| u.as_ref().is_ok_and(|(n, _)| is_shx(n)));
+        let mut registered = false;
+        for (name, bytes) in fonts.into_iter().flatten() {
+            match cadcraft_fonts::shx::register(&name, &bytes) {
+                Ok(()) => registered = true,
+                Err(e) => app.open_failed(format!("{name}: {e}")),
+            }
+        }
+        if registered {
+            let _ = app.run("regenall", serde_json::json!({}));
+        }
+        for upload in files {
             match upload {
                 Ok((name, bytes)) => app.open_bytes(&name, &bytes),
                 Err(e) => app.open_failed(e),
@@ -129,6 +170,11 @@ impl Inbox {
     }
 }
 
+/// Whether `name` is an SHX font or shape file.
+fn is_shx(name: &str) -> bool {
+    name.to_ascii_lowercase().ends_with(".shx")
+}
+
 fn js_error(e: wasm_bindgen::JsValue) -> String {
     e.as_string().unwrap_or_else(|| format!("{e:?}"))
 }

apps/cadcraft/src/main.rs

@@ -146,6 +146,7 @@ pub fn install_io() {
         write: |d, name| cadcraft_io::write(d, name).map_err(|e| e.to_string()),
         plot: Some(|d, space, opts| cadcraft_io::plotter::plot(d, space, opts).map_err(|e| e.to_string())),
     });
+    cadcraft_engine::cmd::file::set_image_decoder(|b| cadcraft_io::raster::decode(b).map_err(|e| e.to_string()));
     cadcraft_engine::cmd::file::set_write_as(|d, name, o| {
         cadcraft_io::write_with(d, name, &cadcraft_io::SaveOptions { version: o.version, binary: o.binary }).map_err(|e| e.to_string())
     });

crates/constraints/src/model.rs

@@ -800,6 +800,7 @@ mod budget_tests {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         }
     }
 

crates/constraints/tests/dof.rs

@@ -302,6 +302,7 @@ fn block_reference_moves_rigidly() {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         }),
     );
     assert_eq!(obj_dof(&d, ins), Some(3));
@@ -343,6 +344,7 @@ fn hostile_new_geometry_never_panics() {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         }),
     );
     let l = line(&mut d, (0.0, 0.0), (0.0, 0.0));

crates/doc/src/array.rs

@@ -228,6 +228,7 @@ impl ArrayParams {
                 rows: 1,
                 col_spacing: 0.0,
                 row_spacing: 0.0,
+                clip: None,
             };
             out.push(Entity { handle: d.new_handle(), common: common.clone(), kind: EntityKind::Insert(ins) });
         }

crates/doc/src/entity/block.rs

@@ -161,6 +161,25 @@ pub struct Insert {
     pub col_spacing: f64,
     #[serde(default)]
     pub row_spacing: f64,
+    /// XCLIP boundary of this reference (other references to the block are not clipped).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub clip: Option<crate::ClipBoundary>,
+}
+impl Default for Insert {
+    fn default() -> Self {
+        Insert {
+            block: String::new(),
+            insert: Vec3::ZERO,
+            scale: unit_scale(),
+            rotation: 0.0,
+            attribs: Vec::new(),
+            cols: 1,
+            rows: 1,
+            col_spacing: 0.0,
+            row_spacing: 0.0,
+            clip: None,
+        }
+    }
 }
 
 fn unit_scale() -> Vec3 {

crates/doc/src/entity/layout.rs

@@ -1,3 +1,5 @@
+use cadcraft_geom::Mat3;
+
 use super::common::Handle;
 use super::{Color, Deserialize, Serialize, Vec2, Vec3, standard, yes};
 
@@ -25,6 +27,39 @@ pub struct Viewport {
     /// Display on (MVIEW ON/OFF). An off viewport shows its border but no model space.
     #[serde(default = "yes")]
     pub on: bool,
+    /// The view twist (DVIEW TWist inside the viewport; DXF group 51): radians counterclockwise,
+    /// the model view seen through the viewport is turned on the sheet by it. 0 is untwisted.
+    #[serde(default, skip_serializing_if = "is_zero_twist")]
+    pub twist: f64,
+}
+fn is_zero_twist(v: &f64) -> bool {
+    *v == 0.0
+}
+impl Viewport {
+    /// The view twist, usable: 0 when it isn't finite.
+    pub fn view_twist(&self) -> f64 {
+        if self.twist.is_finite() { self.twist } else { 0.0 }
+    }
+    /// Paper units per model unit.
+    pub fn scale(&self) -> f64 {
+        self.height / self.view_height
+    }
+    /// Where model point `m` is on the sheet: `center + scale · R(twist)(m − view_center)`.
+    pub fn model_to_paper(&self, m: Vec2) -> Vec2 {
+        self.center.xy() + (m - self.view_center).rotate(self.view_twist()) * self.scale()
+    }
+    /// The model point at sheet point `p` (the inverse of [`Viewport::model_to_paper`]).
+    pub fn paper_to_model(&self, p: Vec2) -> Vec2 {
+        self.view_center + ((p - self.center.xy()) / self.scale()).rotate(-self.view_twist())
+    }
+    /// [`Viewport::model_to_paper`] as a matrix.
+    pub fn model_to_paper_matrix(&self) -> Mat3 {
+        let s = self.scale();
+        Mat3::translate(self.center.xy())
+            .then_before(Mat3::scale(s, s))
+            .then_before(Mat3::rotate(self.view_twist()))
+            .then_before(Mat3::translate(-self.view_center))
+    }
 }
 
 impl Default for Viewport {
@@ -41,6 +76,7 @@ impl Default for Viewport {
             layer_colors: Vec::new(),
             clip: None,
             on: true,
+            twist: 0.0,
         }
     }
 }
@@ -59,8 +95,9 @@ pub struct Image {
     /// The image definition's name (its key in the drawing's image dictionary).
     #[serde(default, skip_serializing_if = "String::is_empty")]
     pub name: String,
-    /// Clip boundary in pixel coordinates (origin at the top-left corner of the image, y down):
-    /// two opposite corners of a rectangle, or a polygon's vertices. Empty: the whole image.
+    /// Clip boundary in pixel coordinates (y down, counted from pixel centres: the centre of the
+    /// top-left pixel is the origin, so the whole image is -0.5 to size - 0.5): two opposite
+    /// corners of a rectangle, or a polygon's vertices. Empty: the whole image.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub clip: Vec<Vec2>,
     /// The clip boundary is applied.

crates/doc/src/extents.rs

@@ -179,6 +179,13 @@ fn bounds_in<'a>(d: &'a Drawing, e: &Entity, depth: usize, blocks: &mut HashMap<
                     }
                 };
                 b = if inner.is_empty() { Bounds2::EMPTY } else { Bounds2::from_points(inner.corners().map(|c| m.apply(c))) };
+                // XCLIP: the reference app takes the boundary's box, also where it reaches past the
+                // block or misses it (an inverted clip can show anything, so it keeps the block's).
+                if let Some(c) = ins.clip.as_ref().filter(|c| c.active() && !c.inverted)
+                    && !b.is_empty()
+                {
+                    b = Bounds2::from_points(c.polygon().into_iter().map(|p| m.apply(p)));
+                }
                 if ins.cols > 1 || ins.rows > 1 {
                     let off =
                         Vec2::new(ins.col_spacing * f64::from(ins.cols.saturating_sub(1)), ins.row_spacing * f64::from(ins.rows.saturating_sub(1)))
@@ -486,6 +493,7 @@ mod tests {
                     rows: 1,
                     col_spacing: 0.0,
                     row_spacing: 0.0,
+                    clip: None,
                 }),
             )
         };

crates/doc/src/lib.rs

@@ -16,9 +16,11 @@ mod header;
 pub mod library;
 mod plotstyle;
 mod plotter;
+mod raster;
 mod refedit;
 mod store;
 mod tables;
+mod xclip;
 
 use std::collections::{BTreeMap, BTreeSet};
 
@@ -33,9 +35,11 @@ pub use gdt::*;
 pub use header::{HVal, Header};
 pub use plotstyle::*;
 pub use plotter::*;
+pub use raster::{Raster, Rasters};
 pub use refedit::{RefEdit, WorkItem};
 pub use store::EntityStore;
 pub use tables::*;
+pub use xclip::{ClipBoundary, MAX_CLIP_VERTICES};
 
 /// File data CADCraft doesn't model, kept for saving (#528).
 pub mod dynblock;
@@ -136,6 +140,8 @@ pub struct Drawing {
     /// for the Linux fonts of text styles, and each style keeps its own in CADCraft xdata, so the
     /// drawing reopens with it. Never set on an open drawing.
     pub portable_fonts: bool,
+    /// The pixels of the raster images that are loaded (IMAGE). Never written to a file.
+    pub rasters: Rasters,
 }
 
 impl Default for Drawing {
@@ -196,6 +202,7 @@ impl Drawing {
             refedit: None,
             skipped_records: BTreeMap::new(),
             portable_fonts: false,
+            rasters: Rasters::default(),
         }
     }
 

crates/doc/src/raster.rs

@@ -0,0 +1,93 @@
+//! Decoded raster image pixels (IMAGE entities). The drawing keeps them for the session only:
+//! they are loaded from the image files after a drawing opens and are never written to a file.
+
+use std::collections::BTreeMap;
+use std::sync::Arc;
+
+/// The pixels of a raster image: 8-bit RGBA, not premultiplied, rows from the top.
+#[derive(Clone, PartialEq)]
+pub struct Raster {
+    width: u32,
+    height: u32,
+    rgba: Vec<u8>,
+    opaque: bool,
+}
+
+impl Raster {
+    /// `None` unless both sides are at least one pixel and `rgba` holds exactly four bytes per pixel.
+    pub fn new(width: u32, height: u32, rgba: Vec<u8>) -> Option<Raster> {
+        let pixels = usize::try_from(width).ok()?.checked_mul(usize::try_from(height).ok()?)?;
+        if pixels == 0 || rgba.len() != pixels.checked_mul(4)? {
+            return None;
+        }
+        let opaque = rgba.as_chunks::<4>().0.iter().all(|[_, _, _, alpha]| *alpha == u8::MAX);
+        Some(Raster { width, height, rgba, opaque })
+    }
+    pub fn width(&self) -> u32 {
+        self.width
+    }
+    pub fn height(&self) -> u32 {
+        self.height
+    }
+    /// Four bytes per pixel (red, green, blue, alpha), `width * height` pixels.
+    pub fn rgba(&self) -> &[u8] {
+        &self.rgba
+    }
+    /// No pixel is transparent.
+    pub fn opaque(&self) -> bool {
+        self.opaque
+    }
+    /// The pixel in column `x` of row `y` (from the top): red, green, blue, alpha.
+    pub fn pixel(&self, x: u32, y: u32) -> Option<[u8; 4]> {
+        if x >= self.width || y >= self.height {
+            return None;
+        }
+        let (x, y, width) = (usize::try_from(x).ok()?, usize::try_from(y).ok()?, usize::try_from(self.width).ok()?);
+        let pixels = self.rgba.as_chunks::<4>().0;
+        pixels.get(y.checked_mul(width)?.checked_add(x)?).copied()
+    }
+}
+
+impl std::fmt::Debug for Raster {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Raster({}x{})", self.width, self.height)
+    }
+}
+
+/// The loaded pixels of a drawing's raster images, by image file path ([`crate::Image::path`]).
+/// Session data: two drawings are equal whatever images they have loaded, and copying a drawing
+/// (undo) shares the pixels.
+#[derive(Clone, Default)]
+pub struct Rasters(Arc<BTreeMap<String, Arc<Raster>>>);
+
+impl Rasters {
+    pub fn get(&self, path: &str) -> Option<&Arc<Raster>> {
+        self.0.get(path)
+    }
+    pub fn insert(&mut self, path: &str, raster: Arc<Raster>) {
+        Arc::make_mut(&mut self.0).insert(path.to_string(), raster);
+    }
+    pub fn remove(&mut self, path: &str) {
+        if self.0.contains_key(path) {
+            Arc::make_mut(&mut self.0).remove(path);
+        }
+    }
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
+impl PartialEq for Rasters {
+    fn eq(&self, _: &Rasters) -> bool {
+        true
+    }
+}
+
+impl std::fmt::Debug for Rasters {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Rasters({})", self.0.len())
+    }
+}

crates/doc/src/tables.rs

@@ -863,7 +863,7 @@ pub struct NamedView {
     /// The layer state restored with the view (its layer snapshot).
     #[serde(default)]
     pub layer_state: Option<String>,
-    /// View twist (radians, counterclockwise); kept for files, not applied to the 2D display.
+    /// View twist (radians, counterclockwise); VIEW Restore applies it to the model space view.
     #[serde(default)]
     pub twist: f64,
     /// The layout a paper space view belongs to (`None`: a model space view; an empty name: a
@@ -884,6 +884,9 @@ pub struct VportTile {
     /// Width / height of the tile on screen when it was saved (0: unknown).
     #[serde(default)]
     pub aspect: f64,
+    /// The tile's view twist (radians, counterclockwise; DXF VPORT group 51 in degrees).
+    #[serde(default)]
+    pub twist: f64,
 }
 
 /// A model space viewport configuration (VPORTS): `*Active` is the one shown, other names are

crates/doc/src/tests.rs

@@ -189,6 +189,7 @@ fn inserts_of_missing_or_empty_blocks_do_not_stretch_extents() {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         })
     };
     d.blocks.insert("Empty".into(), std::sync::Arc::new(Block::new("Empty")));
@@ -242,6 +243,7 @@ fn visible_attributes_of_a_missing_block_still_count() {
                 rows: 1,
                 col_spacing: 0.0,
                 row_spacing: 0.0,
+                clip: None,
             }),
         )
     };
@@ -285,6 +287,7 @@ fn insert_bounds_with_cyclic_block_terminate() {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         }),
     ));
     b.entities.push(Entity::new(Handle(2), line((0.0, 0.0), (1.0, 1.0))));
@@ -303,6 +306,7 @@ fn insert_bounds_with_cyclic_block_terminate() {
                 rows: 1,
                 col_spacing: 0.0,
                 row_spacing: 0.0,
+                clip: None,
             }),
         )
         .unwrap();
@@ -420,6 +424,7 @@ fn plain_insert(block: &str) -> EntityKind {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     })
 }
 

crates/doc/src/xclip.rs

@@ -0,0 +1,85 @@
+//! XCLIP: the clipping boundary of one block or xref reference.
+//!
+//! The boundary is kept in the referenced block's coordinates, so it moves, rotates and scales
+//! with its reference; the block definition and other references to it are untouched. In a file
+//! it is the reference's `ACAD_FILTER` / `SPATIAL` extension-dictionary entry (a SPATIAL_FILTER
+//! object, DXF Reference), read and written by the io crate.
+
+use cadcraft_geom::Vec2;
+use serde::{Deserialize, Serialize};
+
+/// Most boundary vertices a clip keeps (hostile files and parameters are capped to this).
+pub const MAX_CLIP_VERTICES: usize = 4096;
+
+/// A reference's clipping boundary.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ClipBoundary {
+    /// Vertices in the block's coordinates: two opposite corners for a rectangle, three or more
+    /// for a closed polygon (not repeating the first vertex).
+    pub points: Vec<Vec2>,
+    /// Whether clipping is on (XCLIP ON/OFF); an off boundary is kept but nothing is clipped.
+    #[serde(default = "on")]
+    pub enabled: bool,
+    /// Inverted clip: what is inside the boundary is hidden, what is outside shows.
+    #[serde(default)]
+    pub inverted: bool,
+}
+
+fn on() -> bool {
+    true
+}
+
+impl ClipBoundary {
+    /// A boundary from `points` (block coordinates), on and not inverted.
+    pub fn new(points: Vec<Vec2>) -> Self {
+        ClipBoundary { points, enabled: true, inverted: false }
+    }
+
+    /// The closed outline in block coordinates: a rectangle's four corners or the polygon's
+    /// vertices. Empty when the boundary has fewer than two vertices, more than
+    /// [`MAX_CLIP_VERTICES`] or a non-finite one.
+    pub fn polygon(&self) -> Vec<Vec2> {
+        if self.points.len() > MAX_CLIP_VERTICES || !self.points.iter().all(|p| p.is_finite()) {
+            return Vec::new();
+        }
+        match self.points.as_slice() {
+            [a, b] => vec![
+                Vec2::new(a.x.min(b.x), a.y.min(b.y)),
+                Vec2::new(a.x.max(b.x), a.y.min(b.y)),
+                Vec2::new(a.x.max(b.x), a.y.max(b.y)),
+                Vec2::new(a.x.min(b.x), a.y.max(b.y)),
+            ],
+            [_, _, _, ..] => self.points.clone(),
+            _ => Vec::new(),
+        }
+    }
+
+    /// Whether the boundary is a rectangle given by two corners.
+    pub fn is_rectangle(&self) -> bool {
+        self.points.len() == 2
+    }
+
+    /// Whether drawing the reference is clipped by it now (on, with a usable outline).
+    pub fn active(&self) -> bool {
+        self.enabled && self.polygon().len() >= 3
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn rectangle_and_polygon_outlines() {
+        let r = ClipBoundary::new(vec![Vec2::new(2.0, 3.0), Vec2::new(0.0, 0.0)]);
+        assert_eq!(r.polygon(), vec![Vec2::new(0.0, 0.0), Vec2::new(2.0, 0.0), Vec2::new(2.0, 3.0), Vec2::new(0.0, 3.0)]);
+        assert!(r.active() && r.is_rectangle());
+        let bad = ClipBoundary::new(vec![Vec2::new(f64::NAN, 0.0), Vec2::new(1.0, 1.0)]);
+        assert!(bad.polygon().is_empty() && !bad.active());
+        let one = ClipBoundary::new(vec![Vec2::ZERO]);
+        assert!(!one.active());
+        let off = ClipBoundary { enabled: false, ..r };
+        assert!(!off.active());
+    }
+}

crates/engine/src/autosave.rs

@@ -405,10 +405,11 @@ mod native {
     pub fn prune_locks(dir: &Path) {
         let Ok(entries) = std::fs::read_dir(dir) else { return };
         let names: Vec<String> = entries.flatten().take(10_000).map(|e| e.file_name().to_string_lossy().to_string()).collect();
+        // The instances that own autosave files, parsed once rather than once per lock file.
+        let with_files: std::collections::HashSet<&str> = names.iter().filter_map(|f| parse_file_name(f)).map(|(_, i, _)| i).collect();
         for n in &names {
             let Some(instance) = parse_lock_name(n) else { continue };
-            let has_files = names.iter().any(|f| parse_file_name(f).is_some_and(|(_, i, _)| i == instance));
-            if !has_files && !owner_alive(dir, instance) {
+            if !with_files.contains(instance) && !owner_alive(dir, instance) {
                 let _ = std::fs::remove_file(dir.join(n));
             }
         }
@@ -435,7 +436,22 @@ mod native {
         }
         // Create a fresh temporary file exclusively and rename it into place, so a planted
         // `<path>.tmp` symlink in a shared autosave directory cannot redirect the write (CWE-59).
-        crate::atomic_write::write_atomic(Path::new(path), &bytes).map_err(|e| e.to_string())
+        // The file holds unsaved work: owner-only from its creation, whatever the umask.
+        crate::atomic_write::write_atomic_with(Path::new(path), private_mode(), |f| f.write_all(&bytes)).map_err(|e| e.to_string())
+    }
+
+    /// Owner read/write only (`None` where file modes don't exist).
+    fn private_mode() -> Option<std::fs::Permissions> {
+        #[cfg(unix)]
+        return Some(std::os::unix::fs::PermissionsExt::from_mode(0o600));
+        #[cfg(not(unix))]
+        None
+    }
+
+    /// Write this app's lock file at `path` without following a link planted there: the file is
+    /// replaced (exclusive temporary file, then rename), never written through (CWE-59).
+    fn write_lock(path: &Path, id: u32) -> std::io::Result<()> {
+        crate::atomic_write::write_atomic_with(path, private_mode(), |f| f.write_all(id.to_string().as_bytes()))
     }
 
     impl Autosaver {
@@ -586,7 +602,7 @@ mod native {
             for (held, file) in &self.locks {
                 let refreshed = match file {
                     Some(file) => file.set_modified(SystemTime::now()),
-                    None => std::fs::write(held, id.to_string()),
+                    None => write_lock(held, id),
                 };
                 if held == path {
                     current = Some(refreshed);
@@ -595,10 +611,22 @@ mod native {
             if let Some(refreshed) = current {
                 return refreshed;
             }
-            let mut file = OpenOptions::new().write(true).create(true).truncate(false).open(path)?;
+            let mut options = OpenOptions::new();
+            options.write(true).create(true).truncate(false);
+            #[cfg(unix)]
+            {
+                use std::os::unix::fs::OpenOptionsExt;
+                // A symlink planted at the lock path must not be opened (and truncated) through,
+                // nor a FIFO wait for a reader.
+                options.custom_flags(libc::O_NOFOLLOW | libc::O_NONBLOCK).mode(0o600);
+            }
+            let mut file = options.open(path)?;
+            if !file.metadata()?.is_file() {
+                return Err(std::io::Error::new(std::io::ErrorKind::InvalidInput, "the lock file is not a plain file"));
+            }
             if file.try_lock().is_err() {
                 self.locks.push((path.to_path_buf(), None));
-                return std::fs::write(path, id.to_string());
+                return write_lock(path, id);
             }
             file.set_len(0)?;
             file.write_all(format!("{id}{LOCK_HELD}").as_bytes())?;
@@ -627,6 +655,30 @@ mod native {
             }
         }
     }
+
+    #[cfg(all(test, unix))]
+    mod tests {
+        use super::*;
+
+        /// A symlink planted at the lock path is neither opened through nor written through.
+        #[test]
+        fn lock_writes_do_not_follow_a_planted_link() {
+            let dir = std::env::temp_dir().join(format!("cadcraft-lock-link-{}", std::process::id()));
+            std::fs::create_dir_all(&dir).unwrap();
+            let victim = dir.join("victim.txt");
+            std::fs::write(&victim, b"precious").unwrap();
+            let link = dir.join("1-a.lock");
+            std::os::unix::fs::symlink(&victim, &link).unwrap();
+            let mut a = Autosaver::new("1-a");
+            assert!(a.refresh_lock(&link).is_err());
+            assert_eq!(std::fs::read(&victim).unwrap(), b"precious");
+            write_lock(&link, 42).unwrap();
+            assert_eq!(std::fs::read(&victim).unwrap(), b"precious");
+            assert!(!std::fs::symlink_metadata(&link).unwrap().file_type().is_symlink());
+            assert_eq!(std::fs::read(&link).unwrap(), b"42");
+            std::fs::remove_dir_all(dir).unwrap();
+        }
+    }
 }
 
 #[cfg(test)]

crates/engine/src/cmd.rs

@@ -18,6 +18,7 @@ mod gripcmds;
 mod griphot;
 pub(crate) mod groups;
 pub(crate) mod hatch;
+mod image;
 mod inquiry;
 mod layer;
 mod layout;
@@ -200,6 +201,7 @@ pub fn command_specs() -> &'static [CommandSpec] {
         v.extend(layer::specs());
         v.extend(layout::specs());
         v.extend(exchange::specs());
+        v.extend(image::specs());
         v.extend(props::specs());
         v.extend(inquiry::specs());
         v.extend(settings::specs());

crates/engine/src/cmd/array.rs

@@ -159,6 +159,7 @@ pub(crate) fn make_assoc(s: &mut Session, objs: &[Handle], base: Vec2, mut p: Ar
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     }))
 }
 

crates/engine/src/cmd/blocks.rs

@@ -25,6 +25,7 @@ mod dyngrip;
 mod extract;
 pub(crate) mod refedit;
 mod wblock;
+mod xclip;
 
 pub fn specs() -> Vec<CommandSpec> {
     vec![
@@ -92,6 +93,7 @@ pub fn specs() -> Vec<CommandSpec> {
     .chain(attribs::attdisp_menu_specs())
     .chain(xref::specs())
     .chain(refedit::specs())
+    .chain(xclip::specs())
     .chain(bedit::specs())
     .collect()
 }
@@ -228,6 +230,7 @@ fn insert_entity(blk: &Block, at: Vec2, scale: Vec3, rotation: f64, base: Option
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     };
     if let Some(b) = base {
         let landed = ins.transform(blk.base.xy()).apply(b);

crates/engine/src/cmd/blocks/xclip.rs

@@ -0,0 +1,484 @@
+//! XCLIP and XCLIPFRAME: clip block and xref references to a boundary.
+//!
+//! A boundary belongs to one reference ([`cadcraft_doc::Insert::clip`]), in the block's own
+//! coordinates, so it moves, rotates and scales with the reference and other references of the
+//! block stay whole. It is a rectangle, a polygon or the outline of a closed polyline, can hide
+//! what is inside instead of what is outside (Invert clip), and can be turned off, deleted or
+//! turned into a polyline. Clip depth (front and back clipping planes) has no meaning in a 2D
+//! drawing and is ignored. XCLIPFRAME says whether the boundary is drawn and plotted.
+
+use cadcraft_doc::{ClipBoundary, EntityKind, Handle, MAX_CLIP_VERTICES};
+use cadcraft_geom::{PolyVertex, Vec2};
+use serde_json::{Value, json};
+
+use super::super::machines::{SelOutcome, SelectPhase};
+use crate::cmd::{CommandSpec, bad, bool_or, has_doc, point_value, str_param, targets};
+use crate::{Accept, Input, Interactive, Prompt, Result, Session, Step};
+
+pub(super) fn specs() -> Vec<CommandSpec> {
+    vec![
+        CommandSpec::new("xclip", "Clip Xref", run)
+            .menu(&["Modify", "Clip", "Xref"])
+            .alias(&["xc"])
+            .params("{handles? | handle? (block or xref references, default the selection), option?: new|on|off|delete|polyline|clipdepth|query (default new with a boundary, else query), rectangle?: [[x,y],[x,y]] | points?: [[x,y],…] (3 to 4096, drawing coordinates) | polyline?: handle of a closed polyline, invert?: bool (hide what is inside)} → {handles, option} (query: {clips: [{handle, boundary, enabled, inverted}]}; polyline: {polylines})")
+            .enabled(has_doc)
+            .interactive(|_| Ok(Box::new(XclipM::default()))),
+        CommandSpec::new("xclipframe", "Xref Clip Frame", run_frame)
+            .params("{value?: 0 (frames hidden) | 1 (shown and plotted) | 2 (shown, not plotted; the default)} → {XCLIPFRAME}")
+            .enabled(has_doc)
+            .interactive(|_| Ok(Box::new(FrameM))),
+    ]
+}
+
+/// The block references among `hs` (other objects are ignored, as XCLIP's selection does).
+fn references(s: &Session, hs: &[Handle]) -> Vec<Handle> {
+    let Ok(d) = s.doc() else { return Vec::new() };
+    hs.iter().copied().filter(|h| d.entity(*h).is_some_and(|e| matches!(e.kind, EntityKind::Insert(_)))).collect()
+}
+
+/// A rectangle's two corners as a closed outline.
+fn rectangle(a: Vec2, b: Vec2) -> Vec<Vec2> {
+    vec![
+        Vec2::new(a.x.min(b.x), a.y.min(b.y)),
+        Vec2::new(a.x.max(b.x), a.y.min(b.y)),
+        Vec2::new(a.x.max(b.x), a.y.max(b.y)),
+        Vec2::new(a.x.min(b.x), a.y.max(b.y)),
+    ]
+}
+
+/// The boundary a JSON call gives, in drawing coordinates, and whether it is a rectangle.
+fn world_boundary(s: &Session, p: &Value) -> Result<(Vec<Vec2>, bool)> {
+    if let Some(r) = p.get("rectangle") {
+        let pts: Vec<Vec2> = r.as_array().map(|a| a.iter().filter_map(point_value).collect()).unwrap_or_default();
+        let [a, b] = pts.as_slice() else { return Err(bad("xclip", "`rectangle` needs two finite corners [[x,y],[x,y]]")) };
+        if (a.x - b.x).abs() <= 1e-12 || (a.y - b.y).abs() <= 1e-12 {
+            return Err(bad("xclip", "the clipping rectangle must have a width and a height"));
+        }
+        return Ok((vec![*a, *b], true));
+    }
+    if let Some(v) = p.get("polyline") {
+        let h = v
+            .as_str()
+            .and_then(Handle::parse_hex)
+            .or_else(|| v.as_u64().map(Handle))
+            .ok_or_else(|| bad("xclip", "`polyline` must be an object handle"))?;
+        let d = s.doc()?;
+        let e = d.entity(h).ok_or_else(|| bad("xclip", format!("no object {}", h.hex())))?;
+        let closed = matches!(&e.kind, EntityKind::LwPolyline(pl) if pl.closed) || matches!(&e.kind, EntityKind::Polyline3d(pl) if pl.closed);
+        if !closed {
+            return Err(bad("xclip", "select a closed polyline"));
+        }
+        let pts = cadcraft_render::clip::boundary_polygon(&e.kind).ok_or_else(|| bad("xclip", "the polyline does not enclose an area"))?;
+        return Ok((pts, false));
+    }
+    let pts = p.get("points").and_then(Value::as_array).ok_or_else(|| bad("xclip", "a boundary is required: `rectangle`, `points` or `polyline`"))?;
+    if !(3..=MAX_CLIP_VERTICES).contains(&pts.len()) {
+        return Err(bad("xclip", format!("a polygonal boundary needs 3 to {MAX_CLIP_VERTICES} points")));
+    }
+    let pts: Vec<Vec2> =
+        pts.iter().map(|v| point_value(v).ok_or_else(|| bad("xclip", "every boundary point must be a finite [x, y]"))).collect::<Result<_>>()?;
+    Ok((pts, false))
+}
+
+fn run(s: &mut Session, p: &Value) -> Result<Value> {
+    let hs = references(s, &targets(s, p)?);
+    if hs.is_empty() {
+        return Err(bad("xclip", "select block or xref references"));
+    }
+    let has_boundary = ["rectangle", "points", "polyline"].iter().any(|k| p.get(*k).is_some());
+    let option = str_param(p, "option").map(str::to_ascii_lowercase).unwrap_or_else(|| if has_boundary { "new".into() } else { "query".into() });
+    match option.as_str() {
+        "new" | "n" => {
+            let (world, rect) = world_boundary(s, p)?;
+            let outline = if rect { world.first().zip(world.get(1)).map(|(a, b)| rectangle(*a, *b)).unwrap_or_default() } else { world.clone() };
+            if cadcraft_render::clip::PolyClip::new(&outline).is_none() {
+                return Err(bad("xclip", "the clipping boundary encloses no area"));
+            }
+            let invert = bool_or(p, "invert", false);
+            let mut clips = Vec::with_capacity(hs.len());
+            {
+                let d = s.doc()?;
+                for h in &hs {
+                    let Some(EntityKind::Insert(ins)) = d.entity(*h).map(|e| &e.kind) else { continue };
+                    let base = d.block(&ins.block).map(|b| b.base.xy()).ok_or_else(|| bad("xclip", format!("block \"{}\" is missing", ins.block)))?;
+                    let inv = ins.transform(base).inverse().ok_or_else(|| bad("xclip", "a reference with a zero scale can't be clipped"))?;
+                    let points: Vec<Vec2> = world.iter().map(|q| inv.apply(*q)).collect();
+                    // A rotated or skewed reference sees the rectangle as a polygon.
+                    let r = ins.rotation.rem_euclid(std::f64::consts::FRAC_PI_2);
+                    let square = r < 1e-9 || std::f64::consts::FRAC_PI_2 - r < 1e-9;
+                    let points = if rect && !square { outline.iter().map(|q| inv.apply(*q)).collect() } else { points };
+                    clips.push((*h, ClipBoundary { points, enabled: true, inverted: invert }));
+                }
+            }
+            for (h, c) in clips {
+                set_clip(s, h, Some(c))?;
+            }
+        }
+        "on" | "off" => {
+            let on = option == "on";
+            // Every reference is checked before any changes: an error leaves the drawing as it was.
+            let d = s.doc()?;
+            if !hs.iter().all(|h| matches!(d.entity(*h).map(|e| &e.kind), Some(EntityKind::Insert(i)) if i.clip.is_some())) {
+                return Err(bad("xclip", "no clipping boundary on the selected reference"));
+            }
+            // Only the flag changes, once per reference (a selection may name one many times).
+            let mut seen = std::collections::HashSet::new();
+            for h in hs.iter().filter(|h| seen.insert(**h)) {
+                s.doc_mut()?
+                    .modify_entity(*h, |e| {
+                        if let EntityKind::Insert(i) = &mut e.kind
+                            && let Some(c) = &mut i.clip
+                        {
+                            c.enabled = on;
+                        }
+                    })
+                    .map_err(|e| bad("xclip", e.to_string()))?;
+            }
+        }
+        "delete" | "d" => {
+            for h in &hs {
+                set_clip(s, *h, None)?;
+            }
+        }
+        "polyline" | "p" | "generate" => {
+            let mut made = Vec::new();
+            for h in &hs {
+                let Some(world) = world_outline(s, *h) else { continue };
+                let vertices = world.into_iter().map(|p| PolyVertex { p, bulge: 0.0, start_width: 0.0, end_width: 0.0 }).collect();
+                let pl = cadcraft_doc::LwPolyline { vertices, closed: true, const_width: 0.0, elevation: 0.0, plinegen: false };
+                made.push(s.add_entity(EntityKind::LwPolyline(pl))?.hex());
+            }
+            if made.is_empty() {
+                return Err(bad("xclip", "no clipping boundary on the selected references"));
+            }
+            return Ok(json!({ "handles": hexes(&hs), "option": "polyline", "polylines": made }));
+        }
+        // Front and back clipping planes have no meaning in 2D: nothing changes.
+        "clipdepth" | "c" => return Ok(json!({ "handles": hexes(&hs), "option": "clipdepth", "ignored": true })),
+        "query" | "?" => {
+            let clips: Vec<Value> = hs
+                .iter()
+                .map(|h| {
+                    let c = clip_of(s, *h);
+                    json!({
+                        "handle": h.hex(),
+                        "boundary": world_outline(s, *h).map(|w| w.iter().map(|p| [p.x, p.y]).collect::<Vec<_>>()),
+                        "enabled": c.as_ref().is_some_and(|c| c.enabled),
+                        "inverted": c.as_ref().is_some_and(|c| c.inverted),
+                    })
+                })
+                .collect();
+            return Ok(json!({ "clips": clips }));
+        }
+        o => return Err(bad("xclip", format!("unknown option \"{o}\" (new, on, off, delete, polyline, clipdepth or query)"))),
+    }
+    Ok(json!({ "handles": hexes(&hs), "option": option }))
+}
+
+fn hexes(hs: &[Handle]) -> Vec<String> {
+    hs.iter().map(|h| h.hex()).collect()
+}
+
+fn clip_of(s: &Session, h: Handle) -> Option<ClipBoundary> {
+    match &s.doc().ok()?.entity(h)?.kind {
+        EntityKind::Insert(i) => i.clip.clone(),
+        _ => None,
+    }
+}
+
+/// Reference `h`'s boundary outline in drawing coordinates.
+fn world_outline(s: &Session, h: Handle) -> Option<Vec<Vec2>> {
+    let d = s.doc().ok()?;
+    let EntityKind::Insert(i) = &d.entity(h)?.kind else { return None };
+    let c = i.clip.as_ref()?;
+    let m = i.transform(d.block(&i.block)?.base.xy());
+    let poly = c.polygon();
+    (poly.len() >= 3).then(|| poly.into_iter().map(|p| m.apply(p)).collect())
+}
+
+fn set_clip(s: &mut Session, h: Handle, c: Option<ClipBoundary>) -> Result<()> {
+    s.doc_mut()?
+        .modify_entity(h, |e| {
+            if let EntityKind::Insert(i) = &mut e.kind {
+                i.clip = c;
+            }
+        })
+        .map_err(|e| bad("xclip", e.to_string()))
+}
+
+// ---------------- XCLIPFRAME ----------------
+
+fn run_frame(s: &mut Session, p: &Value) -> Result<Value> {
+    let v = match p.get("value").or_else(|| p.get("XCLIPFRAME")) {
+        None | Some(Value::Null) => return Ok(json!({ "XCLIPFRAME": s.doc()?.header.i64("XCLIPFRAME", 2) })),
+        Some(v) => v.as_i64().or_else(|| v.as_str().and_then(|t| t.trim().parse().ok())),
+    };
+    let v = v.filter(|v| (0..=2).contains(v)).ok_or_else(|| bad("xclipframe", "`value` must be 0, 1 or 2"))?;
+    s.doc_mut()?.header.set_i64("XCLIPFRAME", v);
+    Ok(json!({ "XCLIPFRAME": v }))
+}
+
+struct FrameM;
+
+impl Interactive for FrameM {
+    fn name(&self) -> &'static str {
+        "XCLIPFRAME"
+    }
+    fn prompt(&self, s: &Session) -> Prompt {
+        let cur = s.doc().map(|d| d.header.i64("XCLIPFRAME", 2)).unwrap_or(2);
+        Prompt::new("Enter new value for XCLIPFRAME", Accept::TEXT).kw(&["0", "1", "2"]).default(cur.to_string())
+    }
+    fn input(&mut self, s: &mut Session, i: Input) -> Result<Step> {
+        let t = match i {
+            Input::Cancel => return Ok(Step::Cancel),
+            Input::Enter => return Ok(Step::Done),
+            Input::Text(t) | Input::Keyword(t) => t,
+            _ => return Ok(Step::Continue),
+        };
+        match run_frame(s, &json!({ "value": t.trim() })) {
+            Ok(_) => Ok(Step::Done),
+            Err(_) => {
+                s.echo("Requires an integer between 0 and 2.");
+                Ok(Step::Continue)
+            }
+        }
+    }
+}
+
+// ---------------- interactive XCLIP ----------------
+
+#[derive(Default, Clone, Copy, PartialEq, Eq)]
+enum Stage {
+    #[default]
+    Select,
+    Option,
+    DeleteOld,
+    Boundary,
+    Corner1,
+    Corner2,
+    Polygon,
+    Polyline,
+}
+
+#[derive(Default)]
+struct XclipM {
+    stage: Stage,
+    sel: SelectPhase,
+    refs: Vec<Handle>,
+    invert: bool,
+    pts: Vec<Vec2>,
+}
+
+impl XclipM {
+    fn selected(&mut self, s: &mut Session, hs: &[Handle]) -> Result<Step> {
+        self.refs = references(s, hs);
+        if self.refs.is_empty() {
+            s.echo("No block or xref references selected.");
+            return Ok(Step::Done);
+        }
+        self.stage = Stage::Option;
+        Ok(Step::Continue)
+    }
+
+    fn apply(&mut self, s: &mut Session, mut p: Value) -> Result<Step> {
+        p["handles"] = json!(hexes(&self.refs));
+        let r = run(s, &p);
+        s.set_selection(Vec::new());
+        match r {
+            Ok(_) => Ok(Step::Done),
+            Err(e) => {
+                s.echo(e.to_string());
+                Ok(Step::Done)
+            }
+        }
+    }
+
+    /// Delete: as the reference app, with nothing to delete it says so and asks again.
+    fn delete(&mut self, s: &mut Session) -> Result<Step> {
+        if !self.any_clipped(s) {
+            s.echo("No clip boundary found.");
+            return Ok(Step::Continue);
+        }
+        self.apply(s, json!({ "option": "delete" }))
+    }
+
+    fn any_clipped(&self, s: &Session) -> bool {
+        self.refs.iter().any(|h| clip_of(s, *h).is_some())
+    }
+}
+
+fn kw(i: &Input) -> Option<String> {
+    match i {
+        Input::Keyword(k) | Input::Text(k) => Some(k.trim().to_ascii_lowercase()),
+        _ => None,
+    }
+}
+
+impl Interactive for XclipM {
+    fn name(&self) -> &'static str {
+        "XCLIP"
+    }
+
+    fn begin(&mut self, s: &mut Session) -> Result<Step> {
+        self.sel = SelectPhase::begin(s);
+        if self.sel.done {
+            let hs = self.sel.picked.clone();
+            return self.selected(s, &hs);
+        }
+        Ok(Step::Continue)
+    }
+
+    fn prompt(&self, _s: &Session) -> Prompt {
+        match self.stage {
+            Stage::Select => self.sel.prompt(),
+            Stage::Option => Prompt::new("Enter clipping option", Accept::TEXT)
+                .kw(&["ON", "OFF", "Clipdepth", "Delete", "generate Polyline", "New boundary"])
+                .default("New"),
+            Stage::DeleteOld => Prompt::new("Delete old boundary(s)?", Accept::TEXT).kw(&["Yes", "No"]).default("Yes"),
+            Stage::Boundary => Prompt::new("Specify clipping boundary or select invert option", Accept::POINT)
+                .kw(&["Select polyline", "Polygonal", "Rectangular", "Invert clip"])
+                .default("Rectangular"),
+            Stage::Corner1 => Prompt::new("Specify first corner", Accept::POINT),
+            Stage::Corner2 => {
+                let p = Prompt::new("Specify opposite corner", Accept::POINT);
+                match self.pts.first() {
+                    Some(a) => p.corner(*a),
+                    None => p,
+                }
+            }
+            Stage::Polygon => {
+                let msg = if self.pts.is_empty() { "Specify first point" } else { "Specify next point" };
+                let p = Prompt::new(msg, Accept::POINT).base_opt(self.pts.last().copied());
+                if self.pts.is_empty() { p } else { p.kw(&["Undo"]) }
+            }
+            Stage::Polyline => Prompt::new("Select polyline", Accept::SELECT),
+        }
+    }
+
+    fn input(&mut self, s: &mut Session, i: Input) -> Result<Step> {
+        if matches!(i, Input::Cancel) {
+            return Ok(Step::Cancel);
+        }
+        match self.stage {
+            Stage::Select => match self.sel.feed(s, &i)? {
+                SelOutcome::More => Ok(Step::Continue),
+                SelOutcome::Empty => Ok(Step::Done),
+                SelOutcome::Done(hs) => self.selected(s, &hs),
+            },
+            Stage::Option => {
+                let k = if matches!(i, Input::Enter) { Some("new".to_string()) } else { kw(&i) };
+                match k.as_deref() {
+                    Some("on") => self.apply(s, json!({ "option": "on" })),
+                    Some("off") => self.apply(s, json!({ "option": "off" })),
+                    Some(k) if k.starts_with('c') => {
+                        s.echo("Clip depth does not apply to a 2D drawing: front and back clipping planes are ignored.");
+                        Ok(Step::Done)
+                    }
+                    Some(k) if k.starts_with('d') => self.delete(s),
+                    Some(k) if k.starts_with('p') || k.starts_with('g') => self.apply(s, json!({ "option": "polyline" })),
+                    Some(k) if k.starts_with('n') => {
+                        self.stage = if self.any_clipped(s) { Stage::DeleteOld } else { Stage::Boundary };
+                        Ok(Step::Continue)
+                    }
+                    _ => {
+                        s.echo("Invalid option keyword.");
+                        Ok(Step::Continue)
+                    }
+                }
+            }
+            Stage::DeleteOld => match kw(&i).as_deref() {
+                None if matches!(i, Input::Enter) => {
+                    self.stage = Stage::Boundary;
+                    Ok(Step::Continue)
+                }
+                Some(k) if k.starts_with('y') => {
+                    self.stage = Stage::Boundary;
+                    Ok(Step::Continue)
+                }
+                Some(k) if k.starts_with('n') => Ok(Step::Done),
+                _ => Ok(Step::Continue),
+            },
+            Stage::Boundary => match (&i, kw(&i).as_deref()) {
+                (Input::Enter, _) => {
+                    self.stage = Stage::Corner1;
+                    Ok(Step::Continue)
+                }
+                (Input::Point(p), _) => {
+                    // A point starts the default rectangle.
+                    self.pts = vec![*p];
+                    self.stage = Stage::Corner2;
+                    Ok(Step::Continue)
+                }
+                (_, Some(k)) if k.starts_with('i') => {
+                    self.invert = !self.invert;
+                    s.echo(if self.invert {
+                        "Inside mode - Objects inside boundary will be hidden."
+                    } else {
+                        "Outside mode - Objects outside boundary will be hidden."
+                    });
+                    Ok(Step::Continue)
+                }
+                (_, Some(k)) if k.starts_with('s') => {
+                    self.stage = Stage::Polyline;
+                    Ok(Step::Continue)
+                }
+                (_, Some(k)) if k.starts_with('p') => {
+                    self.pts.clear();
+                    self.stage = Stage::Polygon;
+                    Ok(Step::Continue)
+                }
+                (_, Some(k)) if k.starts_with('r') => {
+                    self.stage = Stage::Corner1;
+                    Ok(Step::Continue)
+                }
+                _ => Ok(Step::Continue),
+            },
+            Stage::Corner1 => match i {
+                Input::Point(p) => {
+                    self.pts = vec![p];
+                    self.stage = Stage::Corner2;
+                    Ok(Step::Continue)
+                }
+                _ => Ok(Step::Continue),
+            },
+            Stage::Corner2 => match (i, self.pts.first().copied()) {
+                (Input::Point(b), Some(a)) => self.apply(s, json!({ "option": "new", "rectangle": [[a.x, a.y], [b.x, b.y]], "invert": self.invert })),
+                _ => Ok(Step::Continue),
+            },
+            Stage::Polygon => match i {
+                Input::Point(p) if self.pts.len() < MAX_CLIP_VERTICES => {
+                    self.pts.push(p);
+                    Ok(Step::Continue)
+                }
+                Input::Point(_) => {
+                    s.echo(format!("A boundary has at most {MAX_CLIP_VERTICES} points."));
+                    Ok(Step::Continue)
+                }
+                Input::Keyword(_) | Input::Text(_) => {
+                    self.pts.pop();
+                    Ok(Step::Continue)
+                }
+                Input::Enter if self.pts.len() >= 3 => {
+                    let pts: Vec<[f64; 2]> = self.pts.iter().map(|p| [p.x, p.y]).collect();
+                    self.apply(s, json!({ "option": "new", "points": pts, "invert": self.invert }))
+                }
+                Input::Enter => {
+                    s.echo("A polygonal boundary needs at least three points.");
+                    Ok(Step::Continue)
+                }
+                _ => Ok(Step::Continue),
+            },
+            Stage::Polyline => match i {
+                Input::Pick(hs) => match hs.first() {
+                    Some(h) => {
+                        let h = *h;
+                        self.apply(s, json!({ "option": "new", "polyline": h.hex(), "invert": self.invert }))
+                    }
+                    None => Ok(Step::Continue),
+                },
+                Input::Enter => Ok(Step::Done),
+                _ => Ok(Step::Continue),
+            },
+        }
+    }
+}

crates/engine/src/cmd/blocks/xref.rs

@@ -62,11 +62,20 @@ pub(crate) fn after_open(s: &mut Session, i: usize) {
     st.saved = st.doc.clone();
     let ext = st.doc.extents(&cadcraft_doc::Space::Model);
     if !ext.is_empty() {
-        st.set_view_quiet(crate::View { center: ext.center(), height: (ext.height().max(ext.width() * px.1 / px.0.max(1.0)) * 1.1).max(1e-6) });
+        // Fit in the frame of the saved twist, which open_drawing has restored.
+        let twist = st.view().twist;
+        let (center, w, h) = crate::View::twisted_box(ext, twist);
+        st.set_view_quiet(crate::View { center, height: (h.max(w * px.1 / px.0.max(1.0)) * 1.1).max(1e-6), twist });
     }
     echo_all(s, &out);
 }
 
+/// The file a reference saved as `path` in a drawing at `host` is read from, if there is one
+/// (xrefs and raster images look in the same places).
+pub(crate) fn find_file(path: &str, host: Option<&str>) -> Option<std::path::PathBuf> {
+    load::find(path, host.map(std::path::Path::new), false).ok()
+}
+
 /// The open drawing's path (xref paths are relative to its folder).
 fn host(s: &Session) -> Option<String> {
     s.state().ok().and_then(|st| st.path.clone())

crates/engine/src/cmd/exchange.rs

@@ -55,11 +55,11 @@ pub fn specs() -> Vec<CommandSpec> {
             .alias(&["printpdf", "pdfb"])
             .params("{path?: \"DIR/NAME^NAME2.pdf\" (default: the drawing's file; a `^` splits the name into one book name per row of frames; else returns base64 `data` per book), names?: [book names], frameHeight?: mm (default 297), unit?: mm per drawing unit (default 1)} → {books: [{name, pages, bytes, path? | data}], skipped}: closed polylines of the frame height in model space are sheet frames; each row (same lower edge, bottom to top) is one PDF, its frames left to right one page each on the paper (ISO A-series, either orientation) they match")
             .noundo(),
-        CommandSpec::new("attach", "Attach", |_, _| {
-            Err(EngineError::Other("ATTACH is not available yet: raster images and PDF/DWF/DGN underlays can't be shown yet".into()))
+        CommandSpec::new("attach", "Attach", |s, p| match str_param(p, "path").map(extension) {
+            Some(e) if super::image::is_image_ext(&e) => super::image::run_imageattach(s, p),
+            _ => Err(EngineError::Other("ATTACH is not available yet for this file: only raster images (PNG, JPEG, BMP, TIFF; see IMAGEATTACH) can be attached, PDF/DWF/DGN underlays can't be shown yet".into())),
         })
-        .params("not available yet")
-        .noundo(),
+        .params("{path: image file, …} as IMAGEATTACH; other file types are not available yet"),
         CommandSpec::new("share", "Share", |_, _| {
             Err(EngineError::Other("SHARE is not available yet: there is no online service to share through; EXPORT or PUBLISH the drawing and send the file".into()))
         })
@@ -642,6 +642,7 @@ mod tests {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         })
     }
 

crates/engine/src/cmd/file.rs

@@ -70,6 +70,19 @@ pub fn entity_codec() -> Option<&'static EntityCodec> {
 /// COMPARE (drawing comparison).
 pub mod compare;
 
+/// Decode a raster image file (PNG, JPEG, BMP, TIFF) to pixels: installed by the app with the
+/// image reader, a lower layer.
+pub type ImageHook = fn(&[u8]) -> std::result::Result<cadcraft_doc::Raster, String>;
+
+static IMAGE: OnceLock<ImageHook> = OnceLock::new();
+
+pub fn set_image_decoder(h: ImageHook) {
+    let _ = IMAGE.set(h);
+}
+pub fn image_decoder() -> Option<ImageHook> {
+    IMAGE.get().copied()
+}
+
 /// Hand finished file bytes to the user where there is no file system (the browser: a download).
 /// Arguments: file name, MIME type, bytes. `Ok` only once the delivery was actually started.
 pub type DeliverHook = fn(&str, &str, &[u8]) -> std::result::Result<(), String>;
@@ -311,6 +324,7 @@ pub fn finish_open(s: &mut Session, f: ReadFile) -> Result<Value> {
     let ReadFile { drawing, binary_dxf, name, path } = f;
     let i = add_read(s, drawing, binary_dxf, &name, path);
     super::blocks::xref::after_open(s, i);
+    super::image::after_open(s, i);
     Ok(opened(s, i, true))
 }
 
@@ -320,6 +334,12 @@ fn read_bytes(bytes: &[u8], name: &str, path: Option<String>) -> Result<ReadFile
     // A file that isn't a drawing (an imported SVG) gives the drawing no file name: QSAVE then
     // asks where to save instead of exporting over the original.
     let path = path.filter(|p| is_drawing_file(p));
+    // The SHX fonts its text styles name are looked for beside the drawing too.
+    if let Some(dir) = path.as_deref().and_then(|p| std::path::Path::new(p).parent()) {
+        // A bare file name is in the current folder.
+        let dir = if dir.as_os_str().is_empty() { std::path::Path::new(".") } else { dir };
+        cadcraft_fonts::shx::add_drawing_dir(&std::path::absolute(dir).unwrap_or_else(|_| dir.to_path_buf()));
+    }
     Ok(ReadFile { drawing, binary_dxf: cadcraft_dxf::is_binary(bytes), name: name.to_string(), path })
 }
 
@@ -363,6 +383,7 @@ fn run_open(s: &mut Session, p: &Value) -> Result<Value> {
                 crate::capped_read::read_capped(std::path::Path::new(path), MAX_DRAWING_BYTES).map_err(|e| bad("open", format!("{path}: {e}")))?;
             let i = open_bytes(s, &bytes, path, Some(path.to_string()))?;
             super::blocks::xref::after_open(s, i);
+            super::image::after_open(s, i);
             return Ok(opened(s, i, true));
         }
         #[cfg(target_arch = "wasm32")]
@@ -373,6 +394,7 @@ fn run_open(s: &mut Session, p: &Value) -> Result<Value> {
     let name = str_param(p, "name").unwrap_or("Drawing.dxf");
     let i = open_bytes(s, &bytes, name, None)?;
     super::blocks::xref::after_open(s, i);
+    super::image::after_open(s, i);
     Ok(opened(s, i, false))
 }
 

crates/engine/src/cmd/file/template.rs

@@ -59,7 +59,8 @@ pub(super) fn run_new(s: &mut Session, p: &Value) -> Result<Option<Value>> {
         && hi.y > lo.y
     {
         let center = cadcraft_geom::Vec2::new((lo.x + hi.x) / 2.0, (lo.y + hi.y) / 2.0);
-        st.set_view_quiet(crate::View { center, height: (hi.y - lo.y).max(1e-6) });
+        let twist = st.view().twist;
+        st.set_view_quiet(crate::View { center, height: (hi.y - lo.y).max(1e-6), twist });
     }
     Ok(Some(json!({ "index": i, "title": title, "template": path })))
 }

crates/engine/src/cmd/image.rs

@@ -0,0 +1,353 @@
+//! Raster images (IMAGEATTACH, IMAGE). An IMAGE entity names its file; the pixels are decoded
+//! when the drawing opens or the image is attached and kept with the open drawing
+//! ([`Drawing::rasters`]), never in the file. An image whose file can't be found or read stays in
+//! the drawing as a crossed-out frame.
+
+use std::collections::{BTreeMap, BTreeSet};
+use std::sync::Arc;
+use std::sync::atomic::{AtomicU64, AtomicUsize, Ordering};
+
+use cadcraft_doc::{Drawing, EntityKind, Image, Raster};
+use cadcraft_geom::Vec2;
+use serde_json::{Value, json};
+
+use super::file::base64_decode;
+use super::{CommandSpec, bad, f64_or, point_param, str_param};
+use crate::{Result, Session};
+
+/// Most image files loaded per drawing.
+const MAX_IMAGE_FILES: usize = 1000;
+/// Largest image file read (bytes).
+#[cfg(not(target_arch = "wasm32"))]
+const MAX_IMAGE_BYTES: u64 = 256 << 20;
+/// Most decoded pixel bytes kept per drawing; images past it stay unloaded.
+const MAX_LOADED_BYTES: u64 = 2 << 30;
+/// Most image files decoded at the same time when a drawing opens.
+const MAX_LOADERS: usize = 4;
+/// Longest image path taken from a caller.
+const MAX_PATH: usize = 4096;
+
+pub fn specs() -> Vec<CommandSpec> {
+    vec![
+        CommandSpec::new("imageattach", "Raster Image Reference...", run_imageattach).alias(&["iat"]).params(
+            "{path: PNG/JPEG/BMP/TIFF file (saved as given; a relative path is relative to this drawing's folder), data?: base64 file contents \
+             (instead of reading `path`), at?: [x,y] lower-left corner (default 0,0), scale?: number (default 1: the image is one drawing unit \
+             wide), width?: width in drawing units (instead of `scale`), rotation? (degrees), name? (default: the file name)} → {name, handle, \
+             path, pixels: [w, h], size: [w, h]}",
+        ),
+        CommandSpec::new("image", "Raster Images", run_image)
+            .alias(&["im"])
+            .params("{} → {images: [{name, path, foundAt, status: Loaded|Not Found|Not loaded, references, pixels?: [w, h]}]}")
+            .noundo(),
+    ]
+}
+
+/// Whether `ext` (lower case, no dot) is an image file type IMAGEATTACH reads.
+pub(crate) fn is_image_ext(ext: &str) -> bool {
+    matches!(ext, "png" | "jpg" | "jpeg" | "bmp" | "tif" | "tiff")
+}
+
+/// Every IMAGE entity of `d`: in model space, on the layouts and in the blocks.
+fn images(d: &Drawing) -> impl Iterator<Item = &Image> {
+    let model = std::iter::once(&d.model);
+    let layouts = d.layouts.iter().map(|l| &l.entities);
+    let blocks = d.blocks.values().map(|b| &b.entities);
+    model.chain(layouts).chain(blocks).flat_map(|store| store.iter()).filter_map(|e| match &e.kind {
+        EntityKind::Image(i) => Some(i),
+        _ => None,
+    })
+}
+
+/// The image files `d` names, each once, in the order they are first used.
+fn paths(d: &Drawing) -> Vec<String> {
+    let mut seen = BTreeSet::new();
+    let mut paths = Vec::new();
+    for i in images(d) {
+        if !i.path.trim().is_empty() && seen.insert(i.path.as_str()) {
+            paths.push(i.path.clone());
+        }
+    }
+    paths
+}
+
+/// The contents of the image file saved as `path` in a drawing at `host`.
+fn read_file(path: &str, host: Option<&str>) -> std::result::Result<Vec<u8>, String> {
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        let file = super::blocks::xref::find_file(path, host).ok_or("file not found")?;
+        let len = std::fs::metadata(&file).map_err(|e| e.to_string())?.len();
+        if len > MAX_IMAGE_BYTES {
+            return Err(format!("the file is larger than {} MB", MAX_IMAGE_BYTES >> 20));
+        }
+        // Read no more than the limit: the file can grow or change after the check above.
+        let limit = usize::try_from(MAX_IMAGE_BYTES).unwrap_or(usize::MAX);
+        crate::capped_read::read_capped(&file, limit).map_err(|e| {
+            if e.kind() == std::io::ErrorKind::InvalidData { format!("the file is larger than {} MB", MAX_IMAGE_BYTES >> 20) } else { e.to_string() }
+        })
+    }
+    #[cfg(target_arch = "wasm32")]
+    {
+        let _ = (path, host);
+        Err("files are not available on the web".into())
+    }
+}
+
+/// Decode an image file. A decoder that panics on a damaged file fails this image only: the
+/// drawing it belongs to must still open.
+fn decode(bytes: &[u8]) -> std::result::Result<Raster, String> {
+    let hook = super::file::image_decoder().ok_or("image files can't be read in this build")?;
+    match std::panic::catch_unwind(|| hook(bytes)) {
+        Ok(r) => r,
+        Err(_) => Err("the file is damaged and can't be read".into()),
+    }
+}
+
+fn bytes_of(r: &Raster) -> u64 {
+    u64::try_from(r.rgba().len()).unwrap_or(u64::MAX)
+}
+
+/// Load the images of drawing `i`, just opened. Those that can't be loaded are reported and
+/// stay crossed-out frames; opening never fails over an image.
+pub(crate) fn after_open(s: &mut Session, i: usize) {
+    let Some(st) = s.docs.get_mut(i) else { return };
+    let paths = paths(&st.doc);
+    if paths.is_empty() {
+        return;
+    }
+    let mut rasters = st.doc.rasters.clone();
+    let notes = load_missing(&paths, st.path.as_deref(), &mut rasters);
+    if !rasters.is_empty() {
+        // Loading pixels is not a change to the drawing. A drawing counts as unchanged while
+        // it is the very one that was saved, so the saved one follows.
+        let unchanged = Arc::ptr_eq(&st.doc, &st.saved);
+        Arc::make_mut(&mut st.doc).rasters = rasters;
+        if unchanged {
+            st.saved = st.doc.clone();
+        }
+    }
+    for n in notes {
+        s.echo(n);
+    }
+}
+
+/// Read and decode into `rasters` the files of `paths` that are not in it yet, for a drawing at
+/// `host`. Returns one message per file that could not be loaded.
+fn load_missing(paths: &[String], host: Option<&str>, rasters: &mut cadcraft_doc::Rasters) -> Vec<String> {
+    let mut notes = Vec::new();
+    let mut missing: Vec<&str> = paths.iter().map(String::as_str).filter(|p| rasters.get(p).is_none()).collect();
+    if missing.len() > MAX_IMAGE_FILES {
+        missing.truncate(MAX_IMAGE_FILES);
+        notes.push(format!("Images: only the first {MAX_IMAGE_FILES} image files are loaded"));
+    }
+    let decoded = decode_files(&missing, host);
+    // Kept in the order the drawing uses them, up to the memory limit.
+    let mut kept_bytes = 0u64;
+    for (path, result) in missing.iter().zip(decoded) {
+        match result {
+            Ok(r) => {
+                kept_bytes = kept_bytes.saturating_add(bytes_of(&r));
+                if kept_bytes > MAX_LOADED_BYTES {
+                    notes.push(over_limit(path));
+                    break;
+                }
+                rasters.insert(path, Arc::new(r));
+            }
+            Err(e) => notes.push(format!("Image {path}: {e}")),
+        }
+    }
+    notes
+}
+
+fn over_limit(path: &str) -> String {
+    format!("Image {path}: not loaded (more than {} MB of images)", MAX_LOADED_BYTES >> 20)
+}
+
+/// Read and decode the image files `paths` of a drawing at `host`, a few at a time (decoding is
+/// what opening a drawing with large images waits for). The results are in the order of `paths`.
+fn decode_files(paths: &[&str], host: Option<&str>) -> Vec<std::result::Result<Raster, String>> {
+    // Decoded bytes so far, shared by the loaders: past the limit no further file is started.
+    let decoded_bytes = AtomicU64::new(0);
+    let load = |path: &str| -> std::result::Result<Raster, String> {
+        if decoded_bytes.load(Ordering::Relaxed) > MAX_LOADED_BYTES {
+            return Err(format!("not loaded (more than {} MB of images)", MAX_LOADED_BYTES >> 20));
+        }
+        let r = read_file(path, host).and_then(|bytes| decode(&bytes))?;
+        decoded_bytes.fetch_add(bytes_of(&r), Ordering::Relaxed);
+        Ok(r)
+    };
+    let mut results: Vec<Option<std::result::Result<Raster, String>>> = paths.iter().map(|_| None).collect();
+    let loaders = loader_count(paths.len());
+    if loaders > 1 {
+        // Each loader takes the next file nobody has started.
+        let next = AtomicUsize::new(0);
+        let work = || {
+            let mut done = Vec::new();
+            loop {
+                let index = next.fetch_add(1, Ordering::Relaxed);
+                let Some(path) = paths.get(index) else { break };
+                done.push((index, load(path)));
+            }
+            done
+        };
+        let finished: Vec<_> = std::thread::scope(|scope| {
+            let started: Vec<_> = (0..loaders).filter_map(|_| std::thread::Builder::new().spawn_scoped(scope, work).ok()).collect();
+            started.into_iter().filter_map(|loader| loader.join().ok()).flatten().collect()
+        });
+        for (index, result) in finished {
+            if let Some(slot) = results.get_mut(index) {
+                *slot = Some(result);
+            }
+        }
+    }
+    // One loader, or files a loader that could not start or finish left behind.
+    results.into_iter().zip(paths).map(|(result, path)| result.unwrap_or_else(|| load(path))).collect()
+}
+
+/// How many files are decoded at once: one per processor, at most [`MAX_LOADERS`] (each large
+/// image needs several hundred megabytes while it is decoded) and no more than there are files.
+fn loader_count(files: usize) -> usize {
+    #[cfg(not(target_arch = "wasm32"))]
+    let processors = std::thread::available_parallelism().map(std::num::NonZero::get).unwrap_or(1);
+    #[cfg(target_arch = "wasm32")]
+    let processors = 1;
+    processors.min(MAX_LOADERS).min(files)
+}
+
+/// The file name without folders and extension (either separator).
+fn stem(path: &str) -> String {
+    let file = path.rsplit(['/', '\\']).next().unwrap_or(path);
+    match file.rsplit_once('.') {
+        Some((stem, _)) if !stem.is_empty() => stem.to_string(),
+        _ => file.to_string(),
+    }
+}
+
+/// The definition name for a new image of `path`: the name that file already has in `d`, else
+/// `wanted`, numbered (`wanted_2`, `wanted_3`, …) when another file has taken it.
+fn def_name(d: &Drawing, path: &str, wanted: &str) -> String {
+    if let Some(i) = images(d).find(|i| i.path == path && !i.name.is_empty()) {
+        return i.name.clone();
+    }
+    // The names other files have, compared without regard to case.
+    let taken: BTreeSet<String> = images(d).filter(|i| i.path != path).map(|i| i.name.to_ascii_lowercase()).collect();
+    let free = |name: &str| !taken.contains(&name.to_ascii_lowercase());
+    if free(wanted) {
+        return wanted.to_string();
+    }
+    // One of these is free: there are more candidates than names taken.
+    let candidates = 2..taken.len().saturating_add(3);
+    candidates.map(|n| format!("{wanted}_{n}")).find(|name| free(name)).unwrap_or_else(|| wanted.to_string())
+}
+
+const ID: &str = "imageattach";
+
+pub(crate) fn run_imageattach(s: &mut Session, p: &Value) -> Result<Value> {
+    let path = str_param(p, "path").map(str::trim).filter(|x| !x.is_empty()).ok_or_else(|| bad(ID, "`path` is required"))?.to_string();
+    if path.len() > MAX_PATH {
+        return Err(bad(ID, "`path` is too long"));
+    }
+    let place = placement(p)?;
+    let raster = pixels(s, p, &path)?;
+    let (w, h) = (f64::from(raster.width()), f64::from(raster.height()));
+    // One pixel in drawing units, along the image's bottom edge (`u`) and its left edge (`v`).
+    let pixel = place.width / w;
+    let u = Vec2::from_angle(place.rotation) * pixel;
+    let v = u.perp();
+    if !(pixel.is_normal() && (pixel * h).is_normal() && u.x.is_finite() && u.y.is_finite()) {
+        return Err(bad(ID, "the image would be too small or too large to draw"));
+    }
+    let wanted = str_param(p, "name").map(str::trim).filter(|n| !n.is_empty()).map(str::to_string).unwrap_or_else(|| stem(&path));
+    let name = def_name(s.doc()?, &path, &wanted);
+    let image = Image {
+        insert: place.at.to3(0.0),
+        u: u.to3(0.0),
+        v: v.to3(0.0),
+        size: Vec2::new(w, h),
+        path: path.clone(),
+        name: name.clone(),
+        ..Image::default()
+    };
+    s.doc_mut()?.rasters.insert(&path, raster);
+    let handle = s.add_entity(EntityKind::Image(image))?;
+    Ok(json!({ "name": name, "handle": handle.hex(), "path": path, "pixels": [w, h], "size": [place.width, pixel * h] }))
+}
+
+/// Where and how large IMAGEATTACH puts the image.
+struct Placement {
+    /// The lower-left corner.
+    at: Vec2,
+    /// Radians, counter-clockwise.
+    rotation: f64,
+    /// The image's width in drawing units.
+    width: f64,
+}
+
+/// `at`, `rotation` and the width (`width`, else `scale`: an image is one unit wide at scale 1).
+fn placement(p: &Value) -> Result<Placement> {
+    let at = point_param(p, "at").unwrap_or(Vec2::ZERO);
+    if !(at.x.is_finite() && at.y.is_finite()) {
+        return Err(bad(ID, "`at` must be a point"));
+    }
+    let width = match p.get("width") {
+        Some(v) => v.as_f64().filter(|w| w.is_finite()).ok_or_else(|| bad(ID, "`width` must be a number"))?,
+        None => f64_or(p, "scale", 1.0),
+    };
+    if !(width.is_finite() && width > 0.0) {
+        return Err(bad(ID, "`scale` and `width` must be greater than zero"));
+    }
+    Ok(Placement { at, rotation: f64_or(p, "rotation", 0.0).to_radians(), width })
+}
+
+/// The pixels of the image at `path`: decoded from `data` when the caller hands the file over,
+/// else the ones already loaded for that path, else read from the file.
+fn pixels(s: &Session, p: &Value, path: &str) -> Result<Arc<Raster>> {
+    let bytes = match p.get("data") {
+        Some(data) => {
+            let text = data.as_str().ok_or_else(|| bad(ID, "`data` must be base64 text"))?;
+            base64_decode(text).ok_or_else(|| bad(ID, "`data` is not valid base64"))?
+        }
+        None => {
+            if let Some(loaded) = s.doc()?.rasters.get(path) {
+                return Ok(loaded.clone());
+            }
+            let host = s.state()?.path.clone();
+            read_file(path, host.as_deref()).map_err(|e| bad(ID, format!("{path}: {e}")))?
+        }
+    };
+    Ok(Arc::new(decode(&bytes).map_err(|e| bad(ID, format!("{path}: {e}")))?))
+}
+
+fn run_image(s: &mut Session, _p: &Value) -> Result<Value> {
+    let host = s.state()?.path.clone();
+    let d = s.doc()?;
+    // Per file: its definition name and how many images show it.
+    let mut uses: BTreeMap<&str, (&str, usize)> = BTreeMap::new();
+    for i in images(d) {
+        uses.entry(i.path.as_str()).or_insert((i.name.as_str(), 0)).1 += 1;
+    }
+    let rows: Vec<Value> = paths(d)
+        .iter()
+        .map(|path| {
+            let (name, references) = uses.get(path.as_str()).copied().unwrap_or_default();
+            let mut row = describe(d, path, host.as_deref());
+            row["name"] = json!(name);
+            row["references"] = json!(references);
+            row
+        })
+        .collect();
+    Ok(json!({ "images": rows }))
+}
+
+/// The state of image file `path` of drawing `d` (saved at `host`): where it is and whether its
+/// pixels are loaded.
+fn describe(d: &Drawing, path: &str, host: Option<&str>) -> Value {
+    let loaded = d.rasters.get(path);
+    let found_at = super::blocks::xref::find_file(path, host).map(|f| f.to_string_lossy().into_owned());
+    let status = match (loaded, &found_at) {
+        (Some(_), _) => "Loaded",
+        (None, None) => "Not Found",
+        // The file is there but could not be read as an image.
+        (None, Some(_)) => "Not loaded",
+    };
+    json!({ "path": path, "foundAt": found_at, "status": status, "pixels": loaded.map(|r| json!([r.width(), r.height()])) })
+}

crates/engine/src/cmd/layout.rs

@@ -524,6 +524,7 @@ fn viewport_json(h: Handle, v: &Viewport) -> Value {
         "height": v.height,
         "viewCenter": [v.view_center.x, v.view_center.y],
         "viewHeight": v.view_height,
+        "twist": v.view_twist().to_degrees(),
         "scale": if v.view_height > 0.0 { v.height / v.view_height } else { 0.0 },
         "locked": v.locked,
         "on": v.on,

crates/engine/src/cmd/layout/tests.rs

@@ -283,7 +283,7 @@ fn mspace_edits_model_through_viewport() {
     s.cmdline("circle 10,10 3").unwrap();
     assert_eq!(s.doc().unwrap().model.len(), before + 1);
     // Zooming changes the viewport's model view, not the sheet.
-    s.state_mut().unwrap().set_view(crate::View { center: v.center, height: v.height / 2.0 });
+    s.state_mut().unwrap().set_view(crate::View { center: v.center, height: v.height / 2.0, twist: v.twist });
     let vp2 = viewports(&s, "L").into_iter().find(|(x, _)| *x == h).unwrap().1;
     assert!((vp2.view_height - vp.view_height / 2.0).abs() < 1e-9);
     assert_eq!(s.state().unwrap().paper_view(), pv);

crates/engine/src/cmd/layout/viewports.rs

@@ -329,7 +329,7 @@ pub(super) fn run_vpclip(s: &mut Session, p: &Value) -> Result<Value> {
     let k = cur.view_height / cur.height.max(1e-12);
     let mut v = cur;
     let c = b.center();
-    let view_center = v.view_center + (c - v.center.xy()) * k;
+    let view_center = v.paper_to_model(c);
     let view_height = b.height() * k;
     if view_center.is_finite() && view_height.is_finite() && view_height > 0.0 {
         v.view_center = view_center;

crates/engine/src/cmd/layout/vplayer.rs

@@ -109,7 +109,7 @@ fn parse_color(t: &str) -> Result<Color> {
 fn viewport_at(s: &Session, p: Vec2) -> Option<Handle> {
     let st = s.state().ok()?;
     let at = match st.active_viewport() {
-        Some((_, vp)) => vp.center.xy() + (p - vp.view_center) * (vp.height / vp.view_height),
+        Some((_, vp)) => vp.model_to_paper(p),
         None => p,
     };
     super::viewports::viewport_at(s, at)

crates/engine/src/cmd/mleader_content.rs

@@ -54,6 +54,7 @@ pub(super) fn apply(s: &Session, k: EntityKind, c: &Content) -> Result<EntityKin
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         };
         if *center {
             // Move the block so the centre of its extents lands on the anchor.

crates/engine/src/cmd/modify2/selop.rs

@@ -182,8 +182,7 @@ fn chspace(s: &mut Session, hs: &[Handle], to: Option<&str>, vp: Option<Handle>)
     };
     let m = match viewport_of(s, &layout, vp) {
         Some(v) => {
-            let k = v.view_height / v.height;
-            let to_paper = Mat3::translate(v.center.xy()).then_before(Mat3::scale(1.0 / k, 1.0 / k)).then_before(Mat3::translate(-v.view_center));
+            let to_paper = v.model_to_paper_matrix();
             if target == Space::Model { to_paper.inverse().unwrap_or(Mat3::IDENTITY) } else { to_paper }
         }
         None => Mat3::IDENTITY,

crates/engine/src/cmd/modify2/tests.rs

@@ -411,6 +411,7 @@ fn chspace_json_and_command_line() {
         layer_colors: Vec::new(),
         clip: None,
         on: true,
+        twist: 0.0,
     };
     s.doc_mut().unwrap().add(&Space::Paper("Layout1".into()), Default::default(), EntityKind::Viewport(vp)).unwrap();
     let r = s.execute("chspace", &json!({"handles": [l]})).unwrap();

crates/engine/src/cmd/view.rs

@@ -1,5 +1,5 @@
-//! View menu: ZOOM (with Realtime and Dynamic), PAN, REGEN, REDRAW, named views (VIEW), layout
-//! switching.
+//! View menu: ZOOM (with Realtime and Dynamic), PAN, REGEN, REDRAW, named views (VIEW), the view
+//! twist (DVIEW TWist), layout switching.
 
 use cadcraft_doc::{Space, entity_bounds};
 use cadcraft_geom::{Bounds2, Vec2};
@@ -10,6 +10,7 @@ use super::{CommandSpec, bad, bool_or, f64_or, f64_req, ok, point_param, point_r
 
 use crate::{Accept, Input, Interactive, Prompt, Result, Session, Step, View};
 
+mod dview;
 mod named_views;
 mod vports;
 
@@ -95,10 +96,13 @@ pub fn specs() -> Vec<CommandSpec> {
         .alias(&["r"])
         .noundo()
         .transparent(),
-        CommandSpec::new("view.set", "Set View", run_view_set).params("{center: [x,y], height}").noundo(),
+        dview::spec(),
+        CommandSpec::new("view.set", "Set View", run_view_set)
+            .params("{center: [x,y], height, twist?: degrees (default: keep the current twist; in a layout viewport it is the viewport's twist, an undoable edit; not in Paper space)}")
+            .noundo(),
         CommandSpec::new("view.get", "Get View", |s, _| {
             let v = s.state()?.view();
-            Ok(json!({"center": [v.center.x, v.center.y], "height": v.height, "viewportPx": [s.viewport_px.0, s.viewport_px.1]}))
+            Ok(json!({"center": [v.center.x, v.center.y], "height": v.height, "twist": v.twist.to_degrees(), "viewportPx": [s.viewport_px.0, s.viewport_px.1]}))
         })
         .noundo(),
         CommandSpec::new("layout.set", "Switch Layout", run_layout_set).params("{name: \"Model\" | layout name}").noundo(),
@@ -120,8 +124,11 @@ fn fit(s: &mut Session, b: Bounds2) -> Result<()> {
     let (w, h) = s.viewport_px;
     let st = s.state_mut()?;
     let aspect = st.zoom_aspect(w / h.max(1.0));
-    let height = b.height().max(b.width() / aspect.max(1e-6)).max(1e-9);
-    st.set_zoom_frame(View { center: b.center(), height });
+    // A twisted view fits the box the bounds make on screen.
+    let twist = st.zoom_frame().twist;
+    let (center, bw, bh) = View::twisted_box(b, twist);
+    let height = bh.max(bw / aspect.max(1e-6)).max(1e-9);
+    st.set_zoom_frame(View { center, height, twist });
     Ok(())
 }
 
@@ -150,18 +157,18 @@ pub(crate) fn zoom(s: &mut Session, p: &Value) -> Result<Value> {
             let f = if mode == "in" { 2.0 } else { 0.5 };
             let st = s.state_mut()?;
             let v = st.zoom_frame();
-            st.set_zoom_frame(View { center: v.center, height: v.height / f });
+            st.set_zoom_frame(View { height: v.height / f, ..v });
         }
         "center" | "c" | "dynamic" | "d" => {
             let c = point_req("zoom", p, "center")?;
-            let cur = s.state()?.zoom_frame().height;
-            let h = if p.get("factor").is_some() { factor_height(s, p, cur)? } else { f64_or(p, "height", cur) };
-            s.state_mut()?.set_zoom_frame(View { center: c, height: h.max(1e-9) });
+            let cur = s.state()?.zoom_frame();
+            let h = if p.get("factor").is_some() { factor_height(s, p, cur.height)? } else { f64_or(p, "height", cur.height) };
+            s.state_mut()?.set_zoom_frame(View { center: c, height: h.max(1e-9), ..cur });
         }
         "scale" | "s" => {
             let v = s.state()?.zoom_frame();
             let height = factor_height(s, p, v.height)?;
-            s.state_mut()?.set_zoom_frame(View { center: v.center, height });
+            s.state_mut()?.set_zoom_frame(View { height, ..v });
         }
         "realtime" => {
             let v = s.state()?.zoom_frame();
@@ -169,7 +176,7 @@ pub(crate) fn zoom(s: &mut Session, p: &Value) -> Result<Value> {
             if f <= 0.0 {
                 return Err(bad("zoom", "factor must be positive"));
             }
-            s.state_mut()?.set_zoom_frame(View { center: v.center, height: (v.height / f).clamp(1e-9, 1e12) });
+            s.state_mut()?.set_zoom_frame(View { height: (v.height / f).clamp(1e-9, 1e12), ..v });
         }
         "object" | "o" => {
             let hs = targets(s, p)?;
@@ -242,7 +249,8 @@ fn pan_frac(s: &mut Session, f: Vec2) -> Result<Value> {
     let st = s.state_mut()?;
     let v = st.view();
     let ww = v.height * w / h.max(1.0);
-    st.set_view(View { center: v.center + Vec2::new(f.x * ww, f.y * v.height), height: v.height });
+    // Screen directions: in a twisted view the drawing is turned by the twist.
+    st.set_view(View { center: v.center + Vec2::new(f.x * ww, f.y * v.height).rotate(-v.twist), ..v });
     ok()
 }
 
@@ -258,7 +266,7 @@ fn run_pan(s: &mut Session, p: &Value) -> Result<Value> {
         let b = point_req("pan", p, "to")?;
         v.center - (b - a)
     };
-    st.set_view(View { center: c, height: v.height });
+    st.set_view(View { center: c, ..v });
     ok()
 }
 
@@ -268,9 +276,33 @@ fn run_view_set(s: &mut Session, p: &Value) -> Result<Value> {
     if h <= 0.0 {
         return Err(bad("view.set", "height must be positive"));
     }
-    if !s.state_mut()?.set_view(View { center: c, height: h }) {
+    let twist = match p.get("twist") {
+        Some(t) => t.as_f64().filter(|t| t.is_finite()).ok_or_else(|| bad("view.set", "twist must be a number of degrees"))?.to_radians(),
+        None => s.state()?.view().twist,
+    };
+    // As DVIEW TWist: the Model tab's view or the active layout viewport turns; a layout sheet
+    // (paper space) is never twisted.
+    let target = match dview::target(s) {
+        Ok(t) => Some(t),
+        Err(_) if twist == 0.0 => None,
+        Err(e) => return Err(e),
+    };
+    let before = (s.state()?.doc.clone(), s.state()?.selection.clone());
+    let twist = match target {
+        Some(t @ dview::Target::Viewport(_)) => {
+            dview::set_twist(s, t, twist)?;
+            s.state()?.view().twist
+        }
+        Some(dview::Target::Model) => cadcraft_geom::norm_angle(twist),
+        None => 0.0,
+    };
+    if !s.state_mut()?.set_view(View { center: c, height: h, twist }) {
+        s.state_mut()?.doc = before.0;
         return Err(bad("view.set", "the view is too large to show. Nothing was changed"));
     }
+    if let Some(dview::Target::Viewport(h)) = target {
+        dview::record_viewport_edit(s, before, h)?;
+    }
     ok()
 }
 
@@ -294,7 +326,7 @@ fn run_layout_set(s: &mut Session, p: &Value) -> Result<Value> {
         let page = st.doc.layout(n).map(|l| l.page.clone()).unwrap_or_default();
         let (w, h) = if page.landscape { (page.height_mm, page.width_mm) } else { (page.width_mm, page.height_mm) };
         let unit = if st.doc.header.i64("MEASUREMENT", 0) == 1 { 1.0 } else { 1.0 / 25.4 };
-        st.set_view_quiet(View { center: Vec2::new(w * unit / 2.0, h * unit / 2.0), height: h * unit * 1.15 });
+        st.set_view_quiet(View { center: Vec2::new(w * unit / 2.0, h * unit / 2.0), height: h * unit * 1.15, twist: 0.0 });
     }
     s.touch();
     ok()
@@ -441,7 +473,7 @@ impl Interactive for ZoomM {
                 if st.view_history.last() == Some(&b.screen) {
                     st.view_history.pop();
                 }
-                st.set_zoom_frame(View { center: b.center, height: b.height });
+                st.set_zoom_frame(View { center: b.center, height: b.height, twist: b.frame.twist });
                 return Ok(Step::Done);
             }
             (ZoomStage::Dynamic(mut b), Input::Point(p)) => {
@@ -565,7 +597,7 @@ impl Session {
         let f = 2f64.powf((-dy / half).clamp(-16.0, 16.0));
         let st = self.state_mut()?;
         let v = st.view();
-        st.set_view_quiet(View { center: v.center, height: (v.height / f).clamp(1e-9, 1e12) });
+        st.set_view_quiet(View { height: (v.height / f).clamp(1e-9, 1e12), ..v });
         self.touch();
         Ok(())
     }

crates/engine/src/cmd/view/dview.rs

@@ -0,0 +1,441 @@
+//! DVIEW: the dynamic view, on CADCraft's 2D plan views.
+//!
+//! It starts with "Select objects or <use DVIEWBLOCK>:": the objects
+//! picked are the preview set, and Enter with nothing picked previews the DVIEWBLOCK block (the
+//! drawing's own block of that name, else a built-in sample house). While DVIEW runs only the
+//! preview set is drawn ([`Interactive::display_only`]); the whole drawing is regenerated when it
+//! ends. Then it repeats "Enter option [CAmera/TArget/Distance/POints/PAn/Zoom/TWist/CLip/Hide/
+//! Off/Undo]:" until Enter. TWist, PAn, Zoom, Off and Undo work; the options that need a 3D
+//! camera say they are not available yet and stay at the option prompt.
+//!
+//! DVIEW works on the Model tab's view, or on the active (double-clicked) layout viewport; on a
+//! layout with no active viewport it is not available. A Model tab twist is a view change like
+//! ZOOM (view history, not undo). A layout viewport's twist belongs to the viewport entity, so a
+//! DVIEW that changed it is one undo step.
+
+use std::sync::Arc;
+
+use cadcraft_doc::{Entity, EntityKind, Handle, Insert, Line, Space};
+use cadcraft_geom::{Vec2, Vec3};
+use serde_json::{Value, json};
+
+use super::super::machines::{SelOutcome, SelectPhase, number};
+use super::super::{CommandSpec, bad, f64_req};
+use crate::{Accept, DisplayOnly, EngineError, Input, Interactive, Prompt, Result, Session, Snapshot, Step, View};
+
+/// What DVIEW (and a view twist asked for anywhere) says on a layout with no active viewport.
+pub(super) const PAPER_SPACE: &str = "This command is not available in Paper space.";
+
+/// The option prompt's keywords, in prompt order.
+const OPTIONS: &[&str] = &["CAmera", "TArget", "Distance", "POints", "PAn", "Zoom", "TWist", "CLip", "Hide", "Off", "Undo"];
+
+/// The block DVIEW previews when nothing is selected.
+const DVIEWBLOCK: &str = "DVIEWBLOCK";
+
+pub(super) fn spec() -> CommandSpec {
+    CommandSpec::new("dview", "DView", run_dview)
+        .alias(&["dv"])
+        .params("{twist: degrees counterclockwise} (DVIEW TWist: the Model tab's view twist, or the active layout viewport's, an undoable edit; not in Paper space)")
+        .noundo()
+        .interactive(|s| {
+            // Refused as it starts on a layout with no active viewport.
+            target(s)?;
+            Ok(Box::new(DviewM::default()))
+        })
+}
+
+/// The view DVIEW changes.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub(super) enum Target {
+    /// The Model tab's view.
+    Model,
+    /// The active (MSPACE) layout viewport: its own view twist.
+    Viewport(Handle),
+}
+
+/// The view DVIEW changes: the active layout viewport, else the Model tab's view. A layout with
+/// no active viewport has none.
+pub(super) fn target(s: &Session) -> Result<Target> {
+    let st = s.state()?;
+    if let Some((h, _)) = st.active_viewport() {
+        return Ok(Target::Viewport(h));
+    }
+    if st.space == Space::Model {
+        return Ok(Target::Model);
+    }
+    Err(EngineError::Other(PAPER_SPACE.into()))
+}
+
+/// A twist kept as files hold it: [0, 2π).
+fn normal(twist: f64) -> f64 {
+    cadcraft_geom::norm_angle(twist)
+}
+
+/// The active viewport's twist, if it is `h`.
+fn viewport_twist(s: &Session, h: Handle) -> Option<f64> {
+    s.state().ok()?.active_viewport().filter(|(vh, _)| *vh == h).map(|(_, vp)| vp.view_twist())
+}
+
+/// Turn `target`'s view to `twist` radians. The Model tab's twist is a view change (view
+/// history, like ZOOM); a viewport's is a change to the viewport entity, which the caller
+/// records as an undo step ([`record_viewport_edit`]).
+pub(super) fn set_twist(s: &mut Session, target: Target, twist: f64) -> Result<()> {
+    if !twist.is_finite() {
+        return Err(bad("dview", "the twist must be a finite angle"));
+    }
+    let twist = normal(twist);
+    match target {
+        Target::Model => {
+            let st = s.state_mut()?;
+            let v = st.view();
+            st.set_view(View { twist, ..v });
+        }
+        Target::Viewport(h) => {
+            if viewport_twist(s, h) == Some(twist) {
+                return Ok(());
+            }
+            // A locked viewport keeps its view, the twist with it.
+            if s.state()?.active_viewport().is_some_and(|(vh, vp)| vh == h && vp.locked) {
+                return Err(EngineError::Other("The viewport is locked.".into()));
+            }
+            let space = s.state()?.space.clone();
+            let d = s.doc_mut()?;
+            if let Some(store) = d.space_mut(&space) {
+                store.modify(h, |e| {
+                    if let EntityKind::Viewport(vp) = &mut e.kind {
+                        vp.twist = twist;
+                    }
+                });
+            }
+        }
+    }
+    Ok(())
+}
+
+/// Record a layout viewport's twist change as one undo step, `before` being the drawing (and
+/// selection) before it. Nothing when the twist did not change, and nothing inside a LISP routine
+/// (its own single step holds it).
+pub(super) fn record_viewport_edit(s: &mut Session, before: (Arc<cadcraft_doc::Drawing>, Vec<Handle>), h: Handle) -> Result<()> {
+    let old = before.0.entity(h).and_then(|e| match &e.kind {
+        EntityKind::Viewport(vp) => Some(vp.view_twist()),
+        _ => None,
+    });
+    if old == viewport_twist(s, h) || s.lisp_groups_undo() {
+        return Ok(());
+    }
+    let st = s.state_mut()?;
+    if !Arc::ptr_eq(&before.0, &st.doc) {
+        st.push_undo(Snapshot { label: "DView".into(), doc: before.0, selection: before.1 });
+        st.revision += 1;
+    }
+    Ok(())
+}
+
+/// The drawing and selection now, for [`record_viewport_edit`].
+fn snapshot(s: &Session) -> Result<(Arc<cadcraft_doc::Drawing>, Vec<Handle>)> {
+    let st = s.state()?;
+    Ok((st.doc.clone(), st.selection.clone()))
+}
+
+fn run_dview(s: &mut Session, p: &Value) -> Result<Value> {
+    let t = target(s)?;
+    let deg = f64_req("dview", p, "twist")?;
+    let before = snapshot(s)?;
+    set_twist(s, t, deg.to_radians())?;
+    if let Target::Viewport(h) = t {
+        record_viewport_edit(s, before, h)?;
+    }
+    let v = s.state()?.view();
+    Ok(json!({ "twist": v.twist.to_degrees() }))
+}
+
+/// The built-in DVIEWBLOCK: a house front in the unit square, origin at the lower-left corner
+/// (the size and origin a DVIEWBLOCK of one's own is expected to have). CADCraft's own drawing.
+fn sample_house() -> Vec<(Vec2, Vec2)> {
+    let p = Vec2::new;
+    let mut lines = Vec::new();
+    let mut poly = |pts: &[Vec2], closed: bool| {
+        for w in pts.windows(2) {
+            lines.push((w[0], w[1]));
+        }
+        if closed && let (Some(a), Some(b)) = (pts.last(), pts.first()) {
+            lines.push((*a, *b));
+        }
+    };
+    // Walls.
+    poly(&[p(0.1, 0.0), p(0.9, 0.0), p(0.9, 0.6), p(0.1, 0.6)], true);
+    // Roof with eaves, and a chimney on its right slope.
+    poly(&[p(0.0, 0.55), p(0.5, 1.0), p(1.0, 0.55)], false);
+    poly(&[p(0.7, 0.82), p(0.7, 0.95), p(0.8, 0.95), p(0.8, 0.73)], false);
+    // Door.
+    poly(&[p(0.42, 0.0), p(0.42, 0.35), p(0.58, 0.35), p(0.58, 0.0)], false);
+    // Two windows with their bars.
+    for x in [0.17, 0.67] {
+        poly(&[p(x, 0.25), p(x + 0.16, 0.25), p(x + 0.16, 0.45), p(x, 0.45)], true);
+        poly(&[p(x + 0.08, 0.25), p(x + 0.08, 0.45)], false);
+        poly(&[p(x, 0.35), p(x + 0.16, 0.35)], false);
+    }
+    lines
+}
+
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+enum Stage {
+    #[default]
+    Select,
+    Option,
+    Twist,
+    PanBase,
+    PanSecond(Vec2),
+    Zoom,
+}
+
+/// DVIEW, interactive.
+#[derive(Default)]
+struct DviewM {
+    stage: Stage,
+    sel: SelectPhase,
+    /// The preview set; empty with `sample` set: the DVIEWBLOCK.
+    preview: Vec<Handle>,
+    /// Where the DVIEWBLOCK preview stands: its lower-left corner and size (drawing units), fixed
+    /// as the options start so that PAn and Zoom move the view, not the house.
+    sample: Option<(Vec2, f64)>,
+    /// The views before each DVIEW action, for Undo.
+    undo: Vec<View>,
+    /// What DVIEW works on, and the drawing as it started (a viewport's twist change is one
+    /// undo step).
+    target: Option<Target>,
+    before: Option<(Arc<cadcraft_doc::Drawing>, Vec<Handle>)>,
+}
+
+impl DviewM {
+    fn target(&self, s: &Session) -> Result<Target> {
+        match self.target {
+            Some(t) => Ok(t),
+            None => target(s),
+        }
+    }
+    /// Start the options with this preview set (empty: the DVIEWBLOCK).
+    fn options(&mut self, s: &mut Session, picked: Vec<Handle>) -> Result<Step> {
+        // Objects picked at the prompt don't stay selected.
+        s.set_selection(Vec::new());
+        if picked.is_empty() {
+            let v = s.state()?.view();
+            let size = v.height * 0.5;
+            self.sample = Some((v.center - Vec2::new(size, size) * 0.5, size));
+        }
+        self.preview = picked;
+        self.stage = Stage::Option;
+        Ok(Step::Continue)
+    }
+    /// Show view `v` (centre, height and twist) on the target.
+    fn show(&self, s: &mut Session, v: View) -> Result<()> {
+        let t = self.target(s)?;
+        let before = s.state()?.doc.clone();
+        let twist = normal(v.twist);
+        if let Target::Viewport(_) = t {
+            // The twist is the viewport's; the view inside it then moves as asked.
+            set_twist(s, t, twist)?;
+        }
+        if !s.state_mut()?.set_view(View { twist, ..v }) {
+            s.state_mut()?.doc = before;
+            return Err(EngineError::Other("The view is too large to show.".into()));
+        }
+        Ok(())
+    }
+    /// Apply a view as one DVIEW action (Undo takes it back).
+    fn change(&mut self, s: &mut Session, f: impl FnOnce(View) -> View) -> Result<()> {
+        let v = s.state()?.view();
+        self.show(s, f(v))?;
+        self.undo.push(v);
+        Ok(())
+    }
+    /// The command ends: a viewport twist change becomes one undo step, and the whole drawing is
+    /// regenerated.
+    fn end(&mut self, s: &mut Session) -> Result<()> {
+        if let (Some(Target::Viewport(h)), Some(before)) = (self.target, self.before.take()) {
+            record_viewport_edit(s, before, h)?;
+        }
+        s.touch();
+        Ok(())
+    }
+}
+
+impl Interactive for DviewM {
+    fn name(&self) -> &'static str {
+        "DVIEW"
+    }
+    fn begin(&mut self, s: &mut Session) -> Result<Step> {
+        self.target = Some(target(s)?);
+        self.before = Some(snapshot(s)?);
+        Ok(Step::Continue)
+    }
+    fn prompt(&self, s: &Session) -> Prompt {
+        match self.stage {
+            Stage::Select if self.sel.removing => self.sel.prompt(),
+            Stage::Select => Prompt::new("Select objects or", Accept::SELECT).default("use DVIEWBLOCK"),
+            Stage::Option => Prompt::new("Enter option", Accept::TEXT).kw(OPTIONS),
+            Stage::Twist => {
+                let (au, ap) = s.doc().map(|d| (d.header.i64("AUNITS", 0), d.header.i64("AUPREC", 0))).unwrap_or((0, 0));
+                let cur = s.state().map(|st| st.view().twist).unwrap_or(0.0);
+                // Offered as it would be typed: clockwise is positive when ANGDIR is 1.
+                let cur = if s.angle_settings().clockwise { -cur } else { cur };
+                let center = s.state().map(|st| st.view().center).ok();
+                Prompt::new("Specify view twist angle", Accept::POINT_OR_NUMBER).default(crate::units::format_angle(cur, au, ap)).base_opt(center)
+            }
+            Stage::PanBase => Prompt::new("Specify displacement base point", Accept::POINT),
+            Stage::PanSecond(b) => Prompt::new("Specify second point", Accept::POINT).base(b),
+            Stage::Zoom => Prompt::new("Specify zoom scale factor", Accept::NUMBER).default("1"),
+        }
+    }
+    fn cancelled(&mut self, s: &mut Session) {
+        if let Err(e) = self.end(s) {
+            s.echo(e.to_string());
+        }
+    }
+    fn input(&mut self, s: &mut Session, i: Input) -> Result<Step> {
+        match self.stage {
+            Stage::Select => match self.sel.feed(s, &i)? {
+                SelOutcome::More => Ok(Step::Continue),
+                SelOutcome::Empty => self.options(s, Vec::new()),
+                SelOutcome::Done(hs) => self.options(s, hs),
+            },
+            Stage::Option => {
+                let word = match &i {
+                    Input::Enter => {
+                        self.end(s)?;
+                        return Ok(Step::Done);
+                    }
+                    Input::Keyword(t) | Input::Text(t) => self.prompt(s).match_keyword(t),
+                    _ => None,
+                };
+                match word.as_deref() {
+                    Some("TWist") => self.stage = Stage::Twist,
+                    Some("PAn") => self.stage = Stage::PanBase,
+                    Some("Zoom") => self.stage = Stage::Zoom,
+                    // Perspective is never on in a 2D view: there is nothing to turn off.
+                    Some("Off") => {}
+                    Some("Undo") => {
+                        if let Some(v) = self.undo.pop() {
+                            self.show(s, v)?;
+                        }
+                    }
+                    // CAmera, TArget, Distance, POints, CLip and Hide need a 3D view.
+                    Some(other) => s.echo(format!("DVIEW {other} is not available yet.")),
+                    None => return Err(EngineError::Other("Invalid option keyword.".into())),
+                }
+                Ok(Step::Continue)
+            }
+            Stage::Twist => {
+                let twist = match &i {
+                    Input::Enter => None,
+                    Input::Point(p) => {
+                        let c = s.state()?.view().center;
+                        let d = *p - c;
+                        if d.len() < 1e-12 {
+                            return Err(EngineError::Other("Requires a valid angle.".into()));
+                        }
+                        Some(d.y.atan2(d.x))
+                    }
+                    Input::Text(t) | Input::Keyword(t) if t.trim().is_empty() => None,
+                    Input::Text(t) | Input::Keyword(t) => {
+                        Some(s.angle_settings().rotation(t).ok_or_else(|| EngineError::Other("Requires a valid angle.".into()))?)
+                    }
+                    _ => return Ok(Step::Continue),
+                };
+                if let Some(a) = twist {
+                    self.change(s, |v| View { twist: normal(a), ..v })?;
+                }
+                self.stage = Stage::Option;
+                Ok(Step::Continue)
+            }
+            Stage::PanBase => match i {
+                Input::Point(p) => {
+                    self.stage = Stage::PanSecond(p);
+                    Ok(Step::Continue)
+                }
+                Input::Enter => {
+                    self.stage = Stage::Option;
+                    Ok(Step::Continue)
+                }
+                _ => Err(EngineError::Other("Invalid point.".into())),
+            },
+            Stage::PanSecond(b) => match i {
+                Input::Point(p) => {
+                    self.change(s, |v| View { center: v.center - (p - b), ..v })?;
+                    self.stage = Stage::Option;
+                    Ok(Step::Continue)
+                }
+                Input::Enter => {
+                    self.stage = Stage::Option;
+                    Ok(Step::Continue)
+                }
+                _ => Err(EngineError::Other("Invalid point.".into())),
+            },
+            Stage::Zoom => {
+                let f = match &i {
+                    Input::Enter => None,
+                    Input::Text(t) | Input::Keyword(t) if t.trim().is_empty() => None,
+                    Input::Text(t) | Input::Keyword(t) => match number(t) {
+                        Some(f) if f.is_finite() && f > 0.0 => Some(f),
+                        _ => return Err(EngineError::Other("Requires a positive number.".into())),
+                    },
+                    _ => return Ok(Step::Continue),
+                };
+                if let Some(f) = f.filter(|f| *f != 1.0) {
+                    self.change(s, |v| View { height: v.height / f, ..v })?;
+                }
+                self.stage = Stage::Option;
+                Ok(Step::Continue)
+            }
+        }
+    }
+    fn display_only(&self, s: &Session) -> Option<DisplayOnly> {
+        if self.stage == Stage::Select {
+            return None;
+        }
+        let mut extra = Vec::new();
+        if let Some((corner, size)) = self.sample {
+            let common = s.current_common();
+            let d = s.doc().ok()?;
+            if d.block(DVIEWBLOCK).is_some() {
+                // The drawing's own DVIEWBLOCK, defined in a 1 by 1 unit area.
+                let ins = Insert {
+                    block: DVIEWBLOCK.into(),
+                    insert: corner.to3(0.0),
+                    scale: Vec3::new(size, size, size),
+                    rotation: 0.0,
+                    attribs: Vec::new(),
+                    cols: 1,
+                    rows: 1,
+                    col_spacing: 0.0,
+                    row_spacing: 0.0,
+                    clip: None,
+                };
+                extra.push(Entity { handle: Handle(0), common, kind: EntityKind::Insert(ins) });
+            } else {
+                extra.extend(sample_house().into_iter().map(|(a, b)| Entity {
+                    handle: Handle(0),
+                    common: common.clone(),
+                    kind: EntityKind::Line(Line { a: (corner + a * size).to3(0.0), b: (corner + b * size).to3(0.0) }),
+                }));
+            }
+        }
+        Some(DisplayOnly { handles: self.preview.clone(), extra })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn the_sample_house_fits_the_unit_square() {
+        let lines = sample_house();
+        assert!(lines.len() > 10);
+        for (a, b) in lines {
+            for q in [a, b] {
+                assert!((0.0..=1.0).contains(&q.x) && (0.0..=1.0).contains(&q.y), "{q:?}");
+            }
+        }
+    }
+}

crates/engine/src/cmd/view/named_views.rs

@@ -110,15 +110,25 @@ fn save(s: &mut Session, name: &str, window: Option<Bounds2>, snapshot: bool) ->
         (Space::Paper(l), false) => Some(l.clone()),
         _ => None,
     };
+    // The view this saves: the viewport's model view inside an MSPACE viewport, else the screen.
+    let frame = if in_viewport { st.zoom_frame() } else { st.view() };
+    // The view twist goes with the view (paper space has none).
+    let twist = if layout.is_some() { 0.0 } else { frame.twist };
     let (center, height, width) = match window {
         Some(b) => {
             if !(b.width() > 1e-12 && b.height() > 1e-12 && b.min.is_finite() && b.max.is_finite()) {
                 return Err(EngineError::Other("The window has no area.".into()));
             }
-            (b.center(), b.height(), b.width())
+            // In a twisted view the window's box on screen is larger than its world box.
+            let (center, width, height) = crate::View::twisted_box(b, twist);
+            // Turning corners near the number limit can overflow: save no view that can't be restored.
+            if !(center.is_finite() && width.is_finite() && height.is_finite() && width > 1e-12 && height > 1e-12) {
+                return Err(EngineError::Other("The window is too large for a twisted view.".into()));
+            }
+            (center, height, width)
         }
         None => {
-            let f = if in_viewport { st.zoom_frame() } else { st.view() };
+            let f = frame;
             let aspect = if in_viewport { st.zoom_aspect(w / h.max(1.0)) } else { w / h.max(1.0) };
             (f.center, f.height, f.height * aspect)
         }
@@ -139,7 +149,7 @@ fn save(s: &mut Session, name: &str, window: Option<Bounds2>, snapshot: bool) ->
         }
         d.views.retain(|v| !v.name.eq_ignore_ascii_case(old));
     }
-    d.views.push(NamedView { name: name.to_string(), center, height, width, layer_state, twist: 0.0, layout });
+    d.views.push(NamedView { name: name.to_string(), center, height, width, layer_state, twist, layout });
     let msg = if replaced.is_some() { format!("View \"{name}\" replaced.") } else { format!("View \"{name}\" saved.") };
     Ok(json!({ "name": name, "center": [center.x, center.y], "height": height, "width": width, "message": msg }))
 }
@@ -168,7 +178,7 @@ fn restore(s: &mut Session, name: &str) -> Result<Value> {
             let st = s.state_mut()?;
             st.mspace = None;
             let height = v.height.max(v.width / (w / h.max(1.0)).max(1e-9));
-            st.set_view(View { center: v.center, height });
+            st.set_view(View { center: v.center, height, twist: 0.0 });
         }
         None => {
             // A model space view: into the active MSPACE viewport, else on the Model tab.
@@ -177,8 +187,11 @@ fn restore(s: &mut Session, name: &str) -> Result<Value> {
             }
             let (w, h) = s.viewport_px;
             let st = s.state_mut()?;
+            // In an unlocked MSPACE viewport the saved twist turns the viewport (an edit of the
+            // viewport, recorded as the command's undo step).
             let aspect = st.zoom_aspect(w / h.max(1.0)).max(1e-9);
-            st.set_zoom_frame(View { center: v.center, height: v.height.max(v.width / aspect) });
+            let twist = cadcraft_geom::norm_angle(v.twist);
+            st.set_zoom_frame(View { center: v.center, height: v.height.max(v.width / aspect), twist });
         }
     }
     let mut msg = format!("View \"{}\" restored.", v.name);

crates/engine/src/cmd/view/vports.rs

@@ -104,7 +104,7 @@ fn rect(t: &VportTile) -> Rect {
 }
 
 fn view_of(t: &VportTile) -> View {
-    View { center: t.center, height: t.height }
+    View { center: t.center, height: t.height, twist: if t.twist.is_finite() { t.twist } else { 0.0 } }
 }
 
 fn active_config(d: &Drawing) -> Option<&VportConfig> {
@@ -117,7 +117,7 @@ fn live(st: &DocState, px: (f64, f64)) -> (Vec<VportTile>, usize) {
     let now = st.views.iter().find(|(sp, _)| *sp == Space::Model).map(|(_, v)| *v).unwrap_or_default();
     let Some(cfg) = active_config(&st.doc) else {
         let aspect = px.0 / px.1.max(1.0);
-        return (vec![VportTile { min: Vec2::ZERO, max: Vec2::new(1.0, 1.0), center: now.center, height: now.height, aspect }], 0);
+        return (vec![VportTile { min: Vec2::ZERO, max: Vec2::new(1.0, 1.0), center: now.center, height: now.height, aspect, twist: now.twist }], 0);
     };
     let mut tiles = cfg.tiles.clone();
     let synced =
@@ -125,11 +125,11 @@ fn live(st: &DocState, px: (f64, f64)) -> (Vec<VportTile>, usize) {
     let active = if synced { st.tiles.active.min(tiles.len() - 1) } else { 0 };
     if synced {
         for (t, v) in tiles.iter_mut().zip(&st.tiles.views) {
-            (t.center, t.height) = (v.center, v.height);
+            (t.center, t.height, t.twist) = (v.center, v.height, v.twist);
         }
     }
     if let Some(t) = tiles.get_mut(active) {
-        (t.center, t.height) = (now.center, now.height);
+        (t.center, t.height, t.twist) = (now.center, now.height, now.twist);
     }
     // Screen aspects from the current tile's size in pixels.
     if let Some(cur) = tiles.get(active).copied() {
@@ -171,7 +171,7 @@ fn summary(s: &Session) -> Result<Value> {
     let rows: Vec<Value> = tiles
         .iter()
         .enumerate()
-        .map(|(i, t)| json!({ "index": i + 1, "min": [t.min.x, t.min.y], "max": [t.max.x, t.max.y], "center": [t.center.x, t.center.y], "height": t.height, "current": i == active }))
+        .map(|(i, t)| json!({ "index": i + 1, "min": [t.min.x, t.min.y], "max": [t.max.x, t.max.y], "center": [t.center.x, t.center.y], "height": t.height, "twist": t.twist.to_degrees(), "current": i == active }))
         .collect();
     Ok(json!({ "tiles": rows }))
 }

crates/engine/src/doc_state.rs

@@ -1,5 +1,5 @@
 use super::view::{ModelTiles, View, usable_view};
-use super::{Arc, Drawing, Handle, Space, blockedit, undoctl};
+use super::{Arc, Drawing, Handle, Space, Vec2, blockedit, undoctl};
 
 #[derive(Clone, Debug)]
 pub struct Snapshot {
@@ -80,6 +80,7 @@ impl DocState {
     pub(crate) fn swap_in(&mut self, snap: Snapshot) -> Snapshot {
         let cur = Snapshot { label: snap.label, doc: std::mem::replace(&mut self.doc, snap.doc), selection: std::mem::take(&mut self.selection) };
         self.follow_layout(&cur.doc);
+        self.reconcile_untiled_twist();
         self.revision += 1;
         cur
     }
@@ -135,7 +136,8 @@ impl DocState {
         match self.active_viewport() {
             Some((_, vp)) => {
                 let k = vp.view_height / vp.height;
-                View { center: vp.view_center + (pv.center - vp.center.xy()) * k, height: pv.height * k }
+                // The viewport's twist turns the model view inside it.
+                View { center: vp.paper_to_model(pv.center), height: pv.height * k, twist: vp.view_twist() }
             }
             None => pv,
         }
@@ -150,16 +152,18 @@ impl DocState {
             if vp.locked {
                 // A locked viewport keeps its scale: pan/zoom the sheet instead.
                 let k0 = vp.view_height / vp.height;
-                let pc = vp.center.xy() + (v.center - vp.view_center) / k0;
-                let paper = View { center: pc, height: v.height / k0 };
+                let pc = vp.model_to_paper(v.center);
+                let paper = View { center: pc, height: v.height / k0, twist: pv.twist };
                 if !usable_view(&paper) {
                     return false;
                 }
                 self.put_paper_view(paper);
             } else {
-                let center = v.center - (pv.center - vp.center.xy()) * k;
+                // `v`'s twist is the one the viewport shows (a non-finite one keeps its own).
+                let twist = if v.twist.is_finite() { v.twist } else { vp.view_twist() };
+                let center = v.center - ((pv.center - vp.center.xy()) * k).rotate(-twist);
                 let height = vp.height * k;
-                if !usable_view(&View { center, height }) {
+                if !usable_view(&View { center, height, twist }) {
                     return false;
                 }
                 let doc = Arc::make_mut(&mut self.doc);
@@ -168,6 +172,7 @@ impl DocState {
                         if let cadcraft_doc::EntityKind::Viewport(x) = &mut e.kind {
                             x.view_center = center;
                             x.view_height = height;
+                            x.twist = twist;
                         }
                     });
                 }
@@ -182,6 +187,36 @@ impl DocState {
             Some((_, slot)) => *slot = v,
             None => self.views.push((self.space.clone(), v)),
         }
+        if self.space == Space::Model {
+            self.keep_untiled_twist(v);
+        }
+    }
+    /// An untiled Model tab keeps its view twist in the drawing as a lone `*Active` VPORT tile
+    /// (written as that record's group 51 and read back), so it survives save and reopen. Only a
+    /// change of twist touches the drawing; an untwisted view keeps no record.
+    /// After undo or redo has put back another drawing: its untiled-twist record follows the
+    /// Model tab's live view again (views are not part of the drawing's undo).
+    pub(crate) fn reconcile_untiled_twist(&mut self) {
+        if let Some(v) = self.views.iter().find(|(s, _)| *s == Space::Model).map(|(_, v)| *v) {
+            self.keep_untiled_twist(v);
+        }
+    }
+    fn keep_untiled_twist(&mut self, v: View) {
+        use cadcraft_doc::{VportConfig, VportTile};
+        let twist = cadcraft_geom::norm_angle(v.twist);
+        let active = self.doc.vports.iter().find(|c| c.is_active());
+        if active.is_some_and(|c| c.tiles.len() > 1) {
+            return;
+        }
+        if active.and_then(|c| c.tiles.first()).map_or(0.0, |t| t.twist) == twist {
+            return;
+        }
+        let d = Arc::make_mut(&mut self.doc);
+        d.vports.retain(|c| !c.is_active());
+        if twist != 0.0 {
+            let tile = VportTile { min: Vec2::ZERO, max: Vec2::new(1.0, 1.0), center: v.center, height: v.height, aspect: 1.0, twist };
+            d.vports.insert(0, VportConfig { name: VportConfig::ACTIVE.into(), tiles: vec![tile] });
+        }
     }
     /// Set the view, recording view history. Returns false, changing nothing, when the view (or,
     /// in MSPACE, the viewport view it maps to) isn't finite with a positive height.
@@ -210,7 +245,7 @@ impl DocState {
     /// The view ZOOM starts from: the model view of the active unlocked viewport, else [`Self::view`].
     pub fn zoom_frame(&self) -> View {
         match self.zoom_viewport() {
-            Some(v) => View { center: v.view_center, height: v.view_height },
+            Some(v) => View { center: v.view_center, height: v.view_height, twist: v.view_twist() },
             None => self.view(),
         }
     }
@@ -225,7 +260,9 @@ impl DocState {
             Some(vp) => {
                 let pv = self.paper_view();
                 let k = f.height / vp.height;
-                View { center: f.center + (pv.center - vp.center.xy()) * k, height: pv.height * k }
+                // The frame's twist turns the viewport (a non-finite one keeps the viewport's).
+                let twist = if f.twist.is_finite() { f.twist } else { vp.view_twist() };
+                View { center: f.center + ((pv.center - vp.center.xy()) * k).rotate(-twist), height: pv.height * k, twist }
             }
             None => f,
         };
@@ -233,7 +270,7 @@ impl DocState {
     }
     /// Set without recording view history (realtime pan/zoom frames).
     pub fn set_view_quiet(&mut self, v: View) {
-        if !(v.center.is_finite() && v.height.is_finite() && v.height > 1e-12) {
+        if !usable_view(&v) {
             return;
         }
         self.store_view(v);

crates/engine/src/guard.rs

@@ -66,6 +66,14 @@ impl Interactive for Guarded {
     fn begin(&mut self, s: &mut Session) -> Result<Step> {
         catch_unwind(AssertUnwindSafe(|| self.inner.begin(s))).unwrap_or_else(|p| Err(self.internal(&*p)))
     }
+    fn cancelled(&mut self, s: &mut Session) {
+        if self.broken.get().is_none()
+            && let Err(p) = catch_unwind(AssertUnwindSafe(|| self.inner.cancelled(s)))
+        {
+            let e = self.internal(&*p);
+            s.echo(e.to_string());
+        }
+    }
     fn preview(&self, s: &Session, cursor: Vec2) -> Vec<EntityKind> {
         if self.broken.get().is_some() {
             return Vec::new();
@@ -102,6 +110,15 @@ impl Interactive for Guarded {
             None
         })
     }
+    fn display_only(&self, s: &Session) -> Option<crate::prompt::DisplayOnly> {
+        if self.broken.get().is_some() {
+            return None;
+        }
+        catch_unwind(AssertUnwindSafe(|| self.inner.display_only(s))).unwrap_or_else(|_| {
+            self.broken.set(Some("panic in preview"));
+            None
+        })
+    }
 }
 
 #[cfg(test)]

crates/engine/src/lib.rs

@@ -49,7 +49,7 @@ pub use cadcraft_geom as geom;
 pub use cadcraft_render as render;
 pub use cmd::hatch::{HatchPicks, PatternChoice, PickMode, pattern_choices};
 pub use cmd::{CommandInfo, CommandSpec, command_specs, find_command};
-pub use prompt::{Accept, Drag, Input, Interactive, Picker, Prompt, Step};
+pub use prompt::{Accept, DisplayOnly, Drag, Input, Interactive, Picker, Prompt, Step};
 
 mod doc_state;
 mod error;

crates/engine/src/prompt.rs

@@ -31,7 +31,7 @@ impl Accept {
 /// [Truecolor/COlorbook] <BYLAYER>:". A prompt asking for something else besides its keywords has
 /// it: "Enter block name or [?]:", "Specify insertion base point or [Basepoint/…]:". Read from
 /// AutoCAD's command line over measured runs, where no prompt was written both ways.
-const NO_OR: [&str; 27] = [
+const NO_OR: [&str; 28] = [
     "Bring to front",
     "Calculate rectangle dimensions based on",
     "Choose mode for selected object conversion",
@@ -47,6 +47,7 @@ const NO_OR: [&str; 27] = [
     "Enter leader format option",
     "Enter line spacing type",
     "Enter object ordering option",
+    "Enter option",
     "Enter polyline linetype generation option",
     "Enter property to change",
     "Enter the type of array",
@@ -266,6 +267,9 @@ pub trait Interactive: Send {
     fn begin(&mut self, _s: &mut Session) -> Result<Step> {
         Ok(Step::Continue)
     }
+    /// Called when the command is cancelled from outside (Esc, or another command starting),
+    /// before it finishes: what it records on every exit path.
+    fn cancelled(&mut self, _s: &mut Session) {}
     /// Rubber-band geometry for the cursor position.
     fn preview(&self, _s: &Session, _cursor: Vec2) -> Vec<EntityKind> {
         Vec::new()
@@ -287,6 +291,22 @@ pub trait Interactive: Send {
     fn editing_mtext(&self) -> Option<cadcraft_doc::MText> {
         None
     }
+    /// What the drawing area shows in place of the drawing while the command runs (DVIEW draws
+    /// only its preview set); `None` shows the drawing.
+    fn display_only(&self, _s: &Session) -> Option<DisplayOnly> {
+        None
+    }
+}
+
+/// See [`Interactive::display_only`]: the only things drawn in the current view while a command
+/// runs. The whole drawing is drawn again when it ends.
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct DisplayOnly {
+    /// Objects of the drawing, drawn as they are.
+    pub handles: Vec<Handle>,
+    /// Geometry that is not in the drawing (DVIEW's sample house, or an insert of the drawing's
+    /// DVIEWBLOCK block), with its own properties.
+    pub extra: Vec<cadcraft_doc::Entity>,
 }
 
 /// See [`Interactive::drag`].

crates/engine/src/select.rs

@@ -527,6 +527,7 @@ mod tests {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         };
         let h = d.add(&Space::Model, Common::default(), EntityKind::Insert(insert)).unwrap();
         (d, h)

crates/engine/src/session/files.rs

@@ -6,7 +6,7 @@ impl Session {
         self.untitled_counter += 1;
         let d = if metric { Drawing::new_metric() } else { Drawing::new_imperial() };
         let mut st = DocState::new(d, &format!("Drawing{}", self.untitled_counter), None);
-        st.set_view_quiet(if metric { View { center: Vec2::new(210.0, 148.5), height: 297.0 } } else { View::default() });
+        st.set_view_quiet(if metric { View { center: Vec2::new(210.0, 148.5), height: 297.0, twist: 0.0 } } else { View::default() });
         self.end_running();
         self.docs.push(st);
         self.active = self.docs.len() - 1;
@@ -18,11 +18,13 @@ impl Session {
     pub fn open_drawing(&mut self, d: Drawing, title: &str, path: Option<String>) -> usize {
         let mut st = DocState::new(d, title, path);
         let ext = st.doc.extents(&Space::Model);
-        if !ext.is_empty() {
-            st.set_view_quiet(View {
-                center: ext.center(),
-                height: (ext.height().max(ext.width() * self.viewport_px.1 / self.viewport_px.0.max(1.0)) * 1.1).max(1e-6),
-            });
+        // The current tile (the first), or the lone untiled view, keeps its saved twist.
+        let twist = cadcraft_geom::norm_angle(st.doc.vports.iter().find(|c| c.is_active()).and_then(|c| c.tiles.first()).map_or(0.0, |t| t.twist));
+        if ext.is_empty() {
+            st.set_view_quiet(View { twist, ..st.view() });
+        } else {
+            let (center, w, h) = View::twisted_box(ext, twist);
+            st.set_view_quiet(View { center, height: (h.max(w * self.viewport_px.1 / self.viewport_px.0.max(1.0)) * 1.1).max(1e-6), twist });
         }
         self.end_running();
         self.docs.push(st);

crates/engine/src/session/interactive.rs

@@ -1,3 +1,5 @@
+use crate::DisplayOnly;
+
 use super::{
     Arc, Bounds2, Drag, Drawing, EngineError, Entity, Handle, Input, PendingWindow, Prompt, Result, Running, Session, Snapshot, Step, Value, Vec2,
     assoc, cmd, find_command, guard, pointmod, select, snap, sysvars,
@@ -199,7 +201,7 @@ impl Session {
             Input::Point(p) => {
                 let ap = self.pixel_size() * self.settings.pickbox.max(1.0) * 1.5;
                 if let Some(pw) = self.pending_window.take() {
-                    let crossing = p.x < pw.corner.x;
+                    let crossing = self.window_is_crossing(pw.corner, p);
                     let hs = select::select_window(self.doc()?, &space, Bounds2::new(pw.corner, p), crossing);
                     return Ok(Some(Input::Pick(cmd::groups::expand(self, hs))));
                 }
@@ -279,7 +281,10 @@ impl Session {
         let base = if matches!(input, Some(Input::Point(_))) { self.current_prompt().and_then(|p| p.base) } else { None };
         let Some(mut run) = self.running.take() else { return Ok(()) };
         let step = match input {
-            Some(Input::Cancel) => Ok(Step::Cancel),
+            Some(Input::Cancel) => {
+                run.machine.cancelled(self);
+                Ok(Step::Cancel)
+            }
             Some(i) => {
                 if let Input::Point(p) = &i {
                     self.last_point = *p;
@@ -438,7 +443,8 @@ impl Session {
         }
         if self.running.is_some() {
             if self.suspended.is_some() {
-                if let Some(nested) = self.running.take() {
+                if let Some(mut nested) = self.running.take() {
+                    nested.machine.cancelled(self);
                     self.finish(nested, true);
                 }
                 self.running = self.suspended.take();
@@ -523,6 +529,13 @@ impl Session {
         out
     }
 
+    /// What the drawing area shows in place of the drawing while a command runs (DVIEW's preview
+    /// set, see [`Interactive::display_only`]), also while a transparent command interrupts it.
+    /// `None`: the drawing.
+    pub fn display_only(&self) -> Option<DisplayOnly> {
+        [&self.running, &self.suspended].into_iter().flatten().find_map(|r| r.machine.display_only(self))
+    }
+
     /// The active command's preview as a transform of existing objects (see
     /// [`Interactive::drag`]), with its extra rubber-band geometry as entities.
     pub fn drag(&self, cursor: Vec2) -> Option<(Drag, Vec<Entity>)> {

crates/engine/src/session/picking.rs

@@ -16,6 +16,13 @@ impl Session {
         true
     }
 
+    /// Whether a selection window from `corner` to `p` is a crossing window: it was dragged
+    /// leftwards on screen (in a twisted view, not along the drawing's X axis).
+    pub fn window_is_crossing(&self, corner: Vec2, p: Vec2) -> bool {
+        let twist = self.state().map_or(0.0, |st| st.view().twist);
+        (p - corner).rotate(twist).x < 0.0
+    }
+
     /// A click with no command running: pick/toggle objects or start a selection window.
     ///
     /// PICKADD on (the default): picks add to the selection and Shift removes. PICKADD off: each pick
@@ -24,7 +31,7 @@ impl Session {
         let space = self.space();
         let pickadd = self.settings.pickadd;
         if let Some(pw) = self.pending_window.take() {
-            let crossing = p.x < pw.corner.x;
+            let crossing = self.window_is_crossing(pw.corner, p);
             let hs = select::select_window(self.doc()?, &space, Bounds2::new(pw.corner, p), crossing);
             let hs = cmd::groups::expand(self, hs);
             let mut sel = if pickadd || shift { self.selection() } else { Vec::new() };

crates/engine/src/session/zoom.rs

@@ -23,8 +23,10 @@ impl Session {
         let ext = if ext.is_empty() { self.zoom_limits()? } else { ext };
         let st = self.state_mut()?;
         let aspect = st.zoom_aspect(w / h.max(1.0));
-        let height = ext.height().max(ext.width() / aspect.max(1e-6)).max(1e-6) * 1.05;
-        st.set_zoom_frame(View { center: ext.center(), height });
+        let twist = st.zoom_frame().twist;
+        let (center, bw, bh) = View::twisted_box(ext, twist);
+        let height = bh.max(bw / aspect.max(1e-6)).max(1e-6) * 1.05;
+        st.set_zoom_frame(View { center, height, twist });
         Ok(())
     }
 
@@ -38,7 +40,7 @@ impl Session {
         let h = (v.height / factor).clamp(1e-9, 1e12);
         let k = h / v.height;
         let c = about + (v.center - about) * k;
-        st.set_view_quiet(View { center: c, height: h });
+        st.set_view_quiet(View { center: c, height: h, twist: v.twist });
         Ok(())
     }
 }

crates/engine/src/snap.rs

@@ -714,6 +714,7 @@ impl Sink<'_> {
                     rows: 1,
                     col_spacing: 0.0,
                     row_spacing: 0.0,
+                    clip: None,
                 };
                 block_leaves(d, &ins, &Mat3::IDENTITY, 0, budget, frozen, &mut |k, m| self.object(k, Some(m)));
             }

crates/engine/src/snap/viewport.rs

@@ -40,7 +40,8 @@ impl<'a> Projection<'a> {
         }
         let half = Vec2::new(viewport.width / 2.0, viewport.height / 2.0);
         let paper_clip = Bounds2::new(center - half, center + half);
-        let model_clip = Bounds2::new(viewport.view_center - half / scale, viewport.view_center + half / scale);
+        // The model box the viewport shows (turned, with a view twist).
+        let model_clip = Bounds2::from_points(paper_clip.corners().map(|p| viewport.paper_to_model(p)));
         if ![paper_clip.min, paper_clip.max, model_clip.min, model_clip.max].into_iter().all(Vec2::is_finite) {
             return None;
         }
@@ -48,11 +49,11 @@ impl<'a> Projection<'a> {
     }
 
     pub fn to_model(&self, point: Vec2) -> Vec2 {
-        self.viewport.view_center + (point - self.viewport.center.xy()) / self.scale
+        self.viewport.paper_to_model(point)
     }
 
     fn to_paper(&self, point: Vec2) -> Vec2 {
-        self.viewport.center.xy() + (point - self.viewport.view_center) * self.scale
+        self.viewport.model_to_paper(point)
     }
 
     pub fn hit(&self, mut hit: SnapHit) -> Option<SnapHit> {
@@ -76,7 +77,9 @@ impl<'a> Projection<'a> {
                     if !(center.is_finite() && radius.is_finite() && radius > 0.0) {
                         return None;
                     }
-                    SnapCurve::Arc { center, radius, start, end }
+                    // The arc turns on the sheet with the viewport's twist.
+                    let twist = self.viewport.view_twist();
+                    SnapCurve::Arc { center, radius, start: start + twist, end: end + twist }
                 }
                 SnapCurve::Line { a, b } => {
                     let (a, b) = (self.to_paper(a), self.to_paper(b));

crates/engine/src/spatial.rs

@@ -364,6 +364,7 @@ mod tests {
                     rows: 1,
                     col_spacing: 0.0,
                     row_spacing: 0.0,
+                    clip: None,
                 }),
                 8 if i % 40 == 8 => EntityKind::XLine(cadcraft_doc::RayLine { base: v3(x, y), dir: v3(r.r(-1.0, 1.0), 1.0) }),
                 8 if i % 40 == 18 => EntityKind::Ray(cadcraft_doc::RayLine { base: v3(x, y), dir: v3(1.0, r.r(-1.0, 1.0)) }),
@@ -546,6 +547,7 @@ mod tests {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         };
         let h = d.add(&Space::Model, Common::default(), EntityKind::Insert(insert)).unwrap();
         let small = Bounds2::new(Vec2::new(-2.0, -2.0), Vec2::new(2.0, 2.0));

crates/engine/src/sysvars.rs

@@ -184,6 +184,8 @@ pub fn get(s: &Session, name: &str) -> Option<Value> {
             json!([v.center.x, v.center.y, 0.0])
         }
         "VIEWSIZE" => json!(s.state().ok()?.view().height),
+        // The view twist (DVIEW TWist), in degrees counterclockwise.
+        "VIEWTWIST" => json!(s.state().ok()?.view().twist.to_degrees()),
         "EXTMIN" | "EXTMAX" => {
             let d = s.doc().ok()?;
             let e = d.extents(&s.space());
@@ -260,6 +262,7 @@ const READ_ONLY: &[&str] = &[
     "DISTANCE",
     "VIEWCTR",
     "VIEWSIZE",
+    "VIEWTWIST",
     "EXTMIN",
     "EXTMAX",
     "UNDOCTL",

crates/engine/src/sysvars/table.rs

@@ -74,6 +74,8 @@ const HEADER: &[(&str, Kind, Def)] = &[
     ("TRIMEXTENDMODE", Kind::Choice(&[0, 1]), Def::Int(1)),
     ("TRIMMODE", Kind::Choice(&[0, 1]), Def::Int(1)),
     ("WIPEOUTFRAME", Kind::Choice(&[0, 1, 2]), Def::Int(1)),
+    // XCLIP boundaries: 0 hidden, 1 shown and plotted, 2 shown but not plotted.
+    ("XCLIPFRAME", Kind::Choice(&[0, 1, 2]), Def::Int(2)),
 ];
 
 /// The standard lineweights in hundredths of a millimetre.

crates/engine/src/tests.rs

@@ -185,7 +185,7 @@ fn move_with_pickfirst_and_window_selection() {
     s.execute("line", &json!({"points": [[0, 0], [1, 0]]})).unwrap();
     s.execute("line", &json!({"points": [[5, 5], [6, 5]]})).unwrap();
     s.viewport_px = (1000.0, 1000.0);
-    s.state_mut().unwrap().set_view(View { center: Vec2::new(3.0, 3.0), height: 10.0 });
+    s.state_mut().unwrap().set_view(View { center: Vec2::new(3.0, 3.0), height: 10.0, twist: 0.0 });
     // Window selection from left to right picks only the first line.
     s.cmdline("move").unwrap();
     s.input(Input::Point(Vec2::new(-1.0, -1.0))).unwrap();

crates/engine/src/view.rs

@@ -1,20 +1,38 @@
+use cadcraft_geom::Bounds2;
+
 use super::{Deserialize, Serialize, Vec2};
 
-/// A 2D view of a space: world centre and visible height in drawing units.
+/// A 2D view of a space: world centre and visible height in drawing units, and the view twist
+/// (VIEWTWIST, DVIEW TWist): how far the view is turned on screen, in radians counterclockwise
+/// (the drawing appears turned by `twist`; 0 is the plain plan view).
 #[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
 pub struct View {
     pub center: Vec2,
     pub height: f64,
+    #[serde(default)]
+    pub twist: f64,
 }
 
 impl Default for View {
     fn default() -> Self {
-        View { center: Vec2::new(6.0, 4.5), height: 10.0 }
+        View { center: Vec2::new(6.0, 4.5), height: 10.0, twist: 0.0 }
+    }
+}
+
+impl View {
+    /// Box `b` (world) as a view turned by `twist` shows it: the world centre of the box it
+    /// makes on screen, and that box's width and height (`b`'s own when there is no twist).
+    pub fn twisted_box(b: Bounds2, twist: f64) -> (Vec2, f64, f64) {
+        if twist == 0.0 || !twist.is_finite() {
+            return (b.center(), b.width(), b.height());
+        }
+        let r = Bounds2::from_points(b.corners().map(|p| p.rotate(twist)));
+        (r.center().rotate(-twist), r.width(), r.height())
     }
 }
 
 pub(crate) fn usable_view(v: &View) -> bool {
-    v.center.is_finite() && v.height.is_finite() && v.height > 1e-12
+    v.center.is_finite() && v.height.is_finite() && v.height > 1e-12 && v.twist.is_finite()
 }
 
 /// Tiled model viewports (VPORTS): the session side of the drawing's `*Active` configuration.

crates/engine/tests/audit.rs

@@ -24,6 +24,7 @@ fn insert(block: &str) -> EntityKind {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     })
 }
 

crates/engine/tests/autosave.rs

@@ -487,6 +487,7 @@ fn a_block_editor_that_cannot_be_composed_is_not_autosaved_as_the_old_host() {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     });
     d.model.push(Entity::new(h, kind));
     assert!(s.state().unwrap().recovery_drawing().is_err());

crates/engine/tests/clipboard.rs

@@ -28,6 +28,7 @@ fn insert(d: &mut Drawing, block: &str, at: (f64, f64)) -> Entity {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     });
     Entity { handle: d.new_handle(), common: Common::default(), kind }
 }

crates/engine/tests/compare.rs

@@ -124,6 +124,7 @@ fn hooks() {
                 rows: 1,
                 col_spacing: 0.0,
                 row_spacing: 0.0,
+                clip: None,
             };
             d.add(&Space::Model, Common::default(), EntityKind::Insert(insert)).map_err(|e| e.to_string())?;
             return Ok(d);
@@ -175,6 +176,7 @@ fn hostile_inputs_are_errors() {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     };
     b.entities.push(Entity::new(cadcraft_engine::doc::Handle(0x900), EntityKind::Insert(ins.clone())));
     let d = s.doc_mut().unwrap();

crates/engine/tests/dview.rs

@@ -0,0 +1,381 @@
+//! DVIEW starts with "Select objects or <use DVIEWBLOCK>:", then the option prompt;
+//! TWist, PAn, Zoom, Off and Undo on a 2D view; the 3D options not available yet. It works on the
+//! Model tab and inside an active layout viewport (whose twist is an undoable edit of the
+//! viewport), and not on a layout sheet.
+
+use cadcraft_doc::{EntityKind, Handle, Viewport};
+use cadcraft_engine::geom::Vec2;
+use cadcraft_engine::{Input, Session, View};
+use serde_json::json;
+
+const SELECT: &str = "Select objects or <use DVIEWBLOCK>:";
+const OPTION: &str = "Enter option [CAmera/TArget/Distance/POints/PAn/Zoom/TWist/CLip/Hide/Off/Undo]:";
+const PAPER: &str = "This command is not available in Paper space.";
+
+fn session() -> Session {
+    let mut s = Session::new();
+    s.viewport_px = (1200.0, 800.0);
+    s.execute("line", &json!({ "points": [[0, 0], [100, 50]] })).unwrap();
+    s.execute("view.set", &json!({ "center": [10, 10], "height": 20 })).unwrap();
+    s
+}
+
+fn prompt(s: &Session) -> String {
+    s.current_prompt().map(|p| p.display()).unwrap_or_default()
+}
+
+fn view(s: &Session) -> View {
+    s.state().unwrap().view()
+}
+
+fn near(a: f64, b: f64) -> bool {
+    (a - b).abs() < 1e-9
+}
+
+fn twist_deg(s: &Session) -> f64 {
+    view(s).twist.to_degrees()
+}
+
+fn logged(s: &Session, m: &str) -> bool {
+    s.log.iter().any(|l| l == m)
+}
+
+#[test]
+fn every_prompt_step_on_the_model_tab() {
+    let mut s = session();
+    let undo = s.state().unwrap().undo.len();
+    s.cmdline("dview").unwrap();
+    assert_eq!(prompt(&s), SELECT);
+    // The whole drawing shows while objects are picked.
+    assert!(s.display_only().is_none());
+    // Enter with nothing selected: the DVIEWBLOCK sample (a house of lines) is the preview set.
+    s.cmdline("").unwrap();
+    assert_eq!(prompt(&s), OPTION);
+    let only = s.display_only().unwrap();
+    assert!(only.handles.is_empty());
+    assert!(only.extra.len() > 10 && only.extra.iter().all(|e| matches!(e.kind, EntityKind::Line(_))));
+    twist_pan_and_zoom(&mut s);
+    // The sample house stays where it was put: the view moves over it.
+    assert_eq!(s.display_only().unwrap(), only);
+    off_and_unavailable_options(&mut s);
+    undo_steps(&mut s);
+
+    // An unknown option is refused and asked again.
+    assert!(s.cmdline("bogus").is_ok());
+    assert_eq!(prompt(&s), OPTION);
+
+    // Enter ends DVIEW; the whole drawing shows again, and a Model tab twist is no undo step.
+    s.cmdline("tw").unwrap();
+    s.cmdline("45").unwrap();
+    s.cmdline("").unwrap();
+    assert!(s.current_prompt().is_none());
+    assert!(s.display_only().is_none());
+    assert!(near(twist_deg(&s), 45.0));
+    assert_eq!(s.state().unwrap().undo.len(), undo);
+}
+
+/// DVIEW's TWist, PAn and Zoom steps from the option prompt of a fresh Model tab session.
+fn twist_pan_and_zoom(s: &mut Session) {
+    // TWist: the current twist is the default; a typed angle turns the view.
+    s.cmdline("tw").unwrap();
+    assert_eq!(prompt(s), "Specify view twist angle <0>:");
+    s.cmdline("30").unwrap();
+    assert!(near(twist_deg(s), 30.0));
+    assert_eq!(prompt(s), OPTION);
+    s.cmdline("TWist").unwrap();
+    assert_eq!(prompt(s), "Specify view twist angle <30>:");
+    // Enter keeps it.
+    s.cmdline("").unwrap();
+    assert!(near(twist_deg(s), 30.0));
+
+    // PAn: base point, second point.
+    s.cmdline("pa").unwrap();
+    assert_eq!(prompt(s), "Specify displacement base point:");
+    s.cmdline("0,0").unwrap();
+    assert_eq!(prompt(s), "Specify second point:");
+    s.cmdline("4,0").unwrap();
+    assert_eq!(view(s).center, Vec2::new(6.0, 10.0));
+    assert_eq!(prompt(s), OPTION);
+
+    // Zoom: a scale factor of the current view.
+    s.cmdline("z").unwrap();
+    assert_eq!(prompt(s), "Specify zoom scale factor <1>:");
+    s.cmdline("2").unwrap();
+    assert!(near(view(s).height, 10.0));
+}
+
+/// DVIEW's Off option and the options that need a 3D camera.
+fn off_and_unavailable_options(s: &mut Session) {
+    // Off: perspective is never on in a 2D view, so nothing changes.
+    let before = view(s);
+    s.cmdline("o").unwrap();
+    assert_eq!(prompt(s), OPTION);
+    assert_eq!(view(s), before);
+
+    // The options that need a 3D camera are not available yet and stay at the option prompt.
+    for (typed, name) in [("ca", "CAmera"), ("ta", "TArget"), ("d", "Distance"), ("po", "POints"), ("cl", "CLip"), ("h", "Hide")] {
+        s.cmdline(typed).unwrap();
+        assert!(logged(s, &format!("DVIEW {name} is not available yet.")), "{name}: {:?}", s.log);
+        assert_eq!(prompt(s), OPTION);
+    }
+    assert!(!s.log.iter().any(|l| l.contains("Only the view twist")));
+}
+
+/// DVIEW's Undo after [`twist_pan_and_zoom`].
+fn undo_steps(s: &mut Session) {
+    // Undo takes back one DVIEW action at a time: zoom, pan, twist.
+    s.cmdline("u").unwrap();
+    assert!(near(view(s).height, 20.0));
+    s.cmdline("u").unwrap();
+    assert_eq!(view(s).center, Vec2::new(10.0, 10.0));
+    assert!(near(twist_deg(s), 30.0));
+    s.cmdline("u").unwrap();
+    assert_eq!(view(s).twist, 0.0);
+    // Nothing left to undo: still at the option prompt.
+    s.cmdline("u").unwrap();
+    assert_eq!(prompt(s), OPTION);
+}
+
+#[test]
+fn selected_objects_are_the_preview_set() {
+    let mut s = session();
+    let line = s.doc().unwrap().model.iter().next().map(|e| e.handle).unwrap();
+    s.execute("line", &json!({ "points": [[0, 10], [10, 10]] })).unwrap();
+    s.cmdline("dview").unwrap();
+    s.input(Input::Pick(vec![line])).unwrap();
+    assert_eq!(prompt(&s), SELECT);
+    s.cmdline("").unwrap();
+    assert_eq!(prompt(&s), OPTION);
+    let only = s.display_only().unwrap();
+    assert_eq!(only.handles, vec![line]);
+    assert!(only.extra.is_empty(), "no sample house with a selection");
+    // Picked at the prompt, the objects don't stay selected.
+    assert!(s.selection().is_empty());
+    // Escape ends it too, and the drawing shows again.
+    s.input(Input::Cancel).unwrap();
+    assert!(s.current_prompt().is_none());
+    assert!(s.display_only().is_none());
+}
+
+#[test]
+fn a_dviewblock_of_the_drawings_own_is_previewed() {
+    let mut s = session();
+    s.execute("circle", &json!({ "center": [0.5, 0.5], "radius": 0.5 })).unwrap();
+    let c = s.doc().unwrap().model.iter().last().map(|e| e.handle).unwrap();
+    s.execute("block", &json!({ "name": "DVIEWBLOCK", "base": [0, 0], "handles": [c.hex()], "keep": "delete" })).unwrap();
+    s.cmdline("dview").unwrap();
+    s.cmdline("").unwrap();
+    let only = s.display_only().unwrap();
+    assert_eq!(only.extra.len(), 1);
+    match &only.extra[0].kind {
+        EntityKind::Insert(i) => {
+            assert_eq!(i.block, "DVIEWBLOCK");
+            // Scaled from its 1 by 1 unit area to half the view's height.
+            assert!(near(i.scale.x, 10.0) && near(i.scale.y, 10.0));
+        }
+        k => panic!("{k:?}"),
+    }
+    s.cmdline("").unwrap();
+}
+
+/// A layout with one viewport, `(session, viewport handle)`.
+fn layout_session() -> (Session, Handle) {
+    let mut s = session();
+    s.execute("layout.set", &json!({ "name": "Layout1" })).unwrap();
+    let r = s.execute("mview", &json!({ "p1": [20, 20], "p2": [220, 120] })).unwrap();
+    let h = Handle::parse_hex(r["viewports"][0].as_str().unwrap()).unwrap();
+    (s, h)
+}
+
+fn vp(s: &Session, h: Handle) -> Viewport {
+    match &s.doc().unwrap().entity(h).unwrap().kind {
+        EntityKind::Viewport(v) => v.clone(),
+        _ => panic!("not a viewport"),
+    }
+}
+
+#[test]
+fn on_a_layout_sheet_it_is_not_available() {
+    let (mut s, _) = layout_session();
+    assert_eq!(s.execute("dview", &json!({ "twist": 10 })).unwrap_err().to_string(), PAPER);
+    assert_eq!(s.cmdline("dview").unwrap_err().to_string(), PAPER);
+    assert!(s.current_prompt().is_none());
+    // view.set can't turn the sheet either; an untwisted view is fine.
+    assert_eq!(s.execute("view.set", &json!({ "center": [0, 0], "height": 5, "twist": 15 })).unwrap_err().to_string(), PAPER);
+    s.execute("view.set", &json!({ "center": [0, 0], "height": 5 })).unwrap();
+}
+
+#[test]
+fn inside_an_active_viewport_it_twists_that_viewport_as_one_undo_step() {
+    let (mut s, h) = layout_session();
+    s.execute("mspace", &json!({ "handle": h.hex() })).unwrap();
+    let undo = s.state().unwrap().undo.len();
+    let pv = s.state().unwrap().paper_view();
+    s.cmdline("dview").unwrap();
+    assert_eq!(prompt(&s), SELECT);
+    s.cmdline("").unwrap();
+    s.cmdline("tw").unwrap();
+    s.cmdline("30").unwrap();
+    // The viewport entity carries the twist, and the model view inside it is turned by it.
+    assert!(near(vp(&s, h).twist.to_degrees(), 30.0));
+    assert!(near(twist_deg(&s), 30.0));
+    // The sheet itself is not turned.
+    assert_eq!(s.state().unwrap().paper_view(), pv);
+    s.cmdline("tw").unwrap();
+    s.cmdline("50").unwrap();
+    s.cmdline("").unwrap();
+    assert!(s.current_prompt().is_none());
+    assert!(near(vp(&s, h).twist.to_degrees(), 50.0));
+    // One undo step for the whole DVIEW, which turns the viewport back.
+    assert_eq!(s.state().unwrap().undo.len(), undo + 1);
+    s.execute("undo", &json!({})).unwrap();
+    assert_eq!(vp(&s, h).twist, 0.0);
+
+    // The JSON form and view.set twist the viewport the same way, each one undo step.
+    s.execute("dview", &json!({ "twist": -90 })).unwrap();
+    assert!(near(vp(&s, h).twist.to_degrees(), 270.0));
+    assert_eq!(s.state().unwrap().undo.len(), undo + 1);
+    let v = view(&s);
+    s.execute("view.set", &json!({ "center": [v.center.x, v.center.y], "height": v.height, "twist": 15 })).unwrap();
+    assert!(near(vp(&s, h).twist.to_degrees(), 15.0));
+    assert_eq!(s.state().unwrap().undo.len(), undo + 2);
+    // Setting a view without a twist keeps the viewport's.
+    s.execute("view.set", &json!({ "center": [v.center.x, v.center.y], "height": v.height })).unwrap();
+    assert!(near(vp(&s, h).twist.to_degrees(), 15.0));
+    assert_eq!(s.state().unwrap().undo.len(), undo + 2);
+
+    // Back on the sheet, DVIEW is not available again.
+    s.execute("pspace", &json!({})).unwrap();
+    assert_eq!(s.cmdline("dview").unwrap_err().to_string(), PAPER);
+}
+
+#[test]
+fn a_locked_viewport_keeps_its_twist() {
+    let (mut s, h) = layout_session();
+    s.doc_mut()
+        .unwrap()
+        .modify_entity(h, |e| {
+            if let EntityKind::Viewport(v) = &mut e.kind {
+                v.locked = true;
+            }
+        })
+        .unwrap();
+    s.execute("mspace", &json!({ "handle": h.hex() })).unwrap();
+    let undo = s.state().unwrap().undo.len();
+    assert!(s.execute("dview", &json!({ "twist": 30 })).is_err());
+    let v = view(&s);
+    assert!(s.execute("view.set", &json!({ "center": [v.center.x, v.center.y], "height": v.height, "twist": 30 })).is_err());
+    assert_eq!(vp(&s, h).twist, 0.0);
+    assert_eq!(s.state().unwrap().undo.len(), undo);
+    // A view with the twist it already has is fine.
+    s.execute("view.set", &json!({ "center": [v.center.x, v.center.y], "height": v.height })).unwrap();
+}
+
+#[test]
+fn escape_inside_an_active_viewport_keeps_the_twist_as_one_undo_step() {
+    let (mut s, h) = layout_session();
+    s.execute("mspace", &json!({ "handle": h.hex() })).unwrap();
+    let undo = s.state().unwrap().undo.len();
+    for l in ["dview", "", "tw", "30"] {
+        s.cmdline(l).unwrap();
+    }
+    s.input(Input::Cancel).unwrap();
+    assert!(s.current_prompt().is_none());
+    assert!(near(vp(&s, h).twist.to_degrees(), 30.0));
+    assert_eq!(s.state().unwrap().undo.len(), undo + 1);
+    s.execute("undo", &json!({})).unwrap();
+    assert_eq!(vp(&s, h).twist, 0.0);
+}
+
+#[test]
+fn the_view_inside_a_twisted_viewport_maps_the_screen_like_the_sheet() {
+    let (mut s, h) = layout_session();
+    s.execute("mspace", &json!({ "handle": h.hex() })).unwrap();
+    s.execute("dview", &json!({ "twist": 30 })).unwrap();
+    let st = s.state().unwrap();
+    let (vpe, pv, v) = (vp(&s, h), st.paper_view(), st.view());
+    // The model view's centre is the model point at the sheet's view centre.
+    assert!((vpe.model_to_paper(v.center) - pv.center).len() < 1e-9);
+    assert!(near(v.twist, vpe.twist));
+    // Panning the view inside the viewport moves its model view, keeping the twist.
+    let moved = View { center: v.center + Vec2::new(5.0, -2.0), ..v };
+    s.state_mut().unwrap().set_view(moved);
+    let after = view(&s);
+    assert!((after.center - moved.center).len() < 1e-9, "{after:?}");
+    assert!(near(after.twist, vpe.twist));
+    assert_eq!(s.state().unwrap().paper_view(), pv);
+    // ZOOM Extents fits the turned box of the drawing in the viewport.
+    s.execute("zoom", &json!({ "mode": "extents" })).unwrap();
+    assert!(near(view(&s).twist, vpe.twist));
+}
+
+#[test]
+fn a_viewport_twist_survives_a_dxf_round_trip() {
+    let (mut s, h) = layout_session();
+    s.execute("mspace", &json!({ "handle": h.hex() })).unwrap();
+    s.execute("dview", &json!({ "twist": 30 })).unwrap();
+    let dxf = cadcraft_io::write_dxf(s.doc().unwrap());
+    let back = cadcraft_io::read_dxf(dxf.as_bytes()).unwrap();
+    let twists: Vec<f64> = back
+        .layouts
+        .iter()
+        .flat_map(|l| l.entities.iter())
+        .filter_map(|e| match &e.kind {
+            EntityKind::Viewport(v) if v.id != 1 => Some(v.twist.to_degrees()),
+            _ => None,
+        })
+        .collect();
+    assert_eq!(twists.len(), 1);
+    assert!((twists[0] - 30.0).abs() < 1e-9, "{twists:?}");
+}
+
+#[test]
+fn a_view_saved_in_a_twisted_viewport_restores_its_twist_as_one_undo_step() {
+    let (mut s, h) = layout_session();
+    s.execute("mspace", &json!({ "handle": h.hex() })).unwrap();
+    s.execute("dview", &json!({ "twist": 30 })).unwrap();
+    s.execute("view", &json!({ "option": "save", "name": "Turned" })).unwrap();
+    let saved = s.doc().unwrap().views.iter().find(|v| v.name == "Turned").map(|v| v.twist.to_degrees()).unwrap();
+    assert!(near(saved, 30.0), "saved twist {saved}");
+    let center = vp(&s, h).view_center;
+    s.execute("dview", &json!({ "twist": 0 })).unwrap();
+    s.execute("view.set", &json!({ "center": [80, 40], "height": 3 })).unwrap();
+    let undo = s.state().unwrap().undo.len();
+    s.execute("view", &json!({ "option": "restore", "name": "Turned" })).unwrap();
+    assert!(near(vp(&s, h).twist.to_degrees(), 30.0), "viewport twist {}", vp(&s, h).twist.to_degrees());
+    assert!(near(twist_deg(&s), 30.0));
+    assert!((vp(&s, h).view_center - center).len() < 1e-6, "{:?} vs {center:?}", vp(&s, h).view_center);
+    // The viewport's twist changed: one undo step, which turns it back.
+    assert_eq!(s.state().unwrap().undo.len(), undo + 1);
+    s.execute("undo", &json!({})).unwrap();
+    assert_eq!(vp(&s, h).twist, 0.0);
+}
+
+#[test]
+fn undoing_a_drawing_change_keeps_the_untiled_twist_saved() {
+    let mut s = session();
+    s.execute("line", &json!({ "points": [[0, 10], [5, 10]] })).unwrap();
+    // A Model tab twist is a view change, not an undo step.
+    s.execute("dview", &json!({ "twist": 30 })).unwrap();
+    s.execute("undo", &json!({})).unwrap();
+    assert!(near(twist_deg(&s), 30.0));
+    let saved = |s: &Session| s.doc().unwrap().vports.iter().find(|c| c.is_active()).and_then(|c| c.tiles.first()).map(|t| t.twist.to_degrees());
+    assert!(saved(&s).is_some_and(|t| near(t, 30.0)), "{:?}", saved(&s));
+    s.execute("redo", &json!({})).unwrap();
+    assert!(saved(&s).is_some_and(|t| near(t, 30.0)), "{:?}", saved(&s));
+}
+
+#[test]
+fn a_leftward_drag_on_a_turned_screen_is_a_crossing_window() {
+    let mut s = session();
+    let r = s.execute("line", &json!({ "points": [[200, 0], [260, 0]] })).unwrap();
+    let line = Handle::parse_hex(r["handles"][0].as_str().unwrap()).unwrap();
+    s.execute("dview", &json!({ "twist": 180 })).unwrap();
+    // Turned half way round, a drag towards +X in the drawing runs leftwards on screen.
+    assert!(s.window_is_crossing(Vec2::new(210.0, -5.0), Vec2::new(230.0, 5.0)));
+    assert!(!s.window_is_crossing(Vec2::new(230.0, -5.0), Vec2::new(210.0, 5.0)));
+    // A crossing window takes the line it only partly covers.
+    s.idle_click(Vec2::new(210.0, -5.0), false).unwrap();
+    s.idle_click(Vec2::new(230.0, 5.0), false).unwrap();
+    assert_eq!(s.selection(), vec![line]);
+}

crates/engine/tests/image_attach.rs

@@ -0,0 +1,376 @@
+//! Raster images (#956): IMAGEATTACH from a file and from handed-over bytes, the pixels loaded
+//! again when the drawing is reopened, a missing file left as a frame, and bad input refused.
+
+use std::path::{Path, PathBuf};
+
+use cadcraft_engine::Session;
+use cadcraft_engine::cmd::file::{IoHooks, base64_encode, set_image_decoder, set_io};
+use cadcraft_engine::doc::{Drawing, EntityKind, Image, Raster};
+use serde_json::{Value, json};
+
+fn hooks() {
+    set_io(IoHooks {
+        read: |b, name| cadcraft_io::read(b, name).map_err(|e| e.to_string()),
+        write: |d, name| cadcraft_io::write(d, name).map_err(|e| e.to_string()),
+        plot: None,
+    });
+    set_image_decoder(|b| cadcraft_io::raster::decode(b).map_err(|e| e.to_string()));
+}
+
+/// A fresh folder for one test.
+fn folder(tag: &str) -> PathBuf {
+    let dir = std::env::temp_dir().join(format!("cadcraft-image-{}-{tag}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    dir
+}
+
+/// A PNG file of 4 x 2 pixels.
+fn png() -> Vec<u8> {
+    let px: Vec<u8> = (0..8u8).flat_map(|i| [i * 30, 255 - i * 30, 7, 255]).collect();
+    cadcraft_io::raster::encode_png(&Raster::new(4, 2, px).unwrap()).unwrap()
+}
+
+fn images(s: &Session) -> Vec<Image> {
+    let d = s.doc().unwrap();
+    d.model.iter().filter_map(|e| if let EntityKind::Image(i) = &e.kind { Some(i.clone()) } else { None }).collect()
+}
+
+fn open(s: &mut Session, path: &Path) {
+    s.execute("open", &json!({ "path": path.to_string_lossy() })).unwrap();
+}
+
+fn listed(s: &mut Session) -> Value {
+    s.execute("image", &json!({})).unwrap()["images"].clone()
+}
+
+#[test]
+fn attach_from_bytes_places_the_image() {
+    hooks();
+    let mut s = Session::new();
+    let r = s.execute("imageattach", &json!({ "path": "maps/site.png", "data": base64_encode(&png()), "at": [10, 20], "width": 100 })).unwrap();
+    assert_eq!((r["name"].as_str(), r["pixels"].clone(), r["size"].clone()), (Some("site"), json!([4.0, 2.0]), json!([100.0, 50.0])));
+    let i = images(&s).pop().unwrap();
+    assert_eq!((i.insert.x, i.insert.y, i.u.x, i.u.y, i.v.x, i.v.y), (10.0, 20.0, 25.0, 0.0, 0.0, 25.0));
+    assert_eq!((i.size.x, i.size.y, i.path.as_str(), i.name.as_str()), (4.0, 2.0, "maps/site.png", "site"));
+    assert_eq!(s.doc().unwrap().rasters.get("maps/site.png").map(|r| (r.width(), r.height())), Some((4, 2)));
+    let l = listed(&mut s);
+    assert_eq!((l[0]["status"].as_str(), l[0]["references"].as_u64(), l[0]["pixels"].clone()), (Some("Loaded"), Some(1), json!([4, 2])));
+
+    // A second reference to the same file shares the definition and the pixels; another file
+    // with the same file name gets its own name.
+    s.execute("imageattach", &json!({ "path": "maps/site.png", "at": [200, 0], "rotation": 90, "scale": 8 })).unwrap();
+    let r = s.execute("attach", &json!({ "path": "other/site.png", "data": base64_encode(&png()) })).unwrap();
+    assert_eq!(r["name"], "site_2");
+    let all = images(&s);
+    assert_eq!(all.len(), 3);
+    assert_eq!(all[1].name, "site");
+    assert!((all[1].u.x).abs() < 1e-12 && (all[1].u.y - 2.0).abs() < 1e-12 && (all[1].v.x + 2.0).abs() < 1e-12, "{:?}", all[1]);
+    assert_eq!(listed(&mut s)[0]["references"], 2);
+
+    // Undo takes the reference away; the drawing draws with its pixels.
+    s.execute("undo", &json!({})).unwrap();
+    assert_eq!(images(&s).len(), 2);
+    let list = cadcraft_engine::render::build(s.doc().unwrap(), &cadcraft_engine::doc::Space::Model, &cadcraft_engine::render::Options::default());
+    assert_eq!(list.images.len(), 2);
+}
+
+#[test]
+fn a_file_is_found_next_to_the_drawing_and_loaded_again_on_open() {
+    hooks();
+    let dir = folder("file");
+    std::fs::write(dir.join("map.png"), png()).unwrap();
+    let host = dir.join("host.dxf");
+    std::fs::write(&host, cadcraft_io::write(&Drawing::new_metric(), "host.dxf").unwrap()).unwrap();
+    let mut s = Session::new();
+    open(&mut s, &host);
+    let r = s.execute("imageattach", &json!({ "path": "map.png" })).unwrap();
+    assert_eq!(r["size"], json!([1.0, 0.5]), "one drawing unit wide by default");
+    s.execute("qsave", &json!({})).unwrap();
+
+    // Reopened: the pixels come back from the file.
+    let mut s = Session::new();
+    open(&mut s, &host);
+    assert_eq!(images(&s).len(), 1);
+    assert!(s.doc().unwrap().rasters.get("map.png").is_some());
+    assert!(!s.state().unwrap().is_dirty(), "loading images is not a change");
+    let l = listed(&mut s);
+    assert_eq!(l[0]["status"], "Loaded");
+    assert!(l[0]["foundAt"].as_str().is_some_and(|f| f.ends_with("map.png")));
+
+    // The file gone: the drawing still opens, says so, and keeps the reference.
+    std::fs::remove_file(dir.join("map.png")).unwrap();
+    let mut s = Session::new();
+    open(&mut s, &host);
+    assert_eq!(images(&s).len(), 1);
+    assert!(s.doc().unwrap().rasters.get("map.png").is_none());
+    assert!(s.log.iter().any(|l| l.contains("map.png") && l.contains("file not found")), "{:?}", s.log);
+    assert_eq!(listed(&mut s)[0]["status"], "Not Found");
+
+    // A file that is not an image is reported the same way.
+    std::fs::write(dir.join("map.png"), b"not an image").unwrap();
+    let mut s = Session::new();
+    open(&mut s, &host);
+    assert!(s.doc().unwrap().rasters.get("map.png").is_none());
+    assert!(s.log.iter().any(|l| l.contains("map.png")), "{:?}", s.log);
+    assert_eq!(listed(&mut s)[0]["status"], "Not loaded");
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+#[test]
+fn bad_input_is_refused_and_changes_nothing() {
+    hooks();
+    let mut s = Session::new();
+    let data = base64_encode(&png());
+    for p in [
+        json!({}),
+        json!({ "path": "  " }),
+        json!({ "path": "nowhere/missing.png" }),
+        json!({ "path": "a.png", "data": "***" }),
+        json!({ "path": "a.png", "data": 5 }),
+        json!({ "path": "a.png", "data": base64_encode(b"plain text") }),
+        json!({ "path": "a.png", "data": data, "scale": 0 }),
+        json!({ "path": "a.png", "data": data, "width": -3 }),
+        json!({ "path": "a.png", "data": data, "width": "wide" }),
+        json!({ "path": "a.png", "data": data, "width": 1e-320 }),
+        json!({ "path": "x".repeat(5000), "data": data }),
+    ] {
+        assert!(s.execute("imageattach", &p).is_err(), "{p}");
+    }
+    assert!(images(&s).is_empty());
+    assert!(s.execute("attach", &json!({ "path": "plan.pdf" })).unwrap_err().to_string().contains("not available yet"));
+    assert_eq!(listed(&mut s), json!([]));
+}
+
+#[test]
+fn an_image_among_many_objects_keeps_its_pixels() {
+    // More objects than one build task takes: the display list is built in parts and joined,
+    // and the image must still point at its own pixels.
+    hooks();
+    let mut s = Session::new();
+    for i in 0..700 {
+        s.execute("line", &json!({ "points": [[i, 0], [i, 1]] })).unwrap();
+    }
+    s.execute("imageattach", &json!({ "path": "a.png", "data": base64_encode(&png()), "at": [0, 5], "width": 4 })).unwrap();
+    for i in 0..700 {
+        s.execute("line", &json!({ "points": [[i, 2], [i, 3]] })).unwrap();
+    }
+    s.execute("imageattach", &json!({ "path": "b.png", "data": base64_encode(&png()), "at": [10, 5], "width": 8 })).unwrap();
+    let list = cadcraft_engine::render::build(s.doc().unwrap(), &cadcraft_engine::doc::Space::Model, &cadcraft_engine::render::Options::default());
+    let widths: Vec<f64> = list
+        .prims
+        .iter()
+        .filter_map(|p| match p.kind {
+            cadcraft_engine::render::Kind::Image { index } => list.images.get(index as usize).map(|i| i.right.x * 4.0),
+            _ => None,
+        })
+        .collect();
+    assert_eq!(widths, [4.0, 8.0]);
+}
+
+fn drawn_images(s: &Session) -> usize {
+    cadcraft_engine::render::build(s.doc().unwrap(), &cadcraft_engine::doc::Space::Model, &cadcraft_engine::render::Options::default()).images.len()
+}
+
+#[test]
+fn editing_commands_work_on_images_and_undo_keeps_the_pixels() {
+    hooks();
+    let mut s = Session::new();
+    let r = s.execute("imageattach", &json!({ "path": "a.png", "data": base64_encode(&png()), "at": [10, 0], "width": 4 })).unwrap();
+    let h = r["handle"].as_str().unwrap().to_string();
+
+    // Move, then a quarter turn about the origin: the corner and both axes follow.
+    s.execute("move", &json!({ "handles": [h], "delta": [0, 5] })).unwrap();
+    s.execute("rotate", &json!({ "handles": [h], "base": [0, 0], "angle": 90 })).unwrap();
+    let i = images(&s).pop().unwrap();
+    let close = |a: f64, b: f64| (a - b).abs() < 1e-9;
+    assert!(close(i.insert.x, -5.0) && close(i.insert.y, 10.0), "{i:?}");
+    assert!(close(i.u.x, 0.0) && close(i.u.y, 1.0) && close(i.v.x, -1.0) && close(i.v.y, 0.0), "{i:?}");
+    assert_eq!(drawn_images(&s), 1);
+
+    // A copy is a second reference to the same file.
+    s.execute("copy", &json!({ "handles": [h], "delta": [20, 0] })).unwrap();
+    assert_eq!((images(&s).len(), drawn_images(&s)), (2, 2));
+    assert_eq!(listed(&mut s)[0]["references"], 2);
+    assert_eq!(listed(&mut s).as_array().map(Vec::len), Some(1));
+
+    // Scaled about its corner: twice the size, still the same pixels.
+    s.execute("scale", &json!({ "handles": [h], "base": [-5, 10], "factor": 2 })).unwrap();
+    let i = images(&s).into_iter().find(|i| close(i.insert.x, -5.0)).unwrap();
+    assert!(close(i.u.y, 2.0) && close(i.size.x, 4.0), "{i:?}");
+
+    // Erased, then brought back by undo, with its picture; redo erases again.
+    s.execute("erase", &json!({ "handles": [h] })).unwrap();
+    assert_eq!((images(&s).len(), drawn_images(&s)), (1, 1));
+    s.execute("undo", &json!({})).unwrap();
+    assert_eq!((images(&s).len(), drawn_images(&s)), (2, 2));
+    s.execute("redo", &json!({})).unwrap();
+    assert_eq!(images(&s).len(), 1);
+
+    // Everything undone: no image, and nothing left to draw.
+    for _ in 0..10 {
+        let _ = s.execute("undo", &json!({}));
+    }
+    assert!(images(&s).is_empty());
+    assert_eq!(drawn_images(&s), 0);
+    assert_eq!(listed(&mut s), json!([]));
+}
+
+#[test]
+fn the_alias_and_the_command_line_reach_the_command() {
+    hooks();
+    assert_eq!(cadcraft_engine::cmd::resolve_alias("IAT"), "imageattach");
+    assert_eq!(cadcraft_engine::cmd::resolve_alias("im"), "image");
+    let spec = |id: &str| cadcraft_engine::cmd::command_specs().iter().find(|c| c.id == id).unwrap();
+    assert!(!spec("imageattach").params.is_empty() && !spec("image").params.is_empty());
+    // Typed without a file it has nothing to attach: an error, not a crash or a stuck prompt.
+    let mut s = Session::new();
+    let _ = s.cmdline("imageattach");
+    let _ = s.cmdline("");
+    s.cancel();
+    assert!(s.running.is_none() && images(&s).is_empty());
+}
+
+#[test]
+fn images_in_blocks_and_layouts_are_loaded_on_open() {
+    use cadcraft_engine::doc::geom::{Vec2, Vec3};
+    use cadcraft_engine::doc::{Block, Common, Entity, Space};
+    hooks();
+    let dir = folder("spaces");
+    std::fs::create_dir_all(dir.join("maps")).unwrap();
+    std::fs::write(dir.join("maps").join("a.png"), png()).unwrap();
+    std::fs::write(dir.join("b.png"), png()).unwrap();
+    let image = |path: &str, name: &str| {
+        EntityKind::Image(Image {
+            u: Vec3::new(1.0, 0.0, 0.0),
+            v: Vec3::new(0.0, 1.0, 0.0),
+            size: Vec2::new(4.0, 2.0),
+            path: path.into(),
+            name: name.into(),
+            ..Image::default()
+        })
+    };
+    let mut d = Drawing::new_metric();
+    // The same file in model space, in a block and on a layout; another only on the layout,
+    // saved with a folder that no longer exists (found by its name next to the drawing); and
+    // one that is nowhere.
+    d.add(&Space::Model, Common::default(), image("maps/a.png", "a")).unwrap();
+    let mut blk = Block::new("MAP");
+    let bh = d.new_handle();
+    blk.entities.push(Entity::new(bh, image("maps/a.png", "a")));
+    d.blocks.insert("MAP".into(), std::sync::Arc::new(blk));
+    let layout = Space::Paper("Layout1".into());
+    d.add(&layout, Common::default(), image("maps/a.png", "a")).unwrap();
+    d.add(&layout, Common::default(), image("C:\\old\\place\\b.png", "b")).unwrap();
+    d.add(&layout, Common::default(), image("gone.png", "gone")).unwrap();
+    let host = dir.join("host.dxf");
+    std::fs::write(&host, cadcraft_io::write(&d, "host.dxf").unwrap()).unwrap();
+
+    let mut s = Session::new();
+    open(&mut s, &host);
+    let doc = s.doc().unwrap();
+    assert_eq!(doc.rasters.len(), 2, "each file once");
+    assert!(doc.rasters.get("maps/a.png").is_some() && doc.rasters.get("C:\\old\\place\\b.png").is_some());
+    assert!(!s.state().unwrap().is_dirty());
+    assert_eq!(s.log.iter().filter(|l| l.starts_with("Image ")).count(), 1, "{:?}", s.log);
+    let l = listed(&mut s);
+    let row = |name: &str| l.as_array().unwrap().iter().find(|r| r["name"] == name).cloned().unwrap();
+    assert_eq!((row("a")["status"].clone(), row("a")["references"].clone()), (json!("Loaded"), json!(3)));
+    assert_eq!(row("b")["status"], "Loaded");
+    assert_eq!(row("gone")["status"], "Not Found");
+    let _ = std::fs::remove_dir_all(&dir);
+}
+
+#[test]
+fn a_drawing_opened_from_bytes_gets_its_pixels_handed_over() {
+    // The web app's way: no file system, the drawing arrives as bytes and so do the images.
+    use cadcraft_engine::doc::geom::{Vec2, Vec3};
+    use cadcraft_engine::doc::{Common, Space};
+    hooks();
+    let mut d = Drawing::new_metric();
+    let i = Image {
+        u: Vec3::new(1.0, 0.0, 0.0),
+        v: Vec3::new(0.0, 1.0, 0.0),
+        size: Vec2::new(4.0, 2.0),
+        path: "no-such-folder/web.png".into(),
+        name: "web".into(),
+        ..Image::default()
+    };
+    d.add(&Space::Model, Common::default(), EntityKind::Image(i)).unwrap();
+    let dxf = cadcraft_io::write(&d, "plan.dxf").unwrap();
+
+    let mut s = Session::new();
+    s.execute("open", &json!({ "data": base64_encode(&dxf), "name": "plan.dxf" })).unwrap();
+    assert_eq!(images(&s).len(), 1, "opened with its image reference");
+    assert!(s.doc().unwrap().rasters.is_empty());
+    assert!(s.log.iter().any(|l| l.contains("web.png")), "{:?}", s.log);
+    assert_eq!(listed(&mut s)[0]["status"], "Not Found");
+    assert_eq!(drawn_images(&s), 0);
+
+    // The same file handed over as bytes: the reference that was there draws too.
+    s.execute("imageattach", &json!({ "path": "no-such-folder/web.png", "data": base64_encode(&png()), "at": [10, 0] })).unwrap();
+    assert_eq!((images(&s).len(), drawn_images(&s)), (2, 2));
+    let l = listed(&mut s);
+    assert_eq!((l[0]["status"].clone(), l[0]["references"].clone(), l[0]["name"].clone()), (json!("Loaded"), json!(2), json!("web")));
+
+    // Saved and read back: the references are kept, the pixels are not in the file.
+    let bytes = cadcraft_io::write(s.doc().unwrap(), "plan.dxf").unwrap();
+    let back = cadcraft_io::read(&bytes, "plan.dxf").unwrap();
+    assert!(back.rasters.is_empty());
+    assert_eq!(back.model.iter().filter(|e| matches!(e.kind, EntityKind::Image(_))).count(), 2);
+}
+
+#[test]
+fn many_files_are_loaded_together_and_reported_in_order() {
+    // More files than loaders, with missing and unreadable ones among them: each good file is
+    // loaded, each bad one reported once, in the order the drawing uses them.
+    use cadcraft_engine::doc::geom::{Vec2, Vec3};
+    use cadcraft_engine::doc::{Common, Space};
+    hooks();
+    let dir = folder("many");
+    let mut d = Drawing::new_metric();
+    let mut expected_notes = Vec::new();
+    for n in 0..60u32 {
+        let name = format!("tile{n:02}.png");
+        match n % 10 {
+            3 => expected_notes.push(format!("Image {name}: file not found")),
+            7 => {
+                std::fs::write(dir.join(&name), b"not an image").unwrap();
+                expected_notes.push(format!("Image {name}: "));
+            }
+            _ => {
+                // A different width per file, so a mix-up would show.
+                let px = vec![200u8; (n as usize + 1) * 4];
+                std::fs::write(dir.join(&name), cadcraft_io::raster::encode_png(&Raster::new(n + 1, 1, px).unwrap()).unwrap()).unwrap();
+            }
+        }
+        let i = Image {
+            insert: Vec3::new(f64::from(n) * 3.0, 0.0, 0.0),
+            u: Vec3::new(1.0, 0.0, 0.0),
+            v: Vec3::new(0.0, 1.0, 0.0),
+            size: Vec2::new(f64::from(n + 1), 1.0),
+            path: name.clone(),
+            name: format!("tile{n:02}"),
+            ..Image::default()
+        };
+        d.add(&Space::Model, Common::default(), EntityKind::Image(i)).unwrap();
+    }
+    let host = dir.join("host.dxf");
+    std::fs::write(&host, cadcraft_io::write(&d, "host.dxf").unwrap()).unwrap();
+
+    for _ in 0..3 {
+        let mut s = Session::new();
+        open(&mut s, &host);
+        let doc = s.doc().unwrap();
+        assert_eq!(doc.rasters.len(), 48);
+        for n in 0..60u32 {
+            let loaded = doc.rasters.get(&format!("tile{n:02}.png")).map(|r| r.width());
+            assert_eq!(loaded, if matches!(n % 10, 3 | 7) { None } else { Some(n + 1) }, "tile {n}");
+        }
+        let notes: Vec<&String> = s.log.iter().filter(|l| l.starts_with("Image ")).collect();
+        assert_eq!(notes.len(), expected_notes.len(), "{notes:?}");
+        assert!(notes.iter().zip(&expected_notes).all(|(got, want)| got.starts_with(want.as_str())), "{notes:?}");
+        assert!(!s.state().unwrap().is_dirty());
+    }
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/engine/tests/image_decoder_panic.rs

@@ -0,0 +1,55 @@
+//! A raster image decoder that panics on a damaged file fails that image only (#956): the
+//! drawing it belongs to still opens, and IMAGEATTACH reports an error.
+
+use cadcraft_engine::Session;
+use cadcraft_engine::cmd::file::{IoHooks, base64_encode, set_image_decoder, set_io};
+use cadcraft_engine::doc::geom::{Vec2, Vec3};
+use cadcraft_engine::doc::{Common, Drawing, EntityKind, Image, Line, Space};
+use serde_json::json;
+
+fn hooks() {
+    set_io(IoHooks {
+        read: |b, name| cadcraft_io::read(b, name).map_err(|e| e.to_string()),
+        write: |d, name| cadcraft_io::write(d, name).map_err(|e| e.to_string()),
+        plot: None,
+    });
+    set_image_decoder(|_| panic!("decoder bug"));
+}
+
+#[test]
+fn a_panicking_decoder_fails_the_image_not_the_drawing() {
+    hooks();
+    let dir = std::env::temp_dir().join(format!("cadcraft-image-panic-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    std::fs::write(dir.join("map.png"), b"anything").unwrap();
+    let mut d = Drawing::new_metric();
+    d.add(&Space::Model, Common::default(), EntityKind::Line(Line { a: Vec3::ZERO, b: Vec3::new(5.0, 5.0, 0.0) })).unwrap();
+    let i = Image {
+        u: Vec3::new(1.0, 0.0, 0.0),
+        v: Vec3::new(0.0, 1.0, 0.0),
+        size: Vec2::new(4.0, 2.0),
+        path: "map.png".into(),
+        name: "map".into(),
+        ..Image::default()
+    };
+    d.add(&Space::Model, Common::default(), EntityKind::Image(i)).unwrap();
+    let host = dir.join("host.dxf");
+    std::fs::write(&host, cadcraft_io::write(&d, "host.dxf").unwrap()).unwrap();
+
+    let mut s = Session::new();
+    s.execute("open", &json!({ "path": host.to_string_lossy() })).unwrap();
+    let doc = s.doc().unwrap();
+    assert_eq!(doc.model.len(), 2, "the drawing opened with everything in it");
+    assert!(doc.rasters.is_empty());
+    assert!(s.log.iter().any(|l| l.contains("map.png") && l.contains("damaged")), "{:?}", s.log);
+
+    let before = s.doc().unwrap().model.len();
+    let e = s.execute("imageattach", &json!({ "path": "other.png", "data": base64_encode(b"bytes") })).unwrap_err().to_string();
+    assert!(e.contains("damaged"), "{e}");
+    assert_eq!(s.doc().unwrap().model.len(), before);
+    // The session still works.
+    s.execute("line", &json!({ "points": [[0, 0], [1, 1]] })).unwrap();
+    assert_eq!(s.doc().unwrap().model.len(), before + 1);
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/engine/tests/insert_file.rs

@@ -40,6 +40,7 @@ fn read(bytes: &[u8], _name: &str) -> Result<Drawing, String> {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     };
     d.model.push(Entity::new(Handle(0x61), EntityKind::Insert(ins)));
     Ok(d)

crates/engine/tests/it/blockreplace.rs

@@ -40,6 +40,7 @@ fn drawing() -> (Session, Handle) {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     };
     s.doc_mut().unwrap().add(&Space::Paper("Layout1".into()), Common::default(), EntityKind::Insert(ins)).unwrap();
     (s, Handle::parse_hex(r["handle"].as_str().unwrap()).unwrap())

crates/engine/tests/it/compare_export.rs

@@ -21,6 +21,7 @@ fn insert(block: &str) -> Insert {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     }
 }
 

crates/engine/tests/it/count.rs

@@ -20,6 +20,7 @@ fn insert(block: &str, x: f64, cols: u32, rows: u32) -> EntityKind {
         rows,
         col_spacing: 5.0,
         row_spacing: 5.0,
+        clip: None,
     })
 }
 

crates/engine/tests/it/followups_626.rs

@@ -135,9 +135,9 @@ fn mview_restore_puts_a_saved_configuration_on_a_layout() {
 fn mview_restore_ignores_unusable_tiles_from_files() {
     let (mut s, _) = two_tiles();
     let bad = [
-        VportTile { min: v(f64::NAN, 0.0), max: v(1.0, 1.0), center: v(0.0, 0.0), height: 1.0, aspect: 1.0 },
-        VportTile { min: v(0.5, 0.5), max: v(0.5, 0.9), center: v(0.0, 0.0), height: 1.0, aspect: 1.0 },
-        VportTile { min: v(-3.0, -3.0), max: v(9.0, 9.0), center: v(f64::INFINITY, 0.0), height: -1.0, aspect: f64::NAN },
+        VportTile { min: v(f64::NAN, 0.0), max: v(1.0, 1.0), center: v(0.0, 0.0), height: 1.0, aspect: 1.0, twist: 0.0 },
+        VportTile { min: v(0.5, 0.5), max: v(0.5, 0.9), center: v(0.0, 0.0), height: 1.0, aspect: 1.0, twist: 0.0 },
+        VportTile { min: v(-3.0, -3.0), max: v(9.0, 9.0), center: v(f64::INFINITY, 0.0), height: -1.0, aspect: f64::NAN, twist: 0.0 },
     ];
     if let Some(c) = s.doc_mut().unwrap().vports.iter_mut().find(|c| c.name == "Two") {
         c.tiles = bad.to_vec();

crates/engine/tests/it/main.rs

@@ -165,6 +165,7 @@ mod viewport_clip;
 mod vplayer_prompts;
 mod vports;
 mod wipeout_grips;
+mod xclip;
 mod xdata_follows_entity;
 mod zoom_keywords;
 mod zoom_viewport;

crates/engine/tests/it/measure_distance_snapping.rs

@@ -27,6 +27,7 @@ fn drawing() -> (Drawing, Space) {
             layer_colors: Vec::new(),
             clip: None,
             on: true,
+            twist: 0.0,
         }),
     )
     .unwrap();
@@ -310,6 +311,7 @@ fn viewport_frozen_layers_apply_inside_nested_block_references() {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         })
     };
     let mut outer = Block::new("Outer");

crates/engine/tests/it/named_views.rs

@@ -46,7 +46,7 @@ fn typed_save_restore_list_delete() {
     // Saving is an undo step; a view change is not.
     set_view(&mut s, 0.0, 0.0, 500.0);
     typed(&mut s, &["view", "r", "front"]);
-    assert_eq!(view(&s), View { center: Vec2::new(10.0, 20.0), height: 30.0 });
+    assert_eq!(view(&s), View { center: Vec2::new(10.0, 20.0), height: 30.0, twist: 0.0 });
     // Zoom Previous goes back to the view before the restore.
     s.execute("zoom.previous", &json!({})).unwrap();
     assert_eq!(view(&s).height, 500.0);
@@ -84,6 +84,20 @@ fn window_option_and_json_forms() {
     assert!(s.execute("view", &json!({ "option": "orthographic" })).is_err());
 }
 
+#[test]
+fn a_window_saved_in_a_twisted_view_restores_whole() {
+    let mut s = session();
+    s.execute("view.set", &json!({ "center": [0, 0], "height": 10, "twist": 45 })).unwrap();
+    s.execute("view", &json!({ "option": "window", "name": "Turned", "p1": [0, 0], "p2": [10, 10] })).unwrap();
+    let v = s.doc().unwrap().views.first().cloned().unwrap();
+    // A 10 x 10 world square seen at 45° is 10√2 across on screen.
+    assert!(close(v.width, 200f64.sqrt()) && close(v.height, 200f64.sqrt()), "{} x {}", v.width, v.height);
+    // Corners near the number limit overflow when turned: an error, and the saved view stays.
+    let huge = json!({ "option": "window", "name": "Turned", "p1": [1.4e308, 1.4e308], "p2": [1.5e308, 1.5e308] });
+    assert!(s.execute("view", &huge).is_err());
+    assert!(close(s.doc().unwrap().views.first().unwrap().width, 200f64.sqrt()));
+}
+
 #[test]
 fn layer_snapshot_restores_layers_and_the_setting_turns_it_off() {
     let mut s = session();
@@ -112,7 +126,7 @@ fn paper_space_view_switches_to_its_layout() {
     s.execute("layout.set", &json!({ "name": "Model" })).unwrap();
     s.execute("view", &json!({ "option": "restore", "name": "Sheet" })).unwrap();
     assert_eq!(s.layout_space(), Space::Paper(layout));
-    assert_eq!(view(&s), View { center: Vec2::new(5.0, 4.0), height: 6.0 });
+    assert_eq!(view(&s), View { center: Vec2::new(5.0, 4.0), height: 6.0, twist: 0.0 });
 }
 
 #[test]
@@ -138,7 +152,7 @@ fn zoom_realtime_drags_and_enter_ends() {
     assert_eq!(view(&s).height, 100.0);
     // The JSON form zooms by a factor about the centre.
     s.execute("zoom.realtime", &json!({ "factor": 4 })).unwrap();
-    assert_eq!(view(&s), View { center: Vec2::ZERO, height: 25.0 });
+    assert_eq!(view(&s), View { center: Vec2::ZERO, height: 25.0, twist: 0.0 });
 }
 
 #[test]
@@ -158,10 +172,10 @@ fn zoom_dynamic_places_and_sizes_the_view_box() {
     assert!(close(v.height, 40.0), "{v:?}");
     // Zoom Previous skips the overview.
     s.execute("zoom.previous", &json!({})).unwrap();
-    assert_eq!(view(&s), View { center: Vec2::new(10.0, 10.0), height: 20.0 });
+    assert_eq!(view(&s), View { center: Vec2::new(10.0, 10.0), height: 20.0, twist: 0.0 });
     // JSON: like Center.
     s.execute("zoom.dynamic", &json!({ "center": [1, 2], "height": 3 })).unwrap();
-    assert_eq!(view(&s), View { center: Vec2::new(1.0, 2.0), height: 3.0 });
+    assert_eq!(view(&s), View { center: Vec2::new(1.0, 2.0), height: 3.0, twist: 0.0 });
 }
 
 #[test]

crates/engine/tests/it/purge_mlinestyles.rs

@@ -41,6 +41,7 @@ fn session() -> Session {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     };
     d.add(&Space::Model, Common::default(), EntityKind::Insert(ins)).unwrap();
     s

crates/engine/tests/it/refedit.rs

@@ -20,6 +20,7 @@ fn insert(s: &mut Session, block: &str, at: (f64, f64), scale: f64, rot_deg: f64
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     });
     s.doc_mut().unwrap().add(&Space::Model, Common::default(), kind).unwrap().hex()
 }
@@ -246,6 +247,7 @@ fn a_block_that_references_itself_in_a_file_does_not_hang() {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     });
     let d = s.doc_mut().unwrap();
     let hh = d.new_handle();

crates/engine/tests/it/snap_blocks.rs

@@ -31,6 +31,7 @@ fn insert(s: &mut Session, block: &str, at: (f64, f64), scale: (f64, f64), rotat
         rows: grid.1,
         col_spacing: grid.2,
         row_spacing: grid.3,
+        clip: None,
     });
     s.doc_mut().unwrap().add(&Space::Model, Common::default(), kind).unwrap().hex()
 }

crates/engine/tests/it/snap_tracking.rs

@@ -41,6 +41,7 @@ fn insert_block(s: &mut Session, name: &str, at: Vec2) -> String {
                 rows: 1,
                 col_spacing: 0.0,
                 row_spacing: 0.0,
+                clip: None,
             }),
         )
         .unwrap()

crates/engine/tests/it/vports.rs

@@ -46,15 +46,15 @@ fn split_activate_and_each_tile_keeps_its_view() {
     s.execute("-vports", &json!({ "option": "2", "arrangement": "vertical" })).unwrap();
     assert_eq!(rects(&s), vec![[0.0, 0.0, 0.5, 1.0], [0.5, 0.0, 1.0, 1.0]]);
     // Every new tile starts with the view that was split.
-    assert!(tiles(&s).iter().all(|t| t.view == View { center: Vec2::new(10.0, 10.0), height: 20.0 }));
+    assert!(tiles(&s).iter().all(|t| t.view == View { center: Vec2::new(10.0, 10.0), height: 20.0, twist: 0.0 }));
     let first = current(&s);
     let other = 1 - first;
     s.activate_tile(other).unwrap();
     assert_eq!(current(&s), other);
     s.execute("view.set", &json!({ "center": [50, 25], "height": 5 })).unwrap();
     s.execute("vports.activate", &json!({ "index": first + 1 })).unwrap();
-    assert_eq!(view(&s), View { center: Vec2::new(10.0, 10.0), height: 20.0 });
-    assert_eq!(tiles(&s)[other].view, View { center: Vec2::new(50.0, 25.0), height: 5.0 });
+    assert_eq!(view(&s), View { center: Vec2::new(10.0, 10.0), height: 20.0, twist: 0.0 });
+    assert_eq!(tiles(&s)[other].view, View { center: Vec2::new(50.0, 25.0), height: 5.0, twist: 0.0 });
     // Switching tiles changes no drawing data; arranging them is an undo step.
     assert_eq!(s.state().unwrap().undo.len(), 2, "line + VPORTS");
     s.undo().unwrap();
@@ -82,7 +82,7 @@ fn typed_three_right_then_join_and_single() {
     s.click_tile(bottom).unwrap();
     assert!(s.running.is_none(), "{}", s.prompt_text());
     assert_eq!(rects(&s), vec![[0.0, 0.0, 0.5, 1.0], [0.5, 0.0, 1.0, 1.0]]);
-    assert_eq!(view(&s), View { center: Vec2::new(1.0, 2.0), height: 3.0 });
+    assert_eq!(view(&s), View { center: Vec2::new(1.0, 2.0), height: 3.0, twist: 0.0 });
     // Tiles that don't make a rectangle can't be joined.
     s.execute("-vports", &json!({ "option": "3", "arrangement": "above" })).unwrap();
     let t = tiles(&s);
@@ -93,7 +93,7 @@ fn typed_three_right_then_join_and_single() {
     s.execute("view.set", &json!({ "center": [7, 7], "height": 7 })).unwrap();
     typed(&mut s, &["-vports", "si"]);
     assert!(tiles(&s).is_empty());
-    assert_eq!(view(&s), View { center: Vec2::new(7.0, 7.0), height: 7.0 });
+    assert_eq!(view(&s), View { center: Vec2::new(7.0, 7.0), height: 7.0, twist: 0.0 });
 }
 
 #[test]

crates/engine/tests/it/xclip.rs

@@ -0,0 +1,273 @@
+//! XCLIP and XCLIPFRAME: clipping block and xref references (gap F2).
+
+use cadcraft_engine::doc::{ClipBoundary, Common, EntityKind, Handle, Insert, Space};
+use cadcraft_engine::geom::{Vec2, Vec3};
+use cadcraft_engine::render::{self, Options};
+use cadcraft_engine::{Input, Session};
+use serde_json::{Value, json};
+
+fn h(v: &Value) -> String {
+    v.get("handle").unwrap_or(&v["handles"][0]).as_str().unwrap().to_string()
+}
+
+fn insert(s: &mut Session, block: &str, at: (f64, f64), scale: f64, rot_deg: f64) -> String {
+    let kind = EntityKind::Insert(Insert {
+        block: block.into(),
+        insert: Vec3::new(at.0, at.1, 0.0),
+        scale: Vec3::new(scale, scale, scale),
+        rotation: rot_deg.to_radians(),
+        ..Insert::default()
+    });
+    s.doc_mut().unwrap().add(&Space::Model, Common::default(), kind).unwrap().hex()
+}
+
+/// Block B: a horizontal line (0,0)-(100,0) and a vertical one (50,-50)-(50,50); two references.
+fn setup() -> (Session, String, String) {
+    let mut s = Session::new();
+    let a = h(&s.execute("line", &json!({ "points": [[0, 0], [100, 0]] })).unwrap());
+    let b = h(&s.execute("line", &json!({ "points": [[50, -50], [50, 50]] })).unwrap());
+    s.execute("block", &json!({ "name": "B", "base": [0, 0], "handles": [a, b], "keep": "delete" })).unwrap();
+    let r1 = insert(&mut s, "B", (0.0, 0.0), 1.0, 0.0);
+    let r2 = insert(&mut s, "B", (1000.0, 0.0), 2.0, 90.0);
+    (s, r1, r2)
+}
+
+fn clip(s: &Session, hex: &str) -> Option<ClipBoundary> {
+    match &s.doc().unwrap().entity(Handle::parse_hex(hex).unwrap()).unwrap().kind {
+        EntityKind::Insert(i) => i.clip.clone(),
+        _ => None,
+    }
+}
+
+/// The x extent of what the drawing shows around reference 1 (x < 500).
+fn shown_x(s: &Session) -> (f64, f64) {
+    let list = render::build(s.doc().unwrap(), &Space::Model, &Options::default());
+    let xs: Vec<f64> = list.verts.iter().filter(|v| v.x < 500.0).map(|v| v.x).collect();
+    (xs.iter().copied().fold(f64::MAX, f64::min), xs.iter().copied().fold(f64::MIN, f64::max))
+}
+
+#[test]
+fn rectangular_clip_cuts_only_that_reference() {
+    let (mut s, r1, r2) = setup();
+    assert_eq!(shown_x(&s), (0.0, 100.0));
+    s.execute("setvar", &json!({ "name": "XCLIPFRAME", "value": 0 })).unwrap();
+    let out = s.execute("xclip", &json!({ "handle": r1, "rectangle": [[20, -10], [70, 10]] })).unwrap();
+    assert_eq!(out["option"], "new");
+    let c = clip(&s, &r1).unwrap();
+    assert!(c.enabled && !c.inverted && c.points.len() == 2);
+    let (lo, hi) = shown_x(&s);
+    assert!((lo - 20.0).abs() < 1e-9 && (hi - 70.0).abs() < 1e-9, "{lo} {hi}");
+    assert!(clip(&s, &r2).is_none(), "the other reference stays whole");
+    // The boundary follows its reference.
+    s.execute("move", &json!({ "handles": [r1], "delta": [5, 0] })).unwrap();
+    let (lo, hi) = shown_x(&s);
+    assert!((lo - 25.0).abs() < 1e-9 && (hi - 75.0).abs() < 1e-9, "{lo} {hi}");
+    // Its extents are the clipped part (ZOOM Extents).
+    let d = s.doc().unwrap();
+    let b = cadcraft_engine::doc::entity_bounds(d, d.entity(Handle::parse_hex(&r1).unwrap()).unwrap(), 0);
+    assert!((b.min.x - 25.0).abs() < 1e-9 && (b.max.x - 75.0).abs() < 1e-9 && b.max.y <= 10.0 + 1e-9, "{b:?}");
+    // Query reports it in drawing coordinates.
+    let q = s.execute("xclip", &json!({ "handle": r1, "option": "query" })).unwrap();
+    assert_eq!(q["clips"][0]["boundary"][0], json!([25.0, -10.0]));
+    // OFF shows everything, ON clips again, Delete removes it; undo brings it back.
+    s.execute("xclip", &json!({ "handle": r1, "option": "off" })).unwrap();
+    assert_eq!(shown_x(&s), (5.0, 105.0));
+    s.execute("xclip", &json!({ "handle": r1, "option": "on" })).unwrap();
+    assert!((shown_x(&s).0 - 25.0).abs() < 1e-9);
+    s.execute("xclip", &json!({ "handle": r1, "option": "delete" })).unwrap();
+    assert!(clip(&s, &r1).is_none());
+    s.execute("undo", &json!({})).unwrap();
+    assert!(clip(&s, &r1).is_some());
+}
+
+#[test]
+fn off_on_a_selection_with_an_unclipped_reference_changes_nothing() {
+    let (mut s, r1, r2) = setup();
+    s.execute("xclip", &json!({ "handle": r1, "rectangle": [[20, -10], [70, 10]] })).unwrap();
+    // r2 has no boundary: the command fails, and r1 keeps its clip on.
+    assert!(s.execute("xclip", &json!({ "handles": [r1, r2], "option": "off" })).is_err());
+    assert!(clip(&s, &r1).unwrap().enabled);
+    assert!(clip(&s, &r2).is_none());
+    // A reference named many times is turned off once, its boundary kept.
+    s.execute("xclip", &json!({ "handles": vec![r1.clone(); 1000], "option": "off" })).unwrap();
+    let c = clip(&s, &r1).unwrap();
+    assert!(!c.enabled && c.points.len() == 2);
+}
+
+#[test]
+fn a_clipped_reference_plots_its_contents_on_their_own_layers() {
+    let mut s = Session::new();
+    s.doc_mut().unwrap().layers.push(cadcraft_engine::doc::Layer { name: "Walls".into(), ..Default::default() });
+    let a = h(&s.execute("line", &json!({ "points": [[0, 0], [100, 0]] })).unwrap());
+    let b = h(&s.execute("line", &json!({ "points": [[50, -50], [50, 50]] })).unwrap());
+    s.doc_mut().unwrap().modify_entity(Handle::parse_hex(&a).unwrap(), |e| e.common.layer = "Walls".into()).unwrap();
+    s.execute("block", &json!({ "name": "B", "base": [0, 0], "handles": [a, b], "keep": "delete" })).unwrap();
+    let r = insert(&mut s, "B", (0.0, 0.0), 1.0, 0.0);
+    s.execute("setvar", &json!({ "name": "XCLIPFRAME", "value": 0 })).unwrap();
+    s.execute("xclip", &json!({ "handle": r, "rectangle": [[20, -10], [70, 10]] })).unwrap();
+    let d = s.doc().unwrap();
+    let index = |name: &str| d.layers.iter().position(|l| l.name == name).map(|i| i as u32);
+    let list = render::build_plot(d, &Space::Model, &Options::default());
+    assert_eq!(list.prim_layers.len(), list.prims.len());
+    // The horizontal line is on Walls, the vertical one (layer 0) takes the reference's layer.
+    assert!(list.prim_layers.contains(&index("Walls").unwrap()), "{:?}", list.prim_layers);
+    assert!(list.prim_layers.contains(&index("0").unwrap()), "{:?}", list.prim_layers);
+}
+
+#[test]
+fn extents_are_the_boundary_box_as_in_the_reference_app() {
+    let (mut s, r1, _) = setup();
+    let bounds = |s: &Session| {
+        let d = s.doc().unwrap();
+        cadcraft_engine::doc::entity_bounds(d, d.entity(Handle::parse_hex(&r1).unwrap()).unwrap(), 0)
+    };
+    // A boundary reaching past the block (0..100 x -50..50): its own box, not the overlap.
+    s.execute("xclip", &json!({ "handle": r1, "rectangle": [[50, -20], [150, 30]] })).unwrap();
+    let b = bounds(&s);
+    assert!((b.min - Vec2::new(50.0, -20.0)).len() < 1e-9 && (b.max - Vec2::new(150.0, 30.0)).len() < 1e-9, "{b:?}");
+    // One that misses the block entirely: still its box.
+    s.execute("xclip", &json!({ "handle": r1, "rectangle": [[200, 200], [300, 300]] })).unwrap();
+    let b = bounds(&s);
+    assert!((b.min - Vec2::new(200.0, 200.0)).len() < 1e-9 && (b.max - Vec2::new(300.0, 300.0)).len() < 1e-9, "{b:?}");
+}
+
+#[test]
+fn rotated_and_scaled_reference_gets_a_polygon_in_block_coordinates() {
+    let (mut s, _, r2) = setup();
+    // r2: scale 2, rotated 90 degrees at (1000, 0): the block's x axis points up.
+    s.execute("xclip", &json!({ "handle": r2, "rectangle": [[990, 10], [1010, 50]] })).unwrap();
+    let c = clip(&s, &r2).unwrap();
+    // A 90 degree rotation keeps the rectangle a rectangle: (5..25, -5..5) in the block.
+    let poly = c.polygon();
+    let xs: Vec<f64> = poly.iter().map(|p| p.x).collect();
+    assert!(xs.iter().any(|x| (x - 5.0).abs() < 1e-9) && xs.iter().any(|x| (x - 25.0).abs() < 1e-9), "{poly:?}");
+    // 30 degrees: kept as the four corners.
+    let r3 = insert(&mut s, "B", (2000.0, 0.0), 1.0, 30.0);
+    s.execute("xclip", &json!({ "handle": r3, "rectangle": [[1990, -10], [2010, 10]] })).unwrap();
+    assert_eq!(clip(&s, &r3).unwrap().points.len(), 4);
+}
+
+#[test]
+fn inverted_polygonal_and_polyline_boundaries() {
+    let (mut s, r1, _) = setup();
+    s.execute("setvar", &json!({ "name": "XCLIPFRAME", "value": 0 })).unwrap();
+    s.execute("xclip", &json!({ "handle": r1, "points": [[40, -10], [60, -10], [60, 10], [40, 10]], "invert": true })).unwrap();
+    assert!(clip(&s, &r1).unwrap().inverted);
+    let list = render::build(s.doc().unwrap(), &Space::Model, &Options::default());
+    // The middle of the horizontal line is hidden, both ends show.
+    assert!(!list.verts.iter().any(|v| v.x > 40.5 && v.x < 59.5 && v.y.abs() < 1e-9));
+    assert!(list.verts.iter().any(|v| v.x == 0.0) && list.verts.iter().any(|v| v.x == 100.0));
+    // A closed polyline as the boundary.
+    let pl = h(&s.execute("pline", &json!({ "vertices": [[10, -5], [30, -5], [30, 5], [10, 5]], "closed": true })).unwrap());
+    s.execute("xclip", &json!({ "handle": r1, "polyline": pl })).unwrap();
+    let c = clip(&s, &r1).unwrap();
+    assert!(!c.inverted && c.points.len() == 4);
+    // An open polyline is refused, a bad boundary changes nothing.
+    let open = h(&s.execute("pline", &json!({ "vertices": [[0, 0], [5, 5], [9, 0]] })).unwrap());
+    assert!(s.execute("xclip", &json!({ "handle": r1, "polyline": open })).is_err());
+    assert!(s.execute("xclip", &json!({ "handle": r1, "points": [[0, 0], [1, 1]] })).is_err());
+    assert!(s.execute("xclip", &json!({ "handle": r1, "rectangle": [[0, 0], [0, 10]] })).is_err());
+    assert_eq!(clip(&s, &r1), Some(c));
+    // Generate polyline makes the boundary an object.
+    let n = s.doc().unwrap().model.len();
+    let out = s.execute("xclip", &json!({ "handle": r1, "option": "polyline" })).unwrap();
+    assert_eq!(out["polylines"].as_array().unwrap().len(), 1);
+    assert_eq!(s.doc().unwrap().model.len(), n + 1);
+    // Clip depth has no effect in 2D.
+    assert_eq!(s.execute("xclip", &json!({ "handle": r1, "option": "clipdepth" })).unwrap()["ignored"], true);
+}
+
+#[test]
+fn hostile_params_never_panic() {
+    let (mut s, r1, _) = setup();
+    for p in [
+        json!({ "handle": r1, "points": "x" }),
+        json!({ "handle": r1, "points": [[1e308, 0], [-1e308, 0], [0, 1e308]] }),
+        json!({ "handle": r1, "rectangle": [[f64::MAX, 0]] }),
+        json!({ "handle": r1, "rectangle": 5 }),
+        json!({ "handle": r1, "polyline": "ZZZZ" }),
+        json!({ "handle": r1, "option": "bogus" }),
+        json!({ "handle": "nothex" }),
+        json!({ "handles": [] }),
+        json!({ "handle": r1, "points": vec![[0.0, 0.0]; 5000] }),
+    ] {
+        let _ = s.execute("xclip", &p);
+    }
+    assert!(s.execute("xclipframe", &json!({ "value": 7 })).is_err());
+    assert!(s.execute("xclip", &json!({ "handle": r1, "option": "on" })).is_err(), "no boundary to turn on");
+}
+
+#[test]
+fn typed_xclip_follows_the_prompts() {
+    let (mut s, r1, r2) = setup();
+    let pick = |hex: &str| Input::Pick(vec![Handle::parse_hex(hex).unwrap()]);
+    s.start("xclip").unwrap();
+    s.input(pick(&r1)).unwrap();
+    s.input(Input::Enter).unwrap();
+    assert!(s.prompt_text().contains("Enter clipping option"), "{}", s.prompt_text());
+    s.input(Input::Enter).unwrap(); // New
+    assert!(s.prompt_text().contains("Invert clip"), "{}", s.prompt_text());
+    s.input(Input::Keyword("Invert clip".into())).unwrap();
+    assert!(s.log.iter().any(|l| l.contains("Inside mode")));
+    s.input(Input::Keyword("Rectangular".into())).unwrap();
+    s.input(Input::Point(Vec2::new(10.0, -10.0))).unwrap();
+    s.input(Input::Point(Vec2::new(30.0, 10.0))).unwrap();
+    let c = clip(&s, &r1).unwrap();
+    assert!(c.inverted && c.points.len() == 2);
+    // Again on the clipped reference: "Delete old boundary(s)?", then a polygon.
+    s.cmdline("xclip").unwrap();
+    s.input(pick(&r1)).unwrap();
+    s.input(Input::Enter).unwrap();
+    s.cmdline("n").unwrap();
+    assert!(s.prompt_text().contains("Delete old boundary"), "{}", s.prompt_text());
+    s.cmdline("y").unwrap();
+    s.cmdline("p").unwrap();
+    for p in ["0,-5", "20,-5", "20,5"] {
+        s.cmdline(p).unwrap();
+    }
+    s.input(Input::Enter).unwrap();
+    let c = clip(&s, &r1).unwrap();
+    assert!(!c.inverted && c.points.len() == 3);
+    // OFF, then Delete on two references at once.
+    s.start("xclip").unwrap();
+    s.input(pick(&r1)).unwrap();
+    s.input(Input::Enter).unwrap();
+    s.cmdline("off").unwrap();
+    assert!(!clip(&s, &r1).unwrap().enabled);
+    s.execute("xclip", &json!({ "handle": r2, "rectangle": [[0, 0], [1, 1]] })).unwrap();
+    s.start("xclip").unwrap();
+    s.input(Input::Pick(vec![Handle::parse_hex(&r1).unwrap(), Handle::parse_hex(&r2).unwrap()])).unwrap();
+    s.input(Input::Enter).unwrap();
+    s.cmdline("d").unwrap();
+    assert!(clip(&s, &r1).is_none() && clip(&s, &r2).is_none());
+    // Delete with no boundary left says so and asks again.
+    s.start("xclip").unwrap();
+    s.input(pick(&r1)).unwrap();
+    s.input(Input::Enter).unwrap();
+    s.cmdline("d").unwrap();
+    assert!(s.log.iter().any(|l| l.contains("No clip boundary found.")), "{:?}", s.log);
+    assert!(s.prompt_text().contains("Enter clipping option"), "{}", s.prompt_text());
+    s.input(Input::Cancel).unwrap();
+    // XCLIPFRAME typed.
+    s.cmdline("xclipframe").unwrap();
+    s.cmdline("1").unwrap();
+    assert_eq!(s.execute("getvar", &json!({ "name": "XCLIPFRAME" })).unwrap()["value"], 1);
+}
+
+#[test]
+fn the_frame_shows_and_plots_as_xclipframe_says() {
+    let (mut s, r1, _) = setup();
+    s.execute("xclip", &json!({ "handle": r1, "rectangle": [[20, -10], [70, 10]] })).unwrap();
+    let frame_at = |s: &Session, plot: bool| {
+        let d = s.doc().unwrap();
+        let list =
+            if plot { render::build_plot(d, &Space::Model, &Options::default()) } else { render::build(d, &Space::Model, &Options::default()) };
+        list.verts.iter().any(|v| (v.y - 10.0).abs() < 1e-9 && (v.x - 20.0).abs() < 1e-9)
+    };
+    // Default 2: shown, not plotted.
+    assert!(frame_at(&s, false) && !frame_at(&s, true));
+    s.execute("xclipframe", &json!({ "value": 1 })).unwrap();
+    assert!(frame_at(&s, false) && frame_at(&s, true));
+    s.execute("xclipframe", &json!({ "value": 0 })).unwrap();
+    assert!(!frame_at(&s, false) && !frame_at(&s, true));
+}

crates/engine/tests/shx_beside_drawing.rs

@@ -0,0 +1,34 @@
+//! FF8: the SHX fonts a drawing's text styles name are found beside the drawing it opens. The
+//! font is compiled here from shape source written for the test.
+
+use cadcraft_engine::Session;
+use cadcraft_engine::cmd::file::{IoHooks, set_io};
+use cadcraft_engine::doc::{Drawing, TextStyle};
+use serde_json::json;
+
+#[test]
+fn opening_a_drawing_finds_the_shx_fonts_beside_it() {
+    set_io(IoHooks {
+        read: |b, name| cadcraft_io::read(b, name).map_err(|e| e.to_string()),
+        write: |d, name| cadcraft_io::write(d, name).map_err(|e| e.to_string()),
+        plot: None,
+    });
+    let dir = std::env::temp_dir().join(format!("cadcraft-shx-beside-{}", std::process::id()));
+    let _ = std::fs::remove_dir_all(&dir);
+    std::fs::create_dir_all(&dir).unwrap();
+    let font = cadcraft_fonts::shx::compile("*0,4,beside\n6,2,0,0\n*65,7,UCA\n1,064,040,06C,2,020,0\n").unwrap();
+    std::fs::write(dir.join("cadcraft-beside-engine.shx"), font).unwrap();
+    let mut d = Drawing::new_imperial();
+    d.text_styles.push(TextStyle { name: "Beside".into(), font: "cadcraft-beside-engine.shx".into(), ..TextStyle::default() });
+    let path = dir.join("host.dxf");
+    std::fs::write(&path, cadcraft_io::write(&d, "host.dxf").unwrap()).unwrap();
+
+    assert!(!cadcraft_fonts::TextFont::resolve("cadcraft-beside-engine.shx").is_shx());
+    let mut s = Session::new();
+    s.execute("open", &json!({ "path": path.to_string_lossy() })).unwrap();
+    let style = s.doc().unwrap().text_style("Beside").cloned().unwrap();
+    let font = cadcraft_fonts::TextFont::resolve_style(&style.font, &style.big_font, style.vertical);
+    assert!(font.is_shx());
+    assert!((cadcraft_fonts::text_width(&font, "AA", 3.0, 1.0) - 6.0).abs() < 1e-9);
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/engine/tests/usage.rs

@@ -50,6 +50,7 @@ fn insert(handle: u64, block: &str, layer: &str) -> Entity {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         }),
     );
     e.common = Common { layer: layer.into(), ..Common::default() };

crates/engine/tests/view_twist.rs

@@ -0,0 +1,193 @@
+//! The view twist (VIEWTWIST): DVIEW TWist turns the Model tab's view, ZOOM Previous turns it
+//! back, each VPORTS tile keeps its own (DXF VPORT group 51), and VIEW Save/Restore keep it.
+
+use cadcraft_engine::geom::Vec2;
+use cadcraft_engine::{Session, View, sysvars};
+use serde_json::json;
+
+fn session() -> Session {
+    let mut s = Session::new();
+    s.viewport_px = (1200.0, 800.0);
+    s.execute("line", &json!({ "points": [[0, 0], [100, 50]] })).unwrap();
+    s.execute("view.set", &json!({ "center": [10, 10], "height": 20 })).unwrap();
+    s
+}
+
+fn typed(s: &mut Session, lines: &[&str]) {
+    for l in lines {
+        s.cmdline(l).unwrap();
+    }
+}
+
+fn view(s: &Session) -> View {
+    s.state().unwrap().view()
+}
+
+fn twist_deg(s: &Session) -> f64 {
+    view(s).twist.to_degrees()
+}
+
+fn near(a: f64, b: f64) -> bool {
+    (a - b).abs() < 1e-9
+}
+
+#[test]
+fn dview_twist_sets_viewtwist_and_zoom_previous_turns_it_back() {
+    let mut s = session();
+    assert_eq!(view(&s).twist, 0.0);
+    typed(&mut s, &["dview", "", "tw", "30", ""]);
+    assert!(near(twist_deg(&s), 30.0), "twist {}", twist_deg(&s));
+    let vt = sysvars::get(&s, "VIEWTWIST").and_then(|v| v.as_f64()).unwrap();
+    assert!(near(vt, 30.0), "VIEWTWIST {vt}");
+    // Only the twist changed; the view is not an undo step.
+    assert_eq!((view(&s).center, view(&s).height), (Vec2::new(10.0, 10.0), 20.0));
+    assert_eq!(s.state().unwrap().undo.len(), 1, "just the line");
+    // Zooming keeps the twist; ZOOM Previous steps back through it.
+    s.execute("zoom", &json!({ "mode": "in" })).unwrap();
+    assert!(near(twist_deg(&s), 30.0));
+    s.execute("zoom", &json!({ "mode": "previous" })).unwrap();
+    s.execute("zoom", &json!({ "mode": "previous" })).unwrap();
+    assert_eq!(view(&s).twist, 0.0);
+    assert!(sysvars::is_read_only("VIEWTWIST"));
+    // JSON form; negative angles wrap into 0..360.
+    s.execute("dview", &json!({ "twist": -90 })).unwrap();
+    assert!(near(twist_deg(&s), 270.0));
+    // The 3D options are not available yet; the command carries on.
+    typed(&mut s, &["dview", "", "ca", ""]);
+    assert!(s.current_prompt().is_none());
+    // Not in a layout.
+    let layout = s.doc().unwrap().layouts.first().map(|l| l.name.clone()).unwrap();
+    s.execute("layout.set", &json!({ "name": layout })).unwrap();
+    assert!(s.execute("dview", &json!({ "twist": 10 })).is_err());
+}
+
+const PAPER: &str = "This command is not available in Paper space.";
+
+#[test]
+fn dview_in_paper_space_says_it_is_not_available() {
+    let mut s = session();
+    let layout = s.doc().unwrap().layouts.first().map(|l| l.name.clone()).unwrap();
+    s.execute("layout.set", &json!({ "name": layout })).unwrap();
+    let e = s.execute("dview", &json!({ "twist": 10 })).unwrap_err();
+    assert_eq!(e.to_string(), PAPER);
+    // Typed, it is refused as it starts: no prompt is left open.
+    let e = s.cmdline("dview").unwrap_err();
+    assert_eq!(e.to_string(), PAPER);
+    assert!(s.current_prompt().is_none());
+    // view.set can't turn a layout's view either (an untwisted one is fine).
+    let e = s.execute("view.set", &json!({ "center": [0, 0], "height": 5, "twist": 15 })).unwrap_err();
+    assert_eq!(e.to_string(), PAPER);
+    s.execute("view.set", &json!({ "center": [0, 0], "height": 5 })).unwrap();
+    assert_eq!(view(&s).twist, 0.0);
+}
+
+#[test]
+fn a_single_untiled_view_keeps_its_twist_through_a_dxf_round_trip() {
+    let mut s = session();
+    s.execute("dview", &json!({ "twist": 30 })).unwrap();
+    assert!(s.model_tiles().len() <= 1, "untiled");
+    let dxf = cadcraft_io::write_dxf(s.doc().unwrap());
+    let lines: Vec<&str> = dxf.lines().map(str::trim).collect();
+    let written = lines.windows(2).any(|w| w[0] == "51" && w[1].parse::<f64>().is_ok_and(|a| near(a, 30.0)));
+    assert!(written, "the lone *ACTIVE VPORT carries group 51");
+    let back = cadcraft_io::read_dxf(dxf.as_bytes()).unwrap();
+    let mut o = Session::new();
+    o.viewport_px = (1200.0, 800.0);
+    o.open_drawing(back.clone(), "single", None);
+    assert!(near(twist_deg(&o), 30.0), "twist {}", twist_deg(&o));
+    assert!(o.model_tiles().len() <= 1, "still untiled");
+    // And again: saved from the reopened session, it is still turned.
+    let again = cadcraft_io::read_dxf(cadcraft_io::write_dxf(o.doc().unwrap()).as_bytes()).unwrap();
+    let mut o2 = Session::new();
+    o2.viewport_px = (1200.0, 800.0);
+    o2.open_drawing(again, "again", None);
+    assert!(near(twist_deg(&o2), 30.0));
+    // Turned back (ZOOM Previous here), the drawing keeps no twist.
+    s.execute("zoom", &json!({ "mode": "previous" })).unwrap();
+    assert_eq!(view(&s).twist, 0.0);
+    let back = cadcraft_io::read_dxf(cadcraft_io::write_dxf(s.doc().unwrap()).as_bytes()).unwrap();
+    let mut o3 = Session::new();
+    o3.viewport_px = (1200.0, 800.0);
+    o3.open_drawing(back, "plain", None);
+    assert_eq!(view(&o3).twist, 0.0);
+}
+
+#[test]
+fn zoom_extents_fits_in_the_twisted_frame() {
+    let mut s = session();
+    s.execute("dview", &json!({ "twist": 90 })).unwrap();
+    s.execute("zoom", &json!({ "mode": "extents" })).unwrap();
+    let v = view(&s);
+    // Turned a quarter, the 100 x 50 line's box stands 100 high on screen.
+    assert!(near(v.twist.to_degrees(), 90.0));
+    assert!((v.center - Vec2::new(50.0, 25.0)).len() < 1e-6, "{:?}", v.center);
+    assert!(near(v.height, 105.0), "height {}", v.height);
+}
+
+#[test]
+fn each_tile_keeps_its_twist_through_a_dxf_round_trip() {
+    let mut s = session();
+    s.execute("-vports", &json!({ "option": "2", "arrangement": "vertical" })).unwrap();
+    s.execute("dview", &json!({ "twist": 30 })).unwrap();
+    let first = s.model_tiles().iter().position(|t| t.active).unwrap();
+    s.activate_tile(1 - first).unwrap();
+    assert_eq!(view(&s).twist, 0.0, "the other tile has its own twist");
+    s.execute("dview", &json!({ "twist": 60 })).unwrap();
+    let mut tw: Vec<f64> = s.model_tiles().iter().map(|t| t.view.twist.to_degrees()).collect();
+    tw.sort_by(f64::total_cmp);
+    assert!(near(tw[0], 30.0) && near(tw[1], 60.0), "{tw:?}");
+    // Switching back shows the first tile's twist again.
+    s.activate_tile(first).unwrap();
+    assert!(near(twist_deg(&s), 30.0));
+    // A saved configuration keeps both twists through DXF (VPORT group 51).
+    s.execute("-vports", &json!({ "option": "save", "name": "Pair" })).unwrap();
+    let dxf = cadcraft_io::write_dxf(s.doc().unwrap());
+    let lines: Vec<&str> = dxf.lines().map(str::trim).collect();
+    let written = lines.windows(2).any(|w| w[0] == "51" && w[1].parse::<f64>().is_ok_and(|a| near(a, 30.0)));
+    assert!(written, "group 51 written");
+    let back = cadcraft_io::read_dxf(dxf.as_bytes()).unwrap();
+    let pair = back.vports.iter().find(|c| c.name == "Pair").unwrap();
+    let mut tw: Vec<f64> = pair.tiles.iter().map(|t| t.twist.to_degrees()).collect();
+    tw.sort_by(f64::total_cmp);
+    assert!(near(tw[0], 30.0) && near(tw[1], 60.0), "{tw:?}");
+    // Opened, restoring the configuration shows each tile turned as saved.
+    let mut o = Session::new();
+    o.viewport_px = (1200.0, 800.0);
+    o.open_drawing(back, "pair", None);
+    o.execute("-vports", &json!({ "option": "restore", "name": "Pair" })).unwrap();
+    let mut tw: Vec<f64> = o.model_tiles().iter().map(|t| t.view.twist.to_degrees()).collect();
+    tw.sort_by(f64::total_cmp);
+    assert!(near(tw[0], 30.0) && near(tw[1], 60.0), "{tw:?}");
+}
+
+#[test]
+fn opening_a_tiled_drawing_shows_the_current_tile_twisted() {
+    let mut s = session();
+    s.execute("dview", &json!({ "twist": 45 })).unwrap();
+    s.execute("-vports", &json!({ "option": "2" })).unwrap();
+    let back = cadcraft_io::read_dxf(cadcraft_io::write_dxf(s.doc().unwrap()).as_bytes()).unwrap();
+    let mut o = Session::new();
+    o.viewport_px = (1200.0, 800.0);
+    o.open_drawing(back, "tiled", None);
+    assert!(near(twist_deg(&o), 45.0), "twist {}", twist_deg(&o));
+}
+
+#[test]
+fn view_save_and_restore_keep_the_twist() {
+    let mut s = session();
+    s.execute("dview", &json!({ "twist": 30 })).unwrap();
+    s.execute("view", &json!({ "option": "save", "name": "Turned" })).unwrap();
+    let saved = s.doc().unwrap().views.iter().find(|v| v.name == "Turned").map(|v| v.twist.to_degrees()).unwrap();
+    assert!(near(saved, 30.0));
+    s.execute("dview", &json!({ "twist": 0 })).unwrap();
+    s.execute("view.set", &json!({ "center": [80, 40], "height": 3 })).unwrap();
+    assert_eq!(view(&s).twist, 0.0);
+    s.execute("view", &json!({ "option": "restore", "name": "Turned" })).unwrap();
+    assert!(near(twist_deg(&s), 30.0));
+    assert!((view(&s).center - Vec2::new(10.0, 10.0)).len() < 1e-9);
+    // view.set keeps the twist unless given one.
+    s.execute("view.set", &json!({ "center": [0, 0], "height": 5 })).unwrap();
+    assert!(near(twist_deg(&s), 30.0));
+    s.execute("view.set", &json!({ "center": [0, 0], "height": 5, "twist": 15 })).unwrap();
+    assert!(near(twist_deg(&s), 15.0));
+}

crates/engine/tests/xref.rs

@@ -52,6 +52,7 @@ fn insert(block: &str, x: f64) -> EntityKind {
         rows: 1,
         col_spacing: 0.0,
         row_spacing: 0.0,
+        clip: None,
     })
 }
 

crates/fonts/Cargo.toml

@@ -14,3 +14,4 @@ skrifa = { workspace = true }
 harfrust = { workspace = true }
 unicode-bidi = { workspace = true }
 icu_segmenter = { workspace = true }
+encoding_rs = { workspace = true }

crates/fonts/src/lib.rs

@@ -1,7 +1,8 @@
 //! CADCraft text layout.
 //!
 //! Turns TEXT and MTEXT into stroke polylines with the built-in single-stroke font
-//! ("CADCraft Stroke") or glyph outlines of installed TrueType fonts ([`ttf`]), with a
+//! ("CADCraft Stroke"), the user's SHX shape fonts and big fonts ([`shx`]) or glyph outlines
+//! of installed TrueType fonts ([`ttf`]), with a
 //! per-character fallback to installed fonts for characters the chosen font lacks. Handles the
 //! `%%` control codes, alignment modes, width factor, obliquing, MTEXT inline formatting
 //! (paragraphs, stacking, height changes), word wrap and attachment points.
@@ -18,6 +19,7 @@ pub mod bidi;
 mod complex;
 mod linebreak;
 mod mtext;
+pub mod shx;
 mod stroke;
 pub mod subset;
 pub mod ttf;
@@ -42,8 +44,8 @@ pub struct Run {
 }
 
 /// Replace `%%` control codes: `%%d` degree, `%%p` plus/minus, `%%c` diameter, `%%%` percent,
-/// `%%nnn` character code. Underline/overline toggles (`%%u`, `%%o`) are returned as flags
-/// per character.
+/// `%%nnn` character code, and `\U+XXXX` Unicode escapes. Underline/overline toggles (`%%u`,
+/// `%%o`) are returned as flags per character.
 pub fn decode_controls(s: &str) -> Vec<(char, bool, bool)> {
     let mut out = Vec::with_capacity(s.len());
     let mut under = false;
@@ -52,6 +54,14 @@ pub fn decode_controls(s: &str) -> Vec<(char, bool, bool)> {
     let mut i = 0;
     while i < chars.len() {
         let c = chars.get(i).copied().unwrap_or(' ');
+        // `\U+XXXX`: a Unicode character by its code.
+        if c == '\\'
+            && let Some(u) = unicode_escape(&chars, i)
+        {
+            out.push((u, under, over));
+            i += 7;
+            continue;
+        }
         if c == '%' && chars.get(i + 1) == Some(&'%') {
             let code = chars.get(i + 2).copied().unwrap_or(' ');
             match code.to_ascii_lowercase() {
@@ -83,6 +93,18 @@ pub fn decode_controls(s: &str) -> Vec<(char, bool, bool)> {
     out
 }
 
+/// The character of a `\U+XXXX` escape (four hex digits) starting at `chars[i]`.
+pub(crate) fn unicode_escape(chars: &[char], i: usize) -> Option<char> {
+    if chars.get(i) != Some(&'\\') || !matches!(chars.get(i + 1), Some('U' | 'u')) || chars.get(i + 2) != Some(&'+') {
+        return None;
+    }
+    let hex: String = chars.get(i + 3..i + 7)?.iter().collect();
+    if !hex.chars().all(|c| c.is_ascii_hexdigit()) {
+        return None;
+    }
+    char::from_u32(u32::from_str_radix(&hex, 16).ok()?)
+}
+
 /// Advance width of one character at height 1 and width factor 1.
 pub fn char_advance(c: char) -> f64 {
     match stroke::glyph(c) {
@@ -279,35 +301,65 @@ pub fn space_width(font: &TextFont, height: f64, width_factor: f64) -> f64 {
     {
         return w;
     }
+    if let TextFont::Shx(t) = font {
+        return shx::width(t, " ", height, width_factor);
+    }
     stroke_advance(' ', height, width_factor) + stroke::GAP / stroke::CAP * height * width_factor
 }
 
-/// The font a piece of text is set in: the built-in stroke font or an installed TrueType /
-/// OpenType face (outlines). Either way, characters the font lacks come from a fallback font.
+/// The font a piece of text is set in: the built-in stroke font, an installed TrueType /
+/// OpenType face (outlines) or the user's SHX fonts (a main font and a big font). Whichever,
+/// characters the font lacks come from a fallback font.
 #[derive(Clone, Debug, Default)]
 pub enum TextFont {
     #[default]
     Stroke,
     Outline(ttf::Face),
+    Shx(std::sync::Arc<shx::ShxText>),
 }
 
 impl TextFont {
-    /// Resolve a text style font name: an installed TTF/OTF/TTC when found; else, for a font we
-    /// can't find (an SHX file, a missing TTF), the FONTALT font ([`ttf::font_alt`]) when set;
-    /// else the stroke font.
+    /// Resolve a text style font name (no big font, horizontal): see [`TextFont::resolve_style`].
     pub fn resolve(name: &str) -> TextFont {
-        if let Some(f) = ttf::find(name) {
+        TextFont::resolve_style(name, "", false)
+    }
+
+    /// Resolve a text style's fonts: an installed TTF/OTF/TTC when `font` names one; else the
+    /// SHX font and big font when found ([`shx::find`]), a missing one replaced by the FONTALT
+    /// font ([`ttf::font_alt`], which may name both: `simplex.shx,bigfont.shx`); else FONTALT
+    /// as a TrueType font; else the stroke font (which also draws the characters a missing big
+    /// font would have). `vertical` is the style's vertical flag, honoured by fonts made for it.
+    pub fn resolve_style(font: &str, big_font: &str, vertical: bool) -> TextFont {
+        if let Some(f) = ttf::find(font) {
             return TextFont::Outline(f);
         }
-        let n = name.trim();
-        if n.is_empty() || n.eq_ignore_ascii_case(BUILTIN_FONT) {
+        let n = font.trim();
+        let builtin = n.is_empty() || n.eq_ignore_ascii_case(BUILTIN_FONT);
+        let alt = ttf::font_alt();
+        let (alt_main, alt_big) = alt.split_once(',').map_or((alt.as_str(), ""), |(a, b)| (a.trim(), b.trim()));
+        let main = if builtin { None } else { shx::find(n).or_else(|| shx::find(alt_main)) };
+        let (big, big_name) = match big_font.trim() {
+            "" => (None, ""),
+            b => match shx::find(b) {
+                Some(f) => (Some(f), b),
+                None => (shx::find(alt_big), alt_big),
+            },
+        };
+        if main.is_some() || big.is_some() {
+            return TextFont::Shx(std::sync::Arc::new(shx::ShxText::new(main, big, big_name, vertical)));
+        }
+        if builtin {
             return TextFont::Stroke;
         }
-        ttf::find(&ttf::font_alt()).map(TextFont::Outline).unwrap_or(TextFont::Stroke)
+        ttf::find(alt_main).map(TextFont::Outline).unwrap_or(TextFont::Stroke)
     }
     pub fn is_outline(&self) -> bool {
         matches!(self, TextFont::Outline(_))
     }
+    /// Whether the text is drawn with SHX fonts.
+    pub fn is_shx(&self) -> bool {
+        matches!(self, TextFont::Shx(_))
+    }
 }
 
 /// Shaped text in local or world coordinates: open strokes (stroke-font glyphs, underlines,
@@ -436,6 +488,9 @@ pub fn shape_line_dir(font: &TextFont, s: &str, height: f64, width_factor: f64,
     {
         return sh;
     }
+    if let TextFont::Shx(t) = font {
+        return shx::shape(t, s, height, width_factor, oblique);
+    }
     shape_stroke_dir(s, height, width_factor, oblique, base_rtl)
 }
 
@@ -450,6 +505,9 @@ pub fn text_width(font: &TextFont, s: &str, height: f64, width_factor: f64) -> f
     {
         return w;
     }
+    if let TextFont::Shx(t) = font {
+        return shx::width(t, s, height, width_factor);
+    }
     line_width(s, height, width_factor)
 }
 
@@ -529,7 +587,8 @@ pub fn baseline_start(font: &TextFont, s: &str, p: &TextParams) -> Vec2 {
 fn bottom_depth(font: &TextFont, height: f64) -> f64 {
     match font {
         TextFont::Outline(face) => ttf::descent_ratio(face).map_or(height / 3.0, |r| r * height),
-        TextFont::Stroke => height / 3.0,
+        // AutoCAD places it a third of the height down with SHX fonts.
+        TextFont::Stroke | TextFont::Shx(_) => height / 3.0,
     }
 }
 

crates/fonts/src/mtext.rs

@@ -55,6 +55,13 @@ pub fn plain_mtext(s: &str) -> String {
                         i = j + 1;
                     }
                     'L' | 'l' | 'O' | 'o' | 'K' | 'k' => i += 2,
+                    // `\U+XXXX`: a character by its Unicode code, as the layout reads it.
+                    'U' if crate::unicode_escape(&chars, i).is_some() => {
+                        if let Some(u) = crate::unicode_escape(&chars, i) {
+                            out.push(u);
+                        }
+                        i += 7;
+                    }
                     // Codes with an argument terminated by ';' (\f, \F, \H, \W, \Q, \T, \A, \C, \c, \p).
                     _ => {
                         let mut j = i + 2;
@@ -287,6 +294,13 @@ fn parse(contents: &str, base: Fmt) -> (Vec<Atom>, Vec<Fmt>) {
                     'O' => derive(&mut fmts, &mut cur, &|f| f.over = true),
                     'o' => derive(&mut fmts, &mut cur, &|f| f.over = false),
                     'K' | 'k' => {}
+                    // `\U+XXXX`: a character by its Unicode code.
+                    'U' if i >= 2 && crate::unicode_escape(&chars, i - 2).is_some() => {
+                        if let Some(u) = crate::unicode_escape(&chars, i - 2) {
+                            push_char(&mut word, u, cur);
+                        }
+                        i += 5;
+                    }
                     'S' => {
                         let mut j = i;
                         let (mut top, mut bottom, mut sep) = (String::new(), String::new(), None);
@@ -785,6 +799,8 @@ mod tests {
         assert_eq!(plain_mtext("a\\~b\\\\c"), "a b\\c");
         assert_eq!(plain_mtext("\\H2.5x;Big"), "Big");
         assert_eq!(plain_mtext("unterminated \\H2"), "unterminated ");
+        assert_eq!(plain_mtext("\\U+0041B \\U+00E8"), "AB è");
+        assert_eq!(plain_mtext("\\U+12"), "", "a short escape is a code with an argument");
     }
 
     #[test]

crates/fonts/src/shx/compile.rs

@@ -0,0 +1,313 @@
+//! Shape source (`.shp`) to a compiled SHX file, as COMPILE does.
+//!
+//! A source is a list of definitions: a header line `*number,defbytes,NAME` followed by its
+//! specification bytes (on as many lines as needed, ending with 0). Numbers are decimal, or
+//! hexadecimal after a leading `0` (`012`, `08cfb`); parentheses only group; `;` starts a
+//! comment. A big font starts with `*BIGFONT nchars,nranges,first,last,…` and a Unicode font
+//! with `*UNIFONT,6,name` followed by `above,below,modes,encoding,type,0`. Shape 0 is a text
+//! font's record (`above,below,modes,0`).
+//!
+//! Operands are encoded by what they are: a subshape number takes two bytes in a Unicode font
+//! (and after `7,0` in a big font), displacements and bulges are two's complement, and an arc's
+//! direction byte (`-043`) keeps its sign in the high bit. `defbytes` is not checked: the
+//! program's own length is written.
+
+use super::ShxError;
+use super::parse::{BIGFONT, SHAPES_10, UNIFONT};
+
+/// Largest source compiled.
+const MAX_SOURCE: usize = 8 << 20;
+
+#[derive(Clone, Copy, PartialEq)]
+enum Kind {
+    Shapes,
+    Big,
+    Uni,
+}
+
+struct Shape {
+    number: u16,
+    name: String,
+    program: Vec<u8>,
+}
+
+/// A number token: value (sign included).
+fn number(tok: &str, line: usize) -> Result<i64, ShxError> {
+    let t: String = tok.chars().filter(|c| !matches!(c, '(' | ')') && !c.is_whitespace()).collect();
+    let (neg, digits) = match t.strip_prefix('-') {
+        Some(d) => (true, d),
+        None => (false, t.strip_prefix('+').unwrap_or(&t)),
+    };
+    let err = || ShxError::Source(line, format!("not a number: {tok:?}"));
+    let v = if digits.len() > 1 && digits.starts_with('0') {
+        i64::from_str_radix(digits.get(1..).unwrap_or_default(), 16).map_err(|_| err())?
+    } else {
+        digits.parse::<i64>().map_err(|_| err())?
+    };
+    if v > 0xFFFF {
+        return Err(err());
+    }
+    Ok(if neg { -v } else { v })
+}
+
+/// The comma-separated numbers of a line (comment removed, blank fields skipped).
+fn numbers(text: &str, line: usize) -> Result<Vec<i64>, ShxError> {
+    text.split(',').map(str::trim).filter(|t| !t.is_empty() && *t != "(" && *t != ")").map(|t| number(t, line)).collect()
+}
+
+/// The spec-byte encoder: walks the tokens as the reader walks the bytes.
+struct Enc<'a> {
+    toks: &'a [i64],
+    i: usize,
+    out: Vec<u8>,
+    kind: Kind,
+    line: usize,
+}
+
+impl Enc<'_> {
+    fn next(&mut self) -> Result<i64, ShxError> {
+        let v = self.toks.get(self.i).copied().ok_or_else(|| ShxError::Source(self.line, "the shape ends inside a command".into()))?;
+        self.i += 1;
+        Ok(v)
+    }
+    fn byte(&mut self) -> Result<(), ShxError> {
+        let v = self.next()?;
+        let b = u8::try_from(v).map_err(|_| ShxError::Source(self.line, format!("{v} is not a byte")))?;
+        self.out.push(b);
+        Ok(())
+    }
+    /// Two's complement −128..127.
+    fn signed(&mut self) -> Result<i64, ShxError> {
+        let v = self.next()?;
+        let b = i8::try_from(v).map_err(|_| ShxError::Source(self.line, format!("{v} is not −128..127")))?;
+        self.out.extend(b.to_le_bytes());
+        Ok(v)
+    }
+    /// Sign in the high bit (an arc's direction byte).
+    fn sign_magnitude(&mut self) -> Result<(), ShxError> {
+        let v = self.next()?;
+        let m = u8::try_from(v.unsigned_abs())
+            .ok()
+            .filter(|m| *m < 0x80)
+            .ok_or_else(|| ShxError::Source(self.line, format!("{v} is not an octant byte")))?;
+        self.out.push(if v < 0 { m | 0x80 } else { m });
+        Ok(())
+    }
+    fn word(&mut self) -> Result<(), ShxError> {
+        let v = self.next()?;
+        let w = u16::try_from(v).map_err(|_| ShxError::Source(self.line, format!("{v} is not a shape number")))?;
+        self.out.extend(w.to_be_bytes());
+        Ok(())
+    }
+
+    fn program(mut self) -> Result<Vec<u8>, ShxError> {
+        while self.i < self.toks.len() {
+            let code = self.next()?;
+            let c = u8::try_from(code).map_err(|_| ShxError::Source(self.line, format!("{code} is not a code")))?;
+            self.out.push(c);
+            match c {
+                0 => break,
+                3 | 4 => self.byte()?,
+                7 => match self.kind {
+                    Kind::Uni => self.word()?,
+                    Kind::Big => {
+                        let first = self.toks.get(self.i).copied().unwrap_or(0);
+                        if first == 0 {
+                            self.byte()?;
+                            self.word()?;
+                            for _ in 0..4 {
+                                self.byte()?;
+                            }
+                        } else {
+                            self.byte()?;
+                        }
+                    }
+                    Kind::Shapes => self.byte()?,
+                },
+                8 => {
+                    self.signed()?;
+                    self.signed()?;
+                }
+                9 => loop {
+                    let (x, y) = (self.signed()?, self.signed()?);
+                    if x == 0 && y == 0 {
+                        break;
+                    }
+                },
+                10 => {
+                    self.byte()?;
+                    self.sign_magnitude()?;
+                }
+                11 => {
+                    for _ in 0..4 {
+                        self.byte()?;
+                    }
+                    self.sign_magnitude()?;
+                }
+                12 => {
+                    for _ in 0..3 {
+                        self.signed()?;
+                    }
+                }
+                13 => loop {
+                    let (x, y) = (self.signed()?, self.signed()?);
+                    if x == 0 && y == 0 {
+                        break;
+                    }
+                    self.signed()?;
+                },
+                _ => {}
+            }
+        }
+        if self.out.last() != Some(&0) {
+            self.out.push(0);
+        }
+        Ok(self.out)
+    }
+}
+
+/// Compile shape source into an SHX file (a shape file or text font, a big font, or a Unicode
+/// font, as its first definition says).
+pub fn compile(source: &str) -> Result<Vec<u8>, ShxError> {
+    if source.len() > MAX_SOURCE {
+        return Err(ShxError::TooLarge);
+    }
+    let mut kind = Kind::Shapes;
+    let mut ranges: Vec<(u16, u16)> = Vec::new();
+    let mut uni_info: Option<(String, Vec<u8>)> = None;
+    // Definitions: header (number, name, line) and the numbers that follow it.
+    let mut defs: Vec<(i64, String, usize, Vec<i64>)> = Vec::new();
+    let mut uni_header_pending = false;
+    for (no, raw) in source.lines().enumerate() {
+        let line = no + 1;
+        let text = raw.split(';').next().unwrap_or_default().trim();
+        if text.is_empty() {
+            continue;
+        }
+        if let Some(head) = text.strip_prefix('*') {
+            let upper = head.trim_start().to_ascii_uppercase();
+            if let Some(rest) = upper.strip_prefix("BIGFONT") {
+                kind = Kind::Big;
+                let v = numbers(rest, line)?;
+                let n = usize::try_from(v.get(1).copied().unwrap_or(0)).unwrap_or(0);
+                for k in 0..n {
+                    let lo = v.get(2 + 2 * k).copied().unwrap_or(0);
+                    let hi = v.get(3 + 2 * k).copied().unwrap_or(lo);
+                    let to = |x: i64| u16::try_from(x).map_err(|_| ShxError::Source(line, "bad escape range".into()));
+                    ranges.push((to(lo)?, to(hi)?));
+                }
+                continue;
+            }
+            if upper.starts_with("UNIFONT") {
+                kind = Kind::Uni;
+                let name = head.splitn(3, ',').nth(2).unwrap_or_default().trim().to_string();
+                uni_info = Some((name, Vec::new()));
+                uni_header_pending = true;
+                continue;
+            }
+            uni_header_pending = false;
+            let mut parts = head.splitn(3, ',');
+            let num = number(parts.next().unwrap_or_default().trim(), line)?;
+            let _defbytes = parts.next();
+            let name = parts.next().unwrap_or_default().trim().to_string();
+            defs.push((num, name, line, Vec::new()));
+            continue;
+        }
+        let v = numbers(text, line)?;
+        if uni_header_pending {
+            if let Some((_, info)) = uni_info.as_mut() {
+                for x in v {
+                    info.push(u8::try_from(x).map_err(|_| ShxError::Source(line, "bad font record".into()))?);
+                }
+            }
+            continue;
+        }
+        match defs.last_mut() {
+            Some(d) => d.3.extend(v),
+            None => return Err(ShxError::Source(line, "specification bytes before any *number,defbytes,NAME line".into())),
+        }
+    }
+    let mut shapes: Vec<Shape> = Vec::new();
+    for (num, name, line, toks) in defs {
+        let number = u16::try_from(num).map_err(|_| ShxError::Source(line, format!("shape number {num} out of range")))?;
+        let program = if number == 0 {
+            // The font record: plain bytes.
+            toks.iter().map(|x| u8::try_from(*x).map_err(|_| ShxError::Source(line, "bad font record".into()))).collect::<Result<Vec<u8>, _>>()?
+        } else {
+            Enc { toks: &toks, i: 0, out: Vec::new(), kind, line }.program()?
+        };
+        if shapes.iter().any(|s| s.number == number) {
+            return Err(ShxError::Source(line, format!("shape {number} is defined twice")));
+        }
+        shapes.push(Shape { number, name, program });
+    }
+    if shapes.is_empty() {
+        return Err(ShxError::Empty);
+    }
+    shapes.sort_by_key(|s| s.number);
+    let record = |s: &Shape| -> Result<Vec<u8>, ShxError> {
+        let mut r: Vec<u8> = s.name.bytes().filter(|b| *b != 0).collect();
+        r.push(0);
+        r.extend(&s.program);
+        if r.len() > usize::from(u16::MAX) { Err(ShxError::TooLarge) } else { Ok(r) }
+    };
+    let count = u16::try_from(shapes.len()).map_err(|_| ShxError::TooLarge)?;
+    let len16 = |r: &[u8]| u16::try_from(r.len()).unwrap_or(u16::MAX);
+    let mut out = Vec::new();
+    match kind {
+        Kind::Shapes => {
+            out.extend(SHAPES_10);
+            out.extend(shapes.first().map_or(0, |s| s.number).to_le_bytes());
+            out.extend(shapes.last().map_or(0, |s| s.number).to_le_bytes());
+            out.extend(count.to_le_bytes());
+            let recs: Vec<Vec<u8>> = shapes.iter().map(record).collect::<Result<_, _>>()?;
+            for (s, r) in shapes.iter().zip(&recs) {
+                out.extend(s.number.to_le_bytes());
+                out.extend(len16(r).to_le_bytes());
+            }
+            for r in &recs {
+                out.extend(r);
+            }
+            out.extend(b"EOF");
+        }
+        Kind::Big => {
+            out.extend(BIGFONT);
+            let nranges = u16::try_from(ranges.len()).map_err(|_| ShxError::TooLarge)?;
+            out.extend(count.to_le_bytes());
+            out.extend(count.to_le_bytes());
+            out.extend(nranges.to_le_bytes());
+            for (lo, hi) in &ranges {
+                out.extend(lo.to_le_bytes());
+                out.extend(hi.to_le_bytes());
+            }
+            let recs: Vec<Vec<u8>> = shapes.iter().map(record).collect::<Result<_, _>>()?;
+            let mut off = out.len() + 8 * recs.len();
+            for (s, r) in shapes.iter().zip(&recs) {
+                out.extend(s.number.to_le_bytes());
+                out.extend(len16(r).to_le_bytes());
+                out.extend(u32::try_from(off).map_err(|_| ShxError::TooLarge)?.to_le_bytes());
+                off += r.len();
+            }
+            for r in &recs {
+                out.extend(r);
+            }
+        }
+        Kind::Uni => {
+            out.extend(UNIFONT);
+            let (name, info) = uni_info.unwrap_or_default();
+            out.extend((u32::from(count) + 1).to_le_bytes());
+            let mut rec: Vec<u8> = name.bytes().filter(|b| *b != 0).collect();
+            rec.push(0);
+            rec.extend(&info);
+            out.extend(len16(&rec).to_le_bytes());
+            out.extend(&rec);
+            for s in &shapes {
+                let r = record(s)?;
+                out.extend(s.number.to_le_bytes());
+                out.extend(len16(&r).to_le_bytes());
+                out.extend(r);
+            }
+        }
+    }
+    Ok(out)
+}

crates/fonts/src/shx/mod.rs

@@ -0,0 +1,248 @@
+//! SHX shape fonts: text fonts, big fonts (East Asian double-byte) and Unicode fonts that a
+//! drawing's text styles name, read at run time from files the user has. None is bundled.
+//!
+//! - [`ShxFont::parse`] reads the compiled containers (`shapes 1.0/1.1`, `bigfont 1.0`,
+//!   `unifont 1.0`) and [`ShxFont::glyph`] runs a shape's pen program (the vector length and
+//!   direction codes and special codes 0–14 of the public shape description language) into
+//!   polylines in font units. Every count, offset and loop in a file is bounded: a hostile or
+//!   truncated file never panics, it reads as far as it is valid or not at all.
+//! - [`compile`] turns shape source (`.shp`) into a compiled file, as COMPILE does. The tests
+//!   build every font they use with it: no font file is in this repository.
+//! - Fonts are found by name through the font table (`table`): registered bytes
+//!   ([`register`], the web build's files opened alongside a drawing), an app-set
+//!   [`FontProvider`], the folders of opened drawings ([`add_drawing_dir`]) and the support
+//!   search path ([`set_search_path`], `CADCRAFT_SHXPATH`), after the font map
+//!   ([`set_font_map`]). CADCraft never looks inside another CAD program's installation.
+//! - [`ShxText`] is a text style's pair of fonts (main + big font) and orientation, which the
+//!   text layout draws ([`crate::TextFont::Shx`]): advances are the pen's end positions, so
+//!   widths and extents follow the font's own metrics.
+//!
+//! Binary container layouts (little-endian): a signature line ending in CR LF 0x1A, then
+//! - shapes: first and last shape number, count, an index of (number, record length), the
+//!   records (a NUL-terminated name, then the program) and `EOF`;
+//! - big font: index size, count, escape-range count, the ranges (first, last lead byte),
+//!   an index of (number, record length, file offset) and the records;
+//! - unifont: shape count (32 bits), the length of the font record, the font record (name,
+//!   above, below, modes, encoding, embedding, 0) and then each shape as (number, length,
+//!   record).
+
+mod compile;
+mod parse;
+mod program;
+mod table;
+#[cfg(test)]
+mod tests;
+mod text;
+
+use std::collections::HashMap;
+use std::sync::{Arc, PoisonError, RwLock};
+
+use cadcraft_geom::Vec2;
+
+pub use compile::compile;
+pub use table::{
+    FontProvider, add_drawing_dir, clear_registered, drawing_dirs, find, font_map, generation, register, search_path, set_font_map, set_provider,
+    set_search_path,
+};
+pub use text::ShxText;
+pub(crate) use text::{shape, width};
+
+/// Why a font file can't be read or a shape source can't be compiled.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum ShxError {
+    /// Not an SHX file (unknown signature).
+    NotShx,
+    /// The file ends inside its header or index.
+    Truncated,
+    /// The file is larger, or has more of something, than CADCraft reads.
+    TooLarge,
+    /// The file is well-formed but holds no shape.
+    Empty,
+    /// Shape source error: line and message.
+    Source(usize, String),
+}
+
+impl std::fmt::Display for ShxError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ShxError::NotShx => f.write_str("not an SHX shape or font file"),
+            ShxError::Truncated => f.write_str("the SHX file is truncated"),
+            ShxError::TooLarge => f.write_str("the SHX file is too large"),
+            ShxError::Empty => f.write_str("the SHX file has no shapes"),
+            ShxError::Source(line, msg) => write!(f, "line {line}: {msg}"),
+        }
+    }
+}
+
+impl std::error::Error for ShxError {}
+
+/// The kind of SHX file.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum ShxKind {
+    /// A shape file or a text font with single-byte character codes (`shapes 1.0/1.1`).
+    Shapes,
+    /// A big font: double-byte character codes after an escape (lead) byte.
+    BigFont,
+    /// A Unicode font: shape numbers are Unicode code points.
+    Unifont,
+}
+
+/// A shape's program run into polylines, in font units (pen starts at the origin).
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct ShxGlyph {
+    /// Pen-down runs (two points or more).
+    pub strokes: Vec<Vec<Vec2>>,
+    /// Where the pen ends: the advance to the next character.
+    pub advance: Vec2,
+}
+
+/// One shape record: where its name and program are in [`ShxFont::data`].
+#[derive(Clone, Copy, Debug)]
+pub(crate) struct Record {
+    name: (usize, usize),
+    program: (usize, usize),
+}
+
+/// Glyphs cached per font, keyed by (shape, vertical).
+type GlyphCache = HashMap<(u16, bool), Option<Arc<ShxGlyph>>>;
+
+/// Most glyphs cached per font (a big font has thousands; text uses a few hundred).
+const MAX_CACHED_GLYPHS: usize = 16_384;
+
+/// A parsed SHX file.
+pub struct ShxFont {
+    kind: ShxKind,
+    name: String,
+    /// Shape 0 (the font record) is present: the file is a text font, not only shapes.
+    header: bool,
+    above: f64,
+    below: f64,
+    /// Modes 2: horizontal and vertical (code 14 is honoured).
+    dual: bool,
+    /// Unifont encoding: 0 Unicode, 1 packed multibyte, 2 shape file.
+    encoding: u8,
+    /// Extended big font: the font record gives a character width (subshape cell).
+    char_width: f64,
+    /// Big font escape ranges (lead bytes).
+    ranges: Vec<(u16, u16)>,
+    data: Vec<u8>,
+    records: HashMap<u16, Record>,
+    cache: RwLock<GlyphCache>,
+}
+
+impl std::fmt::Debug for ShxFont {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("ShxFont")
+            .field("kind", &self.kind)
+            .field("name", &self.name)
+            .field("above", &self.above)
+            .field("below", &self.below)
+            .field("dual", &self.dual)
+            .field("shapes", &self.records.len())
+            .finish()
+    }
+}
+
+impl ShxFont {
+    /// Parse a compiled SHX file.
+    pub fn parse(bytes: &[u8]) -> Result<ShxFont, ShxError> {
+        parse::parse(bytes)
+    }
+    pub fn kind(&self) -> ShxKind {
+        self.kind
+    }
+    /// The font name in its font record (shape 0), or empty.
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+    /// Whether the file has a font record (shape 0): a text font rather than a shape file.
+    pub fn is_font(&self) -> bool {
+        self.header
+    }
+    /// Vector units uppercase letters rise above the baseline (big font: the character height).
+    /// Text height `h` draws the font at `h / above` per unit. 0 for a shape file.
+    pub fn above(&self) -> f64 {
+        self.above
+    }
+    /// Vector units lowercase descenders drop below the baseline.
+    pub fn below(&self) -> f64 {
+        self.below
+    }
+    /// The font supports vertical text (modes 2).
+    pub fn is_dual(&self) -> bool {
+        self.dual
+    }
+    /// The units per text height: [`Self::above`], or 1 for a file without a font record.
+    pub fn units_per_height(&self) -> f64 {
+        if self.above > 0.0 { self.above } else { 1.0 }
+    }
+    /// Big font escape ranges: `(first, last)` lead bytes.
+    pub fn escape_ranges(&self) -> &[(u16, u16)] {
+        &self.ranges
+    }
+    /// Whether `b` starts a double-byte character in this big font.
+    pub fn is_lead_byte(&self, b: u8) -> bool {
+        self.ranges.iter().any(|(lo, hi)| (*lo..=*hi).contains(&u16::from(b)))
+    }
+    /// Unifont encoding (0 Unicode, 1 packed multibyte, 2 shape file); 0 for other kinds.
+    pub fn encoding(&self) -> u8 {
+        self.encoding
+    }
+    pub fn shape_count(&self) -> usize {
+        self.records.len()
+    }
+    pub fn has_shape(&self, number: u16) -> bool {
+        number != 0 && self.records.contains_key(&number)
+    }
+    /// The shape numbers in the file, sorted (not shape 0).
+    pub fn shape_numbers(&self) -> Vec<u16> {
+        let mut v: Vec<u16> = self.records.keys().copied().filter(|n| *n != 0).collect();
+        v.sort_unstable();
+        v
+    }
+    /// The name of shape `number` as the file stores it.
+    pub fn shape_name(&self, number: u16) -> Option<String> {
+        let r = self.records.get(&number)?;
+        self.data.get(r.name.0..r.name.1).map(|b| b.iter().map(|c| char::from(*c)).collect())
+    }
+    /// The number of the shape called `name` (case-insensitive), as a linetype's
+    /// `[SHAPE,file.shx]` element names it.
+    pub fn shape_number(&self, name: &str) -> Option<u16> {
+        let want = name.trim();
+        if want.is_empty() {
+            return None;
+        }
+        let mut found: Vec<u16> = self
+            .records
+            .iter()
+            .filter(|(n, r)| **n != 0 && self.data.get(r.name.0..r.name.1).is_some_and(|b| b.eq_ignore_ascii_case(want.as_bytes())))
+            .map(|(n, _)| *n)
+            .collect();
+        found.sort_unstable();
+        found.first().copied()
+    }
+    /// The program bytes of shape `number`.
+    pub(crate) fn program(&self, number: u16) -> Option<&[u8]> {
+        let r = self.records.get(&number)?;
+        self.data.get(r.program.0..r.program.1)
+    }
+    /// Shape `number` drawn horizontally or vertically, in font units; `None` when the font
+    /// has no such shape or its program is broken. Cached.
+    pub fn glyph(&self, number: u16, vertical: bool) -> Option<Arc<ShxGlyph>> {
+        if !self.has_shape(number) {
+            return None;
+        }
+        let vertical = vertical && self.dual;
+        let key = (number, vertical);
+        if let Some(g) = self.cache.read().unwrap_or_else(PoisonError::into_inner).get(&key) {
+            return g.clone();
+        }
+        let g = program::outline(self, number, vertical).ok().map(Arc::new);
+        let mut c = self.cache.write().unwrap_or_else(PoisonError::into_inner);
+        if c.len() >= MAX_CACHED_GLYPHS {
+            c.clear();
+        }
+        c.insert(key, g.clone());
+        g
+    }
+}

crates/fonts/src/shx/parse.rs

@@ -0,0 +1,224 @@
+//! Reading the compiled SHX containers (layouts in the module documentation). Every count and
+//! offset comes from the file, so each is checked against its length; records that run past
+//! the end are dropped and the rest kept.
+
+use std::collections::HashMap;
+use std::sync::RwLock;
+
+use super::{Record, ShxError, ShxFont, ShxKind};
+
+pub(super) const SHAPES_10: &[u8] = b"AutoCAD-86 shapes 1.0\r\n\x1a";
+pub(super) const SHAPES_11: &[u8] = b"AutoCAD-86 shapes 1.1\r\n\x1a";
+pub(super) const BIGFONT: &[u8] = b"AutoCAD-86 bigfont 1.0\r\n\x1a";
+pub(super) const UNIFONT: &[u8] = b"AutoCAD-86 unifont 1.0\r\n\x1a";
+
+/// Largest file read (the largest big fonts are a few megabytes).
+pub(super) const MAX_FILE_BYTES: usize = 32 << 20;
+/// Most escape ranges in a big font (lead bytes: at most 256).
+const MAX_RANGES: usize = 256;
+
+/// A checked little-endian reader.
+struct Rd<'a> {
+    b: &'a [u8],
+    pos: usize,
+}
+
+impl<'a> Rd<'a> {
+    fn take(&mut self, n: usize) -> Result<&'a [u8], ShxError> {
+        let end = self.pos.checked_add(n).ok_or(ShxError::Truncated)?;
+        let s = self.b.get(self.pos..end).ok_or(ShxError::Truncated)?;
+        self.pos = end;
+        Ok(s)
+    }
+    fn u16(&mut self) -> Result<u16, ShxError> {
+        match self.take(2)? {
+            [a, b] => Ok(u16::from_le_bytes([*a, *b])),
+            _ => Err(ShxError::Truncated),
+        }
+    }
+    fn u32(&mut self) -> Result<u32, ShxError> {
+        match self.take(4)? {
+            [a, b, c, d] => Ok(u32::from_le_bytes([*a, *b, *c, *d])),
+            _ => Err(ShxError::Truncated),
+        }
+    }
+}
+
+/// A font being read.
+struct Font {
+    kind: ShxKind,
+    name: String,
+    header: bool,
+    above: f64,
+    below: f64,
+    dual: bool,
+    encoding: u8,
+    char_width: f64,
+    ranges: Vec<(u16, u16)>,
+    records: HashMap<u16, Record>,
+}
+
+impl Font {
+    fn new(kind: ShxKind) -> Font {
+        Font {
+            kind,
+            name: String::new(),
+            header: false,
+            above: 0.0,
+            below: 0.0,
+            dual: false,
+            encoding: 0,
+            char_width: 0.0,
+            ranges: Vec::new(),
+            records: HashMap::new(),
+        }
+    }
+
+    /// Add the record of shape `number` at `start..end` of `data`: a NUL-terminated name, then
+    /// the program. Shape 0 is the font record. A record without a name terminator is dropped;
+    /// the first record of a number wins.
+    fn record(&mut self, data: &[u8], number: u16, start: usize, end: usize) {
+        let Some(bytes) = data.get(start..end) else { return };
+        let Some(nul) = bytes.iter().position(|b| *b == 0) else { return };
+        let name = (start, start + nul);
+        let program = (start + nul + 1, end);
+        if number == 0 {
+            if !self.header {
+                self.font_record(data.get(program.0..program.1).unwrap_or_default(), data.get(name.0..name.1).unwrap_or_default());
+            }
+            return;
+        }
+        self.records.entry(number).or_insert(Record { name, program });
+    }
+
+    /// The font record: above, below, modes (and for a unifont encoding and embedding); an
+    /// extended big font's is character height, 0, modes, character width.
+    fn font_record(&mut self, info: &[u8], name: &[u8]) {
+        self.header = true;
+        self.name = name.iter().take(255).map(|c| char::from(*c)).collect();
+        let byte = |i: usize| info.get(i).copied().unwrap_or(0);
+        self.above = f64::from(byte(0));
+        self.below = f64::from(byte(1));
+        self.dual = byte(2) == 2;
+        if self.kind == ShxKind::Unifont {
+            self.encoding = byte(3);
+        }
+        if self.kind == ShxKind::BigFont && info.len() >= 5 && byte(1) == 0 {
+            // Extended: height, 0, modes, width, 0.
+            self.below = 0.0;
+            self.char_width = f64::from(byte(3));
+        }
+    }
+
+    fn finish(self, data: Vec<u8>) -> Result<ShxFont, ShxError> {
+        if self.records.is_empty() {
+            return Err(ShxError::Empty);
+        }
+        Ok(ShxFont {
+            kind: self.kind,
+            name: self.name,
+            header: self.header,
+            above: self.above,
+            below: self.below,
+            dual: self.dual,
+            encoding: self.encoding,
+            char_width: if self.char_width > 0.0 { self.char_width } else { self.above },
+            ranges: self.ranges,
+            data,
+            records: self.records,
+            cache: RwLock::default(),
+        })
+    }
+}
+
+pub(super) fn parse(bytes: &[u8]) -> Result<ShxFont, ShxError> {
+    if bytes.len() > MAX_FILE_BYTES {
+        return Err(ShxError::TooLarge);
+    }
+    if bytes.starts_with(SHAPES_10) || bytes.starts_with(SHAPES_11) {
+        shapes(bytes)
+    } else if bytes.starts_with(BIGFONT) {
+        bigfont(bytes)
+    } else if bytes.starts_with(UNIFONT) {
+        unifont(bytes)
+    } else {
+        Err(ShxError::NotShx)
+    }
+}
+
+fn shapes(bytes: &[u8]) -> Result<ShxFont, ShxError> {
+    let mut r = Rd { b: bytes, pos: SHAPES_10.len() };
+    let _first = r.u16()?;
+    let _last = r.u16()?;
+    let count = usize::from(r.u16()?);
+    // The whole index must be there before anything is read from it.
+    let index = r.take(count.checked_mul(4).ok_or(ShxError::TooLarge)?)?;
+    let mut f = Font::new(ShxKind::Shapes);
+    let mut pos = r.pos;
+    for [a, b, c, d] in index.as_chunks::<4>().0 {
+        let (number, len) = (u16::from_le_bytes([*a, *b]), usize::from(u16::from_le_bytes([*c, *d])));
+        let Some(end) = pos.checked_add(len).filter(|e| *e <= bytes.len()) else { break };
+        f.record(bytes, number, pos, end);
+        pos = end;
+    }
+    f.finish(bytes.to_vec())
+}
+
+fn bigfont(bytes: &[u8]) -> Result<ShxFont, ShxError> {
+    let mut r = Rd { b: bytes, pos: BIGFONT.len() };
+    let index_size = usize::from(r.u16()?);
+    let count = usize::from(r.u16()?);
+    let nranges = usize::from(r.u16()?);
+    if nranges > MAX_RANGES {
+        return Err(ShxError::TooLarge);
+    }
+    let mut f = Font::new(ShxKind::BigFont);
+    for _ in 0..nranges {
+        let (lo, hi) = (r.u16()?, r.u16()?);
+        f.ranges.push((lo.min(hi), lo.max(hi)));
+    }
+    // The index has `count` entries of 8 bytes; a file whose count doesn't fit but whose index
+    // size does is read by that.
+    let fits = |n: usize| n.checked_mul(8).and_then(|l| r.pos.checked_add(l)).is_some_and(|e| e <= bytes.len());
+    let n = if fits(count) {
+        count
+    } else if fits(index_size) {
+        index_size
+    } else {
+        return Err(ShxError::Truncated);
+    };
+    let index = r.take(n.checked_mul(8).ok_or(ShxError::TooLarge)?)?;
+    for [a, b, c, d, o0, o1, o2, o3] in index.as_chunks::<8>().0 {
+        let number = u16::from_le_bytes([*a, *b]);
+        let len = usize::from(u16::from_le_bytes([*c, *d]));
+        let Ok(off) = usize::try_from(u32::from_le_bytes([*o0, *o1, *o2, *o3])) else { continue };
+        if len == 0 {
+            continue;
+        }
+        let Some(end) = off.checked_add(len).filter(|e| *e <= bytes.len()) else { continue };
+        f.record(bytes, number, off, end);
+    }
+    f.finish(bytes.to_vec())
+}
+
+fn unifont(bytes: &[u8]) -> Result<ShxFont, ShxError> {
+    let mut r = Rd { b: bytes, pos: UNIFONT.len() };
+    let count = r.u32()?;
+    let info_len = usize::from(r.u16()?);
+    let info = r.take(info_len)?;
+    let mut f = Font::new(ShxKind::Unifont);
+    let nul = info.iter().position(|b| *b == 0).unwrap_or(info.len());
+    f.font_record(info.get(nul.saturating_add(1)..).unwrap_or_default(), info.get(..nul).unwrap_or_default());
+    // `count` includes the font record; never trusted beyond the data that is there.
+    let mut left = count.saturating_sub(1);
+    while left > 0 {
+        left -= 1;
+        let Ok(number) = r.u16() else { break };
+        let Ok(len) = r.u16().map(usize::from) else { break };
+        let start = r.pos;
+        let Some(end) = start.checked_add(len).filter(|e| *e <= bytes.len()) else { break };
+        r.pos = end;
+        f.record(bytes, number, start, end);
+    }
+    f.finish(bytes.to_vec())
+}

crates/fonts/src/shx/program.rs

@@ -0,0 +1,344 @@
+//! The shape pen program: vector length/direction bytes and special codes 0–14, run into
+//! polylines. Bounded everywhere: subshape depth, location stack, steps, points, coordinates.
+//!
+//! - A byte with a non-zero high nibble is a vector: length (high nibble) in one of 16
+//!   directions (low nibble, counter-clockwise from east in 22.5° steps; the off-axis ones
+//!   are half-unit or unit steps on the minor axis).
+//! - 0 end, 1 pen down, 2 pen up, 3/4 divide/multiply vector lengths by the next byte,
+//!   5/6 push/pop the location, 7 subshape (one byte; two bytes high first in a Unicode font;
+//!   `0`, a two-byte number, base point, width and height in an extended big font),
+//!   8 one X-Y displacement, 9 displacements up to (0,0), 10 octant arc (radius,
+//!   ±0SC: sign = clockwise, S start octant, C octants, 0 = 8), 11 fractional arc (start
+//!   offset, end offset, high and low radius, ±0SC; offsets in 1/256 of 45° from the octant
+//!   boundaries), 12 bulge arc (dx, dy, bulge: ±127 = semicircle), 13 bulge arcs up to (0,0),
+//!   14 the next command is for vertical text only (dual-orientation fonts).
+//! - Displacements and bulges are two's complement bytes; the arc direction byte keeps its
+//!   sign in the high bit.
+
+use std::f64::consts::{FRAC_PI_4, TAU};
+
+use cadcraft_geom::Vec2;
+
+use super::{ShxFont, ShxGlyph, ShxKind};
+
+/// Subshape nesting (a cycle ends here).
+const MAX_DEPTH: usize = 16;
+/// Location stack (the format promises four).
+const MAX_STACK: usize = 64;
+/// Bytes run per glyph, subshapes included.
+const MAX_STEPS: usize = 200_000;
+/// Points per glyph.
+const MAX_POINTS: usize = 50_000;
+/// Coordinates in font units.
+const MAX_COORD: f64 = 1.0e7;
+/// Arc segments per full turn.
+const ARC_STEPS: f64 = 64.0;
+
+/// Why a program stops early: the glyph is then not drawn.
+#[derive(Debug)]
+pub(super) struct Broken;
+
+type Res = Result<(), Broken>;
+
+struct Pen<'a> {
+    font: &'a ShxFont,
+    vertical: bool,
+    pos: Vec2,
+    down: bool,
+    /// Vector length factor (codes 3 and 4).
+    scale: f64,
+    /// Per-axis factor of an extended big font subshape.
+    axes: Vec2,
+    stack: Vec<Vec2>,
+    strokes: Vec<Vec<Vec2>>,
+    active: Vec<Vec2>,
+    steps: usize,
+    points: usize,
+}
+
+pub(super) fn outline(font: &ShxFont, number: u16, vertical: bool) -> Result<ShxGlyph, Broken> {
+    let mut pen = Pen {
+        font,
+        vertical,
+        pos: Vec2::ZERO,
+        down: true,
+        scale: 1.0,
+        axes: Vec2::new(1.0, 1.0),
+        stack: Vec::new(),
+        strokes: Vec::new(),
+        active: Vec::new(),
+        steps: 0,
+        points: 0,
+    };
+    pen.run(number, 0)?;
+    pen.flush();
+    Ok(ShxGlyph { strokes: pen.strokes, advance: pen.pos })
+}
+
+/// The 16 vector directions (unit length on the major axis).
+fn direction(d: u8) -> Vec2 {
+    let (x, y) = match d & 15 {
+        0 => (1.0, 0.0),
+        1 => (1.0, 0.5),
+        2 => (1.0, 1.0),
+        3 => (0.5, 1.0),
+        4 => (0.0, 1.0),
+        5 => (-0.5, 1.0),
+        6 => (-1.0, 1.0),
+        7 => (-1.0, 0.5),
+        8 => (-1.0, 0.0),
+        9 => (-1.0, -0.5),
+        10 => (-1.0, -1.0),
+        11 => (-0.5, -1.0),
+        12 => (0.0, -1.0),
+        13 => (0.5, -1.0),
+        14 => (1.0, -1.0),
+        _ => (1.0, -0.5),
+    };
+    Vec2::new(x, y)
+}
+
+/// A two's complement operand byte.
+fn signed(b: u8) -> f64 {
+    f64::from(i8::from_le_bytes([b]))
+}
+
+/// A program being read: its bytes and position.
+struct Cur<'p> {
+    b: &'p [u8],
+    pos: usize,
+}
+
+impl Cur<'_> {
+    fn byte(&mut self) -> Result<u8, Broken> {
+        let v = self.b.get(self.pos).copied().ok_or(Broken)?;
+        self.pos += 1;
+        Ok(v)
+    }
+}
+
+impl Pen<'_> {
+    fn step(&mut self) -> Res {
+        self.steps += 1;
+        if self.steps > MAX_STEPS { Err(Broken) } else { Ok(()) }
+    }
+
+    fn flush(&mut self) {
+        if self.active.len() >= 2 {
+            self.strokes.push(std::mem::take(&mut self.active));
+        } else {
+            self.active.clear();
+        }
+    }
+
+    /// Move the pen by `d` font units (already scaled), drawing when the pen is down.
+    fn to(&mut self, target: Vec2) -> Res {
+        if !target.is_finite() || target.x.abs().max(target.y.abs()) > MAX_COORD {
+            return Err(Broken);
+        }
+        if self.down {
+            if self.active.is_empty() {
+                self.active.push(self.pos);
+                self.points += 1;
+            }
+            self.active.push(target);
+            self.points += 1;
+            if self.points > MAX_POINTS {
+                return Err(Broken);
+            }
+        } else {
+            self.flush();
+        }
+        self.pos = target;
+        Ok(())
+    }
+
+    /// A displacement in vector units (times the length factor and the subshape axes).
+    fn by(&mut self, d: Vec2) -> Res {
+        let k = d * self.scale;
+        self.to(self.pos + Vec2::new(k.x * self.axes.x, k.y * self.axes.y))
+    }
+
+    /// An arc of `radius` vector units from the pen, starting at angle `start` on its circle
+    /// and turning `sweep` radians (positive counter-clockwise).
+    fn arc(&mut self, radius: f64, start: f64, sweep: f64) -> Res {
+        let r = radius * self.scale;
+        if !(r.is_finite() && r > 0.0 && sweep.is_finite()) {
+            return Ok(());
+        }
+        let n = if self.down { (sweep.abs() / TAU * ARC_STEPS).ceil().clamp(1.0, ARC_STEPS) as usize } else { 1 };
+        let from = self.pos;
+        let s0 = Vec2::new(start.cos(), start.sin());
+        for i in 1..=n {
+            let a = start + sweep * i as f64 / n as f64;
+            let d = (Vec2::new(a.cos(), a.sin()) - s0) * r;
+            self.to(from + Vec2::new(d.x * self.axes.x, d.y * self.axes.y))?;
+        }
+        Ok(())
+    }
+
+    /// An arc to the displacement `d` with `bulge` (−127..127, ±127 a semicircle).
+    fn bulge(&mut self, d: Vec2, bulge: f64) -> Res {
+        let b = bulge.clamp(-127.0, 127.0) / 127.0;
+        if b == 0.0 || !self.down || d.len2() == 0.0 {
+            return self.by(d);
+        }
+        // Centre from the chord midpoint along its left normal; sweep 4·atan(b).
+        let centre = d * 0.5 + Vec2::new(-d.y, d.x) * ((1.0 - b * b) / (4.0 * b));
+        let rel = -centre;
+        self.arc(rel.len(), rel.y.atan2(rel.x), 4.0 * b.atan())
+    }
+
+    /// The octant byte `±0SC`: (clockwise, start octant, octants with 0 = 8).
+    fn octants(spec: u8) -> (f64, f64, f64) {
+        let sign = if spec & 0x80 != 0 { -1.0 } else { 1.0 };
+        let s = f64::from((spec >> 4) & 7);
+        let c = match spec & 7 {
+            0 => 8.0,
+            c => f64::from(c),
+        };
+        (sign, s, c)
+    }
+
+    /// The vector unit size of an extended big font's subshape cell.
+    fn cell(&self) -> Vec2 {
+        let h = if self.font.above > 0.0 { self.font.above } else { 1.0 };
+        let w = if self.font.char_width > 0.0 { self.font.char_width } else { h };
+        Vec2::new(w, h)
+    }
+
+    fn run(&mut self, number: u16, depth: usize) -> Res {
+        if depth >= MAX_DEPTH {
+            return Err(Broken);
+        }
+        let program = self.font.program(number).ok_or(Broken)?;
+        let mut r = Cur { b: program, pos: 0 };
+        let mut skip = false;
+        while r.pos < r.b.len() {
+            self.step()?;
+            let code = r.byte()?;
+            // Code 14: in a dual-orientation font the next command is for vertical text only.
+            let exec = !skip;
+            skip = false;
+            match code {
+                0 => return Ok(()),
+                1 if exec => self.down = true,
+                2 if exec => {
+                    self.down = false;
+                    self.flush();
+                }
+                3 | 4 => {
+                    let k = f64::from(r.byte()?);
+                    if exec && k > 0.0 {
+                        let s = if code == 3 { self.scale / k } else { self.scale * k };
+                        if !(1e-9..=MAX_COORD).contains(&s) {
+                            return Err(Broken);
+                        }
+                        self.scale = s;
+                    }
+                }
+                5 if exec => {
+                    if self.stack.len() >= MAX_STACK {
+                        return Err(Broken);
+                    }
+                    self.stack.push(self.pos);
+                }
+                6 if exec => {
+                    self.flush();
+                    if let Some(p) = self.stack.pop() {
+                        self.pos = p;
+                    }
+                }
+                7 => self.subshape(&mut r, exec, depth)?,
+                8 | 9 | 12 | 13 => loop {
+                    self.step()?;
+                    let d = Vec2::new(signed(r.byte()?), signed(r.byte()?));
+                    if matches!(code, 9 | 13) && d == Vec2::ZERO {
+                        break;
+                    }
+                    let bulge = if matches!(code, 12 | 13) { signed(r.byte()?) } else { 0.0 };
+                    if exec {
+                        self.bulge(d, bulge)?;
+                    }
+                    if matches!(code, 8 | 12) {
+                        break;
+                    }
+                },
+                10 => {
+                    let radius = f64::from(r.byte()?);
+                    let (sign, s, c) = Self::octants(r.byte()?);
+                    if exec {
+                        self.arc(radius, s * FRAC_PI_4, sign * c * FRAC_PI_4)?;
+                    }
+                }
+                11 => {
+                    let start = f64::from(r.byte()?) / 256.0;
+                    let end = match r.byte()? {
+                        0 => 1.0,
+                        e => f64::from(e) / 256.0,
+                    };
+                    let radius = f64::from(u16::from_be_bytes([r.byte()?, r.byte()?]));
+                    let (sign, s, c) = Self::octants(r.byte()?);
+                    if exec {
+                        // From `start` past the first octant boundary to `end` past the last
+                        // octant's.
+                        self.arc(radius, (s + sign * start) * FRAC_PI_4, sign * (c - 1.0 + end - start) * FRAC_PI_4)?;
+                    }
+                }
+                14 => skip = self.font.dual && !self.vertical && exec,
+                1..=15 => {}
+                v => {
+                    if exec {
+                        self.by(direction(v) * f64::from(v >> 4))?;
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Code 7 and its operands.
+    fn subshape(&mut self, r: &mut Cur, exec: bool, depth: usize) -> Res {
+        match self.font.kind {
+            ShxKind::Unifont => {
+                let n = u16::from_be_bytes([r.byte()?, r.byte()?]);
+                if exec {
+                    self.run(n, depth + 1)?;
+                }
+            }
+            ShxKind::BigFont => {
+                let first = r.byte()?;
+                if first != 0 {
+                    if exec {
+                        self.run(u16::from(first), depth + 1)?;
+                    }
+                    return Ok(());
+                }
+                // Extended: the primitive drawn in the box (x, y, width, height) of the cell.
+                let n = u16::from_be_bytes([r.byte()?, r.byte()?]);
+                let (x, y, w, h) = (f64::from(r.byte()?), f64::from(r.byte()?), f64::from(r.byte()?), f64::from(r.byte()?));
+                if !exec {
+                    return Ok(());
+                }
+                let (pos, axes, down) = (self.pos, self.axes, self.down);
+                let cell = self.cell();
+                self.flush();
+                self.pos = pos + Vec2::new(x * axes.x, y * axes.y) * self.scale;
+                self.axes = Vec2::new(axes.x * w / cell.x, axes.y * h / cell.y);
+                let res = self.run(n, depth + 1);
+                self.flush();
+                self.axes = axes;
+                self.pos = pos;
+                self.down = down;
+                res?;
+            }
+            ShxKind::Shapes => {
+                let n = u16::from(r.byte()?);
+                if exec {
+                    self.run(n, depth + 1)?;
+                }
+            }
+        }
+        Ok(())
+    }
+}

crates/fonts/src/shx/table.rs

@@ -0,0 +1,267 @@
+//! Finding SHX files by the name a text style or linetype gives (`romans.shx`, `GBCBIG`,
+//! `C:\fonts\simplex.shx`): only the file name counts, so a path stored in a drawing never
+//! reaches another folder or computer.
+//!
+//! Order: the font map ([`set_font_map`]) renames the file; then fonts registered by the app
+//! ([`register`]: the web build's files opened alongside a drawing, tests); then the app's
+//! [`FontProvider`]; then, natively, the folders of opened drawings ([`add_drawing_dir`], most
+//! recent first) and the support search path ([`set_search_path`], from `CADCRAFT_SHXPATH` at
+//! start). Results, found or not, are cached until one of these changes ([`generation`]
+//! counts the changes, so a viewer knows to regenerate).
+
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex, MutexGuard, OnceLock, PoisonError};
+
+use super::parse::MAX_FILE_BYTES;
+use super::{ShxError, ShxFont};
+
+/// Where an app finds font files CADCraft can't reach itself (a web page's file store, an
+/// app's own font folder). Called with the normalised file name (`romans.shx`); returns the
+/// file's bytes. Called without the font table's lock held.
+pub trait FontProvider: Send + Sync {
+    fn load(&self, file_name: &str) -> Option<Vec<u8>>;
+}
+
+/// Most fonts kept loaded, and their total bytes.
+const MAX_FONTS: usize = 128;
+const MAX_LOADED_BYTES: usize = 256 << 20;
+/// Most drawing folders and search path entries remembered.
+const MAX_DIRS: usize = 32;
+/// Most font map entries.
+const MAX_MAP: usize = 1024;
+
+#[derive(Default)]
+struct Table {
+    registered: HashMap<String, Arc<ShxFont>>,
+    resolved: HashMap<String, Option<Arc<ShxFont>>>,
+    loaded_bytes: usize,
+    provider: Option<Arc<dyn FontProvider>>,
+    drawing_dirs: Vec<PathBuf>,
+    search_path: Vec<PathBuf>,
+    map: Vec<(String, String)>,
+    generation: u64,
+}
+
+impl Table {
+    /// Forget cached results: something that changes them changed.
+    fn changed(&mut self) {
+        self.resolved.clear();
+        self.loaded_bytes = self.registered.values().map(|f| f.data.len()).sum();
+        self.generation = self.generation.wrapping_add(1);
+    }
+}
+
+fn table() -> MutexGuard<'static, Table> {
+    static T: OnceLock<Mutex<Table>> = OnceLock::new();
+    T.get_or_init(|| {
+        #[cfg(not(target_arch = "wasm32"))]
+        let search_path = std::env::var_os("CADCRAFT_SHXPATH")
+            .map(|p| std::env::split_paths(&p).filter(|d| !d.as_os_str().is_empty()).take(MAX_DIRS).collect())
+            .unwrap_or_default();
+        #[cfg(target_arch = "wasm32")]
+        let search_path = Vec::new();
+        Mutex::new(Table { search_path, ..Table::default() })
+    })
+    .lock()
+    .unwrap_or_else(PoisonError::into_inner)
+}
+
+/// The lookup key of a font name: its lower-case file name with `.shx` (`romans.shx`), or
+/// `None` for a name that isn't an SHX file (a TrueType font, empty, the built-in font).
+pub(crate) fn key(name: &str) -> Option<String> {
+    let base = name.trim().rsplit(['/', '\\']).next()?.trim();
+    if base.is_empty() || base.len() > 255 || base.contains(':') || base.chars().any(char::is_control) {
+        return None;
+    }
+    let lower = base.to_ascii_lowercase();
+    if lower.ends_with(".shx") {
+        return (lower.len() > 4).then_some(lower);
+    }
+    let ext = Path::new(&lower).extension().map(|e| e.to_string_lossy().to_string());
+    match ext.as_deref() {
+        // `txt` (no extension) is a classic style font name; other extensions are other kinds.
+        None => (lower != crate::BUILTIN_FONT.to_ascii_lowercase() && !lower.contains(' ')).then(|| format!("{lower}.shx")),
+        Some(_) => None,
+    }
+}
+
+/// Register font bytes under a file name (the web build's files opened alongside a drawing;
+/// tests). Replaces a font registered under the same name.
+pub fn register(name: &str, bytes: &[u8]) -> Result<(), ShxError> {
+    let k = key(name).ok_or(ShxError::NotShx)?;
+    let font = Arc::new(ShxFont::parse(bytes)?);
+    let mut t = table();
+    if !t.registered.contains_key(&k) && t.registered.len() >= MAX_FONTS {
+        return Err(ShxError::TooLarge);
+    }
+    t.registered.insert(k, font);
+    t.changed();
+    Ok(())
+}
+
+/// Forget every registered font (a web session closing its drawings).
+pub fn clear_registered() {
+    let mut t = table();
+    t.registered.clear();
+    t.changed();
+}
+
+/// Set (or clear) the app's font provider.
+pub fn set_provider(provider: Option<Arc<dyn FontProvider>>) {
+    let mut t = table();
+    t.provider = provider;
+    t.changed();
+}
+
+/// Search the folder of a drawing being opened for the fonts its styles name (most recent
+/// first).
+pub fn add_drawing_dir(dir: &Path) {
+    if dir.as_os_str().is_empty() {
+        return;
+    }
+    let mut t = table();
+    if t.drawing_dirs.first().is_some_and(|d| d == dir) {
+        return;
+    }
+    t.drawing_dirs.retain(|d| d != dir);
+    t.drawing_dirs.insert(0, dir.to_path_buf());
+    t.drawing_dirs.truncate(MAX_DIRS);
+    t.changed();
+}
+
+/// The drawing folders searched, most recent first.
+pub fn drawing_dirs() -> Vec<PathBuf> {
+    table().drawing_dirs.clone()
+}
+
+/// Set the support search path for SHX files: folders separated by `;` (or the platform's
+/// path separator). Empty clears it.
+pub fn set_search_path(list: &str) {
+    let dirs: Vec<PathBuf> = list
+        .split(';')
+        .flat_map(|p| if cfg!(any(windows, target_arch = "wasm32")) { vec![PathBuf::from(p)] } else { std::env::split_paths(p).collect() })
+        .filter(|d| !d.as_os_str().is_empty() && !d.to_string_lossy().trim().is_empty())
+        .take(MAX_DIRS)
+        .collect();
+    let mut t = table();
+    t.search_path = dirs;
+    t.changed();
+}
+
+/// The support search path, `;`-separated.
+pub fn search_path() -> String {
+    table().search_path.iter().map(|p| p.to_string_lossy().to_string()).collect::<Vec<_>>().join(";")
+}
+
+/// Set the font map: one `font;replacement` per line (or separated by `|`), as a font mapping
+/// file lists them. Lines that aren't a pair are ignored; empty clears it.
+pub fn set_font_map(text: &str) {
+    let map: Vec<(String, String)> = text
+        .split(['\n', '|'])
+        .filter_map(|l| {
+            let (a, b) = l.split_once(';')?;
+            Some((key(a)?, b.trim().to_string()))
+        })
+        .filter(|(_, b)| !b.is_empty())
+        .take(MAX_MAP)
+        .collect();
+    let mut t = table();
+    t.map = map;
+    t.changed();
+}
+
+/// The font map, one `font;replacement` per line.
+pub fn font_map() -> String {
+    table().map.iter().map(|(a, b)| format!("{a};{b}")).collect::<Vec<_>>().join("\n")
+}
+
+/// Counts changes to what fonts are found (registration, provider, folders, map).
+pub fn generation() -> u64 {
+    table().generation
+}
+
+/// The SHX font file a style or linetype names, if CADCraft can find and read it.
+pub fn find(name: &str) -> Option<Arc<ShxFont>> {
+    let mut k = key(name)?;
+    let (provider, dirs, generation) = {
+        let t = table();
+        // The font map renames once (a map can't loop).
+        if let Some(to) = t.map.iter().find(|(from, _)| *from == k).and_then(|(_, to)| key(to)) {
+            k = to;
+        }
+        if let Some(f) = t.registered.get(&k) {
+            return Some(f.clone());
+        }
+        if let Some(r) = t.resolved.get(&k) {
+            return r.clone();
+        }
+        let dirs: Vec<PathBuf> = t.drawing_dirs.iter().chain(t.search_path.iter()).cloned().collect();
+        (t.provider.clone(), dirs, t.generation)
+    };
+    let font = provider
+        .and_then(|p| p.load(&k))
+        .or_else(|| read_from(&dirs, &k))
+        .filter(|b| b.len() <= MAX_FILE_BYTES)
+        .and_then(|b| ShxFont::parse(&b).ok())
+        .map(Arc::new);
+    let mut t = table();
+    // Something changed while the file was read: keep the result out of the new cache.
+    if t.generation != generation {
+        return font;
+    }
+    if t.resolved.len() >= MAX_FONTS * 4 {
+        t.resolved.clear();
+        t.loaded_bytes = t.registered.values().map(|f| f.data.len()).sum();
+    }
+    let size = font.as_ref().map_or(0, |f| f.data.len());
+    if t.loaded_bytes.saturating_add(size) > MAX_LOADED_BYTES {
+        // Over the memory bound: used, not kept.
+        return font;
+    }
+    t.loaded_bytes += size;
+    t.resolved.insert(k, font.clone());
+    font
+}
+
+/// Most directory entries looked at for a font file whose name differs only in case.
+#[cfg(not(target_arch = "wasm32"))]
+const MAX_DIR_ENTRIES: usize = 10_000;
+
+/// The file `name` (a lower-case key) in the first of `dirs` that has it, whatever the case of
+/// its name: lower-case, upper-case, else any other case found in the directory (`Simplex.shx`
+/// on a case-sensitive file system).
+#[cfg(not(target_arch = "wasm32"))]
+fn read_from(dirs: &[PathBuf], name: &str) -> Option<Vec<u8>> {
+    use std::io::Read as _;
+    let read = |file: &Path| -> Option<Vec<u8>> {
+        let meta = std::fs::metadata(file).ok()?;
+        if !meta.is_file() || meta.len() > MAX_FILE_BYTES as u64 {
+            return None;
+        }
+        let mut bytes = Vec::new();
+        let limit = u64::try_from(MAX_FILE_BYTES).unwrap_or(u64::MAX).saturating_add(1);
+        std::fs::File::open(file).and_then(|f| f.take(limit).read_to_end(&mut bytes)).ok()?;
+        Some(bytes)
+    };
+    for d in dirs {
+        if let Some(b) = [d.join(name), d.join(name.to_ascii_uppercase())].iter().find_map(|f| read(f)) {
+            return Some(b);
+        }
+        let Ok(entries) = std::fs::read_dir(d) else { continue };
+        let found = entries
+            .take(MAX_DIR_ENTRIES)
+            .filter_map(Result::ok)
+            .find(|e| e.file_name().to_str().is_some_and(|n| n.eq_ignore_ascii_case(name)))
+            .and_then(|e| read(&e.path()));
+        if found.is_some() {
+            return found;
+        }
+    }
+    None
+}
+
+#[cfg(target_arch = "wasm32")]
+fn read_from(_dirs: &[PathBuf], _name: &str) -> Option<Vec<u8>> {
+    None
+}

crates/fonts/src/shx/tests.rs

@@ -0,0 +1,450 @@
+//! SHX tests. Every font here is compiled from shape source written for these tests: no font
+//! file is read from disk or committed.
+
+use std::f64::consts::PI;
+
+use cadcraft_geom::Vec2;
+
+use super::*;
+use crate::{TextFont, TextParams};
+
+/// A small dual-orientation text font: 6 units above, 2 below.
+pub(crate) const TEXT_FONT: &str = "\
+;; CADCraft test font (written for the tests)
+*0,4,cadcraft test
+6,2,2,0
+*32,3,SPACE
+2,060,0
+; A: up 6, right 4, down 6, then a gap of 2
+*65,7,UCA
+1,064,040,06C,2,020,0
+; B: a displacement out and back, then 5 on
+*66,10,UCB
+2,010,1,8,(3,4),8,(-3,-4),2,050,0
+; C: vertical-only moves (code 14)
+*67,12,UCC
+2,14,8,(0,-8),1,064,2,14,8,(0,-6),040,0
+; the degree sign: a full octant circle
+*256,12,DEGREE
+2,8,(1,4),1,10,(1,0),2,8,(2,-4),0
+*257,6,PLUSMINUS
+1,040,2,020,0
+*258,6,DIAMETER
+1,044,2,020,0
+";
+
+/// A Unicode font with the same letters, a subshape and the diameter sign at U+2205.
+const UNI_FONT: &str = "\
+*UNIFONT,6,cadcraft uni
+6,2,0,0,0,0
+*00041,7,uca
+1,064,040,06C,2,020,0
+*000C5,9,ring a
+7,00041,2,8,(-4,7),1,040,2,8,(2,-7),0
+*02205,6,diameter
+1,044,2,020,0
+";
+
+/// A big font with Shift-JIS lead bytes: one square character (U+3042, 0x82A0).
+const BIG_FONT: &str = "\
+*BIGFONT 2,1,081,09F
+*0,4,cadcraft big
+8,0,0,0
+*082A0,7,square
+1,080,084,088,08C,2,080,0
+";
+
+/// An extended big font: two primitives of a 16 x 16 cell drawn into one character.
+const EXT_BIG_FONT: &str = "\
+*BIGFONT 2,1,081,09F
+*0,5,cadcraft ext
+16,0,0,16,0
+*08F01,10,box
+4,2,1,080,084,088,08C,3,2,0
+*082A2,20,two boxes
+7,0,08F01,0,0,8,16,7,0,08F01,8,0,8,16,2,4,2,080,3,2,0
+";
+
+fn font(src: &str) -> ShxFont {
+    ShxFont::parse(&compile(src).unwrap()).unwrap()
+}
+
+/// A shape file (no font record) with one shape from `spec`.
+fn one(spec: &str) -> ShxFont {
+    font(&format!("*1,1,T\n{spec}\n"))
+}
+
+fn adv(spec: &str) -> Vec2 {
+    one(spec).glyph(1, false).unwrap().advance
+}
+
+fn close(a: Vec2, b: Vec2) -> bool {
+    (a - b).len() < 1e-6
+}
+
+fn dir(deg: f64) -> Vec2 {
+    let r = deg.to_radians();
+    Vec2::new(r.cos(), r.sin())
+}
+
+#[test]
+fn every_vector_direction() {
+    let want = [
+        (1.0, 0.0),
+        (1.0, 0.5),
+        (1.0, 1.0),
+        (0.5, 1.0),
+        (0.0, 1.0),
+        (-0.5, 1.0),
+        (-1.0, 1.0),
+        (-1.0, 0.5),
+        (-1.0, 0.0),
+        (-1.0, -0.5),
+        (-1.0, -1.0),
+        (-0.5, -1.0),
+        (0.0, -1.0),
+        (0.5, -1.0),
+        (1.0, -1.0),
+        (1.0, -0.5),
+    ];
+    for (d, (x, y)) in want.iter().enumerate() {
+        let a = adv(&format!("02{d:X},0"));
+        assert!(close(a, Vec2::new(2.0 * x, 2.0 * y)), "direction {d}: {a:?}");
+    }
+    // Length 15, the longest vector.
+    assert!(close(adv("0F0,0"), Vec2::new(15.0, 0.0)));
+}
+
+#[test]
+fn pen_up_down_scale_push_pop() {
+    let f = one("2,010,1,020,2,010,1,010,0");
+    let g = f.glyph(1, false).unwrap();
+    assert_eq!(g.strokes, vec![vec![Vec2::new(1.0, 0.0), Vec2::new(3.0, 0.0)], vec![Vec2::new(4.0, 0.0), Vec2::new(5.0, 0.0)]]);
+    // 4 multiplies, 3 divides: 3 + 1.
+    assert!(close(adv("4,3,010,3,3,010,0"), Vec2::new(4.0, 0.0)));
+    // Push, draw, pop: the next run starts where the push was.
+    let g = one("5,040,6,014,0").glyph(1, false).unwrap();
+    assert_eq!(g.strokes.len(), 2);
+    assert!(close(g.strokes[1][0], Vec2::ZERO) && close(g.advance, Vec2::new(0.0, 1.0)));
+    // An unmatched pop is ignored.
+    assert!(close(adv("6,010,0"), Vec2::new(1.0, 0.0)));
+}
+
+#[test]
+fn displacements() {
+    assert!(close(adv("8,(-3,5),0"), Vec2::new(-3.0, 5.0)));
+    assert!(close(adv("9,(1,1),(2,-1),(-127,0),(0,0),0"), Vec2::new(-124.0, 0.0)));
+}
+
+#[test]
+fn octant_and_fractional_arcs() {
+    // A full circle comes back to where it started.
+    let g = one("10,(2,0),0").glyph(1, false).unwrap();
+    assert!(close(g.advance, Vec2::ZERO));
+    let maxx = g.strokes.iter().flatten().map(|p| p.x).fold(f64::MIN, f64::max);
+    assert!((maxx - 0.0).abs() < 1e-9 && g.strokes.iter().flatten().any(|p| (p.x + 4.0).abs() < 1e-6), "circle left of the pen");
+    // Clockwise from octant 4 (180°), three octants: ends at 45°.
+    assert!(close(adv("10,(1,-043),0"), dir(45.0) - dir(180.0)));
+    // Counter-clockwise quarter from 0°.
+    assert!(close(adv("10,(3,002),0"), (dir(90.0) - dir(0.0)) * 3.0));
+    // The documented fractional example: 55° to 95°, radius 3 (start octant 1, two octants).
+    let a0 = 45.0 + 56.0 / 256.0 * 45.0;
+    let a1 = 90.0 + 28.0 / 256.0 * 45.0;
+    assert!(close(adv("11,(56,28,0,3,012),0"), (dir(a1) - dir(a0)) * 3.0));
+    // High radius byte: 256 + 4.
+    assert!(close(adv("11,(0,0,1,4,001),0"), (dir(45.0) - dir(0.0)) * 260.0));
+}
+
+#[test]
+fn bulge_arcs() {
+    // A counter-clockwise semicircle up the chord bulges to the right... of the chord's left
+    // normal: from (0,0) to (0,4) about (0,2), through (2,2).
+    let g = one("12,(0,4,127),0").glyph(1, false).unwrap();
+    assert!(close(g.advance, Vec2::new(0.0, 4.0)));
+    assert!(g.strokes.iter().flatten().any(|p| close(*p, Vec2::new(2.0, 2.0))), "{:?}", g.strokes);
+    // Bulge 0 is a straight line.
+    assert_eq!(one("12,(3,0,0),0").glyph(1, false).unwrap().strokes, vec![vec![Vec2::ZERO, Vec2::new(3.0, 0.0)]]);
+    // Polyarc: two arcs, then the (0,0) end without a bulge.
+    let g = one("13,(4,0,127),(0,4,-127),(0,0),010,0").glyph(1, false).unwrap();
+    assert!(close(g.advance, Vec2::new(5.0, 4.0)));
+    assert!(g.strokes.iter().flatten().any(|p| (p.y + 2.0).abs() < 1e-6), "first arc dips below");
+}
+
+#[test]
+fn vertical_only_commands_and_text_font_record() {
+    let f = font(TEXT_FONT);
+    assert_eq!((f.kind(), f.name(), f.above(), f.below(), f.is_dual(), f.is_font()), (ShxKind::Shapes, "cadcraft test", 6.0, 2.0, true, true));
+    let h = f.glyph(67, false).unwrap();
+    assert_eq!(h.strokes, vec![vec![Vec2::ZERO, Vec2::new(0.0, 6.0)]]);
+    let v = f.glyph(67, true).unwrap();
+    assert_eq!(v.strokes, vec![vec![Vec2::new(0.0, -8.0), Vec2::new(0.0, -2.0)]]);
+    assert!(close(v.advance, Vec2::new(4.0, -8.0)));
+    // A font that isn't dual runs code 14's command in horizontal text too.
+    let g = one("2,14,8,(0,-8),0").glyph(1, false).unwrap();
+    assert!(close(g.advance, Vec2::new(0.0, -8.0)));
+    assert_eq!(f.shape_number("ucb"), Some(66));
+    assert_eq!(f.shape_name(65).as_deref(), Some("UCA"));
+    assert_eq!(f.shape_numbers().first(), Some(&32));
+}
+
+#[test]
+fn subshapes_shapes_unicode_and_extended_big_font() {
+    let s = font("*1,4,BAR\n1,030,0\n*2,6,TWO\n7,1,7,1,0\n");
+    assert!(close(s.glyph(2, false).unwrap().advance, Vec2::new(6.0, 0.0)));
+    let u = font(UNI_FONT);
+    assert_eq!((u.kind(), u.name(), u.above(), u.encoding()), (ShxKind::Unifont, "cadcraft uni", 6.0, 0));
+    let ring = u.glyph(0xC5, false).unwrap();
+    assert_eq!(ring.strokes.len(), 2, "the A and the ring's bar");
+    assert!(close(ring.advance, Vec2::new(8.0, 0.0)));
+    let e = font(EXT_BIG_FONT);
+    assert_eq!((e.kind(), e.above()), (ShxKind::BigFont, 16.0));
+    let g = e.glyph(0x82A2, false).unwrap();
+    assert_eq!(g.strokes.len(), 2);
+    let xs: Vec<(f64, f64)> = g.strokes.iter().map(|s| s.iter().fold((f64::MAX, f64::MIN), |(a, b), p| (a.min(p.x), b.max(p.x)))).collect();
+    assert_eq!(xs, vec![(0.0, 8.0), (8.0, 16.0)], "each primitive squeezed into half the cell");
+    let ys = g.strokes.iter().flatten().fold((f64::MAX, f64::MIN), |(a, b), p| (a.min(p.y), b.max(p.y)));
+    assert_eq!(ys, (0.0, 16.0));
+    assert!(close(g.advance, Vec2::new(16.0, 0.0)));
+}
+
+#[test]
+fn big_font_header_and_escape_ranges() {
+    let b = font(BIG_FONT);
+    assert_eq!(b.kind(), ShxKind::BigFont);
+    assert_eq!(b.escape_ranges(), &[(0x81, 0x9F)]);
+    assert!(b.is_lead_byte(0x82) && !b.is_lead_byte(0x41) && !b.is_lead_byte(0xA0));
+    assert_eq!(b.above(), 8.0);
+    assert!(b.has_shape(0x82A0));
+}
+
+#[test]
+fn cyclic_and_deep_subshapes_are_bounded() {
+    let f = font("*1,3,SELF\n7,1,0\n*2,3,A\n7,3,0\n*3,3,B\n7,2,0\n*4,3,MISSING\n7,9,0\n");
+    for n in 1..=4 {
+        assert!(f.glyph(n, false).is_none(), "shape {n}");
+    }
+    // A chain deeper than the bound fails; a shallow one draws.
+    let mut src = String::new();
+    for n in 1..=40u16 {
+        if n == 40 {
+            src.push_str(&format!("*{n},2,L\n010,0\n"));
+        } else {
+            src.push_str(&format!("*{n},3,L\n7,{},0\n", n + 1));
+        }
+    }
+    let f = font(&src);
+    assert!(f.glyph(1, false).is_none() && f.glyph(30, false).is_some());
+    // Doubling with subshapes: 2^n steps are cut off by the step bound.
+    let mut src = String::from("*1,2,L\n010,0\n");
+    for n in 2..=10u16 {
+        src.push_str(&format!("*{n},9,D\n7,{0},7,{0},7,{0},7,{0},0\n", n - 1));
+    }
+    let f = font(&src);
+    assert!(f.glyph(10, false).is_none() && f.glyph(3, false).is_some());
+    // Pushes without pops, and runaway scales.
+    let pushes = format!("{}0", "5,".repeat(100));
+    assert!(one(&pushes).glyph(1, false).is_none());
+    let scales = format!("{}010,0", "4,255,".repeat(10));
+    assert!(one(&scales).glyph(1, false).is_none());
+    // A zero radius or a zero factor draws nothing and doesn't fail.
+    assert!(one("10,(0,001),4,0,010,0").glyph(1, false).is_some());
+}
+
+/// Parse every prefix and many mutations of `bytes`; draw every shape of whatever parses.
+fn hammer(bytes: &[u8]) {
+    let draw = |b: &[u8]| {
+        if let Ok(f) = ShxFont::parse(b) {
+            for n in f.shape_numbers() {
+                let _ = f.glyph(n, false);
+                let _ = f.glyph(n, true);
+            }
+            let _ = f.shape_number("X");
+        }
+    };
+    for n in 0..=bytes.len() {
+        draw(&bytes[..n]);
+    }
+    let mut seed: u64 = 0x5EED_1234;
+    for _ in 0..2000 {
+        let mut b = bytes.to_vec();
+        for _ in 0..3 {
+            seed = seed.wrapping_mul(6364136223846793005).wrapping_add(1442695040888963407);
+            let i = (seed >> 33) as usize % b.len().max(1);
+            if let Some(x) = b.get_mut(i) {
+                *x = (seed >> 24) as u8;
+            }
+        }
+        draw(&b);
+    }
+}
+
+#[test]
+fn hostile_files_never_panic() {
+    for src in [TEXT_FONT, UNI_FONT, BIG_FONT, EXT_BIG_FONT] {
+        hammer(&compile(src).unwrap());
+    }
+    // Counts far beyond the data.
+    let mut shapes = parse::SHAPES_10.to_vec();
+    shapes.extend([1, 0, 0xFF, 0xFF, 0xFF, 0xFF]);
+    assert_eq!(ShxFont::parse(&shapes).err(), Some(ShxError::Truncated));
+    let mut big = parse::BIGFONT.to_vec();
+    big.extend([0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF]);
+    assert_eq!(ShxFont::parse(&big).err(), Some(ShxError::TooLarge));
+    let mut big = parse::BIGFONT.to_vec();
+    big.extend([0xFF, 0xFF, 0xFF, 0xFF, 0, 0]);
+    assert_eq!(ShxFont::parse(&big).err(), Some(ShxError::Truncated));
+    // A big font index pointing anywhere.
+    let mut big = parse::BIGFONT.to_vec();
+    big.extend([1, 0, 1, 0, 0, 0, 0x41, 0, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x7F]);
+    assert_eq!(ShxFont::parse(&big).err(), Some(ShxError::Empty));
+    let mut uni = parse::UNIFONT.to_vec();
+    uni.extend([0xFF, 0xFF, 0xFF, 0xFF, 2, 0, b'x', 0]);
+    assert_eq!(ShxFont::parse(&uni).err(), Some(ShxError::Empty));
+    assert_eq!(ShxFont::parse(b"not a font").err(), Some(ShxError::NotShx));
+    assert_eq!(ShxFont::parse(&[]).err(), Some(ShxError::NotShx));
+    // Hostile shape source.
+    for src in ["*1,2,X\n7\n", "*1,2,X\n9,(1,1)\n", "*99999,1,X\n0\n", "*1,1,X\n300,0\n", "010,0\n", "*1,1,X\n1,0zz,0\n", "*1,1,X\n0\n*1,1,Y\n0\n"] {
+        assert!(compile(src).is_err(), "{src:?}");
+    }
+    assert!(compile("").is_err());
+}
+
+/// Register a compiled test font under `name` (each test its own names: the table is shared).
+fn reg(name: &str, src: &str) {
+    register(name, &compile(src).unwrap()).unwrap();
+}
+
+#[test]
+fn text_metrics_follow_the_font() {
+    reg("cadcraft-test-metrics.shx", TEXT_FONT);
+    let f = TextFont::resolve_style("CADCRAFT-TEST-METRICS", "", false);
+    assert!(f.is_shx() && !f.is_outline());
+    let h = 3.0;
+    // Advances are the pen's end positions: A 6, B 6, at h / above = 0.5.
+    assert!((crate::text_width(&f, "AB", h, 1.0) - 6.0).abs() < 1e-9);
+    assert!((crate::text_width(&f, "AB", h, 0.5) - 3.0).abs() < 1e-9);
+    let sh = crate::shape_line(&f, "AB", h, 1.0, 0.0);
+    assert!((sh.width - 6.0).abs() < 1e-9);
+    let ys = sh.strokes.iter().flatten().fold((f64::MAX, f64::MIN), |(a, b), p| (a.min(p.y), b.max(p.y)));
+    assert_eq!(ys, (0.0, 3.0), "cap height = text height");
+    // %%d %%p %%c come from shapes 256-258; \U+0041 is A.
+    assert!((crate::text_width(&f, "%%d", h, 1.0) - 1.5).abs() < 1e-9);
+    assert!((crate::text_width(&f, "%%p%%c", h, 1.0) - 4.0).abs() < 1e-9);
+    assert!((crate::text_width(&f, "\\U+0041", h, 1.0) - 3.0).abs() < 1e-9);
+    assert_eq!(crate::shape_line(&f, "\\U+0041", h, 1.0, 0.0), crate::shape_line(&f, "A", h, 1.0, 0.0));
+    // A character the font lacks comes from the stroke font, with its advance.
+    let z = crate::text_width(&f, "Z", h, 1.0);
+    assert!((z - crate::stroke_advance('Z', h, 1.0)).abs() < 1e-9);
+    assert!(!crate::shape_line(&f, "Z", h, 1.0, 0.0).strokes.is_empty());
+    // Widths and shapes agree, with obliquing, underline and mixed fallbacks.
+    for s in ["AB AZ", "%%uAB%%u", "A\u{3042}B"] {
+        let sh = crate::shape_line(&f, s, h, 0.8, 0.2);
+        assert!((sh.width - crate::text_width(&f, s, h, 0.8)).abs() < 1e-9, "{s}");
+    }
+    // Placement: centred text sits on the alignment point by the font's own width.
+    let p = TextParams { h: crate::Align::Center, align_pt: Some(Vec2::new(10.0, 0.0)), ..TextParams::new(Vec2::ZERO, h) };
+    let (_, bb) = crate::place(&f, "AB", &p);
+    assert!((bb.center().x - 10.0).abs() < 1e-9 && (bb.width() - 6.0).abs() < 1e-9);
+    // MTEXT with the style's SHX font, and its \U+ escape.
+    let mp = crate::MTextParams { font: f.clone(), ..crate::MTextParams::new(Vec2::ZERO, h) };
+    let m = crate::layout_mtext_with("\\U+0041B", &mp);
+    assert_eq!(m.lines, vec!["AB".to_string()]);
+    assert_eq!(crate::space_width(&f, h, 1.0), 3.0);
+}
+
+#[test]
+fn unifont_text_and_specials() {
+    reg("cadcraft-test-uni.shx", UNI_FONT);
+    let f = TextFont::resolve("cadcraft-test-uni.shx");
+    assert!((crate::text_width(&f, "A\u{C5}", 6.0, 1.0) - 14.0).abs() < 1e-9);
+    // %%c is the diameter sign, at U+2205 in this font.
+    assert!((crate::text_width(&f, "%%c", 6.0, 1.0) - 2.0).abs() < 1e-9);
+}
+
+#[test]
+fn big_font_draws_double_byte_characters() {
+    reg("cadcraft-test-main.shx", TEXT_FONT);
+    reg("cadcraft-test-big.shx", BIG_FONT);
+    let f = TextFont::resolve_style("cadcraft-test-main.shx", "cadcraft-test-big.shx", false);
+    let TextFont::Shx(t) = &f else { panic!("SHX") };
+    assert_eq!(t.big_font_encoding(), "Shift_JIS");
+    let h = 2.5;
+    // あ (Shift-JIS 82A0) fills a square cell of the text height.
+    let w = crate::text_width(&f, "\u{3042}", h, 1.0);
+    assert!((w - h).abs() < 1e-9, "{w}");
+    let sh = crate::shape_line(&f, "A\u{3042}", h, 1.0, 0.0);
+    let big: Vec<Vec2> = sh.strokes.iter().flatten().copied().filter(|p| p.x > 2.5 - 1e-9).collect();
+    let ys = big.iter().fold((f64::MAX, f64::MIN), |(a, b), p| (a.min(p.y), b.max(p.y)));
+    assert_eq!(ys, (0.0, h));
+    // Only the big font found: Latin letters from the stroke font, the big font's own.
+    let f = TextFont::resolve_style("cadcraft-missing-main-font.shx", "cadcraft-test-big.shx", false);
+    assert!(f.is_shx());
+    assert!((crate::text_width(&f, "\u{3042}", h, 1.0) - h).abs() < 1e-9);
+    assert!((crate::text_width(&f, "A", h, 1.0) - crate::stroke_advance('A', h, 1.0)).abs() < 1e-9);
+    // Neither found: the stroke font as before.
+    assert!(!TextFont::resolve_style("cadcraft-missing-a.shx", "cadcraft-missing-b.shx", false).is_shx());
+}
+
+#[test]
+fn big_font_code_pages() {
+    for (name, ranges, want) in [
+        ("gbcbig.shx", vec![(0xA1, 0xFE)], "GBK"),
+        ("chineset.shx", vec![(0xA1, 0xFE)], "Big5"),
+        ("whgtxt.shx", vec![(0xA1, 0xFE)], "EUC-KR"),
+        ("extfont2.shx", vec![(0x81, 0x9F)], "Shift_JIS"),
+        ("custom.shx", vec![(0x81, 0x9F), (0xE0, 0xFC)], "Shift_JIS"),
+        ("custom.shx", vec![(0xA1, 0xFE)], "GBK"),
+    ] {
+        let src = format!(
+            "*BIGFONT 1,{},{}\n*0,4,x\n8,0,0,0\n*0FFFF,2,x\n010,0\n",
+            ranges.len(),
+            ranges.iter().map(|(a, b)| format!("0{a:X},0{b:X}")).collect::<Vec<_>>().join(",")
+        );
+        let b = std::sync::Arc::new(font(&src));
+        assert_eq!(ShxText::new(None, Some(b), name, false).big_font_encoding(), want, "{name}");
+    }
+}
+
+#[test]
+fn vertical_text_runs_down() {
+    reg("cadcraft-test-vertical.shx", TEXT_FONT);
+    let v = TextFont::resolve_style("cadcraft-test-vertical.shx", "", true);
+    let sh = crate::shape_line(&v, "CC", 1.0, 1.0, 0.0);
+    let miny = sh.strokes.iter().flatten().map(|p| p.y).fold(f64::MAX, f64::min);
+    // Two characters, each 8 units (8/6 of the height) down.
+    assert!((miny + 16.0 / 6.0).abs() < 1e-9, "{miny}");
+    assert!(sh.strokes.iter().flatten().all(|p| p.y <= 1e-9), "below the insertion point");
+    // A font without modes 2 stays horizontal.
+    reg("cadcraft-test-horizontal.shx", "*0,4,h\n6,2,0,0\n*67,3,C\n1,064,0\n");
+    let h = TextFont::resolve_style("cadcraft-test-horizontal.shx", "", true);
+    assert!(crate::shape_line(&h, "CC", 1.0, 1.0, 0.0).strokes.iter().flatten().all(|p| p.y >= -1e-9));
+}
+
+#[test]
+fn names_and_lookup() {
+    assert_eq!(table::key("ROMANS.SHX").as_deref(), Some("romans.shx"));
+    assert_eq!(table::key("txt").as_deref(), Some("txt.shx"));
+    assert_eq!(table::key(r"C:\Fonts\Simplex.shx").as_deref(), Some("simplex.shx"));
+    assert_eq!(table::key("../x/gbcbig.shx").as_deref(), Some("gbcbig.shx"));
+    for n in ["", "arial.ttf", "CADCraft Stroke", "Times New Roman", ".shx", "a\u{0}.shx"] {
+        assert_eq!(table::key(n), None, "{n:?}");
+    }
+    assert!(register("not-a-font.ttf", &compile(TEXT_FONT).unwrap()).is_err());
+    assert!(register("broken.shx", b"AutoCAD-86 shapes 1.0\r\n\x1a").is_err());
+    // A path stored in a drawing only names the file.
+    reg("cadcraft-test-path.shx", TEXT_FONT);
+    assert!(find(r"\\server\share\CADCRAFT-TEST-PATH.SHX").is_some());
+    assert!(find("cadcraft-never-registered.shx").is_none());
+}
+
+#[test]
+fn arcs_follow_the_circle() {
+    // Every point of an octant arc is on its circle.
+    let g = one("10,(5,034),0").glyph(1, false).unwrap();
+    let c = -dir(135.0) * 5.0;
+    for p in g.strokes.iter().flatten() {
+        assert!(((*p - c).len() - 5.0).abs() < 1e-9);
+    }
+    assert!(close(g.advance, (dir(135.0 + 180.0) - dir(135.0)) * 5.0));
+    let _ = PI;
+}

crates/fonts/src/shx/text.rs

@@ -0,0 +1,202 @@
+//! Text set in SHX fonts: a text style's main font and big font, horizontal or vertical.
+//!
+//! Each character is drawn by the font that has it: a double-byte character of the big font's
+//! code page (its lead byte in an escape range) from the big font, others from the main font
+//! (character code, or Unicode in a Unicode font; `%%d` `%%p` `%%c` from shapes 256–258 or their
+//! older or Unicode places). A font draws at text height / its `above` value, and its pen's end
+//! position is the advance: there is no added letter gap. Characters neither font has come from
+//! the built-in stroke font (and its fallback fonts), so nothing goes missing.
+//!
+//! Vertical text (a style flag, for fonts with modes 2) runs each shape's vertical-only
+//! commands (code 14) and follows the pen downward.
+
+use std::sync::Arc;
+
+use cadcraft_geom::Vec2;
+use encoding_rs::Encoding;
+
+use super::{ShxFont, ShxKind};
+use crate::{Shaped, bidi};
+
+/// A text style's SHX fonts: the main font, the big font and the orientation. Either font may
+/// be missing (not found): its characters then come from the stroke font.
+#[derive(Clone, Debug)]
+pub struct ShxText {
+    pub main: Option<Arc<ShxFont>>,
+    pub big: Option<Arc<ShxFont>>,
+    /// The style is vertical and the main font supports it.
+    pub vertical: bool,
+    /// The big font's code page (from its name and escape ranges).
+    big_encoding: &'static Encoding,
+}
+
+impl ShxText {
+    /// The fonts of a style: `big_name` is the big font's file name (it picks the code page).
+    pub fn new(main: Option<Arc<ShxFont>>, big: Option<Arc<ShxFont>>, big_name: &str, vertical: bool) -> ShxText {
+        let big_encoding = big.as_deref().map_or(encoding_rs::GBK, |b| big_font_encoding(big_name, b.escape_ranges()));
+        let vertical = vertical && main.as_ref().is_some_and(|m| m.is_dual());
+        ShxText { main, big, vertical, big_encoding }
+    }
+    /// The code page of the big font's double-byte codes.
+    pub fn big_font_encoding(&self) -> &'static str {
+        self.big_encoding.name()
+    }
+}
+
+/// The code page a big font's double-byte codes are in: known Japanese, Chinese and Korean
+/// big font names, else its escape ranges (Shift-JIS lead bytes from 0x81; the others start at
+/// 0xA1 or above, read as GBK).
+fn big_font_encoding(name: &str, ranges: &[(u16, u16)]) -> &'static Encoding {
+    let stem = name.trim().rsplit(['/', '\\']).next().unwrap_or_default().to_ascii_lowercase();
+    let stem = stem.trim_end_matches(".shx").trim_start_matches('@');
+    if stem.starts_with("whg") || stem.starts_with("wht") || stem.contains("kor") || stem.contains("ksc") {
+        return encoding_rs::EUC_KR;
+    }
+    if stem.starts_with("chineset") || stem.contains("big5") || stem.starts_with("cht") {
+        return encoding_rs::BIG5;
+    }
+    if stem.starts_with("gb") || stem.starts_with("hz") || stem.contains("chs") {
+        return encoding_rs::GBK;
+    }
+    if stem.starts_with("bigfont") || stem.starts_with("extfont") || stem.contains("jis") || stem.contains("jpn") {
+        return encoding_rs::SHIFT_JIS;
+    }
+    if ranges.iter().any(|(lo, _)| (0x81..0xA1).contains(lo)) { encoding_rs::SHIFT_JIS } else { encoding_rs::GBK }
+}
+
+/// The double-byte code of `c` in `enc`, if it has one.
+fn double_byte(c: char, enc: &'static Encoding) -> Option<u16> {
+    let mut buf = [0u8; 4];
+    let (bytes, _, errors) = enc.encode(c.encode_utf8(&mut buf));
+    match (errors, bytes.as_ref()) {
+        (false, [a, b]) => Some(u16::from_be_bytes([*a, *b])),
+        _ => None,
+    }
+}
+
+/// The shape numbers that may draw `c` in `font`, best first.
+fn candidates(c: char, font: &ShxFont) -> [Option<u16>; 4] {
+    let u = u32::from(c);
+    let unicode = font.kind() == ShxKind::Unifont && font.encoding() == 0;
+    let code = |x: u32| u16::try_from(x).ok();
+    // The special characters of `%%d` `%%p` `%%c`: shapes 256–258, the Latin-1 or Unicode code,
+    // and the oldest fonts' 127–129.
+    let special = match c {
+        '°' => Some((256, 0xB0, 127)),
+        '±' => Some((257, 0xB1, 128)),
+        '⌀' | '∅' => Some((258, u, 129)),
+        _ => None,
+    };
+    if let Some((s, latin, old)) = special {
+        return if unicode {
+            [code(u), code(if c == '⌀' { 0x2205 } else { latin }), Some(s), Some(old)]
+        } else {
+            [Some(s), code(latin), Some(old), None]
+        };
+    }
+    if unicode || u < 0x80 {
+        return [code(u), None, None, None];
+    }
+    // A single-byte font: the Windows Latin-1 code of the character (not the old special
+    // codes 127–129).
+    let mut buf = [0u8; 4];
+    let (bytes, _, errors) = encoding_rs::WINDOWS_1252.encode(c.encode_utf8(&mut buf));
+    match (errors, bytes.as_ref()) {
+        (false, [b]) if !(127..=129).contains(b) => [Some(u16::from(*b)), None, None, None],
+        _ => [None, None, None, None],
+    }
+}
+
+/// The font and shape that draw `c`.
+fn pick(t: &ShxText, c: char) -> Option<(&ShxFont, u16)> {
+    let from_main = || {
+        let m = t.main.as_deref()?;
+        candidates(c, m).into_iter().flatten().find(|n| m.has_shape(*n)).map(|n| (m, n))
+    };
+    let from_big = || {
+        let b = t.big.as_deref()?;
+        let code = double_byte(c, t.big_encoding)?;
+        let [lead, _] = code.to_be_bytes();
+        (b.is_lead_byte(lead) && b.has_shape(code)).then_some((b, code))
+    };
+    if u32::from(c) < 0x100 || matches!(c, '⌀' | '∅') { from_main().or_else(from_big) } else { from_big().or_else(from_main) }
+}
+
+fn finite_or(v: f64, d: f64) -> f64 {
+    if v.is_finite() { v } else { d }
+}
+
+/// Shape one line (baseline at y = 0, x from 0).
+pub(crate) fn shape(t: &ShxText, s: &str, height: f64, width_factor: f64, oblique: f64) -> Shaped {
+    let h = if height.is_finite() && height > 0.0 { height } else { 1.0 };
+    let wf = if width_factor.is_finite() && width_factor.abs() > 1e-6 { width_factor } else { 1.0 };
+    let shear = finite_or(oblique, 0.0).tan().clamp(-10.0, 10.0);
+    let chars = crate::decode_controls(s);
+    let logical: Vec<char> = chars.iter().map(|v| v.0).collect();
+    let mut out = Shaped::default();
+    let mut spans: Vec<(f64, f64, bool, bool)> = Vec::new();
+    let mut pen = Vec2::ZERO;
+    let mut max_x: f64 = 0.0;
+    let runs = if t.vertical { vec![(0..logical.len(), false)] } else { bidi::visual_runs(&logical, None) };
+    for (run, rtl) in runs {
+        let order: Box<dyn Iterator<Item = usize>> = if rtl { Box::new(run.rev()) } else { Box::new(run) };
+        for i in order {
+            let Some(&(c, under, over)) = chars.get(i) else { continue };
+            if bidi::is_format_control(c) {
+                continue;
+            }
+            let c = if rtl { bidi::mirror(c) } else { c };
+            let x0 = pen.x;
+            match pick(t, c).and_then(|(f, n)| Some((f, f.glyph(n, t.vertical)?))) {
+                Some((f, g)) => {
+                    let k = h / f.units_per_height();
+                    let place = |p: Vec2| Vec2::new(pen.x + p.x * k * wf + p.y * k * shear, pen.y + p.y * k);
+                    for st in &g.strokes {
+                        let pts: Vec<Vec2> = st.iter().map(|p| place(*p)).collect();
+                        max_x = pts.iter().fold(max_x, |m, p| m.max(p.x));
+                        out.strokes.push(pts);
+                    }
+                    let adv = Vec2::new(g.advance.x * k * wf, g.advance.y * k);
+                    pen = if t.vertical { pen + adv } else { Vec2::new(pen.x + adv.x, pen.y) };
+                }
+                None => {
+                    // The stroke font draws it, at the pen.
+                    let mut fb = crate::shape_stroke(&c.to_string(), h, wf, oblique);
+                    let at = pen;
+                    fb.map(|p| p + at);
+                    max_x = max_x.max(at.x + fb.width);
+                    out.extend(fb);
+                    if t.vertical {
+                        pen.y -= h * 1.5;
+                    } else {
+                        pen.x += crate::stroke_advance(c, h, wf);
+                    }
+                }
+            }
+            if !t.vertical {
+                spans.push((x0, pen.x, under, over));
+            }
+        }
+    }
+    out.strokes.extend(crate::decorations(&spans, h));
+    out.width = if t.vertical { max_x.max(0.0) } else { pen.x.max(0.0) };
+    out
+}
+
+/// The width of one line: the sum of the advances.
+pub(crate) fn width(t: &ShxText, s: &str, height: f64, width_factor: f64) -> f64 {
+    if t.vertical || bidi::has_rtl(s) {
+        return shape(t, s, height, width_factor, 0.0).width;
+    }
+    let h = if height.is_finite() && height > 0.0 { height } else { 1.0 };
+    let wf = if width_factor.is_finite() && width_factor.abs() > 1e-6 { width_factor } else { 1.0 };
+    crate::decode_controls(s)
+        .into_iter()
+        .filter(|(c, _, _)| !bidi::is_format_control(*c))
+        .map(|(c, _, _)| match pick(t, c).and_then(|(f, n)| Some((f, f.glyph(n, false)?))) {
+            Some((f, g)) => g.advance.x * h / f.units_per_height() * wf,
+            None => crate::stroke_advance(c, h, wf),
+        })
+        .sum::<f64>()
+        .max(0.0)
+}

crates/fonts/tests/shx_lookup.rs

@@ -0,0 +1,76 @@
+//! How SHX fonts are found: drawing folders, the search path, the font map, an app's font
+//! provider and FONTALT. Process-wide settings, so one test in its own binary. The fonts are
+//! compiled here from shape source written for the test; nothing is read from a CAD install.
+
+use std::sync::Arc;
+
+use cadcraft_fonts::shx::{self, FontProvider};
+use cadcraft_fonts::{TextFont, ttf};
+
+const FONT: &str = "*0,4,lookup test\n6,2,0,0\n*65,4,UCA\n1,064,0\n";
+
+struct Provider;
+
+impl FontProvider for Provider {
+    fn load(&self, file_name: &str) -> Option<Vec<u8>> {
+        (file_name == "cadcraft-provided.shx").then(|| shx::compile(FONT).ok()).flatten()
+    }
+}
+
+#[test]
+fn fonts_are_found_where_the_drawing_and_the_app_keep_them() {
+    let bytes = shx::compile(FONT).unwrap();
+    let dir = std::env::temp_dir().join(format!("cadcraft-shx-lookup-{}", std::process::id()));
+    std::fs::create_dir_all(&dir).unwrap();
+    std::fs::write(dir.join("cadcraft-beside.shx"), &bytes).unwrap();
+
+    // Beside the drawing: found once the drawing's folder is known; a later change of folders
+    // starts a new generation (viewers regenerate).
+    assert!(shx::find("cadcraft-beside.shx").is_none());
+    let g = shx::generation();
+    shx::add_drawing_dir(&dir);
+    assert!(shx::generation() != g);
+    assert_eq!(shx::drawing_dirs().first(), Some(&dir));
+    assert!(shx::find("CADCRAFT-BESIDE").is_some_and(|f| f.has_shape(65)));
+    assert!(TextFont::resolve("cadcraft-beside.shx").is_shx());
+    // A file whose name has another case than the drawing's (found on case-sensitive systems
+    // too, by looking through the folder).
+    std::fs::write(dir.join("CadCraft-Mixed.SHX"), &bytes).unwrap();
+    assert!(shx::find("cadcraft-mixed.shx").is_some());
+
+    // The search path, and the font map renaming a font to one that is there.
+    let other = dir.join("lib");
+    std::fs::create_dir_all(&other).unwrap();
+    std::fs::write(other.join("cadcraft-onpath.shx"), &bytes).unwrap();
+    assert!(shx::find("cadcraft-onpath.shx").is_none());
+    shx::set_search_path(&other.to_string_lossy());
+    assert!(shx::find("cadcraft-onpath.shx").is_some());
+    shx::set_font_map("cadcraft-old.shx;cadcraft-onpath.shx\nnonsense");
+    assert_eq!(shx::font_map(), "cadcraft-old.shx;cadcraft-onpath.shx");
+    assert!(shx::find("cadcraft-old").is_some());
+    shx::set_font_map("");
+
+    // An app's provider (the web build's file store).
+    assert!(shx::find("cadcraft-provided.shx").is_none());
+    shx::set_provider(Some(Arc::new(Provider)));
+    assert!(shx::find("cadcraft-provided.shx").is_some());
+    shx::set_provider(None);
+    assert!(shx::find("cadcraft-provided.shx").is_none());
+
+    // FONTALT replaces a missing SHX font (and may name a big font after a comma).
+    assert!(!TextFont::resolve("cadcraft-missing.shx").is_shx());
+    ttf::set_font_alt("cadcraft-beside.shx");
+    assert!(TextFont::resolve("cadcraft-missing.shx").is_shx());
+    assert!(!TextFont::resolve("").is_shx(), "the built-in font is not replaced");
+    ttf::set_font_alt("");
+
+    // Registered bytes (files opened alongside a drawing on the web) and clearing them.
+    shx::register("cadcraft-registered.shx", &bytes).unwrap();
+    assert!(shx::find("cadcraft-registered.shx").is_some());
+    shx::clear_registered();
+    assert!(shx::find("cadcraft-registered.shx").is_none());
+
+    shx::set_search_path("");
+    assert_eq!(shx::search_path(), "");
+    let _ = std::fs::remove_dir_all(&dir);
+}

crates/io/Cargo.toml

@@ -22,6 +22,7 @@ serde = { workspace = true }
 miniz_oxide = "0.9"
 craft-pdf = { workspace = true, features = ["write"] }
 quick-xml = { workspace = true }
+image = { workspace = true }
 
 [dev-dependencies]
 # Reads CADCraft's DWG output as written (tests only; the same version as cadcraft-dwg's).

crates/io/src/dxf_clip.rs

@@ -0,0 +1,551 @@
+//! XCLIP in a file (DXF Reference, SPATIAL_FILTER): a clipped block reference has an extension
+//! dictionary with an `ACAD_FILTER` dictionary whose `SPATIAL` entry is a SPATIAL_FILTER object.
+//! The filter holds the boundary vertices in the reference's coordinates (group 70 the count,
+//! 10/20 the vertices), whether clipping is on (71), the front and back clip (72/73, 40/41) and
+//! two 3×4 matrices (group 40, row by row): the inverse of the reference's transform, which takes
+//! the boundary into the block's coordinates, and the boundary's own transform (identity here).
+//!
+//! An inverted clip ("Invert clip") is marked as the reference app writes it in a file: the
+//! filter has an extension dictionary whose `ACAD_XREC_ROUNDTRIP` entry is an XRECORD holding
+//! `102 ACAD_INVERTEDCLIP_ROUNDTRIP` then the boundary (10/20/30), and
+//! `102 ACAD_INVERTEDCLIP_ROUNDTRIP_COMPARE` then the filter's own vertices. While the filter
+//! still holds those vertices the clip is inverted, with the first list as its boundary. The
+//! reference app shows the flag as group 290 on the object but never writes 290 in a DXF file,
+//! and discards a file whose filter has one; 290 is read when another program wrote it, never
+//! written. The record goes through DWG as it is.
+//!
+//! Reading takes the planar filters the model can hold out of the kept foreign data and puts them
+//! on the references ([`read`]); others (front/back clipping, a skewed boundary transform) stay
+//! foreign and are written back untouched. Writing adds the dictionaries and the filter of every
+//! clipped reference to a copy of the drawing's foreign data ([`prepare`]), which the raw-data
+//! writer (#528) then places on the reference.
+
+use std::collections::{HashMap, HashSet};
+use std::sync::Arc;
+
+use cadcraft_doc::foreign::{Foreign, ForeignObject};
+use cadcraft_doc::{ClipBoundary, Drawing, EntityKind, Handle, MAX_CLIP_VERTICES, RawTag};
+use cadcraft_geom::{Mat3, Vec2};
+
+/// The filter's extension-dictionary entry of the reference app's inverted-clip record.
+const ROUNDTRIP_KEY: &str = "ACAD_XREC_ROUNDTRIP";
+const ROUNDTRIP: &str = "ACAD_INVERTEDCLIP_ROUNDTRIP";
+const COMPARE: &str = "ACAD_INVERTEDCLIP_ROUNDTRIP_COMPARE";
+/// Handles above this are not handed out (the DXF handle space is 64-bit, keep a margin).
+const MAX_HANDLE: u64 = 1 << 48;
+
+fn raw(code: i32, value: impl ToString) -> RawTag {
+    RawTag { code, value: value.to_string() }
+}
+
+/// The handle of dictionary entry `name` (group 3 followed by 350/360).
+fn entry(tags: &[RawTag], name: &str) -> Option<Handle> {
+    tags.windows(2)
+        .find(|w| matches!(w, [k, v] if k.code == 3 && k.value.eq_ignore_ascii_case(name) && matches!(v.code, 350 | 360)))
+        .and_then(|w| w.get(1))
+        .and_then(|v| Handle::parse_hex(&v.value))
+}
+
+/// Remove dictionary entry `name`; returns the handle it named.
+fn remove_entry(tags: &mut Vec<RawTag>, name: &str) -> Option<Handle> {
+    let mut old = None;
+    let mut i = 0;
+    while let (Some(k), Some(v)) = (tags.get(i), tags.get(i + 1)) {
+        if k.code == 3 && k.value.eq_ignore_ascii_case(name) && matches!(v.code, 350 | 360) {
+            old = old.or_else(|| Handle::parse_hex(&v.value));
+            tags.drain(i..i + 2);
+        } else {
+            i += 1;
+        }
+    }
+    old
+}
+
+fn number(tags: &[RawTag], code: i32) -> Option<f64> {
+    tags.iter().find(|t| t.code == code)?.value.trim().parse::<f64>().ok().filter(|n| n.is_finite())
+}
+
+/// Where each handle's object is in `Foreign::objects` (the first, as a scan would find it), so
+/// a file with many references and objects isn't searched once per reference.
+type Index = HashMap<Handle, usize>;
+
+fn index(f: &Foreign) -> Index {
+    let mut idx = Index::with_capacity(f.objects.len());
+    for (i, o) in f.objects.iter().enumerate() {
+        idx.entry(o.handle).or_insert(i);
+    }
+    idx
+}
+
+fn object<'a>(f: &'a Foreign, idx: &Index, h: Handle) -> Option<&'a ForeignObject> {
+    f.objects.get(*idx.get(&h)?)
+}
+
+/// The extension dictionary, ACAD_FILTER dictionary and SPATIAL_FILTER of entity `h`.
+fn chain<'a>(f: &'a Foreign, idx: &Index, h: Handle) -> Option<(Handle, Handle, &'a ForeignObject)> {
+    let xd = f.entities.get(&h)?.xdict?;
+    let fd = entry(&object(f, idx, xd)?.tags, "ACAD_FILTER")?;
+    let sf = entry(&object(f, idx, fd)?.tags, "SPATIAL")?;
+    Some((xd, fd, object(f, idx, sf).filter(|o| o.kind.eq_ignore_ascii_case("SPATIAL_FILTER"))?))
+}
+
+/// A 3×4 matrix (12 values row by row) as a 2D transform, when it is one (no Z mixing).
+fn matrix_2d(m: &[f64]) -> Option<Mat3> {
+    let [a, c, z1, e, b, d, z2, f, z3, z4, one, z5] = <[f64; 12]>::try_from(m).ok()?;
+    let flat = [z1, z2, z3, z4, z5].iter().all(|v| v.abs() <= 1e-9) && (one - 1.0).abs() <= 1e-9;
+    (flat && [a, b, c, d, e, f].iter().all(|v| v.is_finite())).then_some(Mat3 { a, b, c, d, e, f })
+}
+
+fn matrix_values(m: &Mat3) -> [f64; 12] {
+    [m.a, m.c, 0.0, m.e, m.b, m.d, 0.0, m.f, 0.0, 0.0, 1.0, 0.0]
+}
+
+/// The `count` vertices (10/20) a SPATIAL_FILTER holds, as written.
+fn vertices(tags: &[RawTag], count: usize) -> Option<Vec<Vec2>> {
+    // The count is the file's: bound it before allocating.
+    if count > MAX_CLIP_VERTICES {
+        return None;
+    }
+    let mut points = Vec::with_capacity(count);
+    for w in tags.windows(2) {
+        let [x, y] = w else { continue };
+        if x.code != 10 {
+            continue;
+        }
+        if y.code != 20 || points.len() >= count {
+            return None;
+        }
+        points.push(Vec2::new(x.value.trim().parse().ok()?, y.value.trim().parse().ok()?));
+    }
+    (points.len() == count).then_some(points)
+}
+
+/// The handle of an object's own extension dictionary (`102 {ACAD_XDICTIONARY`, 360).
+fn own_xdict(tags: &[RawTag]) -> Option<Handle> {
+    tags.windows(2)
+        .find(|w| matches!(w, [k, v] if k.code == 102 && k.value.trim().eq_ignore_ascii_case("{ACAD_XDICTIONARY") && v.code == 360))
+        .and_then(|w| w.get(1))
+        .and_then(|v| Handle::parse_hex(&v.value))
+}
+
+/// The boundary of an inverted clip as the reference app marks it on `filter` (see above), when
+/// the filter still holds the vertices the mark was made for.
+fn roundtrip(f: &Foreign, idx: &Index, filter: &ForeignObject) -> Option<Vec<Vec2>> {
+    let rec = object(f, idx, entry(&object(f, idx, own_xdict(&filter.tags)?)?.tags, ROUNDTRIP_KEY)?)?;
+    if !rec.kind.eq_ignore_ascii_case("XRECORD") {
+        return None;
+    }
+    let (mut boundary, mut compare) = (Vec::new(), Vec::new());
+    // 0 before either list, 1 in the boundary, 2 in the filter's vertices.
+    let mut list = 0;
+    for w in rec.tags.windows(2) {
+        let [x, y] = w else { continue };
+        match x.code {
+            102 => {
+                list = match x.value.trim() {
+                    v if v.eq_ignore_ascii_case(ROUNDTRIP) => 1,
+                    v if v.eq_ignore_ascii_case(COMPARE) => 2,
+                    _ => 0,
+                }
+            }
+            10 if list != 0 && y.code == 20 => {
+                let into = if list == 1 { &mut boundary } else { &mut compare };
+                if into.len() >= MAX_CLIP_VERTICES {
+                    return None;
+                }
+                into.push(Vec2::new(x.value.trim().parse().ok()?, y.value.trim().parse().ok()?));
+            }
+            _ => {}
+        }
+    }
+    let own = vertices(&filter.tags, usize::try_from(number(&filter.tags, 70)? as i64).ok()?)?;
+    let near = |a: f64, b: f64| (a - b).abs() <= 1e-9 * (1.0 + a.abs().max(b.abs()));
+    let same = own.len() == compare.len() && own.iter().zip(&compare).all(|(p, q)| near(p.x, q.x) && near(p.y, q.y));
+    (same && boundary.len() >= 2).then_some(boundary)
+}
+
+/// The boundary a planar SPATIAL_FILTER holds, in the block's coordinates; with `boundary`, the
+/// clip is inverted and that is its outline (in the filter's coordinates). `None` for anything
+/// the model can't hold as it is (it then stays foreign).
+fn parse_filter(o: &ForeignObject, boundary: Option<&[Vec2]>) -> Option<ClipBoundary> {
+    let count = usize::try_from(number(&o.tags, 70)? as i64).ok()?;
+    if !(2..=MAX_CLIP_VERTICES).contains(&count) {
+        return None;
+    }
+    let normal_up = number(&o.tags, 210).unwrap_or(0.0).abs() <= 1e-9
+        && number(&o.tags, 220).unwrap_or(0.0).abs() <= 1e-9
+        && (number(&o.tags, 230).unwrap_or(1.0) - 1.0).abs() <= 1e-9;
+    let no_depth = number(&o.tags, 72).unwrap_or(0.0) == 0.0 && number(&o.tags, 73).unwrap_or(0.0) == 0.0;
+    if !normal_up || !no_depth {
+        return None;
+    }
+    let m: Vec<f64> = o.tags.iter().filter(|t| t.code == 40).map(|t| t.value.trim().parse::<f64>().unwrap_or(f64::NAN)).collect();
+    let (inverse, own) = match m.len() {
+        24 => (matrix_2d(m.get(..12)?)?, matrix_2d(m.get(12..)?)?),
+        // Without matrices the vertices are taken as the block's own.
+        0 => (Mat3::IDENTITY, Mat3::IDENTITY),
+        _ => return None,
+    };
+    if (own.a - 1.0).abs() > 1e-9
+        || own.b.abs() > 1e-9
+        || own.c.abs() > 1e-9
+        || (own.d - 1.0).abs() > 1e-9
+        || own.e.abs() > 1e-9
+        || own.f.abs() > 1e-9
+    {
+        return None;
+    }
+    let own = vertices(&o.tags, count)?;
+    let outline = boundary.unwrap_or(&own);
+    if !(2..=MAX_CLIP_VERTICES).contains(&outline.len()) {
+        return None;
+    }
+    let points: Vec<Vec2> = outline.iter().map(|p| inverse.apply(*p)).collect();
+    if !points.iter().all(|p| p.is_finite()) {
+        return None;
+    }
+    let inverted = boundary.is_some() || number(&o.tags, 290).is_some_and(|v| v != 0.0);
+    let clip = ClipBoundary { points, enabled: number(&o.tags, 71).unwrap_or(1.0) != 0.0, inverted };
+    cadcraft_render::clip::PolyClip::new(&clip.polygon()).is_some().then_some(clip)
+}
+
+/// Put the planar filters of the file read into `d` on their references, taking them out of
+/// the kept foreign data (the model writes them from now on).
+pub(crate) fn read(d: &mut Drawing) {
+    if d.foreign.objects.is_empty() {
+        return;
+    }
+    let idx = index(&d.foreign);
+    let found: Vec<(Handle, ClipBoundary)> = d
+        .foreign
+        .entities
+        .keys()
+        .filter_map(|h| {
+            let (_, _, o) = chain(&d.foreign, &idx, *h)?;
+            let boundary = roundtrip(&d.foreign, &idx, o);
+            Some((*h, parse_filter(o, boundary.as_deref())?))
+        })
+        .collect();
+    if found.is_empty() {
+        return;
+    }
+    let mut taken = Vec::new();
+    for (h, clip) in found {
+        let set = |e: &mut cadcraft_doc::Entity| {
+            if let EntityKind::Insert(i) = &mut e.kind {
+                i.clip = Some(clip.clone());
+            }
+        };
+        let is_insert = |e: &cadcraft_doc::Entity| matches!(e.kind, EntityKind::Insert(_));
+        let done = if d.entity(h).is_some_and(|e| is_insert(e)) {
+            d.modify_entity(h, set).is_ok()
+        } else {
+            let mut done = false;
+            for b in d.blocks.values_mut() {
+                if b.entities.get(h).is_some_and(|e| is_insert(e)) {
+                    done = Arc::make_mut(b).entities.modify(h, set);
+                    break;
+                }
+            }
+            done
+        };
+        if done {
+            taken.push(h);
+        }
+    }
+    let f = Arc::make_mut(&mut d.foreign);
+    let mut gone = HashSet::new();
+    for h in taken {
+        forget(f, &idx, h, &mut gone);
+    }
+    f.objects.retain(|o| !gone.contains(&o.handle));
+}
+
+/// Take the clip of entity `h` out of the foreign data: the ACAD_FILTER entry and what it holds,
+/// and the extension dictionary when nothing else is left in it. The
+/// objects to remove are added to `gone`; the caller removes them all at once.
+fn forget(f: &mut Foreign, idx: &Index, h: Handle, all_gone: &mut HashSet<Handle>) {
+    let Some(xd) = f.entities.get(&h).and_then(|x| x.xdict) else { return };
+    let mut gone: Vec<Handle> = Vec::new();
+    let mut empty = false;
+    if let Some(o) = idx.get(&xd).copied().and_then(|i| f.objects.get_mut(i)) {
+        gone.extend(remove_entry(&mut o.tags, "ACAD_FILTER"));
+        empty = !o.tags.iter().any(|t| t.code == 3);
+    }
+    // The filter dictionary's entries go with it, and the filter's own extension dictionary.
+    let mut i = 0;
+    while let Some(g) = gone.get(i).copied() {
+        if let Some(o) = object(f, idx, g) {
+            if o.kind.eq_ignore_ascii_case("DICTIONARY") {
+                gone.extend(o.tags.windows(2).filter_map(|w| match w {
+                    [k, v] if k.code == 3 && matches!(v.code, 350 | 360) => Handle::parse_hex(&v.value),
+                    _ => None,
+                }));
+            }
+            gone.extend(own_xdict(&o.tags));
+        }
+        i += 1;
+        if i > MAX_CLIP_VERTICES {
+            break;
+        }
+    }
+    if empty {
+        gone.push(xd);
+        if let Some(x) = f.entities.get_mut(&h) {
+            x.xdict = None;
+        }
+        if f.entities.get(&h).is_some_and(|x| x.is_empty()) {
+            f.entities.remove(&h);
+        }
+    }
+    all_gone.extend(gone);
+}
+
+fn dictionary(h: Handle, owner: Handle) -> ForeignObject {
+    ForeignObject {
+        handle: h,
+        kind: "DICTIONARY".into(),
+        tags: vec![
+            raw(5, h.hex()),
+            raw(102, "{ACAD_REACTORS"),
+            raw(330, owner.hex()),
+            raw(102, "}"),
+            raw(330, owner.hex()),
+            raw(100, "AcDbDictionary"),
+            raw(280, 1),
+            raw(281, 1),
+        ],
+    }
+}
+
+/// The SPATIAL_FILTER of `clip`; `xdict` is its extension dictionary (an inverted clip's).
+/// No group 290: the reference app discards a file whose filter has one.
+fn spatial_filter(h: Handle, owner: Handle, clip: &ClipBoundary, to_world: &Mat3, inverse: &Mat3, xdict: Option<Handle>) -> ForeignObject {
+    let mut tags = vec![raw(5, h.hex()), raw(102, "{ACAD_REACTORS"), raw(330, owner.hex()), raw(102, "}")];
+    if let Some(x) = xdict {
+        tags.extend([raw(102, "{ACAD_XDICTIONARY"), raw(360, x.hex()), raw(102, "}")]);
+    }
+    tags.extend([raw(330, owner.hex()), raw(100, "AcDbFilter"), raw(100, "AcDbSpatialFilter"), raw(70, clip.points.len())]);
+    for p in &clip.points {
+        let q = to_world.apply(*p);
+        tags.push(raw(10, q.x));
+        tags.push(raw(20, q.y));
+    }
+    tags.extend([raw(210, 0.0), raw(220, 0.0), raw(230, 1.0), raw(11, 0.0), raw(21, 0.0), raw(31, 0.0)]);
+    tags.extend([raw(71, i32::from(clip.enabled)), raw(72, 0), raw(73, 0)]);
+    for v in matrix_values(inverse).into_iter().chain(matrix_values(&Mat3::IDENTITY)) {
+        tags.push(raw(40, v));
+    }
+    ForeignObject { handle: h, kind: "SPATIAL_FILTER".into(), tags }
+}
+
+/// The reference app's inverted-clip record for a filter whose vertices are `points` (drawing
+/// coordinates): the boundary and the filter's vertices are the same list.
+fn roundtrip_record(h: Handle, owner: Handle, points: &[Vec2]) -> ForeignObject {
+    let mut tags = vec![raw(5, h.hex()), raw(102, "{ACAD_REACTORS"), raw(330, owner.hex()), raw(102, "}")];
+    tags.extend([raw(330, owner.hex()), raw(100, "AcDbXrecord"), raw(280, 1)]);
+    for name in [ROUNDTRIP, COMPARE] {
+        tags.push(raw(102, name));
+        for p in points {
+            tags.extend([raw(10, p.x), raw(20, p.y), raw(30, 0.0)]);
+        }
+    }
+    ForeignObject { handle: h, kind: "XRECORD".into(), tags }
+}
+
+/// A copy of `d` whose foreign data holds the SPATIAL_FILTER of every clipped reference (any
+/// filter kept from the file for it is replaced). `None` when no reference is clipped.
+pub(crate) fn prepare(d: &Drawing) -> Option<Drawing> {
+    let mut clips: Vec<(Handle, ClipBoundary, Mat3)> = Vec::new();
+    let mut take = |e: &cadcraft_doc::Entity| {
+        if let EntityKind::Insert(i) = &e.kind
+            && let Some(c) = &i.clip
+            && c.polygon().len() >= 3
+            && let Some(base) = d.block(&i.block).map(|b| b.base.xy())
+        {
+            clips.push((e.handle, c.clone(), i.transform(base)));
+        }
+    };
+    d.model.iter().for_each(|e| take(e));
+    d.layouts.iter().flat_map(|l| l.entities.iter()).for_each(|e| take(e));
+    d.blocks.values().filter(|b| b.xref_path.is_none()).flat_map(|b| b.entities.iter()).for_each(|e| take(e));
+    if clips.is_empty() {
+        return None;
+    }
+    let mut out = d.clone();
+    let f = Arc::make_mut(&mut out.foreign);
+    let mut next = d.handseed.max(f.objects.iter().map(|o| o.handle.0).max().unwrap_or(0)).saturating_add(1);
+    fn fresh(next: &mut u64) -> Handle {
+        let h = Handle(*next);
+        *next = next.saturating_add(1);
+        h
+    }
+    let mut idx = index(f);
+    let mut gone = HashSet::new();
+    for (insert, clip, to_world) in clips {
+        let Some(inverse) = to_world.inverse() else { continue };
+        if next.saturating_add(6) >= MAX_HANDLE {
+            break;
+        }
+        // A filter kept from the file for this reference is replaced.
+        forget(f, &idx, insert, &mut gone);
+        let xd = match f.entities.get(&insert).and_then(|x| x.xdict).filter(|h| idx.contains_key(h) && !gone.contains(h)) {
+            Some(h) => h,
+            None => {
+                let h = fresh(&mut next);
+                idx.insert(h, f.objects.len());
+                f.objects.push(dictionary(h, insert));
+                f.entities.entry(insert).or_default().xdict = Some(h);
+                h
+            }
+        };
+        let (fd, sf) = (fresh(&mut next), fresh(&mut next));
+        // An inverted clip's filter has an extension dictionary and the record in it.
+        let marks = clip.inverted.then(|| (fresh(&mut next), fresh(&mut next)));
+        if let Some(o) = idx.get(&xd).copied().and_then(|i| f.objects.get_mut(i)) {
+            o.tags.extend([raw(3, "ACAD_FILTER"), raw(360, fd.hex())]);
+        }
+        let mut filters = dictionary(fd, xd);
+        filters.tags.extend([raw(3, "SPATIAL"), raw(360, sf.hex())]);
+        let mut add = |o: ForeignObject| {
+            idx.insert(o.handle, f.objects.len());
+            f.objects.push(o);
+        };
+        add(filters);
+        add(spatial_filter(sf, fd, &clip, &to_world, &inverse, marks.map(|(x, _)| x)));
+        if let Some((x, r)) = marks {
+            let mut own = dictionary(x, sf);
+            own.tags.extend([raw(3, ROUNDTRIP_KEY), raw(360, r.hex())]);
+            add(own);
+            let world: Vec<Vec2> = clip.points.iter().map(|p| to_world.apply(*p)).collect();
+            add(roundtrip_record(r, x, &world));
+        }
+    }
+    f.objects.retain(|o| !gone.contains(&o.handle));
+    // The writer hands out handles of its own from the seed on: start it past these.
+    out.handseed = out.handseed.max(next);
+    Some(out)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn matrices_round_trip_row_by_row() {
+        let m = Mat3::translate(Vec2::new(10.0, 20.0)).then_before(Mat3::rotate(0.5)).then_before(Mat3::scale(2.0, 2.0));
+        let back = matrix_2d(&matrix_values(&m)).unwrap();
+        assert!((back.a - m.a).abs() < 1e-12 && (back.c - m.c).abs() < 1e-12 && (back.f - m.f).abs() < 1e-12);
+        // Translation is the fourth value of each row.
+        let t = matrix_values(&Mat3::translate(Vec2::new(-5.0, 7.0)));
+        assert_eq!((t[3], t[7]), (-5.0, 7.0));
+        assert!(matrix_2d(&[1.0; 11]).is_none());
+    }
+
+    #[test]
+    fn hostile_filters_stay_foreign() {
+        let o = |tags: Vec<RawTag>| ForeignObject { handle: Handle(1), kind: "SPATIAL_FILTER".into(), tags };
+        assert!(parse_filter(&o(vec![raw(70, 1_000_000_000)]), None).is_none());
+        assert!(parse_filter(&o(vec![raw(70, 3), raw(10, 0), raw(20, 0)]), None).is_none());
+        assert!(parse_filter(&o(vec![raw(70, 2), raw(10, "nan"), raw(20, 0), raw(10, 1), raw(20, 1)]), None).is_none());
+        assert!(parse_filter(&o(vec![raw(70, 2), raw(10, 0), raw(20, 0), raw(10, 1), raw(20, 1), raw(72, 1)]), None).is_none());
+        let ok = parse_filter(&o(vec![raw(70, 2), raw(10, 0), raw(20, 0), raw(10, 1), raw(20, 1)]), None).unwrap();
+        assert_eq!((ok.points.len(), ok.inverted), (2, false));
+    }
+
+    #[test]
+    fn the_writer_starts_its_handles_past_the_clip_objects() {
+        let mut d = Drawing::new_metric();
+        d.blocks.insert("B".into(), Arc::new(cadcraft_doc::Block::new("B")));
+        for i in 0..3 {
+            let clip = ClipBoundary::new(vec![Vec2::ZERO, Vec2::new(1.0, 0.0), Vec2::new(0.0, 1.0)]);
+            let ins = cadcraft_doc::Insert { block: "B".into(), clip: Some(ClipBoundary { inverted: i == 0, ..clip }), ..Default::default() };
+            d.add(&cadcraft_doc::Space::Model, cadcraft_doc::Common::default(), EntityKind::Insert(ins)).unwrap();
+        }
+        let out = prepare(&d).unwrap();
+        let highest = out.foreign.objects.iter().map(|o| o.handle.0).max().unwrap();
+        assert!(out.handseed > highest, "seed {} at or below {highest}", out.handseed);
+    }
+
+    #[test]
+    fn group_290_is_read_but_never_written() {
+        let tags = |invert: &str| vec![raw(70, 2), raw(10, 0), raw(20, 0), raw(10, 1), raw(20, 1), raw(290, invert)];
+        let o = |invert| ForeignObject { handle: Handle(1), kind: "SPATIAL_FILTER".into(), tags: tags(invert) };
+        assert!(parse_filter(&o("1"), None).unwrap().inverted);
+        assert!(!parse_filter(&o("0"), None).unwrap().inverted);
+        assert!(!parse_filter(&o("junk"), None).unwrap().inverted);
+        // The reference app discards a DXF whose filter has 290.
+        let clip = ClipBoundary { inverted: true, ..ClipBoundary::new(vec![Vec2::ZERO, Vec2::new(1.0, 1.0)]) };
+        let written = spatial_filter(Handle(2), Handle(1), &clip, &Mat3::IDENTITY, &Mat3::IDENTITY, Some(Handle(3)));
+        assert!(!written.tags.iter().any(|t| t.code == 290));
+        assert_eq!(own_xdict(&written.tags), Some(Handle(3)));
+    }
+
+    /// The filter, its extension dictionary and the reference app's record, as one foreign set.
+    fn marked(filter_points: &[(f64, f64)], boundary: &[(f64, f64)], compare: &[(f64, f64)]) -> (Foreign, ForeignObject) {
+        let mut tags = vec![raw(5, "10"), raw(102, "{ACAD_XDICTIONARY"), raw(360, "11"), raw(102, "}"), raw(70, filter_points.len())];
+        for (x, y) in filter_points {
+            tags.extend([raw(10, x), raw(20, y)]);
+        }
+        let filter = ForeignObject { handle: Handle(0x10), kind: "SPATIAL_FILTER".into(), tags };
+        let mut f = Foreign::default();
+        let mut dict = dictionary(Handle(0x11), Handle(0x10));
+        dict.tags.extend([raw(3, ROUNDTRIP_KEY), raw(360, "12")]);
+        f.objects.push(dict);
+        let mut rec = vec![raw(100, "AcDbXrecord"), raw(280, 1)];
+        for (name, list) in [(ROUNDTRIP, boundary), (COMPARE, compare)] {
+            rec.push(raw(102, name));
+            for (x, y) in list {
+                rec.extend([raw(10, x), raw(20, y), raw(30, 0)]);
+            }
+        }
+        f.objects.push(ForeignObject { handle: Handle(0x12), kind: "XRECORD".into(), tags: rec });
+        f.objects.push(filter.clone());
+        (f, filter)
+    }
+
+    #[test]
+    fn the_reference_apps_record_marks_an_inverted_clip() {
+        // As the reference app writes an inverted rectangle: a keyhole filter, the rectangle kept.
+        let keyhole = [
+            (0.0, 0.0),
+            (100.0, 0.0),
+            (100.0, 50.0),
+            (0.0, 50.0),
+            (0.0, 10.0),
+            (20.0, 10.0),
+            (20.0, 40.0),
+            (80.0, 40.0),
+            (80.0, 10.0),
+            (20.0, 10.0),
+            (0.0, 10.0),
+        ];
+        let (f, filter) = marked(&keyhole, &[(20.0, 10.0), (80.0, 40.0)], &keyhole);
+        let boundary = roundtrip(&f, &index(&f), &filter).unwrap();
+        let clip = parse_filter(&filter, Some(&boundary)).unwrap();
+        assert!(clip.inverted);
+        assert_eq!(clip.points, vec![Vec2::new(20.0, 10.0), Vec2::new(80.0, 40.0)]);
+        // The simpler form: the filter keeps the boundary itself.
+        let rect = [(20.0, 10.0), (80.0, 40.0)];
+        let (f, filter) = marked(&rect, &rect, &rect);
+        assert!(roundtrip(&f, &index(&f), &filter).is_some());
+        // A filter changed since the record was made (the clip edited elsewhere) isn't inverted.
+        let (f, filter) = marked(&[(0.0, 0.0), (5.0, 5.0)], &rect, &rect);
+        assert!(roundtrip(&f, &index(&f), &filter).is_none());
+    }
+
+    #[test]
+    fn a_hostile_vertex_count_beside_the_record_does_not_allocate() {
+        let rect = [(20.0, 10.0), (80.0, 40.0)];
+        for count in ["9223372036854775807", "1000000000", "1e300"] {
+            let (mut f, mut filter) = marked(&rect, &rect, &rect);
+            for t in filter.tags.iter_mut().filter(|t| t.code == 70) {
+                t.value = count.into();
+            }
+            f.objects.retain(|o| o.handle != filter.handle);
+            f.objects.push(filter.clone());
+            assert!(roundtrip(&f, &index(&f), &filter).is_none(), "{count}");
+            assert!(parse_filter(&filter, None).is_none(), "{count}");
+        }
+    }
+}

crates/io/src/dxf_ext.rs

@@ -881,6 +881,23 @@ pub(crate) fn parse_constraints(text: &str) -> Option<(Vec<Constraint>, Parametr
     Some((p.constraints, p.parametric))
 }
 
+/// A view centre as a file stores it (VIEWPORT and VPORT group 12, VIEW group 10), as the
+/// drawing point at the middle of the view. The stored centre is in display coordinates: their
+/// origin is the view's `target` (VIEWPORT and VPORT group 17, VIEW group 12) and their axes are
+/// turned by the view's `twist` (radians). Turning back keeps a twisted view on its part of the
+/// drawing however far that is from the origin; a non-finite result keeps the stored centre.
+pub(crate) fn dcs_center_to_model(c: cadcraft_geom::Vec2, twist: f64, target: cadcraft_geom::Vec2) -> cadcraft_geom::Vec2 {
+    let m = c.rotate(-twist) + if target.is_finite() { target } else { cadcraft_geom::Vec2::ZERO };
+    if m.is_finite() { m } else { c }
+}
+
+/// The display-coordinate view centre a file stores for the drawing point `m` at the middle of
+/// a view with `twist`, its target at the origin (the inverse of [`dcs_center_to_model`]).
+pub(crate) fn model_center_to_dcs(m: cadcraft_geom::Vec2, twist: f64) -> cadcraft_geom::Vec2 {
+    let c = m.rotate(twist);
+    if c.is_finite() { c } else { m }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

crates/io/src/dxf_mleader.rs

@@ -325,6 +325,7 @@ pub(crate) fn read(tags: &[Tag]) -> MLeader {
             rows: 1,
             col_spacing: 0.0,
             row_spacing: 0.0,
+            clip: None,
         }
     });
     MLeader {

crates/io/src/dxf_read.rs

@@ -139,6 +139,7 @@ fn read_budgeted(bytes: &[u8], mut table_cells_left: usize) -> Result<Drawing> {
         d.layers.insert(0, Layer::default());
     }
     crate::dxf_raw::read(&secs, &mut d);
+    crate::dxf_clip::read(&mut d);
     d.skipped_records = skipped;
     Ok(d)
 }

crates/io/src/dxf_read/common.rs

@@ -23,10 +23,8 @@ impl T<'_> {
     /// origin is the view target (`target`), so the point in the middle of a plan view is their
     /// sum: a file whose view centre is 0,0 keeps the location in the target (#2492). A sum that
     /// overflows leaves the stored centre.
-    pub(super) fn view_center(&self, center: i32, target: i32) -> Vec2 {
-        let c = self.p(center).xy();
-        let sum = c + self.p(target).xy();
-        if sum.is_finite() { sum } else { c }
+    pub(super) fn view_center(&self, center: i32, target: i32, twist: f64) -> Vec2 {
+        crate::dxf_ext::dcs_center_to_model(self.p(center).xy(), twist, self.p(target).xy())
     }
     pub(super) fn all_f(&self, code: i32) -> Vec<f64> {
         self.0.iter().filter(|t| t.code == code).map(Tag::f64).collect()

crates/io/src/dxf_read/document.rs

@@ -333,7 +333,17 @@ pub(super) fn apply_sortents(
     paper_for: &HashMap<String, String>,
     first_layout: &str,
 ) {
-    for (owner, map) in tables {
+    // Each sort rebuilds its whole space, so a space named by many tables is sorted once, by the
+    // last of them (which decided its order anyway); repeated tables made import quadratic.
+    let target = |owner: &String| {
+        let up = brs.get(owner)?.to_ascii_uppercase();
+        Some(if up.starts_with("*PAPER_SPACE") { paper_for.get(&up).cloned().unwrap_or_else(|| first_layout.to_string()) + "\0paper" } else { up })
+    };
+    let last: HashMap<String, usize> = tables.iter().enumerate().filter_map(|(i, (owner, _))| Some((target(owner)?, i))).collect();
+    for (i, (owner, map)) in tables.iter().enumerate() {
+        if target(owner).and_then(|t| last.get(&t)) != Some(&i) {
+            continue;
+        }
         let Some(name) = brs.get(owner) else { continue };
         let up = name.to_ascii_uppercase();
         // A sort handle of 0 draws last (ezdxf `reorder`, which notes AutoCAD defines it, undocumented).

crates/io/src/dxf_read/entities.rs

@@ -167,6 +167,7 @@ pub(super) fn entity_with_table_budget(kind: &str, tags: &[Tag], table_cells_lef
                 rows: t.i(71).unwrap_or(1).clamp(1, 10_000) as u32,
                 col_spacing,
                 row_spacing: t.fd(45, 0.0),
+                clip: None,
             })
         }
         "DIMENSION" => {
@@ -243,20 +244,25 @@ pub(super) fn entity_with_table_budget(kind: &str, tags: &[Tag], table_cells_lef
             k
         }
         "ACAD_TABLE" => EntityKind::Table(acad_table(tags, table_cells_left)),
-        "VIEWPORT" => EntityKind::Viewport(Viewport {
-            center: t.p(10),
-            width: t.fd(40, 1.0),
-            height: t.fd(41, 1.0),
-            // 12/22 is in display coordinates, whose origin is the view target 17/27/37.
-            view_center: t.view_center(12, 17),
-            view_height: t.fd(45, 1.0),
-            id: t.i(69).unwrap_or(0) as u32,
-            locked: t.i(90).unwrap_or(0) & 16384 != 0,
-            frozen_layers: crate::dxf_ext::read_frozen(tags),
-            layer_colors: crate::dxf_ext::read_layer_colors(tags),
-            // Status flags: 65536 = non-rectangular clipping (by the 340 entity), 131072 = off.
-            clip: t.s(340).and_then(|h| Handle::parse_hex(&h)).filter(|h| h.0 != 0 && t.i(90).unwrap_or(0) & 65536 != 0),
-            on: t.i(90).unwrap_or(0) & 131072 == 0,
+        "VIEWPORT" => EntityKind::Viewport({
+            // View twist (group 51, degrees).
+            let twist = t.f(51).map_or(0.0, |a| cadcraft_geom::norm_angle(a.to_radians()));
+            Viewport {
+                center: t.p(10),
+                width: t.fd(40, 1.0),
+                height: t.fd(41, 1.0),
+                // 12/22 is in display coordinates, whose origin is the view target 17/27/37.
+                view_center: t.view_center(12, 17, twist),
+                view_height: t.fd(45, 1.0),
+                id: t.i(69).unwrap_or(0) as u32,
+                locked: t.i(90).unwrap_or(0) & 16384 != 0,
+                frozen_layers: crate::dxf_ext::read_frozen(tags),
+                layer_colors: crate::dxf_ext::read_layer_colors(tags),
+                // Status flags: 65536 = non-rectangular clipping (by the 340 entity), 131072 = off.
+                clip: t.s(340).and_then(|h| Handle::parse_hex(&h)).filter(|h| h.0 != 0 && t.i(90).unwrap_or(0) & 65536 != 0),
+                on: t.i(90).unwrap_or(0) & 131072 == 0,
+                twist,
+            }
         }),
         "WIPEOUT" => {
             let o = t.p(10);
@@ -299,7 +305,9 @@ pub(super) fn acad_table(tags: &[Tag], table_cells_left: &mut usize) -> Table {
     // Large declared sizes must be backed by cell records (no allocation from a bare count).
     let n_cells = tail.iter().filter(|x| x.code == 171).count();
     let declared = rows.saturating_mul(cols);
-    if declared > MAX_CELLS || (declared > 10_000 && n_cells < declared) {
+    // A table with no rows or no columns has no cells: keep neither dimension, so its row heights
+    // and column widths (allocated per dimension, outside the cell budget) are not allocated.
+    if declared == 0 || declared > MAX_CELLS || (declared > 10_000 && n_cells < declared) {
         rows = 0;
         cols = 0;
     }