Simplify: Object › Path › Simplify opens its slider at the Auto-Simplify level for the selection

The Simplify help page says the slider starts at an auto-simplified value
(https://helpx.adobe.com/illustrator/desktop/draw-shapes-and-paths/modify-paths/manually-simplify-paths.html).
The slider opened at a fixed level 50 (1 pt), whatever the size of the
selection, so the first preview was the same tolerance for a 30 pt icon as
for a 1000 pt drawing.

The level Auto-Simplify picks for the selection is now one engine function,
vectorcraft_engine::auto_simplify_level (the existing 1/400-of-the-longer-
side rule in vectorcraft_pathops), which object.path.simplify {auto: true}
and the slider's opening fields both use. Object › Path › Simplify (and
ui.menuDialog, the Properties and contextual task bar buttons, which go
through the same menu dialog) opens the slider there, and the canvas
previews that result; Auto-Simplify still moves the slider back to it.
The retained Simplify dialog path is unchanged.

Verification: simplify_slider_opens_at_the_auto_simplify_level_of_the_selection
opens the slider on 1140, 285 and 28.5 pt waves (levels 35, 55, 89) and
checks the preview is exactly object.path.simplify {auto: true}'s result;
without the change it fails with level 50 != 35, and
simplify_opens_a_slider_whose_drag_previews_fewer_or_more_points fails with
{"level": 50} != {"level": 55}. cargo xtask ci: all 10 steps passed.

crates/engine/src/cmd/mod.rs

@@ -55,7 +55,7 @@ mod paint;
 mod panelcmds;
 pub mod params;
 mod path;
-mod pathops;
+pub(crate) mod pathops;
 mod patterncmds;
 pub mod pdfcmds;
 pub mod perspgrid;

crates/engine/src/cmd/pathops.rs

@@ -801,12 +801,19 @@ fn edit_paths(s: &mut Session, label: &str, f: impl Fn(&PathData) -> PathData) -
     Ok((ids, before, after))
 }
 
+/// Auto-Simplify's level for the selection: [`po::auto_simplify_level`] for the longer side of the
+/// selected objects' bounds. Object › Path › Simplify's slider opens at it, and
+/// `object.path.simplify {auto: true}` simplifies at it.
+pub fn auto_simplify_level(s: &Session) -> Result<f64> {
+    let roots = selected_roots(s)?;
+    let size = s.doc()?.doc.bounds_of(&roots, false).map_or(0.0, |b| b.width().max(b.height()));
+    Ok(po::auto_simplify_level(size))
+}
+
 fn simplify(s: &mut Session, p: &Value) -> Result<Value> {
     // With auto, the slider's level is Auto-Simplify's for the selection's size; otherwise it is the level given.
     let level = if bool_or(p, "auto", false) {
-        let roots = selected_roots(s)?;
-        let size = s.doc()?.doc.bounds_of(&roots, false).map_or(0.0, |b| b.width().max(b.height()));
-        Some(po::auto_simplify_level(size))
+        Some(auto_simplify_level(s)?)
     } else {
         num_param(p, "level").map(|l| if l.is_finite() { l.round().clamp(0.0, 100.0) } else { po::SIMPLIFY_LEVEL })
     };

crates/engine/src/lib.rs

@@ -31,6 +31,7 @@ pub use cmd::clipboard::Clipboard;
 pub use cmd::create::constrain_click;
 pub use cmd::distortcmds::perspective_click;
 pub use cmd::params::{check_keys, check_params};
+pub use cmd::pathops::auto_simplify_level;
 pub use cmd::rasterfx::{export_pdf, flatten_raster_effects};
 pub use cmd::{CommandInfo, CommandSpec, command_specs, find_command};
 pub use journal::Journal;

crates/engine/src/tests_pathops.rs

@@ -521,6 +521,8 @@ fn simplify_level_moves_the_anchor_count_monotonically() {
 fn auto_simplify_keeps_the_shape_within_a_400th_of_its_size() {
     let (mut s, id) = dense_wave(100, 15.0, 8.0, 0.2);
     let original = path_of(&s, id).0.clone();
+    // The level the Simplify slider opens at for this selection is the one auto uses.
+    assert_eq!(crate::auto_simplify_level(&s).unwrap(), 70.0);
     let out = s.execute("object.path.simplify", &json!({"auto": true})).unwrap();
     // 100 pt across: 0.25 pt at most, level 70 (0.25 pt).
     assert_eq!(out["level"], json!(70.0));

crates/pathops/src/edit.rs

@@ -29,7 +29,7 @@ pub fn simplify(path: &PathData, tolerance: f64) -> PathData {
     simplify_with(path, &SimplifyOptions { tolerance, ..Default::default() })
 }
 
-/// The Simplify slider's level for a tolerance of 1 pt, where the slider opens.
+/// The Simplify slider's level for a tolerance of 1 pt, the middle of its scale.
 pub const SIMPLIFY_LEVEL: f64 = 50.0;
 
 /// The tolerance (points) of Simplify slider level `level`, from 0 (the fewest anchor points) to

crates/ui-egui/src/dialogs/simplify_slider.rs

@@ -2,14 +2,17 @@
 //! the fewest anchor points (left) to the closest fit to the original (right), and More Options,
 //! which opens the Simplify dialog at the slider's tolerance. While the strip is open, the canvas
 //! previews `object.path.simplify {level}`; Enter or a click outside the strip keeps the result as
-//! one undo step, and Escape puts the paths back. The slider opens at level 50, a tolerance of
-//! 1 pt (`vectorcraft_pathops::simplify_level_tolerance` maps levels to tolerances).
+//! one undo step, and Escape puts the paths back. The slider opens at Auto-Simplify's level for
+//! the selection (`vectorcraft_engine::auto_simplify_level`), so the canvas first shows the
+//! auto-simplified paths, as the Simplify help page describes
+//! (https://helpx.adobe.com/illustrator/desktop/draw-shapes-and-paths/modify-paths/manually-simplify-paths.html).
+//! `vectorcraft_pathops::simplify_level_tolerance` maps levels to tolerances.
 //!
 //! Fields: `level` (0..=100, the command's parameter).
 
 use egui::{Color32, CornerRadius, Order, Pos2, Sense, Stroke, vec2};
 use serde_json::{Value, json};
-use vectorcraft_engine::{SIMPLIFY_LEVEL, simplify_level_tolerance};
+use vectorcraft_engine::{SIMPLIFY_LEVEL, auto_simplify_level, simplify_level_tolerance};
 use vectorcraft_geom::Rect;
 
 use super::{DialogResult, DialogSpec, form, modal};
@@ -26,9 +29,10 @@ pub(super) const SPEC: DialogSpec = DialogSpec { window: Some(show), confirm, pr
 const CMD: &str = "object.path.simplify";
 const LABEL: &str = "Simplify";
 
-/// The fields the slider opens with.
-pub(crate) fn fields() -> Value {
-    json!({ "level": SIMPLIFY_LEVEL })
+/// The fields the slider opens with: Auto-Simplify's level for the selection, or
+/// [`SIMPLIFY_LEVEL`] without a document.
+pub(crate) fn fields(app: &VectorcraftApp) -> Value {
+    json!({ "level": auto_simplify_level(&app.session).unwrap_or(SIMPLIFY_LEVEL) })
 }
 
 /// Whether the Simplify slider is open.

crates/ui-egui/src/dialogs/tests_modal.rs

@@ -338,9 +338,9 @@ fn slider_strip(ctx: &egui::Context) -> (Rect, Pos2, Pos2, Pos2) {
     (r, Pos2::new(r.left() + 8.0 + 14.0, y), Pos2::new(r.left() + 8.0 + 28.0 + 6.0 + 90.0, y), Pos2::new(r.right() - 8.0 - 14.0, y))
 }
 
-/// Object › Path › Simplify opens a slider under the selection that previews the 1 pt result.
-/// Dragging it to the right previews more anchor points and to the left fewer, and Enter keeps the
-/// result as one undo step.
+/// Object › Path › Simplify opens a slider under the selection that previews the auto-simplified
+/// result (the path is 285 pt wide: level 55, 0.7125 pt). Dragging it to the right previews more
+/// anchor points and to the left fewer, and Enter keeps the result as one undo step.
 #[test]
 fn simplify_opens_a_slider_whose_drag_previews_fewer_or_more_points() {
     let (ctx, mut app) = (ctx(), app_with_dense_path());
@@ -348,8 +348,8 @@ fn simplify_opens_a_slider_whose_drag_previews_fewer_or_more_points() {
     crate::menus::invoke(&mut app, "object.path.simplify", json!({}));
     assert_eq!(app.ui.dialog.as_ref().map(|d| d.kind.as_str()), Some(simplify_slider::KIND));
     settle(&ctx, &mut app);
-    assert_eq!(simplify_preview(&app), json!({"level": 50.0}));
-    assert_eq!(anchor_count(&app), 2, "the 1 pt result");
+    assert_eq!(simplify_preview(&app), json!({"level": 55.0}));
+    assert_eq!(anchor_count(&app), 2, "the auto-simplified result");
     let (_, _, rail, _) = slider_strip(&ctx);
     drag(&ctx, &mut app, rail, vec2(100.0, 0.0));
     assert_eq!(simplify_preview(&app), json!({"level": 100.0}));
@@ -369,6 +369,40 @@ fn simplify_opens_a_slider_whose_drag_previews_fewer_or_more_points() {
     assert_eq!(anchor_count(&app), 2);
 }
 
+/// A wave of 20 anchors `width` pt wide and `width / 5` pt high, selected.
+fn app_with_wave(width: f64) -> VectorcraftApp {
+    let mut app = VectorcraftApp::new(Session::new(), Default::default());
+    app.run("file.new", json!({"width": 2000, "height": 2000})).unwrap();
+    let anchors: Vec<_> = (0..20)
+        .map(|i| {
+            let t = i as f64 / 19.0;
+            json!({"x": 30.0 + width * t, "y": 500.0 + width / 5.0 * (3.0 * std::f64::consts::PI * t).sin()})
+        })
+        .collect();
+    app.run("path.create", json!({"anchors": anchors})).unwrap();
+    app
+}
+
+/// Object › Path › Simplify opens the slider at Auto-Simplify's level for the selection's size,
+/// not at a fixed level, and the canvas previews the paths as Auto-Simplify leaves them.
+#[test]
+fn simplify_slider_opens_at_the_auto_simplify_level_of_the_selection() {
+    let ctx = ctx();
+    // 1/400 of the longer side: 2.85 pt (level 35), 0.7125 pt (55), 0.07125 pt (89).
+    for (width, level) in [(1140.0, 35.0), (285.0, 55.0), (28.5, 89.0)] {
+        let mut app = app_with_wave(width);
+        crate::menus::invoke(&mut app, "object.path.simplify", json!({}));
+        assert_eq!(app.ui.dialog.as_ref().unwrap().f64("level", -1.0), level, "{width} pt");
+        settle(&ctx, &mut app);
+        assert_eq!(simplify_preview(&app), json!({ "level": level }), "{width} pt");
+        let previewed = app.session.doc().unwrap().doc.clone();
+        cancel(&mut app);
+        let auto = app.run("object.path.simplify", json!({"auto": true})).unwrap();
+        assert_eq!(auto["level"], json!(level), "{width} pt");
+        assert_eq!(app.session.doc().unwrap().doc, previewed, "{width} pt: the preview is Auto-Simplify's result");
+    }
+}
+
 /// Escape, taken by the app's key handling before the dialog layer draws, closes the Simplify
 /// slider and puts the paths back as they were, with no undo step.
 #[test]
@@ -420,15 +454,17 @@ fn simplify_slider_stays_where_it_opened_while_the_preview_changes_the_bounds()
     assert_eq!(rect_of(&ctx, egui::Id::new(("dialog", simplify_slider::KIND))), opened);
 }
 
-/// Auto-Simplify moves the slider to the level that keeps the path within 1/400 of its size, and a
-/// click outside the strip keeps the result as one undo step.
+/// Auto-Simplify moves the slider back to the level that keeps the path within 1/400 of its size,
+/// and a click outside the strip keeps the result as one undo step.
 #[test]
 fn simplify_slider_auto_simplify_and_a_click_outside_keep_the_result() {
     let (ctx, mut app) = (ctx(), app_with_dense_path());
     let before = app.session.doc().unwrap().doc.clone();
     let undo_len = app.session.doc().unwrap().history.undo.len();
     crate::menus::invoke(&mut app, "object.path.simplify", json!({}));
+    app.ui.dialog.as_mut().unwrap().fields.insert("level".into(), json!(100));
     settle(&ctx, &mut app);
+    assert_eq!(simplify_preview(&app), json!({"level": 100.0}));
     let (_, auto, ..) = slider_strip(&ctx);
     click(&ctx, &mut app, auto);
     // The path is 285 pt wide: 0.7125 pt at most, level 55.

crates/ui-egui/src/menus.rs

@@ -801,7 +801,7 @@ pub const UI_COMMANDS: &[(&str, &str, &str, &str)] = &[
         "ui.simplifyAuto",
         "Auto-Simplify",
         "",
-        "{} the open Simplify slider (Object › Path › Simplify opens it: dialog `simplifySlider` with field `level` 0..100, object.path.simplify's level, 50 as it opens, previewed on the canvas until ui.dialog.confirm keeps it as one undo step; after OK in the Simplify dialog with `retain` ticked, the menu item opens the dialog `simplify` with the fields of that OK instead) moves to the level object.path.simplify {auto: true} picks for the selection and previews it → {level}; an error when the slider isn't open",
+        "{} the open Simplify slider (Object › Path › Simplify opens it: dialog `simplifySlider` with field `level` 0..100, object.path.simplify's level, opening at the level object.path.simplify {auto: true} picks for the selection, previewed on the canvas until ui.dialog.confirm keeps it as one undo step; after OK in the Simplify dialog with `retain` ticked, the menu item opens the dialog `simplify` with the fields of that OK instead) moves to the level object.path.simplify {auto: true} picks for the selection and previews it → {level}; an error when the slider isn't open",
     ),
     (
         "ui.simplifyMoreOptions",
@@ -3569,7 +3569,7 @@ fn menu_dialog(app: &VectorcraftApp, id: &str) -> Option<(&'static str, Value)>
         // Simplify opens its slider, or the dialog on the fields it was last confirmed with when
         // "Open this dialog with these settings next time" was ticked.
         "object.path.simplify" if app.ui.simplify.is_object() => ("simplify", app.ui.simplify.clone()),
-        "object.path.simplify" => (crate::dialogs::simplify_slider::KIND, crate::dialogs::simplify_slider::fields()),
+        "object.path.simplify" => (crate::dialogs::simplify_slider::KIND, crate::dialogs::simplify_slider::fields(app)),
         "object.path.splitIntoGrid" => {
             // The grid starts at the size of the selection.
             let size =

docs/mcp.md

@@ -2318,9 +2318,10 @@ whose tolerance is at most 1/400 of the selection's longer side, or level 100 wh
 ```
 
 In the desktop app, Object › Path › Simplify opens the slider (`ui.menuDialog {command: "object.path.simplify"}`,
-dialog `simplifySlider` with field `level`) and previews the result until `ui.dialog.confirm`. `ui.simplifyAuto` moves
-the open slider to the Auto-Simplify level, and `ui.simplifyMoreOptions` opens the Simplify dialog at the slider's
-tolerance. When OK confirms the dialog with `retain` ticked, the menu item opens the dialog on those settings next time.
+dialog `simplifySlider` with field `level`) at the Auto-Simplify level for the selection and previews the result until
+`ui.dialog.confirm`. `ui.simplifyAuto` moves the open slider back to the Auto-Simplify level, and `ui.simplifyMoreOptions`
+opens the Simplify dialog at the slider's tolerance. When OK confirms the dialog with `retain` ticked, the menu item opens
+the dialog on those settings next time.
 
 ## Editing a path with the Curvature tool