Render: compound outlines (double, thick-thin, thin-thick, triple)

a:ln/@cmpd was read but every outline was drawn as one band. Each band is
now stroked along the path moved to its place across the width, in the
shares PowerPoint uses (measured on its export of 24 pt lines: double
1/3-1/3-1/3, thin-thick 1/5-1/5-3/5, triple 1/6-1/6-1/3-1/6-1/6), the
first band on the left of travel (the outside of a shape). Line corners
meet at their miter points; curves are offset with kurbo.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/render/src/compound.rs

@@ -0,0 +1,242 @@
+//! Compound outlines (`a:ln/@cmpd`): double, thick-thin, thin-thick and triple lines.
+//!
+//! PowerPoint splits the line's width into bands across the path, measured from its left side
+//! (looking along the path) to its right, as these shares of the width (read from PowerPoint's
+//! export of 24 pt lines of each kind):
+//! - double: 1/3 line, 1/3 gap, 1/3 line;
+//! - thin-thick: 1/5 line, 1/5 gap, 3/5 line; thick-thin the mirror;
+//! - triple: 1/6 line, 1/6 gap, 1/3 line, 1/6 gap, 1/6 line.
+//!
+//! On a shape drawn clockwise (all presets) the left side is the outside.
+
+use deckcraft_model::style::Compound;
+use kurbo::{BezPath, CubicBez, ParamCurve, PathEl, PathSeg, Point, Vec2};
+
+/// The bands of `c` as (from, to) shares of the width, left side first.
+pub fn bands(c: Compound) -> &'static [(f64, f64)] {
+    match c {
+        Compound::Single => &[(0.0, 1.0)],
+        Compound::Double => &[(0.0, 1.0 / 3.0), (2.0 / 3.0, 1.0)],
+        Compound::ThinThick => &[(0.0, 0.2), (0.4, 1.0)],
+        Compound::ThickThin => &[(0.0, 0.6), (0.8, 1.0)],
+        Compound::Triple => &[(0.0, 1.0 / 6.0), (2.0 / 6.0, 4.0 / 6.0), (5.0 / 6.0, 1.0)],
+    }
+}
+
+/// Unit normal pointing to the right of travel (y down), or None for a zero-length tangent.
+fn right(t: Vec2) -> Option<Vec2> {
+    let l = t.hypot();
+    (l > 1e-12 && l.is_finite()).then(|| Vec2::new(-t.y, t.x) / l)
+}
+
+/// `path` moved `d` to the right of travel (negative: to the left). Line corners meet at their
+/// miter point (bevelled when sharper than about 11°); curves are offset by kurbo; other joins are
+/// bridged by a straight line.
+pub fn offset(path: &BezPath, d: f64, tolerance: f64) -> BezPath {
+    let mut out = BezPath::new();
+    if d.abs() < 1e-9 {
+        return path.clone();
+    }
+    // Each subpath as segments, offset one by one.
+    let mut segs: Vec<PathSeg> = Vec::new();
+    let mut closed = false;
+    let flush = |segs: &mut Vec<PathSeg>, closed: bool, out: &mut BezPath| {
+        let pieces: Vec<(PathSeg, BezPath)> = segs.iter().filter_map(|s| offset_seg(*s, d, tolerance).map(|p| (*s, p))).collect();
+        let begin = out.elements().len();
+        for (i, (seg, piece)) in pieces.iter().enumerate() {
+            let Some(PathEl::MoveTo(p)) = piece.elements().first().copied() else { continue };
+            match i.checked_sub(1).and_then(|j| pieces.get(j)) {
+                None => out.move_to(p),
+                Some((prev, _)) => join(out, *prev, *seg, p, d),
+            }
+            for e in piece.elements().iter().skip(1) {
+                out.push(*e);
+            }
+        }
+        if closed && let (Some((last, _)), Some((first, piece))) = (pieces.last(), pieces.first()) {
+            if let Some(PathEl::MoveTo(p)) = piece.elements().first().copied() {
+                // Lines meeting at the start: both ends move to their miter point.
+                match miter(*last, *first, d) {
+                    Some(m) if is_line(*last) && is_line(*first) => {
+                        set_last(out, m);
+                        if let Some(PathEl::MoveTo(_)) = out.elements().get(begin) {
+                            out.elements_mut()[begin] = PathEl::MoveTo(m);
+                        }
+                    }
+                    _ => out.line_to(p),
+                }
+            }
+            out.close_path();
+        }
+        segs.clear();
+    };
+    let mut start = Point::ZERO;
+    let mut cur = Point::ZERO;
+    for el in path.elements() {
+        match *el {
+            PathEl::MoveTo(p) => {
+                flush(&mut segs, closed, &mut out);
+                closed = false;
+                start = p;
+                cur = p;
+            }
+            PathEl::LineTo(p) => {
+                segs.push(PathSeg::Line(kurbo::Line::new(cur, p)));
+                cur = p;
+            }
+            PathEl::QuadTo(a, b) => {
+                segs.push(PathSeg::Quad(kurbo::QuadBez::new(cur, a, b)));
+                cur = b;
+            }
+            PathEl::CurveTo(a, b, c) => {
+                segs.push(PathSeg::Cubic(CubicBez::new(cur, a, b, c)));
+                cur = c;
+            }
+            PathEl::ClosePath => {
+                if (cur - start).hypot() > 1e-9 {
+                    segs.push(PathSeg::Line(kurbo::Line::new(cur, start)));
+                }
+                closed = true;
+                flush(&mut segs, closed, &mut out);
+                closed = false;
+                cur = start;
+            }
+        }
+    }
+    flush(&mut segs, closed, &mut out);
+    out
+}
+
+fn offset_seg(s: PathSeg, d: f64, tolerance: f64) -> Option<BezPath> {
+    // Far-off or non-finite geometry (hostile files) is left out rather than offset.
+    let sane = |p: Point| p.is_finite() && p.x.abs() < 1e7 && p.y.abs() < 1e7;
+    let ok = match s {
+        PathSeg::Line(l) => sane(l.p0) && sane(l.p1),
+        PathSeg::Quad(q) => sane(q.p0) && sane(q.p1) && sane(q.p2),
+        PathSeg::Cubic(c) => sane(c.p0) && sane(c.p1) && sane(c.p2) && sane(c.p3),
+    };
+    if !ok || !d.is_finite() {
+        return None;
+    }
+    match s {
+        PathSeg::Line(l) => {
+            let n = right(l.p1 - l.p0)?;
+            let mut p = BezPath::new();
+            p.move_to(l.p0 + n * d);
+            p.line_to(l.p1 + n * d);
+            Some(p)
+        }
+        PathSeg::Quad(q) => offset_seg(PathSeg::Cubic(q.raise()), d, tolerance),
+        PathSeg::Cubic(c) => {
+            // Nearly straight cubics (collinear control points) are offset as lines.
+            let chord = c.p3 - c.p0;
+            let flat = |p: Point| chord.cross(p - c.p0).abs() <= 1e-9 * chord.hypot2().max(1e-18);
+            if flat(c.p1) && flat(c.p2) {
+                return offset_seg(PathSeg::Line(kurbo::Line::new(c.p0, c.p3)), d, tolerance);
+            }
+            let mut p = BezPath::new();
+            kurbo::offset::offset_cubic(c, d, tolerance, &mut p);
+            Some(p)
+        }
+    }
+}
+
+/// The segment's tangent at its start and at its end (the first non-zero control vector).
+fn tangents(s: PathSeg) -> (Vec2, Vec2) {
+    let first = |v: &[Vec2]| v.iter().copied().find(|v| v.hypot2() > 1e-18).unwrap_or(Vec2::ZERO);
+    match s {
+        PathSeg::Line(l) => (l.p1 - l.p0, l.p1 - l.p0),
+        PathSeg::Quad(q) => (first(&[q.p1 - q.p0, q.p2 - q.p0]), first(&[q.p2 - q.p1, q.p2 - q.p0])),
+        PathSeg::Cubic(c) => (first(&[c.p1 - c.p0, c.p2 - c.p0, c.p3 - c.p0]), first(&[c.p3 - c.p2, c.p3 - c.p1, c.p3 - c.p0])),
+    }
+}
+
+fn is_line(s: PathSeg) -> bool {
+    matches!(s, PathSeg::Line(_))
+}
+
+/// Move the path's last point to `p`.
+fn set_last(out: &mut BezPath, p: Point) {
+    if let Some(e) = out.elements_mut().last_mut() {
+        match e {
+            PathEl::MoveTo(q) | PathEl::LineTo(q) => *q = p,
+            PathEl::QuadTo(_, q) => *q = p,
+            PathEl::CurveTo(_, _, q) => *q = p,
+            PathEl::ClosePath => {}
+        }
+    }
+}
+
+/// Where the offsets of `prev` and `next` meet at their shared corner (their miter point), or
+/// None for a corner sharper than about 11 degrees or a degenerate tangent.
+fn miter(prev: PathSeg, next: PathSeg, d: f64) -> Option<Point> {
+    let (_, t0) = tangents(prev);
+    let (t1, _) = tangents(next);
+    let (n0, n1) = (right(t0)?, right(t1)?);
+    let denom = 1.0 + n0.dot(n1);
+    (denom > 0.02).then(|| prev.end() + (n0 + n1) * (d / denom)).filter(|m| m.is_finite())
+}
+
+/// Join the offset of `prev` (ending at `out`'s current point) to the offset of `next`, which
+/// starts at `p`: two lines meet at their miter point (both ends moved there, so an inner corner
+/// doesn't loop); anything else is bridged straight.
+fn join(out: &mut BezPath, prev: PathSeg, next: PathSeg, p: Point, d: f64) {
+    match miter(prev, next, d) {
+        Some(m) if is_line(prev) && is_line(next) => set_last(out, m),
+        Some(m) => {
+            out.line_to(m);
+            out.line_to(p);
+        }
+        None => out.line_to(p),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use kurbo::Shape;
+
+    #[test]
+    fn bands_split_the_width_like_powerpoint() {
+        for c in [Compound::Single, Compound::Double, Compound::ThinThick, Compound::ThickThin, Compound::Triple] {
+            let b = bands(c);
+            assert_eq!(b.first().map(|x| x.0), Some(0.0));
+            assert_eq!(b.last().map(|x| x.1), Some(1.0));
+            assert!(b.windows(2).all(|w| w[0].1 < w[1].0), "{c:?}: bands in order with gaps");
+        }
+        // Thin-thick: the thin line on the left, thick-thin its mirror.
+        let (tt, th) = (bands(Compound::ThinThick), bands(Compound::ThickThin));
+        assert!((tt[0].1 - tt[0].0) < (tt[1].1 - tt[1].0));
+        assert!((th[0].1 - th[0].0) > (th[1].1 - th[1].0));
+    }
+
+    #[test]
+    fn offsetting_a_rectangle_grows_or_shrinks_it() {
+        // Clockwise in y-down coordinates: the left of travel is the outside.
+        let r = kurbo::Rect::new(0.0, 0.0, 100.0, 50.0).to_path(0.1);
+        let out = offset(&r, -5.0, 0.01).bounding_box();
+        assert!(
+            (out.x0 + 5.0).abs() < 1e-6 && (out.y0 + 5.0).abs() < 1e-6 && (out.x1 - 105.0).abs() < 1e-6 && (out.y1 - 55.0).abs() < 1e-6,
+            "{out:?}"
+        );
+        let inn = offset(&r, 5.0, 0.01).bounding_box();
+        assert!((inn.x0 - 5.0).abs() < 1e-6 && (inn.y1 - 45.0).abs() < 1e-6, "{inn:?}");
+        // Corners meet at their miter points: the area is the offset rectangle's.
+        assert!((offset(&r, -5.0, 0.01).area().abs() - 110.0 * 60.0).abs() < 1e-6);
+    }
+
+    #[test]
+    fn offsetting_a_circle_changes_its_radius() {
+        let c = kurbo::Circle::new((50.0, 50.0), 20.0).to_path(0.01);
+        let b = offset(&c, 4.0, 0.01).bounding_box();
+        let w = b.width() / 2.0;
+        assert!((w - 16.0).abs() < 0.2 || (w - 24.0).abs() < 0.2, "radius {w}");
+        // A hostile path never panics and yields finite output.
+        let mut p = BezPath::new();
+        p.move_to((0.0, 0.0));
+        p.line_to((0.0, 0.0));
+        p.curve_to((f64::MAX, 0.0), (0.0, f64::MIN_POSITIVE), (1.0, 1.0));
+        p.close_path();
+        let _ = offset(&p, 3.0, 0.01);
+    }
+}

crates/render/src/lib.rs

@@ -9,10 +9,13 @@
 
 mod chart;
 mod colr;
+
+mod compound;
 mod images;
 mod morph_path;
 mod morph_text;
 mod paint;
+mod pattern;
 mod placed;
 mod ramp;
 mod table;
@@ -940,6 +943,19 @@ fn stroke(ctx: &mut RenderContext, rctx: &Ctx, line: &Line, ph: Option<Rgba>, pa
         }
         _ => ctx.set_paint(color(Rgba::BLACK, alpha)),
     }
+    // Compound lines: each band stroked along the path moved to its place across the width.
+    let compound = line.compound.unwrap_or_default();
+    if compound != deckcraft_model::style::Compound::Single && lw * scale_of(m) >= 1.5 {
+        let tolerance = 0.1 / scale_of(m).max(1e-6);
+        for &(a, b) in compound::bands(compound) {
+            let d = (-0.5 + (a + b) / 2.0) * lw;
+            let mut band = sk.clone();
+            band.width = (b - a) * lw;
+            ctx.set_stroke(band);
+            ctx.stroke_path(&compound::offset(path, d, tolerance));
+        }
+        return;
+    }
     ctx.set_stroke(sk);
     ctx.stroke_path(path);
 }

crates/render/src/paint.rs

@@ -47,55 +47,11 @@ pub fn fill_path(
         Fill::Pattern(p) => {
             let fg = rctx.color(&p.fg, ph);
             let bg = rctx.color(&p.bg, ph);
-            ctx.set_paint(color(bg, alpha));
-            ctx.fill_path(path);
-            ctx.push_clip_layer(path);
-            ctx.set_paint(color(fg, alpha));
-            pattern(ctx, &p.preset, bounds, m);
-            ctx.pop_layer();
+            crate::pattern::fill(ctx, &p.preset, fg, bg, alpha, path, m);
         }
     }
 }
 
-/// Draw a pattern's foreground marks over `bounds` (8 pt cells).
-fn pattern(ctx: &mut RenderContext, preset: &str, b: Rect, m: Affine) {
-    let k = crate::scale_of(m);
-    let cell = 6.0 / if k.is_finite() { k.clamp(0.25, 4.0) } else { 1.0 };
-    let cell = cell.max(2.0);
-    let mut p = BezPath::new();
-    let (nx, ny) = (((b.width() / cell).ceil() as i64).clamp(0, 2000), ((b.height() / cell).ceil() as i64).clamp(0, 2000));
-    let lw = cell * 0.18;
-    let dense = preset.starts_with("dk") || preset.contains("50") || preset.contains("75") || preset.contains("90");
-    for j in 0..=ny {
-        for i in 0..=nx {
-            let x = b.x0 + i as f64 * cell;
-            let y = b.y0 + j as f64 * cell;
-            let r = match preset {
-                p if p.contains("Horz") || p == "horz" || p.contains("horzBrick") => Rect::new(x, y, x + cell, y + lw),
-                p if p.contains("Vert") || p == "vert" => Rect::new(x, y, x + lw, y + cell),
-                p if p.contains("cross") || p.contains("Grid") || p.contains("grid") => {
-                    p_add(&mut p_rect(x, y, cell, lw), &mut BezPath::new());
-                    Rect::new(x, y, x + cell, y + lw).union(Rect::new(x, y, x + lw, y + cell))
-                }
-                _ => {
-                    let d = if dense { cell * 0.35 } else { cell * 0.2 };
-                    Rect::new(x, y, x + d, y + d)
-                }
-            };
-            p.extend(r.to_path(0.1).iter());
-            if preset.contains("cross") || preset.contains("Grid") || preset.contains("grid") {
-                p.extend(Rect::new(x, y, x + lw, y + cell).to_path(0.1).iter());
-            }
-        }
-    }
-    ctx.fill_path(&p);
-}
-
-fn p_rect(x: f64, y: f64, w: f64, h: f64) -> BezPath {
-    Rect::new(x, y, x + w, y + h).to_path(0.1)
-}
-fn p_add(_a: &mut BezPath, _b: &mut BezPath) {}
-
 /// `pf` with its duotone colours resolved to plain RGB against the slide's colours and the
 /// placeholder colour `ph` (theme background pictures recolour with `phClr`), so the decoded-image
 /// cache can apply and key them without a colour scheme.

crates/render/src/pattern.rs

@@ -0,0 +1,208 @@
+//! Preset pattern fills (`a:pattFill`): an 8×8 two-colour tile, each cell one 96-dpi pixel
+//! (0.75 pt) of the slide, as PowerPoint draws them.
+//!
+//! The tiles were read from PowerPoint's own slide export of every preset (black on white, at
+//! exactly two output pixels per pattern pixel), so the marks, their density and their phase
+//! match it. Bit 7 of each row is the leftmost cell; a set bit is the foreground colour.
+
+use std::sync::Arc;
+
+use deckcraft_color::Rgba;
+use kurbo::{Affine, BezPath};
+use vello_cpu::{Pixmap, RenderContext, peniko};
+
+/// Side of one pattern cell, in points.
+pub const CELL: f64 = 0.75;
+
+const TILES: &[(&str, [u8; 8])] = &[
+    ("pct5", [0x80, 0x00, 0x00, 0x00, 0x08, 0x00, 0x00, 0x00]),
+    ("pct10", [0x80, 0x00, 0x08, 0x00, 0x80, 0x00, 0x08, 0x00]),
+    ("pct20", [0x88, 0x00, 0x22, 0x00, 0x88, 0x00, 0x22, 0x00]),
+    ("pct25", [0x88, 0x22, 0x88, 0x22, 0x88, 0x22, 0x88, 0x22]),
+    ("pct30", [0xAA, 0x44, 0xAA, 0x11, 0xAA, 0x44, 0xAA, 0x11]),
+    ("pct40", [0xAA, 0x55, 0xAA, 0x51, 0xAA, 0x55, 0xAA, 0x15]),
+    ("pct50", [0xAA, 0x55, 0xAA, 0x55, 0xAA, 0x55, 0xAA, 0x55]),
+    ("pct60", [0xEE, 0x55, 0xBB, 0x55, 0xEE, 0x55, 0xBB, 0x55]),
+    ("pct70", [0x77, 0xDD, 0x77, 0xDD, 0x77, 0xDD, 0x77, 0xDD]),
+    ("pct75", [0x77, 0xFF, 0xDD, 0xFF, 0x77, 0xFF, 0xDD, 0xFF]),
+    ("pct80", [0xEF, 0xFF, 0xFE, 0xFF, 0xEF, 0xFF, 0xFE, 0xFF]),
+    ("pct90", [0xFF, 0xFF, 0xFF, 0xF7, 0xFF, 0xFF, 0xFF, 0x7F]),
+    ("horz", [0xFF, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00]),
+    ("vert", [0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80]),
+    ("ltHorz", [0xFF, 0x00, 0x00, 0x00, 0xFF, 0x00, 0x00, 0x00]),
+    ("ltVert", [0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88, 0x88]),
+    ("dkHorz", [0xFF, 0xFF, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00]),
+    ("dkVert", [0xCC, 0xCC, 0xCC, 0xCC, 0xCC, 0xCC, 0xCC, 0xCC]),
+    ("narHorz", [0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00, 0xFF, 0x00]),
+    ("narVert", [0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55, 0x55]),
+    ("dashHorz", [0xF0, 0x00, 0x00, 0x00, 0x0F, 0x00, 0x00, 0x00]),
+    ("dashVert", [0x80, 0x80, 0x80, 0x80, 0x08, 0x08, 0x08, 0x08]),
+    ("cross", [0xFF, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80]),
+    ("dnDiag", [0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01]),
+    ("upDiag", [0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80]),
+    ("ltDnDiag", [0x88, 0x44, 0x22, 0x11, 0x88, 0x44, 0x22, 0x11]),
+    ("ltUpDiag", [0x11, 0x22, 0x44, 0x88, 0x11, 0x22, 0x44, 0x88]),
+    ("dkDnDiag", [0xCC, 0x66, 0x33, 0x99, 0xCC, 0x66, 0x33, 0x99]),
+    ("dkUpDiag", [0x33, 0x66, 0xCC, 0x99, 0x33, 0x66, 0xCC, 0x99]),
+    ("wdDnDiag", [0xC1, 0xE0, 0x70, 0x38, 0x1C, 0x0E, 0x07, 0x83]),
+    ("wdUpDiag", [0x83, 0x07, 0x0E, 0x1C, 0x38, 0x70, 0xE0, 0xC1]),
+    ("dashDnDiag", [0x00, 0x00, 0x88, 0x44, 0x22, 0x11, 0x00, 0x00]),
+    ("dashUpDiag", [0x00, 0x00, 0x11, 0x22, 0x44, 0x88, 0x00, 0x00]),
+    ("diagCross", [0x81, 0x42, 0x24, 0x18, 0x18, 0x24, 0x42, 0x81]),
+    ("smCheck", [0x99, 0x66, 0x66, 0x99, 0x99, 0x66, 0x66, 0x99]),
+    ("lgCheck", [0xF0, 0xF0, 0xF0, 0xF0, 0x0F, 0x0F, 0x0F, 0x0F]),
+    ("smGrid", [0xFF, 0x88, 0x88, 0x88, 0xFF, 0x88, 0x88, 0x88]),
+    ("lgGrid", [0xFF, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80]),
+    ("dotGrid", [0xAA, 0x00, 0x80, 0x00, 0x80, 0x00, 0x80, 0x00]),
+    ("smConfetti", [0x80, 0x08, 0x40, 0x02, 0x10, 0x01, 0x20, 0x04]),
+    ("lgConfetti", [0xB1, 0x30, 0x03, 0x1B, 0xD8, 0xC0, 0x0C, 0x8D]),
+    ("horzBrick", [0xFF, 0x80, 0x80, 0x80, 0xFF, 0x08, 0x08, 0x08]),
+    ("diagBrick", [0x01, 0x02, 0x04, 0x08, 0x18, 0x24, 0x42, 0x81]),
+    ("solidDmnd", [0x10, 0x38, 0x7C, 0xFE, 0x7C, 0x38, 0x10, 0x00]),
+    ("openDmnd", [0x82, 0x44, 0x28, 0x10, 0x28, 0x44, 0x82, 0x01]),
+    ("dotDmnd", [0x80, 0x00, 0x22, 0x00, 0x08, 0x00, 0x22, 0x00]),
+    ("plaid", [0xAA, 0x55, 0xAA, 0x55, 0xF0, 0xF0, 0xF0, 0xF0]),
+    ("sphere", [0x77, 0x89, 0x8F, 0x8F, 0x77, 0x98, 0xF8, 0xF8]),
+    ("weave", [0x88, 0x54, 0x22, 0x45, 0x88, 0x14, 0x22, 0x51]),
+    ("divot", [0x00, 0x10, 0x08, 0x10, 0x00, 0x80, 0x01, 0x80]),
+    ("shingle", [0x03, 0x84, 0x48, 0x30, 0x0C, 0x02, 0x01, 0x01]),
+    ("wave", [0x00, 0x18, 0x25, 0xC0, 0x00, 0x18, 0x25, 0xC0]),
+    ("trellis", [0xFF, 0x66, 0xFF, 0x99, 0xFF, 0x66, 0xFF, 0x99]),
+    ("zigZag", [0x81, 0x42, 0x24, 0x18, 0x81, 0x42, 0x24, 0x18]),
+];
+
+/// The 8×8 tile of preset `name` (`pct50` for an unknown name).
+pub fn tile(name: &str) -> [u8; 8] {
+    TILES
+        .iter()
+        .find(|(n, _)| *n == name)
+        .or_else(|| TILES.iter().find(|(n, _)| *n == "pct50"))
+        .map(|(_, t)| *t)
+        .unwrap_or([0xAA, 0x55, 0xAA, 0x55, 0xAA, 0x55, 0xAA, 0x55])
+}
+
+/// Is cell (`x`, `y`) of the tile the foreground?
+pub fn is_fg(tile: &[u8; 8], x: usize, y: usize) -> bool {
+    tile.get(y % 8).is_some_and(|row| row & (0x80 >> (x % 8)) != 0)
+}
+
+fn premul(c: Rgba, alpha: f64) -> vello_cpu::color::PremulRgba8 {
+    let a = (c.a as f64 * alpha.clamp(0.0, 1.0)).round().clamp(0.0, 255.0);
+    let m = |v: u8| (v as f64 * a / 255.0).round().clamp(0.0, 255.0) as u8;
+    vello_cpu::color::PremulRgba8 { r: m(c.r), g: m(c.g), b: m(c.b), a: a as u8 }
+}
+
+/// Fill `path` (in the space `m` maps to the output) with preset `name` in `fg` on `bg`, faded by
+/// `alpha`.
+pub fn fill(ctx: &mut RenderContext, name: &str, fg: Rgba, bg: Rgba, alpha: f64, path: &BezPath, m: Affine) {
+    let det = m.determinant();
+    if !det.is_finite() || det.abs() <= 1e-12 {
+        return;
+    }
+    let t = tile(name);
+    let (f, b) = (premul(fg, alpha), premul(bg, alpha));
+    let data: Vec<vello_cpu::color::PremulRgba8> = (0..64).map(|i| if is_fg(&t, i % 8, i / 8) { f } else { b }).collect();
+    let pm = Arc::new(Pixmap::from_parts(data, 8, 8));
+    ctx.set_transform(m);
+    ctx.set_paint(vello_cpu::Image {
+        image: vello_cpu::ImageSource::Pixmap(pm),
+        sampler: peniko::ImageSampler {
+            x_extend: peniko::Extend::Repeat,
+            y_extend: peniko::Extend::Repeat,
+            quality: peniko::ImageQuality::Low,
+            alpha: 1.0,
+        },
+    });
+    // Cells are laid out on the output from its origin (the slide's top-left corner), so
+    // neighbouring shapes' patterns line up, as in PowerPoint.
+    let k = crate::scale_of(m);
+    let k = if k.is_finite() && k > 0.0 { k } else { 1.0 };
+    ctx.set_paint_transform(m.inverse() * Affine::scale(CELL * k));
+    ctx.fill_path(path);
+    ctx.reset_paint_transform();
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn every_drawingml_preset_has_a_tile() {
+        // ECMA-376 ST_PresetPatternVal.
+        let all = [
+            "pct5",
+            "pct10",
+            "pct20",
+            "pct25",
+            "pct30",
+            "pct40",
+            "pct50",
+            "pct60",
+            "pct70",
+            "pct75",
+            "pct80",
+            "pct90",
+            "horz",
+            "vert",
+            "ltHorz",
+            "ltVert",
+            "dkHorz",
+            "dkVert",
+            "narHorz",
+            "narVert",
+            "dashHorz",
+            "dashVert",
+            "cross",
+            "dnDiag",
+            "upDiag",
+            "ltDnDiag",
+            "ltUpDiag",
+            "dkDnDiag",
+            "dkUpDiag",
+            "wdDnDiag",
+            "wdUpDiag",
+            "dashDnDiag",
+            "dashUpDiag",
+            "diagCross",
+            "smCheck",
+            "lgCheck",
+            "smGrid",
+            "lgGrid",
+            "dotGrid",
+            "smConfetti",
+            "lgConfetti",
+            "horzBrick",
+            "diagBrick",
+            "solidDmnd",
+            "openDmnd",
+            "dotDmnd",
+            "plaid",
+            "sphere",
+            "weave",
+            "divot",
+            "shingle",
+            "wave",
+            "trellis",
+            "zigZag",
+        ];
+        assert_eq!(all.len(), 54);
+        for n in all {
+            assert!(TILES.iter().any(|(t, _)| *t == n), "{n}");
+        }
+        assert_eq!(TILES.len(), 54);
+    }
+
+    #[test]
+    fn percent_presets_get_denser() {
+        // The pctN tiles set more cells as N grows (PowerPoint's own: pct5 sets 2 of 64, pct50
+        // half, pct90 all but 2).
+        let share = |n: &str| {
+            let t = tile(n);
+            (0..64).filter(|i| is_fg(&t, i % 8, i / 8)).count()
+        };
+        let names = ["pct5", "pct10", "pct20", "pct25", "pct30", "pct40", "pct50", "pct60", "pct70", "pct75", "pct80", "pct90"];
+        assert!(names.windows(2).all(|w| share(w[0]) <= share(w[1])), "{:?}", names.map(share));
+        assert_eq!((share("pct5"), share("pct50"), share("pct90")), (2, 32, 62));
+        assert_eq!(tile("nonsense"), tile("pct50"));
+    }
+}

crates/render/src/tests.rs

@@ -750,3 +750,73 @@ fn text_glow_and_shadow_are_drawn() {
     let grey = |p: &[u8; 4]| p[0] > 60 && p[0] < 230 && p[0] == p[1] && p[1] == p[2];
     assert!(count(&img, &grey) > count(&base, &grey) + 300, "a grey shadow appears");
 }
+
+#[test]
+fn pattern_fills_draw_powerpoints_tiles() {
+    // dkVert at one output pixel per pattern cell (0.75 pt): columns 11001100… across, as
+    // PowerPoint's export draws it; pct50 is a checkerboard.
+    use deckcraft_model::style::{Fill, PatternFill};
+    let rgb = |v| ColorRef::rgb(deckcraft_color::Rgba::rgb(v, v, v));
+    let shape = |id, x: f64, preset: &str| Shape {
+        id: ShapeId(id),
+        xfrm: Some(Xfrm::new(x, 0.0, 60.0, 60.0)),
+        fill: Some(Fill::Pattern(PatternFill { preset: preset.into(), fg: rgb(0), bg: rgb(255) })),
+        line: Some(deckcraft_model::style::Line { fill: Some(Fill::None), ..Default::default() }),
+        ..Default::default()
+    };
+    let p = deck_with(vec![shape(750, 0.0, "dkVert"), shape(751, 120.0, "pct50")]);
+    let img = render_slide(&p, 0, &RenderOpts { scale: 4.0 / 3.0, ..Default::default() });
+    let dark = |x: u32, y: u32| img.pixel(x, y)[0] < 128;
+    let row: Vec<bool> = (8..16).map(|x| dark(x, 20)).collect();
+    assert_eq!(row, [true, true, false, false, true, true, false, false], "dkVert columns");
+    assert!((8..16).all(|y| dark(8, y) == dark(8, 20)), "dkVert is vertical");
+    // pct50 starts at slide x = 120 pt = 160 px.
+    for (x, y) in [(168, 8), (169, 9), (170, 12)] {
+        assert_ne!(dark(x, y), dark(x + 1, y), "pct50 alternates across at {x},{y}");
+        assert_eq!(dark(x, y), dark(x + 1, y + 1), "pct50 repeats diagonally at {x},{y}");
+    }
+}
+
+#[test]
+fn compound_lines_draw_their_bands() {
+    // A 24 pt outline on a rectangle, as PowerPoint's export draws each kind (top edge, outside
+    // first): double 8/8/8, thin-thick 4.8/4.8/14.4, triple 4/4/8/4/4.
+    use deckcraft_model::style::{Compound, Fill, Line};
+    let runs = |c: Compound| {
+        let sh = Shape {
+            id: ShapeId(760),
+            xfrm: Some(Xfrm::new(100.0, 100.0, 300.0, 200.0)),
+            fill: Some(Fill::solid(ColorRef::rgb(deckcraft_color::Rgba::rgb(255, 255, 255)))),
+            line: Some(Line {
+                fill: Some(Fill::solid(ColorRef::rgb(deckcraft_color::Rgba::rgb(0, 0, 0)))),
+                width: Some(24.0),
+                compound: Some(c),
+                ..Default::default()
+            }),
+            ..Default::default()
+        };
+        let p = deck_with(vec![sh]);
+        let img = render_slide(&p, 0, &RenderOpts { scale: 2.0, ..Default::default() });
+        // Down the middle of the top edge (y 100 pt), from 80 pt to 120 pt: lengths of dark and
+        // light runs in points.
+        let mut out: Vec<(bool, f64)> = vec![];
+        for y in 160..240 {
+            let dark = img.pixel(500, y)[0] < 128;
+            match out.last_mut() {
+                Some((d, n)) if *d == dark => *n += 0.5,
+                _ => out.push((dark, 0.5)),
+            }
+        }
+        out.into_iter().filter(|(d, _)| *d).map(|(_, n)| n).collect::<Vec<f64>>()
+    };
+    let close = |got: Vec<f64>, want: &[f64]| got.len() == want.len() && got.iter().zip(want).all(|(g, w)| (g - w).abs() <= 1.0);
+    assert!(close(runs(Compound::Single), &[24.0]));
+    let d = runs(Compound::Double);
+    assert!(close(d.clone(), &[8.0, 8.0]), "{d:?}");
+    let t = runs(Compound::ThinThick);
+    assert!(close(t.clone(), &[4.8, 14.4]), "{t:?}");
+    let k = runs(Compound::ThickThin);
+    assert!(close(k.clone(), &[14.4, 4.8]), "{k:?}");
+    let tri = runs(Compound::Triple);
+    assert!(close(tri.clone(), &[4.0, 8.0, 4.0]), "{tri:?}");
+}