Merge pull request #1619 from marcoarnulfo/fix/ai-zero-length-dots

Strokes: a zero-length subpath draws its round or projecting cap as a dot

crates/effects/src/stroke.rs

@@ -116,10 +116,36 @@ pub fn line_outline(line: &BezPath, st: &StrokeLayer, width: f64, tol: f64) -> B
             out.extend(dot_outline(&d.dots, width, st.cap, tol).iter());
             out
         }
-        (None, None) => plain_outline(line, &style(st, width), tol),
+        (None, None) => {
+            let mut out = plain_outline(line, &style(st, width), tol);
+            out.extend(dot_outline(&point_dots(line), width, st.cap, tol).iter());
+            out
+        }
     }
 }
 
+/// The subpaths of `line` that never leave their first point (`m` then `L` to the same point, as
+/// `.ai` files write dots, #1613), as dots: kurbo strokes nothing for them, where PDF and SVG
+/// viewers paint the cap. They lie along the x axis, which a projecting cap's square follows
+/// (SVG 2, "Path data": zero-length path segments).
+fn point_dots(line: &BezPath) -> Vec<Dot> {
+    let els = line.elements();
+    subpaths(line)
+        .into_iter()
+        .filter_map(|(r, _)| {
+            let sub = els.get(r)?;
+            let at = sub.first()?.end_point()?;
+            let still = sub.iter().all(|e| match e {
+                PathEl::MoveTo(p) | PathEl::LineTo(p) => *p == at,
+                PathEl::QuadTo(a, b) => *a == at && *b == at,
+                PathEl::CurveTo(a, b, c) => *a == at && *b == at && *c == at,
+                PathEl::ClosePath => true,
+            });
+            still.then_some(Dot { at, dir: kurbo::Vec2::new(1.0, 0.0), t: 0.0 })
+        })
+        .collect()
+}
+
 /// `line` stroked with `style`, to fill with the non-zero rule.
 ///
 /// kurbo offsets a closed subpath to both sides, as two contours. Once half the weight is more

crates/render/src/tests.rs

@@ -467,3 +467,39 @@ fn supersampled_art_leaves_no_seam_between_shapes_that_meet() {
     assert_eq!(supersample_factor(5000, 5000), None);
     assert_eq!(supersample_factor(40_000, 10), None);
 }
+
+/// #1613: a zero-length subpath (`m` then `L` to the same point, as `.ai` files write dots) is a
+/// dot as wide as the stroke: a disc under a round cap, a square under a projecting one, nothing
+/// under a butt cap (PDF 32000-1 8.5.3.2, SVG 2 "Path data" zero-length segments).
+#[test]
+fn zero_length_subpaths_draw_dots_with_their_cap() {
+    let dots = |cap: vectorcraft_doc::LineCap| {
+        let mut d = Document::new(100.0, 100.0);
+        let mut bp = BezPath::new();
+        for at in [(30.0, 50.0), (70.0, 50.0)] {
+            bp.move_to(at);
+            bp.line_to(at);
+        }
+        let id = d.alloc_id();
+        let mut n = Node::path(id, vectorcraft_geom::PathData::from_bezpath(&bp), Appearance::basic(Paint::None, Paint::solid(Color::BLACK), 10.0));
+        n.appearance.stroke_mut().unwrap().cap = cap;
+        let l = d.layers[0].id;
+        d.insert(Some(l), 0, n).unwrap();
+        render(&d)
+    };
+    let (black, white) = ([0, 0, 0, 255], [255, 255, 255, 255]);
+    let round = dots(vectorcraft_doc::LineCap::Round);
+    for x in [30, 70] {
+        assert_eq!(round.pixel(x, 50), black, "round dot at {x}");
+        assert_eq!(round.pixel(x + 2, 52), black, "inside the round dot at {x}");
+        assert_eq!(round.pixel(x + 4, 54), white, "the round dot's corner at {x}");
+    }
+    let square = dots(vectorcraft_doc::LineCap::Square);
+    for x in [30, 70] {
+        assert_eq!(square.pixel(x, 50), black, "square dot at {x}");
+        assert_eq!(square.pixel(x + 4, 54), black, "the square dot's corner at {x}");
+        assert_eq!(square.pixel(x + 6, 50), white, "past the square dot at {x}");
+    }
+    let butt = dots(vectorcraft_doc::LineCap::Butt);
+    assert_eq!(butt.pixels.iter().filter(|&&p| p != 255).count(), 0, "a butt cap draws no dot");
+}