Render: a dashed brush stroke keeps the layered path for object opacity

Follow-up to #3697 (CodeRabbit): a brush stroke is drawn as separate
pieces (draw_brush), so folding object opacity into its colour isn't exact.
A non-dashed brush stroke already counted as one paint before #3697; to
keep that change's scope, a dashed stroke counts as one paint only when it
has no brush. dashed_stroke_opacity_folds_into_its_colour checks that a
dashed brush stroke isn't folded; it fails without the change.

crates/render/src/lib.rs

@@ -2231,14 +2231,15 @@ fn single_plain_fill(n: &Node) -> bool {
 
 /// Number of visible painted fill/stroke items (opacity folding is exact only for one). A dashed
 /// stroke is one paint: its dashes are outlined into one path and filled once, so overlapping
-/// dashes don't darken where they overlap.
+/// dashes don't darken where they overlap. A dashed brush stroke isn't: its pieces are drawn one
+/// by one.
 fn painted_items(n: &Node) -> usize {
     n.appearance
         .items
         .iter()
         .filter(|i| match i {
             AppearanceItem::Fill(f) => f.visible && !f.paint.is_none() && matches!(f.paint, vectorcraft_color::Paint::Solid { .. }),
-            AppearanceItem::Stroke(s) => s.visible && !s.paint.is_none() && s.width > 0.0 && matches!(s.paint, vectorcraft_color::Paint::Solid { .. }),
+            AppearanceItem::Stroke(s) => s.visible && !s.paint.is_none() && s.width > 0.0 && matches!(s.paint, vectorcraft_color::Paint::Solid { .. }) && (s.dash.is_none() || s.brush.is_none()),
         })
         .count()
         .max(if n.appearance.items.iter().any(|i| matches!(i, AppearanceItem::Fill(f) if f.visible && !matches!(f.paint, vectorcraft_color::Paint::Solid { .. } | vectorcraft_color::Paint::None)) || matches!(i, AppearanceItem::Stroke(s) if s.visible && !matches!(s.paint, vectorcraft_color::Paint::Solid { .. } | vectorcraft_color::Paint::None))) { 2 } else { 0 })

crates/render/src/tests.rs

@@ -980,6 +980,9 @@ fn dashed_stroke_opacity_folds_into_its_colour() {
     };
     let mut d = Document::new(100.0, 100.0);
     assert_eq!(painted_items(&dashed(&mut d, 0.6, 1.0)), 1, "a dashed stroke takes the folded fast path");
+    let mut brushed = dashed(&mut d, 0.6, 1.0);
+    brushed.appearance.stroke_mut().unwrap().brush = Some("Calligraphic".into());
+    assert_ne!(painted_items(&brushed), 1, "a dashed brush stroke draws its pieces one by one: no folding");
     let folded = render(&doc(0.6, 1.0));
     let layered = render(&doc(1.0, 0.6));
     assert_ne!(folded.pixel(20, 40), [255, 255, 255, 255], "the stroke is drawn");