Merge pull request #4828 from dotCooCoo/fix/brush-warp-mask

Brushes: opacity masks on art brush pieces bend with the art

crates/brush/src/warp.rs

@@ -41,7 +41,8 @@ const MASK_STEPS: usize = 32;
 /// space, so the art keeps its curves (#3926). Where that cannot be done in no more anchors than
 /// chords would take, the path is flattened with `flat_tol` (art space) and subdivided so no chord
 /// is longer than `max_du` along x, as it always was. Stroke widths scale by `width_scale`.
-/// Text, images and symbol instances can't bend and are dropped.
+/// Text, images and symbol instances can't bend and are dropped. The art of a linked opacity mask
+/// bends with the object it masks.
 pub(crate) fn warp_node(n: &Node, f: &dyn Fn(Point) -> Point, flat_tol: f64, max_du: f64, doc_tol: f64, width_scale: f64) -> Option<Node> {
     let mut out = n.clone();
     out.appearance.scale_strokes(width_scale);
@@ -63,9 +64,21 @@ pub(crate) fn warp_node(n: &Node, f: &dyn Fn(Point) -> Point, flat_tol: f64, max
         }
         _ => return None,
     }
+    map_mask(&mut out, |art| warp_node(art, f, flat_tol, max_du, doc_tol, width_scale));
     Some(out)
 }
 
+/// Replace the art of `n`'s linked opacity mask, if it has one, with what `map` makes of it. Where
+/// `map` draws nothing, the mask's art becomes an empty group.
+fn map_mask(n: &mut Node, map: impl FnOnce(&Node) -> Option<Node>) {
+    if let Some(m) = n.extras_if_any().and_then(|e| e.mask.as_mut())
+        && m.linked
+    {
+        let id = m.art.id;
+        m.art = Arc::new(map(&m.art).unwrap_or_else(|| Node::group(id, vec![])));
+    }
+}
+
 /// Each subpath of `p` through `f`: fitted cubics when they take no more anchors than the chords
 /// would, else the chords. Points `f` cannot place (not finite) are left out of the chords.
 fn warp_path(p: &PathData, f: &dyn Fn(Point) -> Point, flat_tol: f64, max_du: f64, fit_tol: f64) -> PathData {
@@ -338,7 +351,8 @@ fn affine_fit(f: &dyn Fn(Point) -> Point, b: Rect, tol: f64) -> Option<Affine> {
 /// Everything else matches [`warp_node`] deliberately, so curves are the only difference between
 /// the two routes: the same node kinds are kept and the rest dropped, `live` is cleared on every
 /// path, an empty path or a group left with no children is dropped, and strokes are scaled by
-/// `width_scale` at every level rather than by the transform's own factor.
+/// `width_scale` at every level rather than by the transform's own factor, the art of linked
+/// opacity masks included.
 fn affine_node(n: &Node, a: Affine, width_scale: f64) -> Option<Node> {
     let mut out = prepared(n, width_scale)?;
     out.transform(a, false);
@@ -365,6 +379,7 @@ fn prepared(n: &Node, width_scale: f64) -> Option<Node> {
         }
         _ => return None,
     }
+    map_mask(&mut out, |art| prepared(art, width_scale));
     Some(out)
 }
 
@@ -416,6 +431,7 @@ fn widen_strokes(n: &Node, factor: &dyn Fn(&Node) -> f64) -> Node {
     if let NodeKind::Group { children, .. } | NodeKind::Layer { children, .. } | NodeKind::Compound { children, .. } = &mut out.kind {
         *children = children.iter().map(|c| Arc::new(widen_strokes(c, factor))).collect();
     }
+    map_mask(&mut out, |art| Some(widen_strokes(art, factor)));
     out
 }
 
@@ -590,6 +606,9 @@ fn anchors_of(n: &Node) -> usize {
         if let Some(c) = n.children() {
             stack.extend(c.iter().map(Arc::as_ref));
         }
+        if let Some(m) = &n.extras().mask {
+            stack.push(&m.art);
+        }
     }
     total
 }
@@ -1133,4 +1152,52 @@ mod tests {
             }
         }
     }
+
+    /// A linked opacity mask on brush art bends and widens with the art, on a bent run and on a
+    /// straight one, so a mask drawn over the art still covers it. An unlinked mask stays put.
+    #[test]
+    fn a_linked_opacity_mask_bends_with_the_art() {
+        let b = Rect::new(0.0, -20.0, 40.0, 20.0);
+        let stroked = |id: u64| {
+            Node::path(
+                NodeId(id),
+                vectorcraft_geom::shapes::ellipse(b),
+                Appearance::basic(
+                    vectorcraft_color::Paint::solid(vectorcraft_color::Color::BLACK),
+                    vectorcraft_color::Paint::solid(vectorcraft_color::Color::BLACK),
+                    2.0,
+                ),
+            )
+        };
+        let masked = |linked: bool| {
+            let mut n = stroked(0);
+            let mut mask = vectorcraft_doc::OpacityMask::new(stroked(1), true);
+            mask.linked = linked;
+            n.extras_mut().mask = Some(Box::new(mask));
+            n
+        };
+        let round = vectorcraft_geom::shapes::ellipse(Rect::new(0.0, 0.0, 400.0, 400.0)).to_bezpath();
+        let bent_track = tracks(&round, 0.05).remove(0);
+        let mut line = BezPath::new();
+        line.move_to((0.0, 0.0));
+        line.line_to((320.0, 0.0));
+        let straight_track = tracks(&line, 0.01).remove(0);
+        let along = AlongMap::linear(b.width(), 100.0, 140.0);
+        for (name, t) in [("bent", &bent_track), ("straight", &straight_track)] {
+            let out = bend(t, &masked(true), b, along, 2.0).expect("the art is drawn");
+            let mask = out.extras().mask.as_ref().expect("the mask is kept");
+            assert_eq!(mask.art.kind, out.kind, "{name} run: the mask's art bends with the art it was drawn over");
+            assert_eq!(mask.art.appearance, out.appearance, "{name} run: the mask's strokes widen with the art's");
+
+            let out = bend(t, &masked(false), b, along, 2.0).expect("the art is drawn");
+            let mask = out.extras().mask.as_ref().expect("the mask is kept");
+            assert_eq!(*mask.art, stroked(1), "{name} run: an unlinked mask stays where it was");
+
+            let out = bend_widened(t, &masked(true), b, along, 2.0, &|_| 0.5).expect("the art is drawn");
+            let mask = out.extras().mask.as_ref().expect("the mask is kept");
+            assert_eq!(mask.art.kind, out.kind, "{name} run, widened: the mask's art bends with the art");
+            assert_eq!(mask.art.appearance, out.appearance, "{name} run, widened: the mask's strokes narrow with the art's");
+        }
+        assert_eq!(anchors_of(&masked(true)), 8, "the anchor budget counts the mask's art");
+    }
 }