Render: moved stretched type redraws where its strokes reach

Follows #3484: characters' strokes stretch with the type, past what its scale factor covers.

crates/doc/src/text.rs

@@ -1713,18 +1713,17 @@ impl TextObject {
     /// How far the characters' strokes paint past their glyphs, in document space: they scale
     /// with the type.
     pub fn char_stroke_outset(&self) -> f64 {
-        self.char_strokes(CharStyle::stroke_outset)
+        let k = crate::node::Scaling::factor(self.xf).unwrap_or(1.0);
+        self.runs.iter().map(|r| r.style.stroke_outset()).fold(0.0, f64::max) * k
     }
     /// How far the characters' strokes can paint past their glyphs, their miter spikes and square
     /// caps included ([`StrokeLayer::reach`]), in document space: what a change of the type must
-    /// redraw. The visual bounds take [`Self::char_stroke_outset`].
+    /// redraw. They stretch with the type, so this is as far as its transform takes them on either
+    /// axis. The visual bounds take [`Self::char_stroke_outset`].
     pub fn char_stroke_reach(&self) -> f64 {
-        self.char_strokes(|style| if style.has_stroke() { style.stroke_layer().reach() } else { 0.0 })
-    }
-    /// The farthest `outset` of the characters' styles, scaled with the type.
-    fn char_strokes(&self, outset: impl Fn(&CharStyle) -> f64) -> f64 {
-        let k = crate::node::Scaling::factor(self.xf).unwrap_or(1.0);
-        self.runs.iter().map(|r| outset(&r.style)).fold(0.0, f64::max) * k
+        let reach = self.runs.iter().filter(|r| r.style.has_stroke()).map(|r| r.style.stroke_layer().reach()).fold(0.0, f64::max);
+        let [a, b, c, d, ..] = self.xf.as_coeffs();
+        reach * (a.abs() + c.abs()).max(b.abs() + d.abs())
     }
     pub fn transform(&mut self, a: Affine) {
         self.xf = a * self.xf;

crates/render/src/tests_changed.rs

@@ -235,3 +235,26 @@ fn an_edit_while_a_pattern_is_edited_changes_everything() {
     new.node_mut(loose).unwrap().transform(Affine::translate((7.0, 3.0)), false);
     assert_eq!(changed(&old, &new), Changed::Everything);
 }
+
+/// Type stretched more on one axis than its area grows: its characters' strokes stretch with it.
+#[test]
+fn moving_stretched_type_changes_where_its_stretched_strokes_reach() {
+    let mut old = Document::new(110.0, 80.0);
+    let l = old.layers[0].id;
+    let style = vectorcraft_doc::text::CharStyle {
+        size: 4.0,
+        stroke: Paint::solid(Color::BLACK),
+        stroke_width: 1.0,
+        stroke_join: vectorcraft_doc::LineJoin::Miter,
+        stroke_miter_limit: 10.0,
+        ..Default::default()
+    };
+    let mut t = vectorcraft_doc::text::TextObject::point(Point::ZERO, "VAWV", style);
+    t.cached_bounds = Some(vectorcraft_text::layout(vectorcraft_text::FontDb::global(), &t).bounds);
+    // Its area stays, so its scale factor is 1, while it grows ten times as wide.
+    t.xf = Affine::translate((10.0, 40.0)) * Affine::scale_non_uniform(10.0, 0.1);
+    let text = old.insert(Some(l), 0, Node::new(NodeId(0), NodeKind::Text(Box::new(t)))).unwrap();
+    let mut new = old.clone();
+    new.node_mut(text).unwrap().transform(Affine::translate((9.0, 7.0)), false);
+    area(redraw(&old, &new));
+}