Shapes: a speech bubble's wedge mirrors with its tip, at 7..10 twelfths on the far side as presetShapeDefinitions give it

crates/geom/src/preset.rs

@@ -1860,10 +1860,10 @@ fn wedge_rect(w: f64, h: f64, a0: f64, a1: f64, r: f64) -> Geometry {
     let r = r.min(w / 2.0).min(h / 2.0);
     // Walk clockwise from the top-left; insert the wedge on the edge facing the tip.
     let horiz = dx.abs() > dy.abs();
-    let (bx0, bx1) = (w * 5.0 / 12.0, w * 7.0 / 12.0);
-    let (by0, by1) = (h * 5.0 / 12.0, h * 7.0 / 12.0);
-    let (bx0, bx1) = if tip.x < w / 2.0 { (w * 2.0 / 12.0, w * 5.0 / 12.0) } else { (bx0 + w / 12.0 * 2.0 - w / 12.0 * 2.0, bx1 + w * 2.0 / 12.0) };
-    let (by0, by1) = if tip.y < h / 2.0 { (h * 2.0 / 12.0, h * 5.0 / 12.0) } else { (by0, by1 + h * 2.0 / 12.0) };
+    // The wedge's base: 2..5 twelfths of the edge on the tip's side of the centre when it is
+    // before it, 7..10 twelfths when after (presetShapeDefinitions' xg1/xg2, yg1/yg2).
+    let (bx0, bx1) = if tip.x < w / 2.0 { (w * 2.0 / 12.0, w * 5.0 / 12.0) } else { (w * 7.0 / 12.0, w * 10.0 / 12.0) };
+    let (by0, by1) = if tip.y < h / 2.0 { (h * 2.0 / 12.0, h * 5.0 / 12.0) } else { (h * 7.0 / 12.0, h * 10.0 / 12.0) };
     b.m(r, 0.0);
     if !inside && !horiz && dy < 0.0 {
         b.l(bx0, 0.0).l(tip.x, tip.y).l(bx1, 0.0);
@@ -2590,4 +2590,46 @@ mod tests {
             assert!(g.paths.iter().any(|p| p.stroke && p.fill == FillMode::None), "{name}: the curve is outlined");
         }
     }
+
+    /// The end points of a path's move/line elements, in order.
+    fn vertices(p: &BezPath) -> Vec<Point> {
+        p.elements()
+            .iter()
+            .filter_map(|e| match e {
+                kurbo::PathEl::MoveTo(q) | kurbo::PathEl::LineTo(q) => Some(*q),
+                _ => None,
+            })
+            .collect()
+    }
+
+    #[test]
+    fn wedge_callout_mirrors_with_its_tip() {
+        // A tip below and right of the centre draws the mirror image of the same tip on the left;
+        // the same for a tip right of the centre, above or below it. presetShapeDefinitions puts
+        // the wedge's base at 2..5 twelfths of the edge on the near side of the centre and at
+        // 7..10 twelfths on the far side.
+        let (w, h) = (240.0, 120.0);
+        // Sorted and deduplicated: the outline closes on the corner it starts from, which the
+        // mirror moves to the opposite corner.
+        let sorted = |mut v: Vec<Point>| {
+            v.sort_by(|a, b| a.x.total_cmp(&b.x).then(a.y.total_cmp(&b.y)));
+            v.dedup_by(|a, b| (*a - *b).hypot() < 1e-9);
+            v
+        };
+        for (right, left, flip_x) in [([10000.0, 80000.0], [-10000.0, 80000.0], true), ([80000.0, 10000.0], [80000.0, -10000.0], false)] {
+            let a = vertices(&build("wedgeRectCallout", w, h, &right).unwrap().paths[0].path);
+            let b = vertices(&build("wedgeRectCallout", w, h, &left).unwrap().paths[0].path);
+            let b: Vec<Point> = b.iter().map(|p| if flip_x { Point::new(w - p.x, p.y) } else { Point::new(p.x, h - p.y) }).collect();
+            let (a, b) = (sorted(a), sorted(b));
+            assert_eq!(a.len(), b.len(), "{right:?}: {a:?} vs mirrored {left:?}: {b:?}");
+            for (p, q) in a.iter().zip(&b) {
+                assert!((*p - *q).hypot() < 1e-6, "{right:?}: {a:?}\n is not the mirror of {left:?}: {b:?}");
+            }
+        }
+        // The bottom wedge of a tip right of the centre leaves the edge at 7/12 and 10/12 of the width.
+        let a = vertices(&build("wedgeRectCallout", w, h, &[10000.0, 80000.0]).unwrap().paths[0].path);
+        for x in [w * 7.0 / 12.0, w * 10.0 / 12.0] {
+            assert!(a.iter().any(|p| (p.x - x).abs() < 1e-6 && (p.y - h).abs() < 1e-6), "no wedge corner at ({x}, {h}): {a:?}");
+        }
+    }
 }