Ellipse: dragging a pie widget on the canvas sets its pie angle

The Selection tool shows two pie widgets just outside a selected live
ellipse while the bounding box shows: one at the Pie Start Angle and
one at the Pie End Angle. Dragging one sets its angle to the angle of
the outline's point that lies in the direction of the pointer from the
ellipse's center, in one undo step, through `object.setLiveShape`'s
`pieStart` or `pieEnd`. Double-clicking one makes the ellipse whole
again (0° to 360°). Where the two widgets coincide, as on a whole
ellipse, a press takes the End widget.

Docs: docs/target-app-parity.md, docs/ui-parity.md.

crates/engine/src/tests_livecorners.rs

@@ -331,6 +331,56 @@ fn an_ellipse_takes_pie_angles_and_inverts() {
     assert!(s.execute("object.setLiveShape", &json!({"pieStart": "half"})).is_err());
 }
 
+/// The Selection tool's pie widgets: dragging the End widget from 0° to straight up sets Pie End
+/// Angle to 90 in one undo step; on an inverted pie a drag moves only the dragged angle; a
+/// double-click on a widget makes the ellipse whole again in one step.
+#[test]
+fn dragging_and_double_clicking_the_pie_widgets() {
+    use vectorcraft_tools::{Mods, PointerEvent, PointerKind};
+    let mut s = Session::new();
+    s.execute("file.new", &json!({"width": 300, "height": 300})).unwrap();
+    let id = NodeId(s.execute("shape.ellipse", &json!({"x": 50, "y": 100, "width": 200, "height": 100})).unwrap()["id"].as_u64().unwrap());
+    let pie = |s: &Session| match &s.doc().unwrap().doc.node(id).unwrap().kind {
+        NodeKind::Path { live: Some(l), .. } => match &**l {
+            LiveShape::Ellipse { pie, .. } => *pie,
+            k => panic!("{k:?}"),
+        },
+        k => panic!("{k:?}"),
+    };
+    let near = |a: (f64, f64), b: (f64, f64)| (a.0 - b.0).abs() < 1e-9 && (a.1 - b.1).abs() < 1e-9;
+    let steps = |s: &Session| s.doc().unwrap().history.undo.len();
+    let v = ViewInfo::default();
+    s.select_tool("selection", v).unwrap();
+    let gesture = |s: &mut Session, events: &[(PointerKind, f64, f64)]| {
+        for (kind, x, y) in events {
+            s.pointer(&PointerEvent::new(*kind, *x, *y).with_mods(Mods::default()), v).unwrap();
+        }
+    };
+    // The center is (150, 150); both widgets of the whole ellipse sit 12 pt right of (250, 150).
+    let n = steps(&s);
+    gesture(&mut s, &[(PointerKind::Down, 262.0, 150.0), (PointerKind::Drag, 150.0, 20.0), (PointerKind::Up, 150.0, 20.0)]);
+    assert!(near(pie(&s), (0.0, 90.0)), "{:?}", pie(&s));
+    assert_eq!(steps(&s), n + 1);
+    // Inverted, the pie runs from 90° to 360°: dragging the End widget (back at 0°) to 270°
+    // leaves the start at 90°.
+    s.execute("object.setLiveShape", &json!({"invertPie": true})).unwrap();
+    assert!(near(pie(&s), (90.0, 360.0)));
+    gesture(&mut s, &[(PointerKind::Down, 262.0, 150.0), (PointerKind::Drag, 150.0, 280.0), (PointerKind::Up, 150.0, 280.0)]);
+    assert!(near(pie(&s), (90.0, 270.0)), "{:?}", pie(&s));
+    // The Start widget sits 12 pt above the top of the outline, at 90°.
+    let n = steps(&s);
+    gesture(
+        &mut s,
+        &[(PointerKind::Down, 150.0, 88.0), (PointerKind::Up, 150.0, 88.0), (PointerKind::Down, 150.0, 88.0), (PointerKind::Up, 150.0, 88.0)],
+    );
+    assert_eq!(steps(&s), n, "two clicks record no undo step");
+    gesture(&mut s, &[(PointerKind::DoubleClick, 150.0, 88.0)]);
+    assert_eq!(pie(&s), (0.0, 360.0));
+    assert_eq!(steps(&s), n + 1);
+    s.execute("edit.undo", &json!({})).unwrap();
+    assert!(near(pie(&s), (90.0, 270.0)));
+}
+
 /// #812: a polygon's Polygon Properties: its angle, radius and side length, each one undo step;
 /// Make Sides Equal after an uneven scale; bad values are errors.
 #[test]