M8: a click with the Bend tool curves a sharp point, its handles along the line between its neighbours (#1875) (#1877)

* M8: a click with the Bend tool curves a sharp point, its handles along the line between its neighbours (#1875)

A release without movement on a sharp point between two segments runs ops::auto_smooth instead of cancelling; a curved point still sharpens, a drag still sets the handles by hand, an endpoint is left alone. Tests; docs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Vector edit hit test: the nearer of a handle's end and a point wins

A short path's handles end within the point's hit tolerance; a click on the point is on the point, one on the handle's end still takes the handle. Test short_handles_leave_their_point_clickable.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* Vector edit hit test: the nearer of a handle's end and a point is judged on the page

Candidates stay within the tolerance as before; ranking by page distance keeps a non-uniform scale from favouring the wrong one. Test a_handle_and_a_point_are_compared_on_the_page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Vector edit hit test: a handle wins a tie with a point, as before

A handle snapped onto another point stays selectable there. Test a_handle_on_another_point_is_still_the_handles (fails with the strict comparison).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

crates/engine/src/canvas/vectoredit.rs

@@ -403,7 +403,9 @@ fn visible_handles(net: &VectorNetwork, ve: &VectorEdit) -> Vec<(usize, bool)> {
 }
 
 /// Hit test in page coordinates with a tolerance in page units. Visible handles win, then
-/// vertices, then segments.
+/// vertices, then segments; between a handle and a point both within reach, the nearer one on
+/// the page, the handle on a tie (the handles of a short segment end a few pixels from their
+/// point, and a click on the point is on the point, #1875).
 pub fn hit(doc: &Document, ve: &VectorEdit, p: Point, tol: f64) -> Option<VHit> {
     let net = network(doc, ve.id)?;
     let w = doc.world_transform(ve.id);
@@ -414,17 +416,31 @@ pub fn hit(doc: &Document, ve: &VectorEdit, p: Point, tol: f64) -> Option<VHit>
     if !(lp.x.is_finite() && lp.y.is_finite()) {
         return None;
     }
-    for (si, start) in visible_handles(net, ve) {
-        let (Some(seg), Some(t)) = (net.segments.get(si), net.handle(si, start)) else { continue };
-        let Some(v) = net.vertices.get(if start { seg.a } else { seg.b }) else { continue };
-        if (Point::new(v.x + t.0, v.y + t.1) - lp).hypot() <= tl {
-            return Some(VHit::Handle { seg: si, start });
-        }
-    }
-    let nearest_vertex =
-        net.vertices.iter().enumerate().map(|(i, v)| (i, (v.point() - lp).hypot())).filter(|(_, d)| *d <= tl).min_by(|a, b| a.1.total_cmp(&b.1));
-    if let Some((index, _)) = nearest_vertex {
-        return Some(VHit::Vertex { index });
+    // Candidates are within the tolerance as before; the nearest is judged on the page, where a
+    // non-uniform scale doesn't distort it.
+    let on_page = |q: Point| (w * q - p).hypot();
+    let nearest_handle = visible_handles(net, ve)
+        .into_iter()
+        .filter_map(|(si, start)| {
+            let (seg, t) = (net.segments.get(si)?, net.handle(si, start)?);
+            let v = net.vertices.get(if start { seg.a } else { seg.b })?;
+            let end = Point::new(v.x + t.0, v.y + t.1);
+            ((end - lp).hypot() <= tl).then(|| ((si, start), on_page(end)))
+        })
+        .min_by(|a, b| a.1.total_cmp(&b.1));
+    let nearest_vertex = net
+        .vertices
+        .iter()
+        .enumerate()
+        .filter(|(_, v)| (v.point() - lp).hypot() <= tl)
+        .map(|(i, v)| (i, on_page(v.point())))
+        .min_by(|a, b| a.1.total_cmp(&b.1));
+    match (nearest_handle, nearest_vertex) {
+        // A tie (a handle's end on another point) goes to the handle, as handles always won before.
+        (Some(((seg, start), dh)), Some((_, dv))) if dh <= dv => return Some(VHit::Handle { seg, start }),
+        (Some(((seg, start), _)), None) => return Some(VHit::Handle { seg, start }),
+        (_, Some((index, _))) => return Some(VHit::Vertex { index }),
+        (None, None) => {}
     }
     use figcraft_geom::kurbo::ParamCurveNearest;
     let nearest_seg = (0..net.segments.len())

crates/engine/src/canvas/vectoredit/pointer.rs

@@ -1072,12 +1072,18 @@ impl Session {
                 }
             }
             VGesture::BendVertex { v, moved, smooth, .. } => {
+                let id = ve.id;
                 if moved {
                     self.commit_interaction()?;
                 } else if smooth {
-                    let id = ve.id;
                     self.preview(|doc, _| edit(doc, id, |net| ops::make_sharp(net, v)))?;
                     self.commit_interaction()?;
+                } else if network(self.doc()?, id).is_some_and(|n| n.incident(v).len() == 2) {
+                    // "Click on a point or path where you want to add a curve" (Edit vector
+                    // layers): a sharp point between two segments gets handles along the line
+                    // between its neighbours (#1875); an endpoint has nothing to curve.
+                    self.preview(|doc, _| edit(doc, id, |net| ops::auto_smooth(net, v)))?;
+                    self.commit_interaction()?;
                 } else {
                     self.cancel_interaction()?;
                 }

crates/engine/src/canvas/vectoredit/tests.rs

@@ -119,6 +119,16 @@ fn bend_tool_smooths_and_sharpens_points() {
     let n = net(&s, id);
     let v = vertex_at(&n, 100.0, 0.0);
     assert!(n.incident(v).iter().all(|(s, st)| n.handle(*s, *st) == Some((0.0, 0.0))), "a click sharpens it");
+    // Clicked again, the sharp corner curves: handles along the line between its neighbours
+    // (0,0) and (100,100), a third of the way to each (the box refits around the bulge, so the
+    // point is found by its index).
+    click(&mut s, 100.0, 0.0);
+    let n = net(&s, id);
+    assert_eq!(n.mirroring(v), HandleMirroring::Angle);
+    for (seg, st) in n.incident(v) {
+        let h = n.handle(seg, st).unwrap();
+        assert!((h.0.abs() - 100.0 / 3.0 / 2f64.sqrt()).abs() < 1e-6 && (h.0 - h.1).abs() < 1e-6, "along the neighbours' line: {h:?}");
+    }
     // ⌘-drag on a segment with the Move tool bends it.
     ex(&mut s, "vector.edit.tool", json!({"tool": "move"}));
     let mut down = ev(PointerKind::Down, 0.0, 50.0);
@@ -130,6 +140,123 @@ fn bend_tool_smooths_and_sharpens_points() {
     assert!(b.x0 < -25.0, "bent outwards: {b:?}");
 }
 
+/// #1875: a line whose middle point was moved off the line, clicked with the Bend tool, curves
+/// there ("Click on a point or path where you want to add a curve", Edit vector layers): the
+/// handles run along the line between the neighbours, a third of the way to each, in one undo
+/// step; an endpoint is left alone; a click on the curved point makes it sharp again.
+#[test]
+fn a_bend_click_curves_a_sharp_point_between_its_neighbours() {
+    let mut s = Session::new();
+    let r = ex(&mut s, "vector.create", json!({"points": [[0, 0], [50, 30], [100, 0]], "closed": false}));
+    let id = crate::params::id_of(&r["id"]).unwrap();
+    ex(&mut s, "vector.edit.begin", json!({"id": id}));
+    ex(&mut s, "vector.edit.tool", json!({"tool": "bend"}));
+    let (v, end) = (vertex_at(&net(&s, id), 50.0, 30.0), vertex_at(&net(&s, id), 0.0, 0.0));
+    let before = s.undo_depth().0;
+    click(&mut s, 50.0, 30.0);
+    let n = net(&s, id);
+    let reach = (50f64.powi(2) + 30f64.powi(2)).sqrt() / 3.0;
+    for (seg, st) in n.incident(v) {
+        let h = n.handle(seg, st).unwrap();
+        assert!((h.0.abs() - reach).abs() < 1e-6 && h.1.abs() < 1e-6, "along the neighbours' line, a third of the way: {h:?}");
+    }
+    assert_eq!(n.mirroring(v), HandleMirroring::Angle);
+    assert_eq!(s.undo_depth().0, before + 1, "one undo step");
+    // An endpoint has nothing to curve: the click changes nothing and leaves no undo step.
+    click(&mut s, 0.0, 0.0);
+    let n = net(&s, id);
+    assert!(n.incident(end).iter().all(|(sg, st)| n.handle(*sg, *st) == Some((0.0, 0.0))));
+    assert_eq!(s.undo_depth().0, before + 1);
+    // The curved point clicked again is sharp again.
+    click(&mut s, 50.0, 30.0);
+    let n = net(&s, id);
+    assert!(n.incident(v).iter().all(|(sg, st)| n.handle(*sg, *st) == Some((0.0, 0.0))));
+}
+
+/// Between a handle's end and a point both within reach, the nearer on the page wins, also under a
+/// non-uniform scale (10× wide here), where local distances would pick the point.
+#[test]
+fn a_handle_and_a_point_are_compared_on_the_page() {
+    let mut s = Session::new();
+    let r = ex(&mut s, "vector.create", json!({"points": [[0, 0], [5, 0]], "closed": false}));
+    let id = crate::params::id_of(&r["id"]).unwrap();
+    {
+        let node = s.doc_mut().unwrap().get_mut(id).unwrap();
+        let mut n = VectorNetwork::default();
+        n.vertices.push(figcraft_doc::Vertex::new(0.0, 0.0));
+        n.vertices.push(figcraft_doc::Vertex::new(5.0, 0.0));
+        let mut seg = figcraft_doc::Segment::line(0, 1);
+        seg.ta = (0.5, -0.9);
+        n.segments.push(seg);
+        node.kind = figcraft_doc::NodeKind::Vector { network: n };
+        node.transform = figcraft_geom::Affine::scale_non_uniform(10.0, 1.0);
+    }
+    ex(&mut s, "vector.edit.begin", json!({"id": id}));
+    ex(&mut s, "vector.edit.select", json!({"vertices": [0]}));
+    let doc = s.doc().unwrap().clone();
+    // On the page the point is at (0, 0) and its handle's end at (5, -0.9): from (4, 0) the
+    // handle's end is 1.3 away and the point 4, though locally the point is the nearer.
+    assert_eq!(hit(&doc, &ve(&s), pt(4.0, 0.0), 6.0), Some(VHit::Handle { seg: 0, start: true }));
+    assert_eq!(hit(&doc, &ve(&s), pt(0.0, 0.0), 6.0), Some(VHit::Vertex { index: 0 }));
+}
+
+/// A handle whose end lies exactly on another point (snapped there) can still be taken there: on a
+/// tie the handle wins, as handles always did.
+#[test]
+fn a_handle_on_another_point_is_still_the_handles() {
+    let mut s = Session::new();
+    let r = ex(&mut s, "vector.create", json!({"points": [[0, 0], [10, 0]], "closed": false}));
+    let id = crate::params::id_of(&r["id"]).unwrap();
+    {
+        let node = s.doc_mut().unwrap().get_mut(id).unwrap();
+        let mut n = VectorNetwork::default();
+        n.vertices.push(figcraft_doc::Vertex::new(0.0, 0.0));
+        n.vertices.push(figcraft_doc::Vertex::new(10.0, 0.0));
+        let mut seg = figcraft_doc::Segment::line(0, 1);
+        seg.ta = (10.0, 0.0);
+        n.segments.push(seg);
+        node.kind = figcraft_doc::NodeKind::Vector { network: n };
+        node.transform = figcraft_geom::Affine::IDENTITY;
+    }
+    ex(&mut s, "vector.edit.begin", json!({"id": id}));
+    ex(&mut s, "vector.edit.select", json!({"vertices": [0]}));
+    let doc = s.doc().unwrap().clone();
+    // Where the points are on the page now (entering edit mode may refit the layer's box).
+    let n = net(&s, id);
+    let w = doc.world_transform(id);
+    let (p0, p1) = (w * n.vertices[0].point(), w * n.vertices[1].point());
+    // Point 0's handle ends on point 1: there the handle; on point 0, the point.
+    assert_eq!(hit(&doc, &ve(&s), p1, 6.0), Some(VHit::Handle { seg: 0, start: true }));
+    assert_eq!(hit(&doc, &ve(&s), p0, 6.0), Some(VHit::Vertex { index: 0 }));
+}
+
+/// A short path's handles end a few pixels from their point: a click on the point is still on the
+/// point (the nearer of the two wins), so the Bend tool can sharpen it again, while a click on the
+/// handle's end still takes the handle.
+#[test]
+fn short_handles_leave_their_point_clickable() {
+    let mut s = Session::new();
+    let r = ex(&mut s, "vector.create", json!({"points": [[0, 0], [6, 10], [12, 0]], "closed": false}));
+    let id = crate::params::id_of(&r["id"]).unwrap();
+    ex(&mut s, "vector.edit.begin", json!({"id": id}));
+    ex(&mut s, "vector.edit.tool", json!({"tool": "bend"}));
+    let v = vertex_at(&net(&s, id), 6.0, 10.0);
+    click(&mut s, 6.0, 10.0);
+    let n = net(&s, id);
+    let curved = |n: &VectorNetwork| n.incident(v).iter().all(|(sg, st)| n.handle(*sg, *st).is_some_and(|h| h != (0.0, 0.0)));
+    assert!(curved(&n));
+    let reach = (6f64.powi(2) + 10f64.powi(2)).sqrt() / 3.0;
+    assert!(reach < 6.0, "the handles end within the 6 px hit tolerance: {reach}");
+    // A click on the handle's end takes the handle (nothing changes); one on the point sharpens it.
+    let (sg, st) = n.incident(v)[0];
+    let h = n.handle(sg, st).unwrap();
+    click(&mut s, 6.0 + h.0, 10.0 + h.1);
+    assert!(curved(&net(&s, id)), "the handle's end is the handle's");
+    click(&mut s, 6.0, 10.0);
+    let n = net(&s, id);
+    assert!(n.incident(v).iter().all(|(sg, st)| n.handle(*sg, *st) == Some((0.0, 0.0))), "the point is the point's: sharp again");
+}
+
 #[test]
 fn paint_bucket_fills_and_unfills_areas() {
     let mut s = Session::new();