Live Paint: the Live Paint tools skip hidden edges

An edge hidden on its own (for example with Object > Hide) while its
Live Paint group stays visible could still be highlighted, selected or
stroked, and a hidden edge nearer the pointer kept a visible one from
being picked.

lp_part_at now takes the nearest visible edge (visible_edge_near), inside
and outside the faces, for the hover, the Live Paint Selection click and
the Bucket's Shift-click. The Bucket's Shift-click sends nothing where no
edge is highlighted, and livePaint.strokeEdge also skips hidden edges, so
the Bucket strokes the edge it highlights.

crates/engine/src/cmd/buildcmds.rs

@@ -766,7 +766,7 @@ fn lp_stroke_edge(s: &mut Session, p: &Value) -> Result<Value> {
     let tol = f64_or(p, "tolerance", 4.0).clamp(0.0, 1000.0);
     let edge = s.edit("Live Paint Bucket", |d, _| {
         let n = d.node(g).filter(|n| is_live_paint(n)).ok_or_else(|| bad(C, format!("{g} is not a Live Paint group")))?;
-        let eid = edge_near(n, pt, tol).map(|e| e.id).ok_or_else(|| EngineError::Other("no Live Paint edge near that point".into()))?;
+        let eid = b::visible_edge_near(n, pt, tol).map(|e| e.id).ok_or_else(|| EngineError::Other("no Live Paint edge near that point".into()))?;
         let e = d.node_mut(eid).ok_or(EngineError::NoNode(eid))?;
         e.appearance.set_stroke(paint.clone());
         if let Some(st) = e.appearance.stroke_mut() {

crates/engine/src/tests_build.rs

@@ -531,6 +531,28 @@ fn live_paint_stroke_edge() {
     assert!(s.execute("livePaint.strokeEdge", &json!({"group": g.0, "point": [300, 300]})).is_err());
 }
 
+#[test]
+fn live_paint_stroke_edge_skips_hidden_edges() {
+    let mut s = session();
+    let g = live(&mut s);
+    // The vertical edge at x=100 is hidden on its own; the group stays visible.
+    let vertical_at = |s: &Session, x: f64| -> Vec<u64> {
+        vectorcraft_tools::builder::edges(&node(s, g))
+            .iter()
+            .filter(|e| e.geometric_bounds().is_some_and(|bb| (bb.x0 - x).abs() < 1e-6 && (bb.x1 - x).abs() < 1e-6))
+            .map(|e| e.id.0)
+            .collect()
+    };
+    let hidden = vertical_at(&s, 100.0);
+    assert!(!hidden.is_empty());
+    s.execute("object.setProps", &json!({"ids": hidden, "visible": false})).unwrap();
+    // 1 pt from the hidden edge, the nearest visible edge within the tolerance is the one at x=50.
+    let r = s.execute("livePaint.strokeEdge", &json!({"group": g.0, "point": [99, 50], "tolerance": 60})).unwrap();
+    assert!(vertical_at(&s, 50.0).contains(&r["edge"].as_u64().unwrap()), "{r}");
+    // With only the hidden edge within the tolerance, no edge is stroked.
+    assert!(s.execute("livePaint.strokeEdge", &json!({"group": g.0, "point": [99, 50]})).is_err());
+}
+
 #[test]
 fn live_paint_release_and_expand() {
     let mut s = session();