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Fix #309: Pen: Alt pressed mid-drag keeps the curve into the new anchor 

Pressing Alt while dragging out a smooth point set its incoming handle to
the anchor itself, so the segment just shaped turned straight. The Pen
now remembers the incoming handle it last previewed and keeps it while
Alt is held, so only the outgoing handle follows the pointer: a corner
with curves on both sides, as in the reference app. Alt held from the
start of the drag still gives an outgoing handle only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
theironchef 2026-10-07 03:38:33 -07:00 committed by bflatastic
parent 5cacbe36b3
commit bef928bf17
1 changed files with 42 additions and 3 deletions
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45
crates/tools/src/pen.rs
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@ -1,7 +1,8 @@
//! The Pen tool (P).
//!
//! Click adds a corner anchor; click-drag adds a smooth anchor with symmetric handles (Alt-drag
//! breaks the handles); Shift constrains to 45°. Clicking the first anchor closes the path.
//! Click adds a corner anchor; click-drag adds a smooth anchor with symmetric handles (Alt breaks
//! them: the incoming handle stays where it was when Alt went down and only the outgoing one
//! follows the pointer); Shift constrains to 45°. Clicking the first anchor closes the path.
//! Enter/Esc (or switching tools) ends the path. Clicking the end of a selected open path continues
//! it. The rubber-band preview shows the next segment. On a selected blend's spine a click adds a
//! point (on a point no key object sits on: deletes it).
@ -18,6 +19,8 @@ pub struct PenTool {
drawing: bool,
drag: Option<(Point, bool)>,
hover: Option<Point>,
/// The incoming handle of the anchor being dragged out, as last previewed.
in_h: Point,
}
/// The open path the pen is extending: the single selected open path.
@ -67,6 +70,7 @@ impl Tool for PenTool {
return vec![Action::Begin("Close Path".into()), Action::Preview("path.close".into(), json!({"id": id.0}))];
}
self.drag = Some((p, false));
self.in_h = p;
return vec![Action::Begin("Pen".into()), Action::Preview("path.appendAnchor".into(), json!({"id": id.0, "x": p.x, "y": p.y}))];
}
if let Some(acts) = spine_click(cx, p, tol) {
@ -107,7 +111,10 @@ impl Tool for PenTool {
json!({"id": id.0, "in": [2.0 * a.x - out_h.x, 2.0 * a.y - out_h.y], "independent": alt}),
)];
}
let in_h = if alt { a } else { a - (out_h - a) };
// Alt pressed mid-drag keeps the curve already shaped into the anchor: only the
// outgoing handle follows. Held from the start, the incoming handle stays retracted.
let in_h = if alt { self.in_h } else { a - (out_h - a) };
self.in_h = in_h;
vec![Action::Preview(
"path.appendAnchor".into(),
json!({"id": id.0, "x": a.x, "y": a.y, "in": [in_h.x, in_h.y], "out": [out_h.x, out_h.y]}),
@ -210,6 +217,38 @@ mod tests {
assert_eq!(t.pointer(&cx, &PointerEvent::new(PointerKind::Up, 10.0, 10.0)), vec![Action::Commit]);
}
#[test]
fn alt_pressed_mid_drag_keeps_the_incoming_handle() {
let (mut d, _) = doc_with_rect();
let l = d.layers[0].id;
let id = d.alloc_id();
let line = vectorcraft_geom::shapes::line(Point::new(10.0, 300.0), Point::new(60.0, 300.0));
d.insert(Some(l), 1, vectorcraft_doc::Node::path(id, line, vectorcraft_doc::Appearance::default_art())).unwrap();
let mut s = Selection::default();
s.set([id]);
let p = paint();
let cx = cx(&d, &s, &p);
let mut t = PenTool { drawing: true, ..PenTool::default() };
let alt = Mods { alt: true, ..Mods::default() };
let handles = |acts: Vec<Action>| match acts.as_slice() {
[Action::Preview(c, v)] if c == "path.appendAnchor" => (v["in"].clone(), v["out"].clone()),
other => panic!("not an anchor preview: {other:?}"),
};
t.pointer(&cx, &PointerEvent::new(PointerKind::Down, 400.0, 420.0));
let drag = PointerEvent::new(PointerKind::Drag, 450.0, 420.0);
assert_eq!(handles(t.pointer(&cx, &drag)), (json!([350.0, 420.0]), json!([450.0, 420.0])));
// Alt goes down: the curve shaped so far stays, and only the outgoing handle moves on.
let drag = PointerEvent::new(PointerKind::Drag, 450.0, 470.0).with_mods(alt);
assert_eq!(handles(t.pointer(&cx, &drag)), (json!([350.0, 420.0]), json!([450.0, 470.0])));
let drag = PointerEvent::new(PointerKind::Drag, 400.0, 480.0).with_mods(alt);
assert_eq!(handles(t.pointer(&cx, &drag)), (json!([350.0, 420.0]), json!([400.0, 480.0])));
assert_eq!(t.pointer(&cx, &PointerEvent::new(PointerKind::Up, 400.0, 480.0).with_mods(alt)), vec![Action::Commit]);
// Alt held from the start: the new anchor gets an outgoing handle only.
t.pointer(&cx, &PointerEvent::new(PointerKind::Down, 300.0, 440.0).with_mods(alt));
let drag = PointerEvent::new(PointerKind::Drag, 340.0, 440.0).with_mods(alt);
assert_eq!(handles(t.pointer(&cx, &drag)), (json!([300.0, 440.0]), json!([340.0, 440.0])));
}
#[test]
fn clicking_a_selected_blend_spine_adds_a_point() {
let (mut d, _) = doc_with_rect();