Selection tool: Shift+drag on a selected object moves it, constrained

Pressing with Shift on an object that was already selected toggled it
out of the selection at once and went idle, so the drag that followed
moved nothing. The toggle now waits for the release: a Shift-click
still takes the object out of the selection, while a Shift-drag moves
the selection constrained, as it already did for unselected objects
and when Shift was pressed mid-drag.

Fixes #224.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U9TrG4w49oSRYbP3cqxA3D

crates/tools/src/select.rs

@@ -21,6 +21,9 @@ enum State {
     Moving {
         start: Point,
         began: bool,
+        /// Shift-pressed on this selected object: released without a drag, it leaves the
+        /// selection.
+        deselect: Option<NodeId>,
     },
     Scaling {
         handle: Handle,
@@ -141,16 +144,19 @@ impl Tool for SelectionTool {
                     Some(h) => {
                         let top = h.top_object(cx.isolation);
                         let mut out = vec![];
+                        let mut deselect = None;
                         if m.shift {
-                            out.push(Action::Exec("select.toggle".into(), json!({ "id": top.0 })));
+                            // A Shift-click takes a selected object out of the selection when it
+                            // is released; a Shift-drag moves the selection, constrained.
                             if cx.selection.contains(top) {
-                                self.state = State::Idle;
-                                return out;
+                                deselect = Some(top);
+                            } else {
+                                out.push(Action::Exec("select.toggle".into(), json!({ "id": top.0 })));
                             }
                         } else if !cx.selection.contains(top) {
                             out.push(Action::Exec("select.set".into(), json!({ "ids": [top.0] })));
                         }
-                        self.state = State::Moving { start: p, began: false };
+                        self.state = State::Moving { start: p, began: false, deselect };
                         out
                     }
                     None => {
@@ -185,7 +191,7 @@ impl Tool for SelectionTool {
                     d = vectorcraft_geom::Vec2::new((b.x0 + d.x).round() - b.x0, (b.y0 + d.y).round() - b.y0);
                     self.guides.clear();
                 }
-                self.state = State::Moving { start, began: true };
+                self.state = State::Moving { start, began: true, deselect: None };
                 self.measure = Some((p, cx.offset_label(d.x, d.y)));
                 out.push(Action::Preview("object.transform".into(), json!({ "matrix": matrix_json(Affine::translate(d)), "copy": m.alt })));
                 out
@@ -215,12 +221,16 @@ impl Tool for SelectionTool {
                 self.state = State::Idle;
                 c.finish()
             }
-            (PointerKind::Up, State::Moving { began, .. }) => {
+            (PointerKind::Up, State::Moving { began, deselect, .. }) => {
                 self.state = State::Idle;
                 self.measure = None;
                 self.guides.clear();
                 self.targets = None;
-                if began { vec![Action::Commit] } else { vec![] }
+                match (began, deselect) {
+                    (true, _) => vec![Action::Commit],
+                    (false, Some(id)) => vec![Action::Exec("select.toggle".into(), json!({ "id": id.0 }))],
+                    (false, None) => vec![],
+                }
             }
             (PointerKind::Up, State::Scaling { .. } | State::Rotating { .. }) => {
                 self.state = State::Idle;
@@ -339,6 +349,48 @@ mod tests {
         assert_eq!(a, vec![Action::Commit]);
     }
 
+    #[test]
+    fn shift_drag_on_a_selected_object_moves_it_constrained() {
+        let (d, id) = doc_with_rect();
+        let mut s = Selection::default();
+        s.add(id);
+        let p = paint();
+        let cx = cx(&d, &s, &p);
+        let mut t = SelectionTool::default();
+        let shift = |kind, x, y| ev(kind, x, y).with_mods(Mods { shift: true, ..Mods::default() });
+        // Pressing keeps the selection: nothing is toggled yet.
+        assert!(t.pointer(&cx, &shift(PointerKind::Down, 150.0, 150.0)).is_empty());
+        let a = t.pointer(&cx, &shift(PointerKind::Drag, 190.0, 160.0));
+        assert_eq!(a[0], Action::Begin("Move".into()));
+        assert!(
+            matches!(&a[1], Action::Preview(c, v) if c == "object.transform"
+                && v["matrix"][4].as_f64().is_some_and(|x| x > 39.0) && v["matrix"][5] == 0.0),
+            "moved right, constrained to horizontal: {a:?}"
+        );
+        assert_eq!(t.pointer(&cx, &shift(PointerKind::Up, 190.0, 160.0)), vec![Action::Commit]);
+    }
+
+    #[test]
+    fn shift_click_toggles_an_object_on_release() {
+        let (d, id) = doc_with_rect();
+        let p = paint();
+        let shift = |kind, x, y| ev(kind, x, y).with_mods(Mods { shift: true, ..Mods::default() });
+        let toggle = vec![Action::Exec("select.toggle".into(), json!({"id": id.0}))];
+        // Selected: it leaves the selection when the click is released.
+        let mut s = Selection::default();
+        s.add(id);
+        let cx1 = cx(&d, &s, &p);
+        let mut t = SelectionTool::default();
+        assert!(t.pointer(&cx1, &shift(PointerKind::Down, 150.0, 150.0)).is_empty());
+        assert_eq!(t.pointer(&cx1, &shift(PointerKind::Up, 150.0, 150.0)), toggle);
+        // Not selected: it joins the selection at once, ready to be dragged.
+        let s = Selection::default();
+        let cx2 = cx(&d, &s, &p);
+        let mut t = SelectionTool::default();
+        assert_eq!(t.pointer(&cx2, &shift(PointerKind::Down, 150.0, 150.0)), toggle);
+        assert!(t.pointer(&cx2, &shift(PointerKind::Up, 150.0, 150.0)).is_empty());
+    }
+
     #[test]
     fn marquee_selects() {
         let (d, id) = doc_with_rect();