#1284: double-clicking a shape tool adds a comp-sized shape layer

Double-click a shape tool in the toolbar to add a shape layer the size of the composition, at
its centre, for backgrounds, mattes and overlays, as After Effects does. It uses layer.newShape
with the tool's kind, so the undo label and the command are the same as drawing one.

Covered by tests::a_comp_sized_shape_layer_sits_on_the_comp_centre; the double-click itself is
not covered by an automated test.

Claude-Session: https://claude.ai/code/session_0136kZtXrYo5VUWEFxWduwUD

crates/engine/src/tests.rs

@@ -246,6 +246,18 @@ fn text_shape_mask_matte_parent() {
     assert_eq!(info["layers"].as_array().unwrap().len(), 2);
 }
 
+/// A shape layer the size of the comp and placed at its default position covers the frame: the
+/// Shape Tool's double-click (#1284) makes one this way, for backgrounds, mattes and overlays.
+#[test]
+fn a_comp_sized_shape_layer_sits_on_the_comp_centre() {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"width": 400, "height": 300, "duration": 2})).unwrap();
+    let sh = s.execute("layer.newShape", json!({"kind": "rect", "size": [400, 300], "fill": "#ff0000"})).unwrap()["layer"].as_u64().unwrap();
+    let l = s.active_comp().unwrap().layer(effectcraft_project::LayerId(sh)).unwrap().clone();
+    let pos = l.props.prop("transform/position").unwrap().value.clone();
+    assert!(matches!(pos, effectcraft_keyframe::Value::Vec3(p) if (p[0] - 200.0).abs() < 1e-9 && (p[1] - 150.0).abs() < 1e-9), "{pos:?}");
+}
+
 /// The toolbar's Fill / Stroke change a selected shape layer's paint (#205): a shape drawn
 /// without a stroke gets one, later edits change it, and the Contents "Add:" items (#206) include
 /// an empty Path and a Gradient Stroke that render.

crates/ui-egui/src/header.rs

@@ -82,6 +82,15 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
         {
             app.ui.status = e;
         }
+        // Double-click a shape tool: a shape layer filling the composition, centred, for
+        // backgrounds, mattes and overlays (as After Effects does).
+        if cur.is_shape()
+            && resp.double_clicked()
+            && let Some((w, h)) = app.session.active_comp().map(|c| (c.width, c.height))
+            && let Err(e) = crate::menus::invoke(app, ui.ctx(), "layer.newShape", json!({"kind": crate::panels::viewer::shape_kind(cur), "size": [w, h]}))
+        {
+            app.ui.status = e;
+        }
         if slot.len() > 1 {
             let held_for = resp.is_pointer_button_down_on().then(|| ui.input(|i| i.pointer.press_start_time().map(|s| i.time - s))).flatten();
             if let Some(seconds) = held_for

crates/ui-egui/src/panels/viewer.rs

@@ -2138,7 +2138,7 @@ struct ShapeDrag {
 }
 
 /// The kind `tool` draws, as `shape.newShape` / `layer.addMask` name it.
-fn shape_kind(tool: Tool) -> &'static str {
+pub(crate) fn shape_kind(tool: Tool) -> &'static str {
     match tool {
         Tool::Rectangle => "rect",
         Tool::RoundedRect => "rounded",