Project panel: items dropped on New Composition make a comp (#227)

Dragging Project items onto the Create a new Composition button at the
bottom of the Project panel did nothing. As in After Effects, the
button now takes the drop and runs File > New Comp from Selection with
the dragged items (the selection when the dragged item is in it): one
item becomes a comp of its size, frame rate and duration holding it,
and several open the New Composition from Selection dialog. The button
is outlined while items are dragged over it.

Test: project_items_dropped_on_new_comp_make_a_composition.

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

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

@@ -2,8 +2,9 @@
 //! search, item list with columns (Name, Label, then the visible optional columns: Type, Size,
 //! Media Duration, Frame Rate, File Path, Comment — shown or hidden from the header's context
 //! menu), folders (drag items into and out of them), renaming (Enter, or double-click the name),
-//! the label colour picker, and the bottom bar (interpret, new folder, new comp, bit depth,
-//! delete). Edits are `project.*` engine commands, so they are undoable.
+//! the label colour picker, and the bottom bar (interpret, new folder, new comp: click, or drop
+//! items on it for a comp from them, bit depth, delete). Edits are engine commands, so they are
+//! undoable.
 
 use std::sync::{Arc, Mutex};
 
@@ -699,6 +700,21 @@ pub fn show(app: &mut EffectcraftApp, ui: &mut egui::Ui, rect: Rect) {
                 _ => app.ui.status = "Interpret Footage: select a footage item".into(),
             }
         }
+        // Items dropped on Create a new Composition: New Comp from Selection with them (After
+        // Effects; several items ask how in its dialog).
+        if id == "newComp"
+            && let Some(DragPayload::Item(iid)) = egui::DragAndDrop::payload::<DragPayload>(&ctx).as_deref()
+            && ui.rect_contains_pointer(r)
+        {
+            p.rect_stroke(r, 4.0, Stroke::new(2.0, t.accent), egui::StrokeKind::Inside);
+            if ctx.input(|i| i.pointer.any_released()) {
+                if !app.session.state.project_selection.contains(&ItemId(*iid)) {
+                    app.session.state.project_selection = vec![ItemId(*iid)];
+                }
+                actions.push(("file.newCompFromSelection".into(), json!({})));
+                egui::DragAndDrop::clear_payload(&ctx);
+            }
+        }
         x += 26.0;
     }
     let depth = app.session.project.settings.bit_depth.label();

crates/ui-egui/tests/ui_drag_drop.rs

@@ -136,3 +136,32 @@ fn effects_dropped_on_the_viewer_go_on_the_layer_under_the_pointer() {
     let effects = |id: u64| comp.layer(effectcraft_engine::project::LayerId(id)).unwrap().effects().map_or(0, |fx| fx.groups().count());
     assert_eq!((effects(top), effects(middle)), (1, 0), "on Top, which is under the pointer");
 }
+
+/// #227: Project items dropped on Create a new Composition (the Project panel's footer) make a
+/// composition from them, as File ▸ New Comp from Selection does; several items ask how in its
+/// dialog.
+#[test]
+fn project_items_dropped_on_new_comp_make_a_composition() {
+    let (mut h, clip) = harness();
+    let comps = |h: &Harness<'_, EffectcraftApp>| h.state().session.project.comps().count();
+    let before = comps(&h);
+    let item = rect(&h, &format!("project.item.{clip}.name")).center();
+    let button = rect(&h, "project.newComp").center();
+    drag(&mut h, item, button, Modifiers::NONE);
+    assert_eq!(comps(&h), before + 1);
+    let comp = h.state().session.active_comp().unwrap();
+    assert_eq!((comp.width, comp.height, comp.duration.seconds()), (160, 90, 1.0), "the item's settings");
+    assert_eq!(stack(&h), ["Clip"], "holding the item");
+    assert_ne!(h.state().session.active_comp_id().map(|c| c.0), Some(clip), "a new comp, open");
+    assert!(h.state().dialog.is_none());
+
+    // Two selected items, one dragged: New Composition from Selection asks how.
+    let main = h.state().session.project.items.values().find(|i| i.name == "Main").unwrap().id;
+    h.state_mut().session.state.project_selection = vec![effectcraft_engine::project::ItemId(clip), main];
+    h.run_steps(2);
+    let item = rect(&h, &format!("project.item.{clip}.name")).center();
+    drag(&mut h, item, button, Modifiers::NONE);
+    assert_eq!(h.state().dialog, Some(effectcraft_ui_egui::Dialog::Form));
+    assert!(h.state().auto.find("form.field.single").is_some(), "the New Composition from Selection dialog");
+    assert_eq!(comps(&h), before + 1, "nothing made yet");
+}