Add Alt+Drag layer duplication to Layers Panel

frontend/src/components/panels/Layers.svelte

@@ -66,6 +66,11 @@
 	let justFinishedDrag = false; // Used to prevent click events after a drag
 	let dragInPanel = false;
 
+	// Alt+Drag duplication
+	let altKeyPressedDuringDrag = false;
+	let originalLayersBeforeDuplication: bigint[] | undefined = undefined;
+	let duplicatedLayerIds: bigint[] | undefined = undefined;
+
 	// Interactive clipping
 	let layerToClipUponClick: LayerListingInfo | undefined = undefined;
 	let layerToClipAltKeyPressed = false;
@@ -107,6 +112,8 @@
 		addEventListener("pointermove", draggingPointerMove);
 		addEventListener("mousedown", draggingMouseDown);
 		addEventListener("keydown", draggingKeyDown);
+		addEventListener("keyup", draggingKeyUp);
+		addEventListener("blur", () => internalDragState?.active && abortDrag());
 
 		addEventListener("pointermove", clippingHover);
 		addEventListener("keydown", clippingKeyPress);
@@ -124,6 +131,7 @@
 		removeEventListener("pointermove", draggingPointerMove);
 		removeEventListener("mousedown", draggingMouseDown);
 		removeEventListener("keydown", draggingKeyDown);
+		removeEventListener("keyup", draggingKeyUp);
 
 		removeEventListener("pointermove", clippingHover);
 		removeEventListener("keydown", clippingKeyPress);
@@ -469,11 +477,43 @@
 		abortDrag();
 	}
 
+	async function startDuplicates() {
+		originalLayersBeforeDuplication = [...$nodeGraph.selected];
+		editor.handle.duplicateSelectedLayers();
+
+		await tick();
+		duplicatedLayerIds = [...$nodeGraph.selected];
+	}
+
+	function stopDuplicates() {
+		if (!originalLayersBeforeDuplication || !duplicatedLayerIds) return;
+
+		duplicatedLayerIds.forEach(layerId => {
+			editor.handle.deleteNode(layerId);
+		});
+
+		editor.handle.deselectAllLayers();
+		originalLayersBeforeDuplication.forEach((layerId, index) => {
+			const ctrl = index > 0;
+			editor.handle.selectLayer(layerId, ctrl, false);
+		});
+
+		originalLayersBeforeDuplication = undefined;
+		duplicatedLayerIds = undefined;
+	}
+
 	function abortDrag() {
+		if (altKeyPressedDuringDrag && originalLayersBeforeDuplication) {
+			stopDuplicates();
+		}
+
 		internalDragState = undefined;
 		draggingData = undefined;
 		fakeHighlightOfNotYetSelectedLayerBeingDragged = undefined;
 		dragInPanel = false;
+		altKeyPressedDuringDrag = false;
+		originalLayersBeforeDuplication = undefined;
+		duplicatedLayerIds = undefined;
 	}
 
 	function draggingMouseDown(e: MouseEvent) {
@@ -489,6 +529,18 @@
 			justFinishedDrag = true;
 			abortDrag();
 		}
+
+		if (e.key === "Alt" && !altKeyPressedDuringDrag) {
+			altKeyPressedDuringDrag = true;
+			startDuplicates();
+		}
+	}
+
+	function draggingKeyUp(e: KeyboardEvent) {
+		if (e.key === "Alt" && altKeyPressedDuringDrag) {
+			altKeyPressedDuringDrag = false;
+			stopDuplicates();
+		}
 	}
 
 	function fileDragOver(e: DragEvent) {

frontend/wasm/src/editor_api.rs

@@ -665,6 +665,13 @@ impl EditorHandle {
 		self.dispatch(message);
 	}
 
+	/// Duplicate the currently selected layers
+	#[wasm_bindgen(js_name = duplicateSelectedLayers)]
+	pub fn duplicate_selected_layers(&self) {
+		let message = DocumentMessage::DuplicateSelectedLayers;
+		self.dispatch(message);
+	}
+
 	/// Move a layer to within a folder and placed down at the given index.
 	/// If the folder is `None`, it is inserted into the document root.
 	/// If the insert index is `None`, it is inserted at the start of the folder.