Add CanvasPointer callback for node widgets (#363)

* Add CanvasPointer callback for node widgets

* Add API documentation

* nit - Docs

src/CanvasPointer.ts

@@ -5,6 +5,11 @@ import { dist2 } from "./measure"
 /**
  * Allows click and drag actions to be declared ahead of time during a pointerdown event.
  *
+ * By default, it retains the most recent event of each type until it is reset (on pointerup).
+ * - {@link eDown}
+ * - {@link eMove}
+ * - {@link eUp}
+ *
  * Depending on whether the user clicks or drags the pointer, only the appropriate callbacks are called:
  * - {@link onClick}
  * - {@link onDoubleClick}

src/LGraphCanvas.ts

@@ -2517,6 +2517,13 @@ export class LGraphCanvas {
 
   #processWidgetClick(e: CanvasPointerEvent, node: LGraphNode, widget: IWidget) {
     const { pointer } = this
+
+    // Custom widget - CanvasPointer
+    if (typeof widget.onPointerDown === "function") {
+      const handled = widget.onPointerDown(pointer, node, this)
+      if (handled) return
+    }
+
     const width = widget.width || node.width
 
     const oldValue = widget.value

src/types/widgets.ts

@@ -1,5 +1,5 @@
 import { CanvasColour, Point, Size } from "../interfaces"
-import type { LGraphCanvas, LGraphNode } from "../litegraph"
+import type { CanvasPointer, LGraphCanvas, LGraphNode } from "../litegraph"
 import type { CanvasMouseEvent, CanvasPointerEvent } from "./events"
 
 export interface IWidgetOptions<TValue = unknown> extends Record<string, unknown> {
@@ -151,4 +151,19 @@ export interface IBaseWidget<TElement extends HTMLElement = HTMLElement> {
     H: number,
   ): void
   computeSize?(width: number): Size
+
+  /**
+   * Callback for pointerdown events, allowing custom widgets to register callbacks to occur
+   * for all {@link CanvasPointer} events.
+   *
+   * This callback is operated early in the pointerdown logic; actions that prevent it from firing are:
+   * - `Ctrl + Drag` Multi-select
+   * - `Alt + Click/Drag` Clone node
+   * @param pointer The CanvasPointer handling this event
+   * @param node The node this widget belongs to
+   * @param canvas The LGraphCanvas where this event originated
+   * @return Returning `true` from this callback forces Litegraph to ignore the event and
+   * not process it any further.
+   */
+  onPointerDown(pointer: CanvasPointer, node: LGraphNode, canvas: LGraphCanvas): boolean
 }