The widgets framework will call the PFNDRAWHANDLER with the same parameters normally passed to IDecorator_Draw(), and additionally passes an additional parameter that identifies a pointer to private data owned and managed by the application, which the application provides to the draw decorator at the time the draw handler is registered.
pCxt: A pointer to private data allocated and managed by the caller that has registered the draw handler with the draw decorator. This data pointer is passed into the draw handler, providing the callback with access to this private storage.
piCanvas: Pointer to the ICanvas interface that will provide drawing services to the decorator.
x: Horizontal position of the left side of the decorator, offset from the left side of the ICanvas object.
y: Vertical position of the top of the decorator, offset from the left side of the ICanvas object
typedef void (*PFNDRAWHANDLER)(void *pCxt, ICanvas *piCanvas, int x, int y);