wParam = (DWORD) (LPVOID) prc;
lParam = 0;
Notifies a rendering driver that the window specified for ICM_DRAW_BEGIN needs to be redrawn. The window has moved or become temporarily obscured.
This message is supported by hardware that performs its own asynchronous decompression, timing, and drawing.
Overlay drivers use this message to draw when the window is obscured or moved. When a window specified for ICM_DRAW_BEGIN is completely hidden by other windows, the destination rectangle is empty. Drivers should turn off overlay hardware when this condition occurs.
ICM_DRAW_BEGIN