DirectDraw manages clip lists by using the DirectDrawClipper object. A clip list is a series of rectangles that describes the visible areas of the surface. A DirectDrawClipper object can be attached to any surface. A window handle can also be attached to a DirectDrawClipper object, in which case DirectDraw updates the DirectDrawClipper clip list with the clip list from the window as it changes.
Although the clip list is visible from the DirectDraw HAL, DirectDraw calls the HAL only for blitting with rectangles that meet the clip list requirements. For instance, if the upper-right rectangle of a surface was clipped and the application directed DirectDraw to blit the surface onto the primary surface, DirectDraw would have the HAL do two blits, the first being the upper-left corner of the surface, and the second being the bottom half of the surface.
Through the IDirectDrawClipper::SetClipList method, you can passing an entire clip list to the driver (if the driver supports this) rather than calling the driver multiple times, once for each rectangle in the clip list. Additionally, you can set the clipper to a single window by calling the IDirectDrawClipper::SetHWnd method, specifying the target window's handle. If you set a clipper using a window handle, you cannot set additional rectangles.
Clipping for overlay surfaces is supported only if the overlay hardware can support clipping and if destination color keying is not active.