In DirectX 2, clippers can be shared between multiple surfaces. For example, the same clipper can be set on both the front and back buffers of a flipping chain. When a clipper is attached to a surface by using the IDirectDrawSurface::SetClipper method, the surface increments the reference count of that clipper. When the reference count of the surface reaches 0, it will decrement the reference count of the attached clipper. In addition, if a clipper is detached from a surface by calling IDirectDrawSurface::SetClipper with a NULL clipper interface pointer, the reference count of the surface's clipper will be decremented.
Note If IDirectDrawSurface::SetClipper is called several times consecutively on the same surface for the same clipper, the reference count for the clipper will be incremented only once. Subsequent calls will not affect the clipper's reference count.