The handling routine in the graphics engine does the necessary calculations and calls the GreNotifyClipChange routine in the presentation driver so that the driver can receive the new clip regions.

VisRegionNotify is used only by display drivers. These drivers maintain an HDC_IS_DIRTY flag that is set ON by GreDeviceInvalidateClipRegion and cleared by GreNotifyClipChange. In the display driver, the handling routines for all drawing functions should check the HDC_IS_DIRTY flag, and if it is set, call VisRegionNotify before drawing.

VisRegionNotify is available across the system at Ring 3. Presentation drivers do not need to import this function through the module definition file.