DdResetVisrgn function

[This function is subject to change with each operating system revision. Instead, use the Microsoft DirectDraw and Microsoft Direct3DAPIs; these APIs insulate applications from such operating system changes, and hide many other difficulties involved in interacting directly with display drivers.]

Wrapper for the NtGdiDdResetVisrgn function and enables timely user-mode information on the clipping region for windows on the desktop.

GdiEntry6 is defined as an alias for this function.


   HWND                      hWnd



Pointer to the user-mode object of any surface belonging to the DirectDraw device for which clipping is to be reset. See the DDK documentation for details.



Return value

If successful, this function returns TRUE; otherwise it returns FALSE.


Clipping can change asynchronously from the point of view of user-mode threads. The kernel-mode parts of DirectDraw and Windows Graphics Device Interface (GDI) maintain a counter that is incremented whenever the clipping list for the entire desktop changes. A call to this function records this counter with every existing DirectDraw primary surface on the system.

At any later time when one of these primary surfaces is modified by a IDirectDrawSurface7::Blt or IDirectDrawSurface7::Lock operation (see DDK documentation), the counter recorded with the surface is compared with the global counter. If these values are different, an error code DDERR_VISRGNCHANGED is returned to the user-mode code. The user-mode code will then re-query the current clipping for the desktop, call NtGdiDdResetVisrgn, and re-try the IDirectDrawSurface7::Blt applied to the primary surface, respecting the new clipping. Eventually, the clipping that was sampled by the user-mode code will be the same as the current clipping owned by kernel mode, and the IDirectDrawSurface7::Blt will be allowed to continue.

Applications are advised to use the IDirectDrawClipper interface or IDirect3DDevice8::Present method to handle asynchronous clipping changes. These constructs implement asynchronous clipping in an automated and operating-system-independent way.


Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]



See also

Graphics Low Level Client Support