The IDirect3DDevice3::DeleteViewport method removes the specified viewport from the list of viewport objects associated with the device and decrements the reference count of the viewport.
HRESULT DeleteViewport(
  LPDIRECT3DVIEWPORT3 lpDirect3DViewport  
);
 If the method succeeds, the return value is D3D_OK.
If the method fails, the return value may be one of the following values:
| DDERR_INVALIDOBJECT | 
| DDERR_INVALIDPARAMS | 
This method fails, returning DDERR_INVALIDPARAMS, if you attempt to delete a viewport from the device without previously assigning the viewport with a call to IDirect3DDevice3::AddViewport.
In the IDirect3DDevice2 interface, this method accepts a pointer to an IDirect3DViewport interface, not an IDirect3DViewport3 interface.
  Windows NT/2000: Requires Windows 2000.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in d3d.h.
  Import Library: Use ddraw.lib.