IDirect3DDevice::DeleteViewport
HRESULT DeleteViewport(LPDIRECT3DVIEWPORT lpDirect3DViewport);
Removes the specified viewport from the list of viewport objects associated with the device.
·Returns D3D_OK if successful, or an error otherwise, which may be one of the following values:
lpDirect3DViewport
Address of the Direct3DViewport object that should be disassociated with this Direct3DDevice object.