Enabling Depth Buffering
After you create a depth buffer, as described in Creating a Depth Buffer, you enable depth buffering by calling the IDirect3DDevice9::SetRenderState method. Set the D3DRS_ZENABLE render state to enable depth-buffering. Use the D3DZB_TRUE member of the D3DZBUFFERTYPE enumerated type (or TRUE) to enable z-buffering, D3DZB_USEW to enable w-buffering, or D3DZB_FALSE(or FALSE) to disable depth buffering.
To use w-buffering, your application must set a compliant projection matrix even if it doesn't use the Microsoft?Direct3D?transformation pipeline. For information about providing an appropriate projection matrix, see A W-Friendly Projection Matrix
. The projection matrix discussed in What Is the Projection Transformation?