Enabling Depth Buffering (Direct3D 9)
After you create a depth buffer, as described in Creating a Depth Buffer (Direct3D 9), 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.
Note
To use w-buffering, your application must set a compliant projection matrix even if it doesn't use the Direct3D transformation pipeline. For information about providing an appropriate projection matrix, see A W-Friendly Projection Matrix
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