Promoting Z Buffers to 32 Bits Per Pixel
This topic applies to DirectX 8.0 and later.
A display driver whose display device does not support rendering to z and color buffers with differing pixel depths must transparently promote a 16 bits per pixel (bpp) z buffer to 32 bpp in order to render both the z buffer and a 32 bpp color buffer at the same time. Note, however, that the z buffer cannot also have stencil bits. Therefore, applications are not required to correct this mismatch in buffer pixel depth.
If the driver's display device can render to z and color buffers of differing pixel depth, the driver sets the D3DFORMAT_OP_ZSTENCIL_WITH_ARBITRARY_COLOR_DEPTH flag in the dwOperations member of the DDPIXELFORMAT structure for z-buffer formats. The Direct3D runtime then lets applications render to any mismatch of z- and color-pixel depths.
If the driver does not set D3DFORMAT_OP_ZSTENCIL_WITH_ARBITRARY_COLOR_DEPTH for z-buffer formats, the runtime only lets applications render to a mismatch of 32 bpp color buffer and 16 bpp z buffer with no stencil bits as described in the introductory paragraph. In this case, the driver allocates a 32 bpp z buffer in place of the requested 16 bpp z buffer.
If D3DFORMAT_OP_ZSTENCIL_WITH_ARBITRARY_COLOR_DEPTH is not set, the runtime does not let applications render to the following mismatch scenarios:
16 bpp color buffer and 32 bpp z buffer at the same time. For rendering to succeed in this scenario, the driver would have to substitute a 16 bpp z buffer for the 32 bpp z buffer, which would degrade z precision and cause noticeable artifacts.
Any z format whose depth stencil does not occupy the same number of bits per pixel as the color buffer (in other words, mismatching z and stencil surfaces). For rendering to succeed in this scenario, the driver would have to change the number of stencil bits, which would also cause noticeable artifacts.