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Pixel fog gets its name from the fact that it is calculated on a per-pixel basis in the device driver. (This is unlike vertex fog, in which Direct3D computes fog effects when it performs transformation and lighting.) Pixel fog is sometimes called "table fog" because some drivers use a precalculated look-up table to determine the fog factor (using the depth of each pixel) to be applied in blending computations.
Pixel fog can be applied using any of the fog formulas identified by members of the D3DFOGMODE enumerated type. Pixel-fog formula implementations are driver-specific, and if a driver doesn't support a complex fog formula, it should degrade to a less complex formula.
Pixel fog can be applied using any of the fog formulas identified by members of the CONST_D3DFOGMODE enumeration. Pixel-fog formula implementations are driver-specific, and if a driver doesn't support a complex fog formula, it should degrade to a less complex formula.
Note As discussed in Range-Based Fog, pixel fog does not support range-based fog calculations.