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C.2 Polygon Offset

Depth values of fragments generated by the rasterization of a polygon may be shifted toward or away from the origin, as an affine function of the window coordinate depth slope of the polygon. Shifted depth values allow coplanar geometry, especially facet outlines, to be rendered without depth buffer artifacts. They may also be used by future shadow generation algorithms.

The additions match those of the EXT_polygon_offset extension, with two exceptions. First, the offset is enabled separately for POINT , LINE , and FILL rasterization modes, all sharing a single affine function definition. (Shifting the depth values of the outline fragments, instead of the fill fragments, allows the contents of the depth buffer to be maintained correctly.) Second, the offset bias is specified in units of depth buffer resolution, rather than in the [0,1] depth range.

David Blythe
Sat Mar 29 02:23:21 PST 1997