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Next: 2.13.9 Final Color Processing Up: 2.13 Colors and Coloring Previous: 2.13.7 Flatshading

2.13.8 Color and Texture Coordinate Clipping


After lighting, clamping or masking and possible flatshading, colors are clipped. If the color is associated with a vertex that lies within the clip volume, it is unaffected by clipping. If a primitive is clipped, however, the colors assigned to vertices produced by clipping are clipped colors.

Let the color assigned to the two vertices and of an unclipped edge be and . The value of t (section 2.11) for a clipped point is used to obtain the color associated with as

(For a color index color, multiplying a color by a scalar means multiplying the index by the scalar. For an RGBA color, it means multiplying each of R, G, B, and A by the scalar.) Polygon clipping may create a clipped vertex along an edge of the clip volume's boundary. This situation is handled by noting that polygon clipping proceeds by clipping against one plane of the clip volume's boundary at a time. Color clipping is done in the same way, so that clipped points always occur at the intersection of polygon edges (possibly already clipped) with the clip volume's boundary.

Texture coordinates must also be clipped when a primitive is clipped. The method is exactly analogous to that used for color clipping.

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