| 摘要 |
Shading values are generated for the vertices of a polygon clipped by a view volume without performing unnecessary lighting calculations for polygons lying entirely outside the view volume. Each polygon vertex is transformed and tested to determine whether it is within the view volume. If a tested vertex lies within the view volume, lighting calculations are performed for that vertex. If the polygon lies entirely outside the view volume, no lighting calculations are performed for any of the vertices of the polygon, and only a subset of the coordinate transformation calculation is performed. Complete transformation and lighting calculations are performed for vertices lying outside the view volume only if necessary for determining by interpolation the values for new vertices formed by clipping.
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