| 摘要 |
A clip testing unit within a graphics accelerator for comparing a value of a given homogeneous coordinate of a vertex position of a polygon relative to a plurality of clipping planes. The plurality of clipping planes includes both regular and guard band clipping planes. The clip testing unit includes registers for receiving and storing a W value corresponding to the vertex position, as well as a coordinate input register for receiving and storing the given homogeneous coordinate. The W value is conveyed to a guard band W generation unit, which generates a guard band W value in response thereto. The clip testing unit also includes a clip compare unit coupled to receive the W value, the guard band W value and the value of the given coordinate. The clip compare unit receives and compares the W value and the value of the given coordinate, generating one or more first clip signals in response thereto. The one or more first clip signals indicate whether the value of the given coordinate is outside of a regular clipping space defined by the regular clipping planes. Furthermore, the clip compare unit receives and compares the guard band W value and the value of the given coordinate, generating one or more second clip signals in response thereto. The one or more second clip signals indicate whether the value of the given coordinate is outside of a guard band clipping space defined by the guard band clipping planes. Because the first and second clip comparisons are performed substantially concurrently by the clip compare unit, the clip testing performance of the graphics accelerator is advantageously increased.
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