Importance

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Abstract

A computer graphics system utilizes caching of pixel Z values to improve rendering performance. Apparatus for updating the Z values corresponding to pixels of a computer graphics display includes a memory for storing current Z values representing depths at corresponding pixel locations, a Z cache for storing a subset of the current Z values which are stored in the memory, and a comparator for comparing a new Z value with a corresponding current Z value and indicating a pass when the new Z value satisfies a predetermined criteria. The current Z value is read from the Z cache when the current Z value is stored in the Z cache and is read from the memory when the current Z value is not stored in the Z cache. The new Z value is written into the Z cache when the comparator indicates a pass. Each cache entry preferably includes a tile of current Z values corresponding to pixels having a predefined relationship. Different tile configurations may be selected for optimum rendering performance.

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First Claim