Patent ID: 7375727

Claim:
A graphics system comprising: a conservative culling stage with an input and an output, and including processing logic for testing geometric objects for occlusion, and including a conservative culling stage depth buffer; and a renderer with a rendering depth buffer; said conservative culling stage input connected with a geometric processor for receiving said geometric objects; said conservative culling stage processing logic accessing said conservative culling stage depth buffer for occlusion testing of said geometric objects; and said conservative culling stage output connected to said renderer for supplying potentially visible geometric objects to said renderer; whereby efficiency in rendering is improved; wherein said conservative culling stage depth buffer is a hierarchical depth buffer that is organized as a plurality of nested tiles, and said conservative culling stage depth buffer contains a depth value for each tile; wherein the graphics system is adapted for halting occlusion testing of a geometric object within a tile that a Geometric object overlaps utilizing: logic for establishing the nearest depth value for said geometric object within said tile; logic for computing the difference between said depth value for said tile in said conservative culling stage depth buffer and said nearest depth value, said difference indicating how much nearer said nearest depth value is than said depth value for said tile; and logic for halting the occlusion testing of said geometric object within said tile if said difference is less than a predetermined threshold value which is greater than zero; whereby the number of depth comparisons that are performed is reduced.