Method and apparatus for performing occlusion testing while exploiting frame to frame temporal coherence

The present invention relates to computer graphics display systems and, more particularly, to a method and apparatus for performing occlusion culling operations in a computer graphics display system while exploiting frame-to-frame temporal coherence. A method and apparatus is provided for performing occlusion testing in a computer graphics display system. The apparatus comprises logic configured to determine whether or not an object of a current image frame was occluded in a previous image frame. If a determination is made that the object was not occluded in the previous image frame, then the logic causes the object of the current image frame to be rendered to a frame buffer of the computer graphics display system. The current and previous image frames are each comprised of a plurality of objects, and the logic determines whether or not each of the objects of the current image frame were occluded in the previous image frame. The logic causes any objects of the current image frame that were not occluded in the previous image frame to be rendered to the frame buffer. Once all of the objects of the current image frame that were not occluded in the previous image frame have been rendered to the frame buffer, the logic determines whether or not any of the rendered objects of the current image frame are occluded. If the logic determines that a particular rendered object of the current image frame is not occluded, the logic determines whether or not the particular object was occluded in the previous image frame. If so, then the logic determines that a prediction error has occurred because the object was not rendered even though it is visible. In accordance with a first embodiment of the present invention, when the logic determines that a prediction error has occurred, it causes the visible object to be rendered to the frame buffer to correct the error. In accordance with a second embodiment of the present invention, the logic waits until all of the objects have been tested and then causes all of the visible objects to be rendered to the frame buffer.