VISIBLE PICKING IN A GRAPHICS SYSTEM

19-91-028 VISIBLE PICKING IN A GRAPHICS SYSTEM A multiple-pass system for determining the primitives that are visible in a predetermined pick aperture for a "visible pick" operation. On the first pass, the primitives contained within the pick aperture and thus potentially visible are selected, and each selected primitive is assigned a pick index as an identifier. On the second pass, the pick indices of the selected primitives are rendered to a temporary frame buffer area, using a Z-buffer for hidden surface removal so that only the pick indices of the primitives visible within the pick aperture are stored in the corresponding frame buffer portion. On the third pass, the frame buffer portion corresponding to the pick aperture is read to determine the pick indices of the visible primitives. This information is then used to report back to the host the picked primitives.