Hewlett-packard Company

Daniel M Olsen

Noel D Scott

Robert J Casey

An occlusion culling circuit for use in a graphics computer receives graphics primitives data including x and y coordinates for each pixel, a z depth value, and r, g, b, and a or index color data. For each group of primitives, the graphics computer scans the primitive and determines a volume which completely bounds the primitive. The z depth values for the pixels comprising the bounding volume are then compared by the occlusion culling circuit to the depths of the pixels in the already rendered primitives to determine whether any pixels in the incoming primitive are visible. If no pixels are visible, the occlusion culling circuit clears the result register and receives the next graphics primitive. If, on the other hand, one or more pixels is visible, the occlusion culling circuit completely renders the primitives bounded by the bounding volume. Since the graphics primitives which are totally occluded can bypass the more intensive pixel by pixel processing and storage, the speed and efficiency of the graphics computer can be significantly increased.

System and method for accelerated occlusion culling

A solution to the problem of determining the degree of visibility for a bounding volume is to first sort the bounding volumes into an order in which they can be tested, after which they are rendered as if they were polygons in their own right. Prior to the testing of the next bounding volume a Bounding Volume Visibility (BVV) mode is enabled. This temporarily suspends write operations to the frame buffer and it resets a TOTAL PIXEL COUNTER and a VISIBLE PIXEL COUNTER. Then the polygon sides of the bounding volume are rendered, with each and every pixel of those polygons being checked for depth, as would be the pixels for 'real' polygons. Each such pixel rendered causes an increment of the TOTAL PIXEL COUNTER, while each such pixel that meets the depth criteria in use causes an increment of the VISIBLE PIXEL COUNTER. The BVV mode is subsequently turned off, and the values of the two counters inspected. The inspecting entity may be software associated with the graphics application. It can decide whether or not to render the image polygons within the bounding volume just tested. The values of the counts in the TOTAL PIXEL COUNTER and the VISIBLE PIXEL COUNTER can be of assistance in this decision. That is, if the count in the VISIBLE PIXEL COUNTER is small in comparison to that in the TOTAL PIXEL COUNTER, then it may be desirable to programmatically ignore the image polygons in that bounding volume. On the other hand, if the counts are anywhere near equal, then it is probably wise to render those image polygons. The BVV mode is then turned back on at the start of the next bounding volume in the sorted list thereof, and so on.

Growing community of inventors

Fort Collins, CO, United States of America

Daniel M Olsen