Hierarchical Back-Face Culling

We present a sub linear algorithm for computing and culling back facing polygons that yields a signi cant performance improvement in the interactive rendering of large polygonal models The algorithm partitions a polygonal model it into hierarchical clusters based on the normals and positions of the polygons It does not explicitly compute all the back facing polygons but rather decides in expected constant time whether an entire cluster is back facing As a pre processing step the algorithm partitions the space into regions with respect to each cluster During rendering it exploits frame to frame coherence to track the view point The algorithm has been applied to a number of models and its performance is a function of number of clusters the depth of the hierarchies and the characteristics of the graphics system In practice we are able to cull of the polygons in about of the total CPU time per frame on an SGI Indigo Extreme for models composed of tens of thousands of polygons It improves the overall frame rate by as compared to hardware back face culling CR