Coherency (data locality) is one of the most important factors that influences the performance of distributed ray tracing systems, especially when object dataflow approach is employed. The enormous cost associated with remote fetches must be reduced to improve the efficiency of the parallel renderer. Objects once fetched should be maximally utilized before replacing them with other objects. In this paper, we describe a parallel volume ray caster that eliminates thrashing by efficiently advancing a rayfront in a front-to-back manner. The method adopts an image-order approach, but capitalizes on the advantages of object-order algorithms as well to almost eliminate the communication overheads. Unlike previous algorithms, we have successfully preserved the thrashless property across a number of incrementally changing screen positions also. The use of efficient data structures and object ordering scheme has enabled complete latency hiding of non-local objects. The sum total of all these result in a scalable parallel volume renderer with the most coherent screen traversal. Comparison with other existing screen traversal schemes delineates the advantages of our approach.

Proceedings of the 1996 Conference on Graphics Interface, Toronto, Ontario, Canada, 22 - 24 May 1996, 70-77