Raytracing Dynamic Scenes on GPU

Sashidhar Guntury
International Institute of Information Technology, Hyderabad – 500 032, INDIA
International Institute of Information Technology, 2011


   title={Raytracing Dynamic Scenes on GPU},

   author={Sashidhar Guntury},



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Raytracing dynamic scenes at interactive rates to realtime rates has received a lot of attention recently. In this dissertation, We present a few strategies for high performance ray tracing on an off-theshelf commodity Graphics Processing Unit (GPU) traditionally used for accelerating gaming and other graphics applications. We utilize the Grid datastructure for spatially arranging the triangles and raytracing efficiently. The construction of grids needs sorting, which is fast on todays GPUs. Through results we demonstrate that the grid acceleration structure is competitive with other hierarchical acceleration datastructures and can be considered as the datastructure of choice for dynamic scenes as per-frame rebuilding is required. We advocate the use of appropriate data structures for each stage of raytracing, resulting in multiple structure building per frame. A perspective grid built for the camera achieves perfect coherence for primary rays. A perspective grid built with respect to each light source provides the best performance for shadow rays. We develop a model called Spherical light grids to handle lights positioned inside the model space. However, since perspective grids are best suited for rays with a directions, we resort back to uniform grids to trace arbitrarily directed reflection rays. Uniform grids are best for reflection and refraction rays with little coherence. We propose an Enforced Coherence method to bring coherence to them by rearranging the ray to voxel mapping using sorting. This gives the best performance on GPUs with only user managed caches. We also propose a simple, Independent Voxel Walk method, which performs best by taking advantage of the L1 and L2 caches on recent GPUs. We achieve over 10 fps of total rendering on the Conference model with one light source and one reflection bounce, while rebuilding the data structure for each stage. Ideas presented here are likely to give high performance on the future GPUs as well as other manycore architectures.
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