Hybrid Ray Tracing and Path Tracing of Bezier Surfaces Using A Mixed Hierarchy

Rohit Nigam, P. J. Narayanan
Center for Visual Information Technology, IIIT-Hyderabad, India
8th Indian Conference on Vision, Graphics and Image Processing, 2012


   title={Hybrid Ray Tracing and Path Tracing of Bezier Surfaces Using A Mixed Hierarchy},

   author={Nigam, Rohit and Narayanan, P. J.},



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We present a scheme for interactive ray tracing of Bezier bicubic patches using Newton iteration in this paper. We use a mixed hierarchy representation as the acceleration structure. This has a bounding volume hierarchy above the patches and a fixed depth subpatch tree below it. This helps reduce the number of ray-patch intersections that needs to be evaluated and provides good initialization for the iterative step, keeping the memory requirements low. We use Newton iteration on the generated list of ray patch intersections in parallel. Our method can exploit the cores of the CPU and the GPU with OpenMP on the CPU and CUDA on the GPU by sharing work between them according to their relative speeds. A data parallel framework is used throughout starting with a list of rays, which is transformed to a list of ray-patch intersections by traversal and then to intersections and a list of secondary rays by root finding. Shadow and reflection rays can be handled exactly in the same manner as a result. We also show how our method extends easily to generate soft shadows using area light sources and path tracing by tracing a large number of rays per pixel. We render a million pixel image of the Teapot model at 125 fps on a system with an Intel i7 920 and a Nvidia GTX580 for primary rays only and at about 65 fps with one pass of shadow and refection rays.
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