Efficient Ray Tracing of Parametric Surfaces for Advanced Effects

Ray Tracing is one of the most important rendering techniques used in computer graphics. Ray traced images are more accurate and photo-realistic as compared to direct rendering. Ray Tracing was earlier considered impractical for rendering scenes at interactive rates because of its high computational cost. However, with the advancements in modern Graphics Processing Units (GPU) and CPUs, ray tracing at interactive rates has now become possible. Parametric patches have been widely used in many fields to describe a model accurately. They provide a compact and effective way of representing an object and also possess the ability to remain curved on zooming. Ray Tracing of parametric surfaces was considered to be a static process because of the high complexity of intersection algorithms. With advancements in ray tracing techniques and high compute power devices, recent works on ray tracing parametric surfaces have reported near interactive results. We present a scheme for interactive ray tracing of Bezier bicubic patches using Newton iteration in this dissertation. 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. We are able to significantly outperform multi-core CPU implementation and previous GPU implementation using the mixed hierarchy model. Shadow and reflection rays can be handled exactly in the same manner as a result. The secondary ray list is again sent to the starting of the algorithm to perform mixed hierarchy traversal and intersection tests. We perform fixed depth multiple bounce ray tracing. We also show how our method extends easily to generate soft shadows using area light sources. These effects provide higher realism to the ray traced images. 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. We are able to ray trace bigguy in a box scene with multi-bounce at near interactive rates. We