Hybrid shadow testing scheme for ray tracing

Abstract

The paper presents a new shadow testing acceleration scheme for ray tracing called hybrid shadow testing (HST) based on conditional switching between the conventional shadow testing method and Crow's shadow volume method, where the shadow polygons as well as the object polygons are registered onto the corresponding cells under the 3D space subdivision environment. Despite the preprocessing time needed for the generation and registration of the shadow polygons, the total shadow testing time of HST was approximately 50% of that of conventional shadow testing for several examples, while the total ray tracing time was typically reduced by 30%. This is due to the selective use of the shadow volume method, with a compromise between maximizing use of the shadow's spatial coherency and minimizing the computational overhead for checking ray intersections with the shadow polygons. A parameter N th , denoting the critical number of shadow polygons between successive reflection points, was used as a guideline for switching the shadow testing scheme between the conventional method and shadow volume method. A method for calculating N th from statistical data such as the number of object polygons, average polygon size, and average peripheral length of the polygons was proposed, resulting in good agreement with the experimental results.