A Visibility Field for Ray Tracing

This paper presents a type of visibility data structure for accelerated ray tracing. The visibility field is constructed by choosing a regular point subdivision over a hemisphere to obtain a set of directions. Corresponding to each direction there is then a rectangular grid of parallel beams, with each beam referencing a set of identifiers corresponding to objects that intersect it. Objects lying along a beam are sorted using a 1D BSP along the beam direction. The beam corresponding to any ray can be looked up in small constant time and the set of objects corresponding to the beam can then be searched for intersection with the ray using an optimised traversal strategy. This approach trades off rendering speed for memory usage and pre-processing time. The data structure is also very suitable for hemisphere integration tasks due to its spherical nature and results for one such task - ambient occlusion - are also presented. Results for several scenes with various rendering methods are presented and compare favourably with a well established approach, the single-ray coherent ray tracing approach of Wald and Slusallek et al.