Ray-specialized acceleration structures for ray tracing

The key to efficient ray tracing is the use of effective acceleration data structures. Traditionally, acceleration structures have been constructed under the assumption that rays approach from any direction with equal probability. However, we observe that for any particular frame the system has significant knowledge about the rays, especially eye rays and hard/soft shadow rays. In this paper we demonstrate that by using this information in conjunction with an appropriate acceleration structure - a set of one or more perspective grids - that ray tracing performance can be significantly improved over prior approaches. This acceleration structure can easily be rebuilt per frame, and provides significantly improved performance for rays originating at or near particular points such as the eye point and the light source(s), without sacrificing the ability to trace arbitrary rays. We demonstrate true real-time frame rates on a game-like scene rendered on an eight-core desktop PC at 1920times1200 resolution for primary visibility, and hard shadows, along with lower frame rates for Monte Carlo soft shadows. In particular, we demonstrate the fastest hard shadow ray-tracing results that we are aware of. We argue that the perspective grid acceleration structure provides insight into why the Z buffer algorithm is faster than traditional ray tracing and shows there is a useful continuum of visibility algorithms between the two traditional approaches.