Accelerated Bounded-Error Ray Tracing Using Per-Surface Radiance Interpolants

Ray tracing, which computes radiance, is usually regarded as an off-line rendering algorithm that is too slow for interactive use. In this paper, we present a system that uses per-surface four-dimensional interpolants to approximate radiance, while providing guaranteed error bounds. Our system exploits object-space, ray-space, image-space and temporal coherence to accelerate ray tracing. Our system explicitly decouples the two primary operations of a ray tracer — shading and visibility determination at each pixel — and accelerates each of them independently. Shading is accelerated by lazily collecting 4D radiance samples, and quadrilinearly interpolating them to approximate radiance. Interpolation error does not exceed a user-specified bound that the user can vary to trade performance for quality. Error is bounded by adaptive sampling at discontinuities and radiance non-linearities. Visibility determination at a pixel is also accelerated by reprojecting interpolants as the user’s viewpoint changes. A fast scan-line algorithm then achieves high performance without sacrificing image quality. The combination of lazy interpolants and reprojection speeds up ray tracers substantially for smoothly varying viewpoints. We expect our techniques to be useful in accelerating both interactive and batch ray tracers.