Interactive Screen-Space Accurate Photon Tracing on GPUs

Abstract

Recent advances in algorithms and graphics hardware have opened the possibility to render caustics at interactive rates on commodity PCs. This paper extends on this work in that it presents a new method to directly render caustics on complex objects, to compute one or several refractions at such objects and to simulate caustics shadowing. At the core of our method is the idea to avoid the construction of photon maps by tracing photons in screen-space on programmable graphics hardware. Our algorithm is based on the rasterization of photon paths into texture maps. Intersection events are then resolved on a per-fragment basis using layered depth images. To correctly spread photon energy in screen-space we render aligned point sprites at the diffuse receivers where photons terminate. As our method does neither require any pre-processing nor an intermediate radiance representation it can efficiently deal with dynamic scenery and scenery that is modified, or even created on the GPU.