Approximate Ray-Tracing on the GPU with Distance Impostors László Szirmay-Kalos Barnabás Aszódi István Lazányi Mátyás Premecz TU Budapest, Hungary

GPU rendering versus Ray-Tracing Inremental rendering on the GPU Non-coherent Ray tracing

Previous work Ray-tracing on the GPU Ray-tracing on the GPU –Ray-engine (Carr et. al): Bad complexity: time  rays  triangles Bad complexity: time  rays  triangles –Regular grid (Purcell et. al): Problematic for dynamic objects Problematic for dynamic objects Environment mapping (Blinn) Environment mapping (Blinn) –Environment is at infinity –Localization with simple proxy geometry (Bjorke)

Contribution of this paper GPU friendly approximate ray tracing algorithm for casting incoherent rays needed, for example, when computing GPU friendly approximate ray tracing algorithm for casting incoherent rays needed, for example, when computing –Reflections –Refractions –Caustics –…

distance radiance Distance Impostors

Ray-Tracing with Distance Impostors

Approximation

Approximation Error 1 iteration 4 iterations8 iterations

Reflections radiance

Problems of environment map based reflections Environment mapReference

Localized Reflections distance radiance

Comparison of Localized Refrections

Refractions radiance environment

Multiple Localized Refractions distance normals environment

Comparison of Multiple Refractions

Multiple refraction results 109 FPS

Caustics distance texture u, v texture uv, power

32 x 32 Texture modulation Texture uv of photon positions Vertex shader Billboard positions filter Pixel shader Lit texture or Light map 256 x 256

Caustics Results: 180 FPS

Application: Ray-tracing effects in games

Conclusions Distance impostors to represent geometry in ray tracing Distance impostors to represent geometry in ray tracing Iterative ray tracing algorithm Iterative ray tracing algorithm Applications (100+ FPS): Applications (100+ FPS): –Localized reflections –Single and multiple localized refractions –Caustics