Approximate Ray-Approximate Ray-Tracing on the GPU with Tracing on the GPU with

Distance ImpostorsDistance Impostors

László Szirmay-KalosLászló Szirmay-KalosBarnabás AszódiBarnabás AszódiIstván LazányiIstván LazányiMátyás PremeczMátyás Premecz

TU Budapest, Hungary

GPU rendering versus GPU rendering versus Ray-TracingRay-Tracing

Inremental rendering on the GPU

Non-coherent Ray tracing

Previous workPrevious work

Ray-tracing on the GPURay-tracing on the GPU– Ray-engine (Carr et. al): Ray-engine (Carr et. al):

Bad complexity: time Bad complexity: time rays rays triangles triangles

– Regular grid (Purcell et. al): Regular grid (Purcell et. al): Problematic for dynamic objectsProblematic for dynamic objects

Environment mapping (Blinn)Environment mapping (Blinn)– Environment is at infinityEnvironment is at infinity– Localization with simple proxy Localization with simple proxy

geometrygeometry (Bjorke) (Bjorke)

Contribution of this Contribution of this paperpaper GPU friendly approximate ray GPU friendly approximate ray

tracing algorithm for casting tracing algorithm for casting incoherent rays needed, for incoherent rays needed, for example, example, when computingwhen computing– ReflectionReflectionss– RefractionRefractionss– CausticsCaustics– ……

distanceradiance

Distance ImpostorsDistance Impostors

Ray-Tracing withRay-Tracing with

Distance ImpostorsDistance Impostors

ApproximationApproximation

Approximation ErrorApproximation Error

1 iteration 4 iterations 8 iterations

ReflectionsReflections

radiance

Problems of Problems of environment map environment map based reflectionsbased reflections

Environment map Reference

Localized ReflectionsLocalized Reflections

distanceradiance

Comparison of Comparison of Localized RefrectionsLocalized Refrections

RefractionsRefractions

radiance

environment

Multiple Localized Multiple Localized RefractionsRefractions

distancenormals

environment

Comparison of Comparison of Multiple RefractionsMultiple Refractions

Multiple refraction Multiple refraction resultsresults109 FPS109 FPS

CausticsCaustics

distancetexture u, v

texture uv, power

32 x 32

Texture modulationTexture modulation

Texture uv of photon positions

Vertexshader

Billboardpositions

filter

Pixelshader

Lit texture orLight map256 x 256

Caustics Results: 180 Caustics Results: 180 FPSFPS

Application: Ray-Application: Ray-tracing effects in tracing effects in gamesgames

ConclusionsConclusions

Distance impostors to represent Distance impostors to represent geometry in ray tracinggeometry in ray tracing

Iterative ray tracing algorithmIterative ray tracing algorithm Applications (100+ FPS):Applications (100+ FPS):

– Localized reflectionsLocalized reflections– Single and multiple localized Single and multiple localized

refractionsrefractions– CausticsCaustics