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1、RaytracingPrefilteredOcclusionforAggregateGeometryDylanLacewell1,2BrentBurley1SolomonBoulos3PeterShirley4,21WaltDisneyAnimationStudios2UniversityofUtah3StanfordUniversity4NVIDIACorporationFigure1:ComputingshadowsusingaprefilteredBVHismoreefficientthanusin
2、ganordinaryBVH.(a)UsinganordinaryBVHwith4shadowrayspershadingpointrequires112secondsforshadowrays,andproducessignificantvisiblenoise.(b)UsingaprefilteredBVHwith9shadowraysrequires74seconds,andvisiblenoiseisdecreased.(c)Reducingnoisetoasimilarlevelwithano
3、rdinaryBVHrequires25shadowraysand704seconds(about9.5×slower).Allimagesuse5×5samplesperpixel.Thesceneconsistsofabout2Mtriangles,eachofwhichissemi-opaque(α=0.85)toshadowrays.ABSTRACTaggregategeometry,itsufficestouseaprefilteringalgorithmthatisWeprefilterocc
4、lusionofaggregategeometry,e.g.,foliageorhair,linearinthenumberofnodesintheBVH.Oncebuilt,aprefilteredstoringlocalocclusionasadirectionalopacityineachnodeofaBVHdoesnotneedtobeupdatedunlessgeometrychanges.boundingvolumehierarchy(BVH).Duringintersection,wet
5、ermi-Duringrendering,weterminateshadowraysatsomelevelofthenateraysearlyatBVHnodesbasedonraydifferential,andcompos-BVH,dependentonthedifferential[10]ofeachray,andreturntheitethestoredopacities.Thismakesintersectioncostindependentofstoredopacityatthenode
6、.Thecombinedopacityoftherayiscom-geometriccomplexityforrayswithlargedifferentials,andsimulta-putedbycompositingtheopacitiesofoneormorenodesthattheneouslyreducesthevarianceofocclusionestimates.Thesetworayintersects,inanyorder.Thisearlyterminationelimina
7、tesmanyalgorithmicimprovementsresultinsignificantperformancegainsray-triangleintersections,andmakesintersectioncostindependentforsoftshadowsandambientocclusion.Theprefilteredopacityofgeometriccomplexityforrayswithlargeenoughdifferentials.datadependsonlyo
8、ngeometry,notlights,andcanbecomputedinInaddition,prefilteringalsoreducesthevarianceofocclusionesti-lineartimebasedonassumptionsaboutthestatisticsofaggregatematesonaggregategeometry,whichinturnreducesnoiseartifactsgeometry.foragivennumber
