Shadow Mapping for Hemispherical and Omnidirectional Light Sources

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1、ShadowMappingforHemisphericalandOmnidirectionalLightSourcesStefanBrabecThomasAnnenHans-PeterSeidelComputerGraphicsGroupMax-Planck-InstitutfurInfomatik¨Stuhlsatzenhausweg85,66123Saarbrucken,Germany¨fbrabec,tannen,hpseidelg@mpi-sb.mpg.deAbstractInthispaperwepresentashadowmappingtechniqueforhemisph

2、ericalandomnidirec-tionallightsourcesusingdual-paraboloidmapping.Incontrasttothetraditionalper-spectiveprojectionthisparameterizationhasthebenefitthatonlyaminimalnumberofrenderingpassesisneededduringgenerationoftheshadowmaps,makingthemethodsuitablefordynamicenvironmentsandrealtimeapplications.Byu

3、tilizingprogrammablefeaturesavailableonstate-of-the-artgraphicscardsweshowhowthealgorithmcanbeefficientlymappedtohardware.Keywords:ShadowAlgorithms,ShadowMapping,Dual-ParaboloidMapping,GraphicsHardware.1IntroductionandBackgroundOneofthemostchallengingeffectinthefieldofrealtimerenderingistheaccurat

4、eandfastcalculationofshadows.Formostapplications,e.g.incomputergames,shadowsarestillproblematicduetotheirglobalnature.Inordertodecideifagivensurfacepixelcanbeseenbyalightsourceonehastocheckalargenumberofpotentialoccludersthatmayblockthepathfromlighttosurface.Althoughtherearealargenumberofshadowa

5、lgorithms,onlyasmallsubsetofalgo-rithmsarereallyappropriateforrealtimerendering.Nearlyalltechniquesinthissubsetcanfurtherbecategorizedintotwomainbranchesofalgorithms:ThosewhicharebasedonCrow’sshadowvolumesapproach[3],andthosethatarevariantsofWilliams’shadowmappingtechnique[13].Bothcategorieshave

6、theirprosandcons:Theshadowvolumeapproachiscapableofproducingveryaccurateshadowsduetotheobjectspacecalculation.Foreach(possible)blockerobject,asemi-infiniteshadowvolumeisconstructedwhichdefinesthevolumeinwhichallpixelsinsidecannotbeseenbythelightsource.Althoughtheactualshadowvolumein-outtestcanbeac

7、celeratedbyusinggraphicshardware,theCPUstillhastoperformthetime-consumingtaskofconstructingtheactualshadowvolumes.TheshadowmappingtechniqueontheotherhanddoesnotneedanyCPUtimeatallsinceallstepscanbydirectlyimplementedonthegra