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1、ii“paper”—2008/3/20—15:47—page19—#1iiVol.13,No.1:19–29RobustSoftShadowMappingwithBackprojectionandDepthPeelingLouisBavoil,StevenP.Callahan,andClaudioT.SilvaScientificComputingandImagingInstitute,UniversityofUtahAbstract.Softshadowmappingisanattractivesolutiontotheproblemofreal
2、-timesoftshadowsbecauseitworkswithanykindofrasterizablegeometry(inpartic-ularalpha-transparenttexturesandhair),itdoesnotrequireanyprecomputation,anditissimpletoimplementontheGPU.However,state-of-the-artapproacheshaveseverallimitationsthatpreventthemfrombeingpracticalforallsce
3、nes.First,parametertuningisrequiredtoavoidsurfaceacne.Second,gapsbetweenshadowmappixelsareeitherignored,whichresultsinlightbleeding,orhandledusinggapfilling,whichresultsinovershadowing.Wepresentamorerobustsoftshadowmappingtechnique,basedonarecentbackprojectionalgorithm,thatuse
4、sdepthpeelingtoaddresstheproblemsofsur-faceacneandlightbleeding.Ouralgorithmusesamulti-layershadowmaptoreducelightbleeding,andmidpointshadowmapstohandleself-shadowingmorerobustly.Itprovideshigh-qualitysoftshadowingforcomplexscenes,whilestillmaintaininginteractiverenderingrate
5、s.Sourcecodeisavailableonline.1.IntroductionShadowmapping[Williams78]isareal-timealgorithmforrenderinghardshadowsfrompointlightsthatmapsverywelltoGPUs.Inthisclassicalgo-rithm,apreliminarypassrendersthescenefromtheviewpointofthelightintoadepthbuffer(dubbedashadowmap).Then,image
6、fragmentsaretrans-formedtotheimagespaceofthelight,andtheirdepthsarecomparedtothe©AKPeters,Ltd.191086-7651/06$0.50perpageiiiiii“paper”—2008/3/20—15:47—page20—#2ii20journalofgraphicstoolsshadowmapdepthstodetermineifthefragmentisoccludedfromthelight.Theadvantagesofshadowmappinga
7、reitsspeedandsimplicity.Aphysically-basedsoftshadowmappingalgorithmwithself-shadowingwasproposedrecentlybyGuennebaudetal.[Guennebaudetal.06],whichcom-putesapercentageoflightseenfromeverypixelintheimage.Thisisdonebybackprojectingtheoccludersintheshadowmapontothelightplaneandde
8、terminingthemagnitudeoftheocclusion.Thealgorithmaddressesmanyoftheis
