Shadow Mapping with Today’s OpenGL Hardware

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1、ShadowMappingwithToday’sOpenGLHardwareCEDEC2001Tokyo,Japan2MarkJ.KilgardGraphicsSoftwareEngineerNVIDIACorporation3MotivationforBetterShadows•Shadowsincreasescenerealism•Realworldhasshadows•Morecontrolofthegame’sfeel•dramaticeffects•spookyeffects•Otherartformsrecognize

2、thevalueofshadows•Butyetmostgameslackrealisticshadows4CommonReal-timeShadowTechniquesProjectedShadowplanarvolumesshadowsHybridapproachesLightmaps5ProblemswithCommonShadowTechniques•Mostlytrickswithlotsoflimitations•Projectedplanarshadows•wellworksonlyonflatsurfaces•St

3、enciledshadowvolumes•determiningtheshadowvolumeishardwork•Lightmaps•totallyunsuitedfordynamicshadows•Ingeneral,hardtogeteverythingshadowingeverything6IntroducingAnotherTechnique:ShadowMapping•Image-spaceshadowdetermination•LanceWilliamspublishedthebasicideain1978•Byco

4、incidence,sameyearJimBlinninventedbumpmapping(agreatvintageyearforgraphics)•Completelyimage-spacealgorithm•meansnoknowledgeofscene’sgeometryisrequired•mustdealwithaliasingartifacts•Wellknownsoftwarerenderingtechnique•Pixar’sRenderManusesthealgorithm•Basicshadowingtech

5、niqueforToyStory,etc.7ShadowMappingReferences•ImportantSIGGRAPHpapers•LanceWilliams,“CastingCurvedShadowsonCurvedSurfaces,”SIGGRAPH78•WilliamReeves,DavidSalesin,andRobertCook(Pixar),“Renderingantialiasedshadowswithdepthmaps,”SIGGRAPH87•MarkSegal,et.al.(SGI),“FastShado

6、wsandLightingEffectsUsingTextureMapping,”SIGGRAPH928TheShadowMappingConcept(1)•Depthtestingfromthelight’spoint-of-view•Twopassalgorithm•First,renderdepthbufferfromthelight’spoint-of-view•theresultisa“depthmap”or“shadowmap”•essentiallya2Dfunctionindicatingthedepthofthe

7、closestpixelstothelight•Thisdepthmapisusedinthesecondpass9TheShadowMappingConcept(2)•Shadowdeterminationwiththedepthmap•Second,renderscenefromtheeye’spoint-of-view•Foreachrasterizedfragment•determinefragment’sXYZpositionrelativetothelight•thislightpositionshouldbesetu

8、ptomatchthefrustumusedtocreatethedepthmap•comparethedepthvalueatlightpositionXYinthedepthmaptofragment’slightpositionZ10TheS