《计算机图形学》Extra Lectures 反射与透射-（英文）教学课件（非AI生成）.ppt

ReflectionandTransmission1

IntroductionInteractionsbetweenlightandmaterialsBlinn-PhongmodelAbsorptionDiffuseandspecularreflectionsPurelylocalReflection:TranslucentsurfacesRefractionFrenseleffectChromaticdispersion2

GlobalvsLocalMostoftheseeffectscanonlybecomputedinaglobalrenderersuchasaraytracer3

RayTracingRaytracerscanmakeuseofalltheseeffectsinaglobalcalculationbytracingraysRN-NLT4

EnvironmentalMapCanusealltheseeffectsImplementinCgwithvertexandfragmentprograms5

RefractionWithpurerefraction,allthelightistransmittedbuttheangleofrefractionisdeterminedbySnell’slaw?lsinθl=?tsinθtwhere?land?tarethespeedoflightrelativetothespeedoflightinavacuumLet?=?l/?t6

ComputingT?2sin2θl=?2(1-cos2θl)=sin2θt=1-cos2θtSolvingforcosθtAssumingnormalizedvectorscosθt=T·N=(1-?2(1-cos2θl))1/2wherecosθl=T·NT,N,andLmustbecoplanarT=aL+bNandT·T=1SolvingT=-1/?L–(cosθt-1/?cosθl)N7

NotesCriticalangle:totalinternalreflection1=?2(1-cos2θl)Snell’slawisastatementthatlighttakestheshortestpath(intime)Canapplytoreflectionmaps(seeCgTutorial)viavertexprogram8

FresnelEffectSomelightisreflectedandsometransmittedatsurfacebetweentwomaterialsAmountoflightreflectedisgreatestatshallowangleApproximation:useaffinecombinationofrefractedandreflectedcolorswherea=max(0,min(1,bias+scale?(1+L·N)power))9

ChromaticDispersionTherefractioncoefficientisactuallyafunctionofwavelengthh=h(l)N-NLTbTgTr10

ChromaticDispersionwithShadersEasytodowithreflectionmapsUsethreevaluesofhMakeuseofvectoroperations11