Rendering Polygonal Scenes with Di raction Account

Renderingolygonal PSceneswithDi ractiont AccounLilian eneau, Av eriaux hel Mic  MCOM IR SIC, UMR 6615 CNRSep ardort Boulev 3 2  el - -  TBP 17986960 uturoscop e F Cedex, rance Feneau@sic.sp2mi.univ-p v oitiers.fr aCT ABSTRAGlobal pro cessing of di raction phenomena y b a half-plane as w prop osed y b eneau Av eriaux, and using  Mthe Geometrical Theory of Di raction.In this , theory di raction ys ra are emitted y b di raction pts oinb elonging to thehalf-plane edge(ordihedron edge).Thesolution en giv for nding thesepts oinb eingumerical, nitisdiculttot implemen andleadsw loprecisionsolutionswithaw sloalgorithm.Inthis pap ere w rstprop osea new geometric solution for nding thedihedron di raction pts, oinh whicleads to an t ecienanalytic algorithm.Next e w t presenan tation implemen of a racing y-T Ra are w softfor p olygonal sceneswith an automatic di raction t. treatmenSince this implies di raction y b dihedra,e w t presen the dihedron data structure and the corresp onding algorithm h whic es solv o w t problems :theexistence of di raction paths, and the impy ossibilit for dihedra to share their edge.These ts elemen leadto an tation implemen of a racing y-T Ra are w soft with rst di raction t accoun for y an p olygonal scenes.ords: KeywRendering hniques, ec T Di raction, GTD, racing. y-T Ra1ODUCTION INTRThe quest for realism has ys a alw b een a ma jor preo c-cupation among the image rendering . y unit comm o Te hiev acthisgoal,hers researce v haaddedysically phbased e ects, from reection on p erfect mirrors withy-tracing ra to glare e ects [Sp enc95].Allable observopticphenomenaaredescrib edy bone or more ysical ph . theoryus Th realism in imagerendering can b e ed hiev ac y b including these theoriesin computational mo dels, if p ossible.Inthisy a wultiple mreectionsondi usesur-facescanb ecomparedtothermalhanges excandleadstoy radiositcomputation]. [Goral84olariza- Ption], ol 90 [Wbirefringence] anne94 [Tandterfer- inences ] [Calle94 ] [Dias94 can b e added to a y-tracer rasincethe phenomena can b emo delled y b Geometri-calTheoryofOptics.Causticscanb eundersto o de likt Ferma'sprinciplee ects] h92 [Mitcandleadsto umerical n computations or te-Carlo Mon metho ds[Jense97 ].tomic Ascatteringcanb een takto inac-t counwithphasefunctionsandgeometricaloptics,and is used in te-Carlo Mon based pro cesses] [Blasi94erez97 [P].e Lik inglobal tion, illumina lo calrenderingmeth-o ds ely tensiv in use the conceptof , y ra i.e.geometri-cal optic , theory for instance theCook-Torrance'smo del [Co]. ok81 ulation Sim of the subsurface scatter-ing leads to skin or leaf reections ]. [Hanra93 Di rac-tion y b a subsurface structure leads to a mo del basedonchhoff Kir's w la [He91].e, Ey elash, ey and w ebro ey di raction ere w also de-scrib ed using a y-tracer ra metho d and a ltering pro-cess]. am90 [NakThismetho dhasb eented augmen