CS 445 / 645 Introduction to Computer GraphicsAssignment FourFrom Fall ‘03Raytracing vs. RadiosityComplex Indirect IlluminationSlide 6Which is better?Slide 8Lighting Example: Cornell BoxLighting Example: Diffuse ReflectionLighting Example: ShadowsLighting Example: Soft ShadowsRadiosity: Cornell ExpermentRadiosity: Cornell ExperimentVery Early RadiositySlide 16Early RadiosityThe ‘Rendering Equation’RadiosityRadiosity TermsBasic elements of radiositySlide 22Basis elements of radiosityRadiosity equationForm factor, FjkSlide 26Slide 27Slide 28Slide 29Slide 30Consider three surfacesExtending to more surfacesSolving for all PatchesBack to the Form FactorsForm factorsSlide 36Slide 37Slide 38Form Factor – Another imageForm Factor – Another ModelBRDFsSlide 42View-dependent vs View-independentSlide 44Aliasing in radiosityNon-axis aligned meshesDoing a better job with discontinuitiesEngine RoomArchitectural designCS 445 / 645Introduction to Computer GraphicsLecture 17Lecture 17RadiosityRadiosityLecture 17Lecture 17RadiosityRadiosityAssignment FourWrite a ray tracerWrite a ray tracerYou’ll have complete controlYou’ll have complete control•Input file formatInput file format•User interfaceUser interface•Data structuresData structures•Form a two-person groupForm a two-person groupWrite a ray tracerWrite a ray tracerYou’ll have complete controlYou’ll have complete control•Input file formatInput file format•User interfaceUser interface•Data structuresData structures•Form a two-person groupForm a two-person groupFrom Fall ‘03Adam Jones, Richard SunShane LiesegangWilliam KammersellRaytracing vs. RadiosityBoth accomplish global illuminationBoth accomplish global illumination•RaytracingRaytracing–Follow rays of energy as they bounce through a sceneFollow rays of energy as they bounce through a sceneWhich rays? Which rays? Pick some. Randomness helps. Pick some. Randomness helps. Monte Carlo. Still a research topic.Monte Carlo. Still a research topic.How many rays? How many rays? Depends on the scene. Still a Depends on the scene. Still a topic of research debate.topic of research debate.Both accomplish global illuminationBoth accomplish global illumination•RaytracingRaytracing–Follow rays of energy as they bounce through a sceneFollow rays of energy as they bounce through a sceneWhich rays? Which rays? Pick some. Randomness helps. Pick some. Randomness helps. Monte Carlo. Still a research topic.Monte Carlo. Still a research topic.How many rays? How many rays? Depends on the scene. Still a Depends on the scene. Still a topic of research debate.topic of research debate.Derek Juba and Matt HeltonUVa Intro to Gaphics, Fall 2003Complex Indirect IlluminationModeling: Stephen Duck; Rendering: Henrik Wann JensenCourtyard House with Curved ElementsMies van der RoheRaytracing vs. RadiosityBoth accomplish global illuminationBoth accomplish global illumination•RadiosityRadiosity–Compute energy transfer between finite-sized patches of surfaces in the sceneWhich patches? Must subdivide the sceneMust subdivide the scenesomehowsomehowHow does energy transfer between patches?How does energy transfer between patches?Approximating modelsApproximating modelsStill an area of researchStill an area of researchBoth accomplish global illuminationBoth accomplish global illumination•RadiosityRadiosity–Compute energy transfer between finite-sized patches of surfaces in the sceneWhich patches? Must subdivide the sceneMust subdivide the scenesomehowsomehowHow does energy transfer between patches?How does energy transfer between patches?Approximating modelsApproximating modelsStill an area of researchStill an area of researchWhich is better?Raytraced RadiosityHerik Wann Jensen•Radiosity captures the sum of light transfer wellRadiosity captures the sum of light transfer well–But it models all surfaces as diffuse reflectorsBut it models all surfaces as diffuse reflectors–Can’t model specular reflections or refractionCan’t model specular reflections or refractionImages are viewpoint independentImages are viewpoint independent•Raytracing captures the complex behavior of light rays as they reflect and Raytracing captures the complex behavior of light rays as they reflect and refractrefract–Works best with specular surfaces. Why?Works best with specular surfaces. Why?Diffuse surface converts light ray into many. Ray tracing follows Diffuse surface converts light ray into many. Ray tracing follows one ray and does not capture the full effect of the diffusion.one ray and does not capture the full effect of the diffusion.Must use ambient term to replace absent diffusionMust use ambient term to replace absent diffusion•Radiosity captures the sum of light transfer wellRadiosity captures the sum of light transfer well–But it models all surfaces as diffuse reflectorsBut it models all surfaces as diffuse reflectors–Can’t model specular reflections or refractionCan’t model specular reflections or refractionImages are viewpoint independentImages are viewpoint independent•Raytracing captures the complex behavior of light rays as they reflect and Raytracing captures the complex behavior of light rays as they reflect and refractrefract–Works best with specular surfaces. Why?Works best with specular surfaces. Why?Diffuse surface converts light ray into many. Ray tracing follows Diffuse surface converts light ray into many. Ray tracing follows one ray and does not capture the full effect of the diffusion.one ray and does not capture the full effect of the diffusion.Must use ambient term to replace absent diffusionMust use ambient term to replace absent diffusionLighting Example: Cornell BoxSurface ColorLighting Example: Diffuse ReflectionSurface Color Diffuse ShadingLighting Example: ShadowsNo Shadows ShadowsLighting Example: Soft ShadowsHard ShadowsPoint Light SourceSoft ShadowsArea Light SourceRadiosity: Cornell ExpermentMeasured SimulatedProgram of Computer GraphicsCornell UniversityRadiosity: Cornell ExperimentMeasured SimulatedDifferenceVery Early RadiosityParry Moon and Domina Spencer Lighting Design (1948 - MIT)Very Early RadiosityGoral et al. 1984.Goral et al. 1984.•Note the color bleedingNote the color bleedingGoral et al. 1984.Goral et al. 1984.•Note the color bleedingNote the color bleedingEarly RadiosityShenchang Eric Chang et al., Cornell 1988The ‘Rendering
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