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MIT 6 837 - Real-Time Shadows

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Real-Time ShadowsLast Time?Textures can AliasScheduleRayTracer::traceRay confusionQuestions?TodayWhy are Shadows Important?Shadows as a Depth CueFor Intuition about Scene LightingShadows as the Origin of PaintingShadows and ArtSlide 13ShadowsSoft ShadowsSlide 16Shadows in Ray TracingTraditional Ray TracingRay Tracing + Soft ShadowsSlide 20Slide 21Cast Shadows on Planar SurfacesLimitations of Planar ShadowsShadow/View DualityTexture MappingFake Shadows using Projective TexturesProjective Texture Shadow LimitationsSlide 28Slide 29Shadow MapsShadow MappingShadow Map Look UpLimitations of Shadow Maps1. Field of View Problem2. The Bias (Epsilon) Nightmare2. Bias (Epsilon) for Shadow Maps3. Shadow Map Aliasing3. Shadow Map Filtering3. Percentage Closer FilteringSlide 40Projective Texturing + Shadow MapShadows in ProductionHardware Shadow MapsSlide 44Slide 45Stencil BufferStencil Buffer – Real-time MirrorShadow VolumesSlide 49Slide 50Shadow Volumes w/ the Stencil BufferIf the Eye is in Shadow...1. Test Eye with Respect to Volumes2. Clip the Shadow Volumes3. "Z-Fail" Shadow VolumesSlide 56Optimizing Shadow VolumesLimitations of Shadow VolumesSlide 59Next Time:MIT EECS 6.837, Durand and CutlerReal-Time ShadowsMIT EECS 6.837, Durand and CutlerLast Time?•Perspective-Correct Interpolation•Texture Coordinates•Procedural Solid Textures•Other Mapping–Bump–Displacement–Environment–LightingMIT EECS 6.837, Durand and CutlerTextures can Alias•Aliasing is the under-sampling of a signal, and it's especially noticeable during animationnearest neighbormipmaps & linear interpolationMIT EECS 6.837, Durand and CutlerSchedule•Quiz 1: Tuesday October 26th, in class(1 week from today!)•Review Session: Monday October 25th,7:30-9pm, 1-150•Assignment 6: due Wednesday November 3rdMIT EECS 6.837, Durand and CutlerRayTracer::traceRay confusionOUTPUT: radiance (color & amount of light) along directionOUTPUT: intersection pointVec3f RayTracer::traceRay(Ray &ray, float tmin, int bounces, float weight, float indexOfRefraction, Hit &hit)scene->getGroup()->intersect(ray,hit,t)should only be called once, from within RayTracer::traceRay** This will help you implement and debug fast raytracing (assignment 6)MIT EECS 6.837, Durand and CutlerQuestions?MIT EECS 6.837, Durand and CutlerToday•Why are Shadows Important?•Shadows & Soft Shadows in Ray Tracing•Planar Shadows•Projective Texture Shadows•Shadow Maps•Shadow VolumesMIT EECS 6.837, Durand and CutlerWhy are Shadows Important?•Depth cue•SceneLighting•Realism•Contact pointsMIT EECS 6.837, Durand and CutlerShadows as a Depth CueMIT EECS 6.837, Durand and CutlerFor Intuition about Scene Lighting•Position of the light (e.g. sundial)•Hard shadows vs. soft shadows•Colored lights•Directional light vs. point lightMIT EECS 6.837, Durand and CutlerShadows as the Origin of PaintingMIT EECS 6.837, Durand and CutlerShadows and Art•Only in Western pictures (here Caravaggio)MIT EECS 6.837, Durand and CutlerToday•Why are Shadows Important?•Shadows & Soft Shadows in Ray Tracing•Planar Shadows•Projective Texture Shadows•Shadow Maps•Shadow VolumesMIT EECS 6.837, Durand and CutlerShadows•One shadow ray per intersection per point light sourceno shadow raysone shadow rayMIT EECS 6.837, Durand and CutlerSoft Shadows•Caused by extended light sources•Umbra –source completely occluded•Penumbra –Source partially occluded•Fully litMIT EECS 6.837, Durand and CutlerSoft Shadows•Multiple shadow rays to sample area light sourceone shadow raylots of shadow raysMIT EECS 6.837, Durand and CutlerShadows in Ray Tracing•Shoot ray from visible point to light source•If blocked, discard light contribution•Optimizations?–Stop after first intersection (don’t worry about tmin)–Coherence: remember the previous occluder,and test that object firstMIT EECS 6.837, Durand and CutlerTraditional Ray TracingMIT EECS 6.837, Durand and CutlerRay Tracing + Soft ShadowsMIT EECS 6.837, Durand and CutlerQuestions?MIT EECS 6.837, Durand and CutlerToday•Why are Shadows Important?•Shadows & Soft Shadows in Ray Tracing•Planar Shadows•Projective Texture Shadows–Shadow View Duality –Texture Mapping•Shadow Maps•Shadow VolumesMIT EECS 6.837, Durand and CutlerCast Shadows on Planar Surfaces•Draw the object primitives a second time, projected to the ground planeMIT EECS 6.837, Durand and CutlerLimitations of Planar Shadows•Does not produce self-shadows, shadows cast on other objects, shadows on curved surfaces, etc.MIT EECS 6.837, Durand and CutlerShadow/View Duality•A point is lit if it is visible from the light source•Shadow computation similar to view computationMIT EECS 6.837, Durand and CutlerTexture Mapping•Don't have to represent everything with geometryMIT EECS 6.837, Durand and CutlerFake Shadows using Projective Textures•Separate obstacle and receiver•Compute b/w image of obstacle from light•Use image as projective texture for each receiverImage from light source BW image of obstacle Final imageFigure from Moller & Haines “Real Time Rendering”MIT EECS 6.837, Durand and CutlerProjective Texture Shadow Limitations•Must specify occluder & receiver•No self-shadows•ResolutionFigure from Moller & Haines “Real Time Rendering”MIT EECS 6.837, Durand and CutlerQuestions?MIT EECS 6.837, Durand and CutlerToday•Why are Shadows Important?•Shadows & Soft Shadows in Ray Tracing•Planar Shadows•Projective Texture Shadows•Shadow Maps•Shadow VolumesMIT EECS 6.837, Durand and CutlerShadow Maps•In Renderman–(High-end production software)MIT EECS 6.837, Durand and CutlerShadow Mapping•Texture mapping with depth information•Requires 2 passes through the pipeline:–Compute shadow map (depth from light source) –Render final image,check shadow map to see if points are in shadowFoley et al. “Computer Graphics Principles and Practice”MIT EECS 6.837, Durand and CutlerShadow Map Look Up•We have a 3D point (x,y,z)WS•How do we look up the depth from the shadow map?•Use the 4x4 perspective projection matrix from the light source to get (x',y',z')LS•ShadowMap(x',y') < z'?Foley et al. “Computer Graphics Principles and Practice”(x,y,z)WS(x',y',z')LSMIT EECS 6.837, Durand and CutlerLimitations of Shadow Maps1. Field of View2. Bias (Epsilon)3. AliasingMIT EECS 6.837, Durand and Cutler1. Field of View Problem•What if point to


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MIT 6 837 - Real-Time Shadows

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