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How to make a PIXAR movie

How to make a PIXAR movie. Global Illumination Effects. Motivation. Realistic illumination of the scene. Motivation. Soft shadows. Motivation. Subsurface scattering. Motivation. Many algorithms exist Photon mapping Ambient Occlusion …

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How to make a PIXAR movie

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  1. Howtomake a PIXAR movie

    Global Illumination Effects
  2. Motivation Realisticilluminationofthescene
  3. Motivation Soft shadows
  4. Motivation Subsurfacescattering
  5. Motivation Manyalgorithmsexist Photon mapping AmbientOcclusion … Common goal: Solvingpartsofthe Rendering Equation
  6. Problems Scene changes -> New computation Still not possible in real-time UsesRaytracingorRadiosity Alreadyexplained Goingtobeexplainednow
  7. Photons Haveenergy h: Planck constant v: Frequencyoflight
  8. RadiometricQuantities
  9. Radiance θ: angle betweensurface‘s normal andω cosθ: Lambertianlaw Constant along a ray
  10. Irradiance
  11. BRDF Bidirectionalreflectancedistributionfunction Howmuchlightisreflected
  12. ReflectionEquation Integrateoverthehemisphere
  13. Rendering Equation Radiance BRDF Geometryfactor Visibility Emittedlight Surfaces
  14. Radiosity Ideal diffuse reflectioncanbesimulatedwithRadiosity Uses finite elements IntroducedbyGoral et al.
  15. Radiosity Origin: Thermal heattransfer Developed in 1984, still in use Modellingof diffuse lighting Doesn‘taccountforspecularlighting Independent ofviewer Therefore: Staysconstant in constantscene
  16. RadiosityEquation constant Emissivity Radiosity Reflectivity Form factor
  17. Form Factors
  18. Form Factors
  19. Nusselt Analog Simple geometric analog forcalculating form factors B A
  20. HemicubeAlgorithm Hemicubeinsteadofhemisphere
  21. HemicubeAlgorithm Idea: Precomputedelta form factorsanalytically Count coveredpixels Sumupcovereddelta form factorstothetrue form factor
  22. HemicubeExample
  23. HemicubeAlgorithm on GPU Useprojectioncenterasviewport Usecurrentfaceasviewing plane Do therendering Grab thecolourbuffer (IDs ofpatches) Count colouredpixels Visibilitytestperformedbydepthtest
  24. RadiosityAlgorithm Compute form factors Solve linear equationsystem for i = 1, … , n
  25. Von Neumann Series 0 Bounces 1 Bounce 2 Bounces 3 Bounces
  26. Jacobi Iteration
  27. Shooting / Gathering
  28. RadiosityResult
  29. Radiosity vs. Ray Tracing
  30. RadiosityConclusion Old, but still in use Usedforsimulating diffuse lighting Resultcanbeused in combinationwithother GI algorithms
  31. AmbientOcclusion Motivation Ambienttermconstant in Phong model Not veryrealistic Idea: Computeocclusionofeachface
  32. AmbientOcclusion Result: Occludedareasappeardarkerthanbrigtherones MultiplywithusualPhong model 2 possibilities: Screen space Objectspace
  33. Screen Space AmbientOcclusion Can becompletelydone on GPU Nopreprocessing Independent ofscenecomplexity Idea: Insteadofperformingfullraytracinguseocclusioninformationfrom z-buffer
  34. Screen Space AmbientOcclusion Take 3D samplesaroundeachpoint Determineocclusionofeachpointbytestingagainstthedepthbuffer Farsampleswithlessinfluence Useblurringfor smooth results
  35. Screen Space AmbientOcclusion
  36. Object Space AmbientOcclusion Definesurfaceelementas an orienteddisk UseHeron‘sformula , Store position, normal andarea in textureforpixelshader
  37. Object Space AmbientOcclusion Computeaccessibilityvalueat eachelement (% ofhemisphere) Approximation based on the solid angle of an orienteddisk Stronglydependent on scene complexity
  38. Object Space AmbientOcclusion
  39. AmbientOcclusionResults
  40. AmbientOcclusionResults
  41. AmbientOcclusionConclusion Can bepreprocessedforeachobject Used in thecurrentversionofPIXAR‘sRenderMan
  42. Outlook Fastercomputation Cheaper Artistscanseeresultsfaster More realisticlighting
  43. Conclusion Veryimportantforanyanimatedmovie Computation time not tooimportant
  44. Thanksforyourattention!
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