1 / 44

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 …

inara
Download Presentation

How to make a PIXAR movie

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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!

More Related