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Moving Frostbite to Physically Based Rendering

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  1. 1. Moving to PBR Sébastien Lagarde & Charles de Rousiers
  2. 2. Acknowledgments • Contributions from *many* people • This talk and the course notes are about: 1. Summarizing all of the steps to move an engine to PBR 2. Using the state of the art in our base implementation 3. Small improvements in quality
  3. 3. Disclaimer • This presentation is about:  A high level overview  Steps to move to PBR • Courses notes come with full details and code …
  4. 4. What is the scope of PBR?
  5. 5. What is the scope of PBR?
  6. 6. What is the scope of PBR? Environment
  7. 7. What is the scope of PBR? Environment
  8. 8. What is the scope of PBR? Environment 1 Materials 2 Lighting 3 Camera
  9. 9. What is the scope of PBR? Environment 1 Materials 2 Lighting 3 Camera
  10. 10. What is the scope of PBR? Environment 1 Materials 2 Lighting 3 Camera
  11. 11. Reference framework • Need good reference  Export to offline path-tracer  In-engine reference
  12. 12. Materials
  13. 13. Material – Standard Model • Standard material  80% of appearance types  Model • Specular: Microfacet model with GGX NDF • Diffuse: Disney’s model • Other material types  Subsurface material  Single layer coated material DielectricConductor
  14. 14. Material – Specular 4 (n.v) F(v, h, f0) G(v, l, h ) D(h, ɑ) (n.l) Fs(v, l) = Schlick GGX Height- Correlated Smith [Heitz14]
  15. 15. Material – Specular Standard (uncorrelated) Smith G Term DielectricMetal
  16. 16. Material – Specular Height-correlated Smith G Term DielectricMetal
  17. 17. Material - Specular Height-correlated Smith G Term Correlated Standard
  18. 18. Material – Diffuse • Disney Diffuse [Burley12]  Coupled roughness between diffuse and specular  Retro-reflection
  19. 19. Material – Diffuse Lambertian Diffuse RoughSmooth
  20. 20. Material – Diffuse Disney Diffuse RoughSmooth
  21. 21. Material - Diffuse Disney’s Diffuse Disney LambertDisney Lambert Smooth Roughness
  22. 22. Material – Diffuse Original Disney Diffuse Renormalized Disney Diffuse Diffuse + Specular
  23. 23. Material – Diffuse Disney Diffuse
  24. 24. Material – Diffuse Renormalized Disney Diffuse
  25. 25. Material – Parameterization Normal BaseColor Smoothness Metallic Reflectance Normal BaseColor Reflectance Smoothness Metallic
  26. 26. Material – Parameterization (1 –Smoothness) (1 –Smoothness) 2 (1 –Smoothness) 3 (1 –Smoothness) 4 Burley12 Smoothness
  27. 27. Material – Parameterization Fresnel0 Reflectance 0 255 ConductorsDielectrics CommonMicro occlusion Gem stones 0 1 128
  28. 28. Material – Parameterization
  29. 29. Lighting
  30. 30. Lighting
  31. 31. Lighting
  32. 32. Lighting
  33. 33. Lighting
  34. 34. Lighting • Lighting coherence  All BRDFs must be integrated properly with all light types  All lights need to manage both direct and indirect lighting  All lighting is composed properly (SSR/local IBL/…)  All lights have the correct ratio between each other
  35. 35. Lighting – Units & Frame of Reference Light Power
  36. 36. Lighting – Units & Frame of Reference Light Power 15 lm 1 200 lm 2 600 lm 64 000 lux
  37. 37. Lighting – Units & Frame of Reference Luminous power Lumens Lux Illuminance Luminous intensity Candela Luminance Candela/m2 Photometric Unit System
  38. 38. Lighting – Units & Frame of Reference Luminous power (lm), Luminance (cd/m2), or EVArea Luminous power (lm)Punctual Photometric Emissive Sun Luminous intensity (cd) Luminance (cd/m2) or EV Illuminance (lux)
  39. 39. Lighting – Analytical Lights • Parameterization 1,000 k 10,000 k
  40. 40. Lighting – Units & Frame of Reference
  41. 41. Lighting – Analytical Lights
  42. 42. Lighting – Analytical Lights Point Sphere Line Tube Spot Disk Frustum Rectangle Punctual Area
  43. 43. Lighting – Analytical Lights • Punctual lights  Unit: Lum. power (lm) or Lum. intensity (cd)  Use smooth attenuation [Karis13] Inverse square Karis13 Distance Falloff Attenuation Radius
  44. 44. Lighting – Analytical Lights • Photometric lights  Unit: luminous intensity (cd)  Applied to point and spot lights Simple / Isotropic Profile IES photometric Profile Artists Measured
  45. 45. Lighting – Analytical Lights • Area lights  Unit: Luminous power (lm), Luminance (cd/m2 or EV)  Separate diffuse and specular evaluation
  46. 46. Lighting – Analytical Lights • Area lights Without horizon handling With horizon handling Large area light Horizon handling
  47. 47. Lighting – Analytical Lights • Diffuse area lights  3 integration techniques: • Analytic Form factors (radiosity) / view factors (heat transfer) • MRP Solid angles x Most Representative Point lighting [Drobot14] • Structured sampling of light shape Solid angles x average cos
  48. 48. Lighting – Analytical lights • Area lights: Diffuse term Sphere Tube Disk Rectangle View factor Mix of sphere and rectangle View factor Structured sampling
  49. 49. Lighting – Analytical Lights • Specular area lights  No satisfying method  Shortest distance to reflection ray with energy conservation [Karis13]
  50. 50. Lighting – Analytical Lights • Sun light  Units: Illuminance (lux)  Facing disk with non-null solid angle
  51. 51. Lighting – Analytical Lights • Emissive surfaces  Units: Luminance (cd/m2 or EV)  ”Visible part” of a light  Does not emit light
  52. 52. Lighting – Image-Based Lights • Types of IBLs  Distant light probe  Local light probes  Screen-space reflections  Planar reflections
  53. 53. Lighting – Image-Based Lights • Types of IBLs  Distant light probe  Local light probes  Screen-space reflections  Planar reflections Focus
  54. 54. Lighting – Image-Based Lights • Units: Luminance (cd/m2 or EV) • Source for the distant light probe  HDRI  Procedural sky
  55. 55. Lighting – Image-Based Lights • Light probe lighting: Integral[Env. lighting x BRDF] • Pre-integration by separating: • Integral of Lighting x NDF, for V = N • Integral of BRDF, for all V & roughness values Specular [Karis13] & Diffuse
  56. 56. Lighting – Image-Based Lights • Light probe lighting: Integral[Env. lighting x BRDF] • Pre-integration by separating: • Integral of Lighting x NDF, for V = N • Integral of BRDF, for all V & roughness values Specular [Karis13] & Diffuse LD DFG
  57. 57. Lighting – Image-Based Lights • Light probe lighting: pre-integration Isotropic approximation Reference Error due to LD pre-integration with V = N
  58. 58. Lighting – Image-Based Lights • Light probe lighting: pre-integration  LD needs to be computed each time the lighting changes  Needs to be fast (real-time capture / refresh)  Deals with HDR source • Integration method for LD  Importance sampling  Multiple importance sampling  Filtered importance sampling
  59. 59. Lighting – Image-Based Lights • Light probe lighting: pre-integration  LD needs to be computed each time the lighting changes  Needs to be fast (real-time capture / refresh)  Deals with HDR source • Integration method for LD  Importance sampling  Multiple importance sampling  Filtered importance sampling Faster convergence
  60. 60. Lighting – Image-Based Lights • Light probe: pre-integration Filtered importance sampling Importance sampling
  61. 61. Lighting – Image-based lights • Light probe: pre-integration Pre-Filtered importance sampling Importance sampling Filtered ISSimple IS
  62. 62. Lighting – Image-Based Lights Light probe • Runtime evaluation N
  63. 63. Lighting – Image-Based Lights Light probe • Runtime evaluation N
  64. 64. Lighting – Image-Based Lights Light probe • Runtime evaluation N
  65. 65. Lighting – Image-Based Lights Light probe • Runtime evaluation N
  66. 66. Lighting – Image-Based Lights Mirror Direction DielectricMetal
  67. 67. Lighting – Image-Based Lights Dominant Direction DielectricMetal
  68. 68. Lighting – Image-Based Lights Main Direction DominantReferenceMirrorReference
  69. 69. Lighting – Image-Based Lights • Local light probes  Acquire surrounding geometry  Approximate local parallax: box & sphere proxy [Lagarde12]
  70. 70. RGB Dielectric Conductor Sky is handled by distant light probe
  71. 71. ConductorDielectric
  72. 72. Lighting – Image-Based Lights • Distant & local light probes composition  Lots of local light probes across level  Local light probes can overlap each other  Distant light probe contains sky information RGB Alpha
  73. 73. Probe Lighting – Image-Based Lights • Distance-based roughness Probe
  74. 74. Probe Lighting – Image-Based Lights • Distance-based roughness Probe
  75. 75. Probe Lighting – Image-Based Lights • Distance-based roughness Probe
  76. 76. Probe Lighting – Image-Based Lights • Distance-based roughness Probe
  77. 77. Probe Lighting – Image-Based Lights • Distance-based roughness Probe
  78. 78. Camera
  79. 79. Camera – Physically Based Camera • Transforming scene luminance to pixel value
  80. 80. Camera – Settings Sensor (Sensitivity) Aperture Lens Shutter Speed f/1.4 1/125s ISO 100 f/2.8 1/125s ISO 100 f/5.6 1/125s ISO 100 f-Stop 1/s ISO
  81. 81. Camera – Exposure Scene luminance Sensor illumiance CCD ADC FilmStock Sensor exposure Quantized value Pixel value Normalized value lux lux.scd/m2
  82. 82. Camera – Exposure Incident Luminance Camerarange 1 0 Camera range Pixelvalue 1 0 1. Film stock / tone map 2. Style (LUT / grading) 3. sRGB / Rec709 1 Exposure computation based on HSBS sensitivity
  83. 83. Camera – Exposure • Sunny 16 rule as validation  Sky 20,000 lux  Sun 100,000 lux f/16 1/125s ISO 100
  84. 84. Transition to PBR
  85. 85. Transition – Steps 1. Standard material + viewer first + educating key artists 2. PBR / non-PBR in parallel, with automatic conversion 3. Evangelize PBR to game teams + validation tools Fresnel0 Diffuse Albedo Illuminance
  86. 86. Acknowledgements • EA Frostbite - Alex Fry, Christian Bense, Noah Klabunde, Henrik Fernlund, the rendering team • EA DICE - Yasin Uludag, Arne Schober • Lucasfilm: Lutz Latta, Cliff Ramshaw, Rodney Huff, Rogers Cordes • Graphics community: Michał Drobot, Benjamin Rouveyrol, Eric Heitz, Juan Cañada, Ondra Karlík, Tomasz Stachowiak, Brian Karis • Stephen Hill & Stephen McAuley
  87. 87. QUESTIONS? Sébastien Lagarde Lagardese@hotmail.fr Twitter: @seblagarde Charles de Rousiers Charles.derousiers@frostbite.com Twitter: @kiwaiii
  88. 88. References • [Burley12] Brent Burley, “Physically Based Shading at Disney”, SIGGRAPH’12, PBR Course • [Karis13] Brian Karis, “Real Shading in Unreal Engine 4”, SIGRRAPH’13, PBR Course • [Drobot14] Michal Drobot, ”Physically Based Area Lights”, GPU Pro 5 • [Heitz14] Eric Heitz, ”Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs”, JCGT, 2014 • [Lagarde12] Sébastien Lagarde, “Local Image-based Lighting With Parallax- Corrected Cubemaps”, SIGGRAPH’12
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