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GDC 2016 End-to-End Approach to Physically Based Rendering


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Physically based rendering is gaining increasing traction in the gaming world and with its list of benefits, this growth is no surprise. When the guesswork around authoring surface attributes is removed and artists can set up a material once to be efficiently reused throughout a game, they can spend much more time focusing on the more creative (and fun!) aspects of texturing. Yet in order to take full advantage of a physically based approach and ensure that each material responds as desired to any lighting condition, it is necessary to author with an awareness of how light actually interacts with different surfaces. This talk provides an easily accessible introduction to the principles of lighting and energy conservation before exploring guidelines for authoring infallible surface attribute maps. We will demonstrate the principles discussed and highlight the effect decisions made at the material creation stage affect the final render.

*Presentation was co-presented with Sam Bugden : Senior Technical Artist, Geomerics.

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GDC 2016 End-to-End Approach to Physically Based Rendering

  1. 1. An End-to-End Approach to Physically Based Rendering _ __ Wes McDermott Community Manager – Tech Artist, Allegorithmic _ Sam Bugden Senior Technical Artist, Geomerics
  2. 2. Session: Context ● Still a lot of confusion and misunderstanding about PBR ● A lot of PBR learning material not very ‘artist friendly’ ● Completely new approach to the way we think about how we author our content Character model created by Michael Pavlovich
  3. 3. High-level look into: 1. Understanding PBR 2. Authoring Workflow & Guidelines 3. Troubleshooting Physically-Based Scenes 4. Q&A Session: Purpose Character model created by Michael Pavlovich
  4. 4. 1. Understanding PBR _ __
  5. 5. What is PBR? As the name suggests, physically-based rendering (PBR) is a method of shading & rendering, used in order to provide a more accurate representation of the real (physics-based) world around us.
  6. 6. Why bother to learn the science? ● As artists it’s important for us to understand how light interacts with surfaces in order for us to be able to realistically re-create this within our own content. Better understanding = Better content
  7. 7. Key Concepts of PBR 1. Specular and Diffuse Reflection 2. Microfacet Theory 3. F0 Reflectance 4. Energy Conservation Material by Pierre Fleau
  8. 8. When light hits a surface Incident RaySpecular Reflection Refracted Scattered Diffuse Reflection Air Surface Absorbed
  9. 9. Colour Incoming Light Blue Light Reflected Rest of the light rays are absorbed
  10. 10. Not all surfaces are perfectly smooth!
  11. 11. Not all surfaces are perfectly smooth! Microfacet Theory
  12. 12. Measuring Reflectance Edge = High Reflectance Centre = Low Reflectance F0 A smooth, dielectric surface Fresnel Fresnel at 0 Degrees Viewing Angle
  13. 13. Enforcing the physics Light reflected off a surface will never be brighter than the light that fell upon it. Incoming Light Outgoing Light <
  14. 14. Enforcing the physics Energy Conservation Incoming Light Outgoing Light <
  15. 15. 2. Authoring Workflow & Guidelines _ __
  16. 16. Base Color Roughness Metallic Diffuse Glossiness Specular Normal Ambient Occlusion Metallic Workflow Specular Workflow
  17. 17. Base Color (Albedo) ● Devoid of lighting information *exception micro-occlusion ● No dark values below 30 sRGB (50 sRGB – strict mode) ● No bright values above 240 sRGB
  18. 18. >30 sRGB >30 sRGB Character model created by Michael Pavlovich
  19. 19. Metal Reflectance Values Base Color & Metallic ● 70-100% specular (180-255 sRGB) ● Some metals can be corroded ● Painted or coated metal is dielectric ● Dielectric layer affects metallic map examples: dirt and rust
  20. 20. Titanium sRGB (93,186,177) Base Color Metallic 70 - 100% Specular Diffuse Reflected Color Metal Reflectance Value
  21. 21. MetallicDirt layer on metal
  22. 22. F0 (Fresnel 0 Angle) 2-5% Reflective Common dielectrics ex. wood, concrete, plastic 100% Reflective at grazing angleFresnelF0 Plastic sRGB(59,59,59)
  23. 23. 0% 8%2% 4% 5% 0.0 1.00.5 Common Dielectrics Remapped Range Shader Range GemstonesAir Custom Dielectric IOR Ex. Water = 0.255
  24. 24. Roughness (micro-surface) RoughSmooth
  25. 25. 3. Troubleshooting Physically-Based Scenes _ __
  26. 26. Summary 1. Understanding PBR: ● Many great benefits to using PBR, but we must fully embrace it and its rules in order to truly get the best out of it. ● In order for us to do this, its crucial that we spend some time looking at the basic scientific theories and principles which underpin PBR, as the better our understanding is – the better our content will become. Character model created by Michael Pavlovich
  27. 27. Summary 2. Authoring Workflow & Guidelines: ● Base Color is devoid of lighting info and no dark values below 30 sRGB or bright values above 240 sRGB ● Metal reflectance is 70-100% specular (180-255 sRGB) and the metallic map values are mainly binary (black or white). ● The roughness map is the most creative map to author. You can’t go wrong here. White = rough and black = smooth. Character model created by Michael Pavlovich
  28. 28. Summary 3. Troubleshooting Physically-Based Scenes ● PBR materials can often miss-direct us about the roots cause of issues in our scene ● When objects are not behaving as expected, investigate the material properties before adjusting other elements such as lighting or reflections. Character model created by Michael Pavlovich
  29. 29. 4. Q&A – Thanks for your time!  _ __