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Physically-Based Shading
Computer Graphics Seminar
MTAT.03.305
Raimond Tunnel
Intro into: https://cglearn.eu/pub/advanced-computer-graphics/physically-based-shading
Physically-Based Shading Computer Graphics Seminar MTAT.03.305 - - PowerPoint PPT Presentation
Physically-Based Shading Computer Graphics Seminar MTAT.03.305 - - PowerPoint PPT Presentation
Physically-Based Shading Computer Graphics Seminar MTAT.03.305 Raimond Tunnel Intro into: https://cglearn.eu/pub/advanced-computer-graphics/physically-based-shading Phongs Lighting Model Phongs Lighting Model Phongs Lighting Model
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Phong’s Lighting Model
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Phong’s Lighting Model
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Phong’s Lighting Model
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Specular
Not just a highlight
vs
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Specular
Not just a highlight
vs
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Specular
Not just a highlight
vs
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Diffuse*
Diffuse light should also use the environment.
vs
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Dielectrics and Metals
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Dielectrics
pixel
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Dielectrics
Color comes from the diffuse Dielectrics also have specular!
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Metals
pixel
electron gas
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Metals
Metals are specular only!
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Dielectrics and Metals
electrons absorb the complementary wavelengths electron gas absorbs the complementary wavelengths dissipates the energy
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Dielectrics and Metals
electrons absorb the complementary wavelengths absorbed by the electron gas
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Dielectrics and Metals
Specify how much light is absorbed / reflected.
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Fresnel
Amount of light reflected ( ) depends on:
- 1. Phase velocity of light in the material
- 2. Angle of incidence
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Fresnel
- 1. Phase velocity of light in the material
https://en.wikipedia.org/wiki/File:Wave_group.gif
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Fresnel
- 1. Phase velocity of light in the material
Index of refraction Speed of light in a vacuum Phase velocity of light in the material
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Fresnel
- 1. Phase velocity of light in the material
material
~n
Air 1.00 Water 1.33 Window glass 1.52 Sapphire 1.76 Diamond 2.42
https://en.wikipedia.org/wiki/List_of_refractive_indices
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Fresnel
- 2. Angle of incidence
Steep angle: Penetrates the material Grazing angle: Ricochets off
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Fresnel
Schlick’s approximation
air material
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Fresnel
Schlick’s approximation
air material
This works well
- nly for dielectrics!
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Fresnel
https://refractiveindex.info/?shelf=3d&book=plastics&page=ps
visible light ~1.62 ~1.58
Polystyrene (common plastic)
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Fresnel
https://refractiveindex.info/?shelf=3d&book=metals&page=aluminium
visible light ~4.57 ~0.43
Aluminium Complex IoR. Changes a lot.
~2.31 ~8.46
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Fresnel
https://refractiveindex.info/?shelf=3d&book=metals&page=brass
visible light ~1.82 ~1.50
Brass Complex IoR. Changes a lot.
~0.46 ~4.42
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Fresnel
The value is the reflected spectra at 0°. We can specify it ourselves instead of relying on the calculation with the index of refraction.
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Fresnel
material dielectrics gold aluminium copper iron
https://80.lv/articles/the-newbies-pbr-cheat-sheet/
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Fresnel
absorbed by the electron gas
Metals Dielectrics
diffusely scattered back out in material color
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Fresnel
Metals: in material color Dielectrics: uniform
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Fresnel
20% 80% 40% 60%
All objects are more reflective at grazing angles.
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Fresnel
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Dielectrics and Metals
color color black white
absorbed scattered
copper
light source color tinted
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Dielectrics and Metals
– is the material metal (1) or dielectric (0)
– color for metals, ~0.03 for dielectrics
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Interesting Links
https://psgraphics.blogspot.com/2020/03/fresnel-equations-schlick-approximation.ht ml - Peter Shirley, 13.03.2020 https://otik.zcu.cz/bitstream/11025/11214/1/Lazanyi.pdf - Lazanyi, 2005, a way to use Schlick with complex number IoR. https://www.scratchapixel.com/lessons/3d-basic-rendering/introduction-to-shading/re flection-refraction-fresnel - Reflection, Refraction (Transmission) and Fresnel
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In Game Engines and Graphics Libraries
What tools are these?
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Microfacets
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Microfacets
Surfaces are not generally microscopically flat!
pixel pixel
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Microfacets
The microfacet function
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Microfacets
The microfacet function We look at all the directions on a hemisphere for microfacet normals
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Microfacets
The microfacet function Given one microsurface with normal , how much light it radiates
The material (BRDF) of one microsurface.
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Microfacets
The microfacet function The total area of the microsurfaces that are with the normal . The distribution term.
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Microfacets
The microfacet function What percentage of the microsurfaces are illuminated? The geometry term.
masking shadowing V-cavities:
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Microfacets
The microfacet function Contribution into the viewer’s pixel.
(projected area)
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Microfacets
The microfacet function Contribution of the incoming light.
(projected area)
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Microfacets
Usually that integral is difficult to solve analytically! And you do not want to do some big sum in the fragment shader to approximate it…
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Oren-Nayar (1994) σ = 1.4
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Oren-Nayar (1994)
A numerical approximation for: – ideal diffuse reflector – Gaussian: macrosurface normal,
user parameter
– V-cavities
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Oren-Nayar (1994)
– the color
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Oren-Nayar (1994)
Authors were inspired by previous research about shading the moon (eg by Ernst Öpik in 1924).
http://kevin-george-2n3x.squarespace.com/blog/2014/5/25/shading-diffuse-models
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Cook-Torrance (1982)
An analytical solution for: – ideal specular reflector – Beckmann: macrosurface normal,
user parameter
– V-cavities
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Cook-Torrance (1982)
(Beckmann distribution) The integral was analytically converted to a finite equation!
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Cook-Torrance (1982)
red plastic aluminium
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Metallic-Roughness Workflow
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Links, examples and further materials in: Thanks
https://cglearn.eu/pub/advanced-computer-graphics/ physically-based-shading