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Initial implementation of Disney Principled (#2004)
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This changelist adds an initial MaterialX graph for the Disney Principled BSDF, as described in Brent Burley's 2012 and 2015 presentations.

For simplicity, the original separated interfaces for `disney_brdf_2012` and `disney_bsdf_2015` have been merged into a single `disney_principled` interface, providing artists with a unified entry point for the shading model.

Where possible, the original empirical approach of Disney Principled has been preserved, including the use of the `burley_diffuse_bsdf` and `generalized_schlick_bsdf` nodes, though a few simplifications have been employed, including the use of the `layer` node for physically based layering and the `sheen_bsdf` node for the sheen layer.
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jstone-lucasfilm authored Sep 7, 2024
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10 changes: 10 additions & 0 deletions documents/Specification/MaterialX.PBRSpec.md
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Expand Up @@ -381,6 +381,14 @@ Note that the standard library includes definitions for [**`displacement`**](./M
This section contains examples of shading model implementations using the MaterialX PBS library. For all examples, the shading model is defined via a <nodedef> interface plus a nodegraph implementation. The resulting nodes can be used as shaders by a MaterialX material definition.


## Disney Principled BSDF

This shading model was presented by Brent Burley from Walt Disney Animation Studios in 2012[^Burley2012], with additional refinements presented in 2015[^Burley2015].

A MaterialX definition and nodegraph implementation of the Disney Principled BSDF can be found here:
[https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/libraries/bxdf/disney_principled.mtlx](https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/libraries/bxdf/disney_principled.mtlx)


## Autodesk Standard Surface

This is a surface shading model used in Autodesk products created by the Solid Angle team for the Arnold renderer. It is an über shader built from ten different BSDF layers[^Georgiev2019].
Expand Down Expand Up @@ -430,6 +438,8 @@ The MaterialX PBS Library includes a number of nodegraphs that can be used to ap

[^Burley2012]: Brent Burley, **Physically-Based Shading at Disney**, <https://media.disneyanimation.com/uploads/production/publication_asset/48/asset/s2012_pbs_disney_brdf_notes_v3.pdf>, 2012

[^Burley2015]: Brent Burley, **Extending the Disney BRDF to a BSDF with Integrated Subsurface Scattering**, <https://blog.selfshadow.com/publications/s2015-shading-course/burley/s2015_pbs_disney_bsdf_notes.pdf>, 2015

[^Christensen2015]: Per H. Christensen, Brent Burley, **Approximate Reflectance Profiles for Efficient Subsurface Scattering**, <http://graphics.pixar.com/library/ApproxBSSRDF/> 2015

[^Conty2017]: Alejandro Conty, Christopher Kulla, **Production Friendly Microfacet Sheen BRDF**, <https://fpsunflower.github.io/ckulla/data/s2017_pbs_imageworks_sheen.pdf>, 2017
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4 changes: 1 addition & 3 deletions documents/Specification/MaterialX.Specification.md
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Expand Up @@ -2387,7 +2387,7 @@ Custom nodes that output data types with a "shader" semantic are referred to in
The attributes for &lt;nodedef> elements as they pertain to the declaration of shaders are:

* `name` (string, required): a user-chosen name for this shader node definition element.
* `node` (string, required): the name of the shader node being defined, which typically matches the name of an associated shader function such as “blinn_phong”, “Disney_BRDF_2012”, “volumecloud_vol”. Just as for custom nodes, this shading program may be defined precisely through an &lt;implementation> or &lt;nodegraph>, or left to the application to locate by name using any shader definition method that it chooses.
* `node` (string, required): the name of the shader node being defined, which typically matches the name of an associated shader function such as “blinn_phong”, “disney_principled”, “volumecloud_vol”. Just as for custom nodes, this shading program may be defined precisely through an &lt;implementation> or &lt;nodegraph>, or left to the application to locate by name using any shader definition method that it chooses.

The child &lt;output> element within the &lt;nodedef> defines the "data type" of the output for this shader, which must have been defined with a "shader" semantic; see the [Custom Data Types](#custom-data-types) section above and discussion below for details.

Expand Down Expand Up @@ -2707,8 +2707,6 @@ Example uses for variants include defining a number of allowable colors and text
Variants and variantsets are not intrinsically associated with any particular material; they merely state a number of values for a number of named inputs/tokens. However, variantsets may state that they are associated with specific shader-semantic nodes and/or &lt;nodedef> declarations by providing stringarray-type `node` and/or `nodedef` attributes:

```xml
<variantset name="damagevars" node="Disney_BRDF_2012,Disney_BRDF_2015">
...
<variantset name="costumevars" nodedef="ND_unifiedsrf_studio">
...
```
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25 changes: 0 additions & 25 deletions libraries/bxdf/disney_brdf_2015.mtlx
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140 changes: 140 additions & 0 deletions libraries/bxdf/disney_principled.mtlx
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<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709">

<nodedef name="ND_disney_principled" node="disney_principled" nodegroup="pbr" doc="The Disney Principled BSDF">
<input name="baseColor" type="color3" value="0.16, 0.16, 0.16" uiname="Base Color" uifolder="Base" />
<input name="metallic" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Metallic" uifolder="Base" />
<input name="roughness" type="float" value="0.5" uimin="0.0" uimax="1.0" uiname="Roughness" uifolder="Base" />
<input name="anisotropic" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Anisotropic" uifolder="Specular" />
<input name="specular" type="float" value="0.5" uimin="0.0" uimax="1.0" uiname="Specular" uifolder="Specular" />
<input name="specularTint" type="float" value="0" uimin="0.0" uimax="1.0" uiname="Specular Tint" uifolder="Specular" />
<input name="sheen" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Sheen" uifolder="Sheen" />
<input name="sheenTint" type="float" value="0.5" uimin="0.0" uimax="1.0" uiname="Sheen Tint" uifolder="Sheen" />
<input name="clearcoat" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Clearcoat" uifolder="Clearcoat" />
<input name="clearcoatGloss" type="float" value="1.0" uimin="0.0" uimax="1.0" uiname="Clearcoat Gloss" uifolder="Clearcoat" />
<input name="specTrans" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Spec Trans" uifolder="Transmission" />
<input name="ior" type="float" value="1.5" uisoftmin="1.0" uisoftmax="3.0" uiname="IOR" uifolder="Transmission" />
<input name="subsurface" type="float" value="0.0" uiname="Subsurface" uifolder="Subsurface" />
<input name="subsurfaceDistance" type="color3" value="1.0, 1.0, 1.0" uiname="Subsurface Distance" uifolder="Subsurface" />
<output name="out" type="surfaceshader" />
</nodedef>

<nodegraph name="NG_disney_principled" nodedef="ND_disney_principled">

<!-- Diffuse Layer -->
<invert name="invert_metalness" type="float">
<input name="in" type="float" interfacename="metallic" />
</invert>
<burley_diffuse_bsdf name="diffuse_bsdf" type="BSDF">
<input name="weight" type="float" nodename="invert_metalness" />
<input name="color" type="color3" interfacename="baseColor" />
<input name="roughness" type="float" interfacename="roughness" />
</burley_diffuse_bsdf>

<!-- Subsurface Layer -->
<subsurface_bsdf name="subsurface_bsdf" type="BSDF">
<input name="color" type="color3" interfacename="baseColor" />
<input name="radius" type="color3" interfacename="subsurfaceDistance" />
</subsurface_bsdf>
<mix name="subsurface_mix" type="BSDF">
<input name="bg" type="BSDF" nodename="diffuse_bsdf" />
<input name="fg" type="BSDF" nodename="subsurface_bsdf" />
<input name="mix" type="float" interfacename="subsurface" />
</mix>

<!-- Sheen Layer -->
<mix name="sheen_color" type="color3">
<input name="bg" type="color3" value="1, 1, 1" />
<input name="fg" type="color3" interfacename="baseColor" />
<input name="mix" type="float" interfacename="sheenTint" />
</mix>
<sheen_bsdf name="sheen_bsdf" type="BSDF">
<input name="weight" type="float" interfacename="sheen" />
<input name="color" type="color3" nodename="sheen_color" />
</sheen_bsdf>
<layer name="sheen_layer" type="BSDF">
<input name="top" type="BSDF" nodename="sheen_bsdf" />
<input name="base" type="BSDF" nodename="subsurface_mix" />
</layer>

<!-- Transmission Layer -->
<dielectric_bsdf name="transmission_bsdf" type="BSDF">
<input name="tint" type="color3" interfacename="baseColor" />
<input name="ior" type="float" interfacename="ior" />
<input name="roughness" type="vector2" value="0.0, 0.0" />
<input name="scatter_mode" type="string" value="T" />
</dielectric_bsdf>
<mix name="transmission_mix" type="BSDF">
<input name="bg" type="BSDF" nodename="sheen_layer" />
<input name="fg" type="BSDF" nodename="transmission_bsdf" />
<input name="mix" type="float" interfacename="specTrans" />
</mix>

<!-- Dielectric Layer -->
<roughness_anisotropy name="specular_roughness" type="vector2">
<input name="roughness" type="float" interfacename="roughness" />
<input name="anisotropy" type="float" interfacename="anisotropic" />
</roughness_anisotropy>
<multiply name="dielectric_intensity" type="float">
<input name="in1" type="float" interfacename="specular" />
<input name="in2" type="float" value="0.08" />
</multiply>
<mix name="dielectric_tint" type="color3">
<input name="bg" type="color3" value="1, 1, 1" />
<input name="fg" type="color3" interfacename="baseColor" />
<input name="mix" type="float" interfacename="specularTint" />
</mix>
<generalized_schlick_bsdf name="dielectric_bsdf" type="BSDF">
<input name="weight" type="float" nodename="dielectric_intensity" />
<input name="color0" type="color3" nodename="dielectric_tint" />
<input name="roughness" type="vector2" nodename="specular_roughness" />
</generalized_schlick_bsdf>
<layer name="dielectric_layer" type="BSDF">
<input name="top" type="BSDF" nodename="dielectric_bsdf" />
<input name="base" type="BSDF" nodename="transmission_mix" />
</layer>

<!-- Metallic Layer -->
<generalized_schlick_bsdf name="metallic_bsdf" type="BSDF">
<input name="color0" type="color3" interfacename="baseColor" />
<input name="roughness" type="vector2" nodename="specular_roughness" />
</generalized_schlick_bsdf>
<mix name="metallic_mix" type="BSDF">
<input name="bg" type="BSDF" nodename="dielectric_layer" />
<input name="fg" type="BSDF" nodename="metallic_bsdf" />
<input name="mix" type="float" interfacename="metallic" />
</mix>

<!-- Coat Layer -->
<multiply name="coat_intensity" type="float">
<input name="in1" type="float" interfacename="clearcoat" />
<input name="in2" type="float" value="0.04" />
</multiply>
<invert name="coat_roughness" type="float">
<input name="in" type="float" interfacename="clearcoatGloss" />
</invert>
<convert name="coat_roughness_vector" type="vector2">
<input name="in" type="float" nodename="coat_roughness" />
</convert>
<roughness_dual name="coat_roughness_dual" type="vector2">
<input name="roughness" type="vector2" nodename="coat_roughness_vector" />
</roughness_dual>
<generalized_schlick_bsdf name="coat_bsdf" type="BSDF">
<input name="weight" type="float" nodename="coat_intensity" />
<input name="roughness" type="vector2" nodename="coat_roughness_dual" />
</generalized_schlick_bsdf>
<layer name="coat_layer" type="BSDF">
<input name="top" type="BSDF" nodename="coat_bsdf" />
<input name="base" type="BSDF" nodename="metallic_mix" />
</layer>

<!-- Surface Constructor -->
<surface name="surface_constructor" type="surfaceshader">
<input name="bsdf" type="BSDF" nodename="coat_layer" />
</surface>

<!-- Output -->
<output name="out" type="surfaceshader" nodename="surface_constructor" />
</nodegraph>

</materialx>
12 changes: 12 additions & 0 deletions resources/Materials/Examples/DisneyPrincipled/disney_principled_carpaint.mtlx
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<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709">
<disney_principled name="SR_carpaint" type="surfaceshader">
<input name="baseColor" type="color3" value="0.0518895, 0.29606, 0.425324" />
<input name="roughness" type="float" value="0.4" />
<input name="anisotropic" type="float" value="0.5" />
<input name="clearcoat" type="float" value="1.0" />
</disney_principled>
<surfacematerial name="DisneyPrincipled_Carpaint" type="material">
<input name="surfaceshader" type="surfaceshader" nodename="SR_carpaint" />
</surfacematerial>
</materialx>
17 changes: 10 additions & 7 deletions libraries/bxdf/disney_brdf_2012.mtlx → ...Principled/disney_principled_default.mtlx
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<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709">
<nodedef name="ND_disney_brdf_2012_surface" node="disney_brdf_2012" nodegroup="pbr">
<disney_principled name="SR_default" type="surfaceshader">
<input name="baseColor" type="color3" value="0.16, 0.16, 0.16" />
<input name="metallic" type="float" value="0" />
<input name="subsurface" type="float" value="0" />
<input name="specular" type="float" value="0.5" />
<input name="roughness" type="float" value="0.5" />
<input name="specularTint" type="float" value="0" />
<input name="anisotropic" type="float" value="0" />
<input name="specularTint" type="float" value="0" />
<input name="sheen" type="float" value="0" />
<input name="sheenTint" type="float" value="0.5" />
<input name="clearcoat" type="float" value="0" />
<input name="clearcoatGloss" type="float" value="1" />
<output name="out" type="surfaceshader" />
</nodedef>
<implementation name="IM_disney_brdf_2012_surface_brdf_explorer" nodedef="ND_disney_brdf_2012_surface" target="brdf_explorer" file="https://github.com/wdas/brdf/blob/master/src/brdfs/disney.brdf" />
<input name="specTrans" type="float" value="0" />
<input name="ior" type="float" value="1.5" />
<input name="subsurface" type="float" value="0" />
<input name="subsurfaceDistance" type="color3" value="1, 1, 1" />
</disney_principled>
<surfacematerial name="DisneyPrincipled_Default" type="material">
<input name="surfaceshader" type="surfaceshader" nodename="SR_default" />
</surfacematerial>
</materialx>
12 changes: 12 additions & 0 deletions resources/Materials/Examples/DisneyPrincipled/disney_principled_glass.mtlx
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<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709">
<disney_principled name="SR_glass" type="surfaceshader">
<input name="baseColor" type="color3" value="1, 1, 1" />
<input name="roughness" type="float" value="0.01" />
<input name="specTrans" type="float" value="1" />
<input name="ior" type="float" value="1.52" />
</disney_principled>
<surfacematerial name="DisneyPrincipled_Glass" type="material">
<input name="surfaceshader" type="surfaceshader" nodename="SR_glass" />
</surfacematerial>
</materialx>
11 changes: 11 additions & 0 deletions resources/Materials/Examples/DisneyPrincipled/disney_principled_gold.mtlx
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<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709">
<disney_principled name="SR_gold" type="surfaceshader">
<input name="baseColor" type="color3" value="0.944, 0.776, 0.373" />
<input name="metallic" type="float" value="1" />
<input name="roughness" type="float" value="0.02" />
</disney_principled>
<surfacematerial name="DisneyPrincipled_Gold" type="material">
<input name="surfaceshader" type="surfaceshader" nodename="SR_gold" />
</surfacematerial>
</materialx>
10 changes: 10 additions & 0 deletions resources/Materials/Examples/DisneyPrincipled/disney_principled_plastic.mtlx
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<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709">
<disney_principled name="SR_plastic" type="surfaceshader">
<input name="baseColor" type="color3" value="0.104704, 0.241883, 0.818" />
<input name="roughness" type="float" value="0.324675" />
</disney_principled>
<surfacematerial name="DisneyPrincipled_Plastic" type="material">
<input name="surfaceshader" type="surfaceshader" nodename="SR_plastic" />
</surfacematerial>
</materialx>

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