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Coat layer should affect emission in USD translation (AcademySoftware…
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…Foundation#2087)

The standard_surface coat parameters are currently affecting the baseColor of UsdPreviewSurface. It should also affect emission color.

Initial translation from `open_pbr_surface` to `standard_surface` (AcademySoftwareFoundation#1949)

- Authored an initial pass at the translation from OpenPBR to standard surface.
- This would help to support OpenPBR in applications using earlier versions of MaterialX, which only have access to Standard Surface, but may want to participate in the OpenPBR ecosystem before they upgrade.

Update `standard_surface` to `open_pbr` translation graph   (AcademySoftwareFoundation#1956)

Replacing coat_affect_roughness with a constant value, since a coating always affects roughness in OpenPBR and is not dependent on the value of coat_darkening.

Improved `open_pbr_surface` to `standard_surface` translation (AcademySoftwareFoundation#1958)

Integrated the logic of coat_darkening from OpenPBR into the calculations of base_color and subsurface_color.

Initial translation from `standard_surface` to `open_pbr_surface` (AcademySoftwareFoundation#1934)

1. Authored an initial pass at the translation graph between standard surface and OpenPBR
2. Added units to standard surface thin film thickness documentation

Update documentation of OpenPBR and Standard Surface translations (AcademySoftwareFoundation#1963)

Clarified documentation where the motivation for the conversion might not be clear - both for the translation graph from OpenPBR to Standard Surface, and the translation graph from Standard Surface to OpenPBR.

Decrement translation graphs minor version (backport)

Consider subsurface color in dielectric albedo
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JGamache-autodesk committed Nov 5, 2024
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2 changes: 1 addition & 1 deletion libraries/bxdf/standard_surface.mtlx
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<input name="coat_affect_roughness" type="float" value="0" uimin="0" uimax="1" uiname="Coat Affect Roughness" uifolder="Coat" uiadvanced="true"
doc="Controls the roughness of the specular reflection in the layers below the clear-coat." />
<input name="thin_film_thickness" type="float" value="0" uimin="0.0" uisoftmax="2000.0" uiname="Thin Film Thickness" uifolder="Thin Film" uiadvanced="true"
doc="The thickness of the thin film layer on a surface. Use for materials such as multitone car paint or soap bubbles." />
doc="The thickness of the thin film layer on a surface. Use for materials such as multitone car paint or soap bubbles (in nanometers)." />
<input name="thin_film_IOR" type="float" value="1.5" uimin="0.0" uisoftmin="1.0" uisoftmax="3.0" uiname="Thin Film Index of Refraction" uifolder="Thin Film" uiadvanced="true"
doc="The index of refraction of the medium surrounding the material." />
<input name="emission" type="float" value="0" uimin="0.0" uisoftmax="1.0" uiname="Emission" uifolder="Emission"
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362 changes: 362 additions & 0 deletions libraries/bxdf/translation/open_pbr_to_standard_surface.mtlx
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<?xml version="1.0"?>
<materialx version="1.38">

<nodedef name="ND_open_pbr_surface_to_standard_surface" node="open_pbr_surface_to_standard_surface" nodegroup="translation">
<input name="base_weight" type="float" value="1.0" />
<input name="base_color" type="color3" value="0.8, 0.8, 0.8" />
<input name="base_diffuse_roughness" type="float" value="0.0" />
<input name="base_metalness" type="float" value="0.0" />

<input name="specular_weight" type="float" value="1.0" />
<input name="specular_color" type="color3" value="1, 1, 1" />
<input name="specular_roughness" type="float" value="0.3" />
<input name="specular_ior" type="float" value="1.5" />
<input name="specular_roughness_anisotropy" type="float" value="0.0" />

<input name="transmission_weight" type="float" value="0.0" />
<input name="transmission_color" type="color3" value="1, 1, 1" />
<input name="transmission_depth" type="float" value="0.0" />
<input name="transmission_scatter" type="color3" value="0, 0, 0" />
<input name="transmission_scatter_anisotropy" type="float" value="0.0" />
<input name="transmission_dispersion_scale" type="float" value="0.0" />

<input name="subsurface_weight" type="float" value="0" />
<input name="subsurface_color" type="color3" value="0.8, 0.8, 0.8" />
<input name="subsurface_radius" type="float" value="1.0" />
<input name="subsurface_radius_scale" type="color3" value="1.0, 0.5, 0.25" />
<input name="subsurface_scatter_anisotropy" type="float" value="0.0" />

<input name="fuzz_weight" type="float" value="0.0" />
<input name="fuzz_color" type="color3" value="1, 1, 1" />
<input name="fuzz_roughness" type="float" value="0.5" />

<input name="coat_weight" type="float" value="0.0" />
<input name="coat_color" type="color3" value="1, 1, 1" />
<input name="coat_roughness" type="float" value="0.0" />
<input name="coat_roughness_anisotropy" type="float" value="0.0" />
<input name="coat_ior" type="float" value="1.6" />
<input name="coat_darkening" type="float" value="1.0" />

<input name="thin_film_weight" type="float" value="0" />
<input name="thin_film_thickness" type="float" value="0.5" />
<input name="thin_film_ior" type="float" value="1.4" />

<input name="emission_luminance" type="float" value="0.0" />
<input name="emission_color" type="color3" value="1, 1, 1" />

<input name="geometry_opacity" type="float" value="1" />
<input name="geometry_thin_walled" type="boolean" value="false" />

<!--Outputs-->
<output name="base_out" type="float" />
<output name="base_color_out" type="color3" />
<output name="diffuse_roughness_out" type="float" />
<output name="metalness_out" type="float" />

<output name="specular_out" type="float"/>
<output name="specular_color_out" type="color3" />
<output name="specular_roughness_out" type="float" />
<output name="specular_IOR_out" type="float" />
<output name="specular_anisotropy_out" type="float" />

<output name="transmission_out" type="float" />
<output name="transmission_color_out" type="color3" />
<output name="transmission_depth_out" type="float" />
<output name="transmission_scatter_out" type="color3" />
<output name="transmission_scatter_anisotropy_out" type="float" />
<output name="transmission_dispersion_out" type="float" />

<output name="subsurface_out" type="float" />
<output name="subsurface_color_out" type="color3" />
<output name="subsurface_radius_out" type="color3" />
<output name="subsurface_scale_out" type="float" />
<output name="subsurface_anisotropy_out" type="float" />

<output name="sheen_out" type="float" />
<output name="sheen_color_out" type="color3" />
<output name="sheen_roughness_out" type="float" />

<output name="coat_out" type="float" />
<output name="coat_color_out" type="color3" />
<output name="coat_roughness_out" type="float" />
<output name="coat_anisotropy_out" type="float" />
<output name="coat_IOR_out" type="float" />
<output name="coat_affect_roughness_out" type="float" />

<output name="thin_film_thickness_out" type="float" />
<output name="thin_film_IOR_out" type="float" />

<output name="emission_out" type="float" />
<output name="emission_color_out" type="color3" />

<output name="opacity_out" type="color3" />
<output name="thin_walled_out" type="boolean" />
</nodedef>

<nodegraph name="NG_open_pbr_surface_to_standard_surface" nodedef="ND_open_pbr_surface_to_standard_surface">

<!-- Coat Darkening -->
<subtract name="coat_ior_minus_one" type="float">
<input name="in1" type="float" interfacename="coat_ior" />
<input name="in2" type="float" value="1.0" />
</subtract>
<add name="coat_ior_plus_one" type="float">
<input name="in1" type="float" value="1.0" />
<input name="in2" type="float" interfacename="coat_ior" />
</add>
<divide name="coat_ior_to_F0_sqrt" type="float">
<input name="in1" type="float" nodename="coat_ior_minus_one" />
<input name="in2" type="float" nodename="coat_ior_plus_one" />
</divide>
<multiply name="coat_ior_to_F0" type="float">
<input name="in1" type="float" nodename="coat_ior_to_F0_sqrt" />
<input name="in2" type="float" nodename="coat_ior_to_F0_sqrt" />
</multiply>
<!-- approximate Kcoat, "internal diffuse reflection coefficient" of coat -->
<subtract name="one_minus_coat_F0" type="float">
<input name="in1" type="float" value="1.0" />
<input name="in2" type="float" nodename="coat_ior_to_F0" />
</subtract>
<multiply name="coat_ior_sqr" type="float">
<input name="in1" type="float" interfacename="coat_ior" />
<input name="in2" type="float" interfacename="coat_ior" />
</multiply>
<divide name="one_minus_coat_F0_over_eta2" type="float">
<input name="in1" type="float" nodename="one_minus_coat_F0" />
<input name="in2" type="float" nodename="coat_ior_sqr" />
</divide>
<subtract name="Kcoat" type="float">
<input name="in1" type="float" value="1.0" />
<input name="in2" type="float" nodename="one_minus_coat_F0_over_eta2" />
</subtract>
<!-- approximate base metal albedo estimate, Emetal -->
<multiply name="Emetal" type="color3">
<input name="in1" type="color3" interfacename="base_color" />
<input name="in2" type="float" interfacename="specular_weight" />
</multiply>
<!-- approximate base dielectric albedo estimate, Edielectric -->
<mix name="Edielectric" type="color3">
<input name="fg" type="color3" interfacename="subsurface_color" />
<input name="bg" type="color3" interfacename="base_color" />
<input name="mix" type="float" interfacename="subsurface_weight" />
</mix>
<!-- thus calculate overall base albedo estimate approximation, Ebase -->
<mix name="Ebase" type="color3">
<input name="fg" type="color3" nodename="Emetal" />
<input name="bg" type="color3" nodename="Edielectric" />
<input name="mix" type="float" interfacename="base_metalness" />
</mix>
<!-- final base darkening factor due to coat: base_darkening = (1 - Kcoat) / (1 - Ebase*Kcoat) -->
<multiply name="Ebase_Kcoat" type="color3">
<input name="in1" type="color3" nodename="Ebase" />
<input name="in2" type="float" nodename="Kcoat" />
</multiply>
<subtract name="one_minus_Kcoat" type="float">
<input name="in1" type="float" value="1.0" />
<input name="in2" type="float" nodename="Kcoat" />
</subtract>
<subtract name="one_minus_Ebase_Kcoat" type="color3">
<input name="in1" type="color3" value="1.0, 1.0, 1.0" />
<input name="in2" type="color3" nodename="Ebase_Kcoat" />
</subtract>
<convert name="one_minus_Kcoat_color" type="color3">
<input name="in" type="float" nodename="one_minus_Kcoat" />
</convert>
<divide name="base_darkening" type="color3">
<input name="in1" type="color3" nodename="one_minus_Kcoat_color" />
<input name="in2" type="color3" nodename="one_minus_Ebase_Kcoat" />
</divide>
<multiply name="coat_weight_times_coat_darkening" type="float">
<input name="in1" type="float" interfacename="coat_weight" />
<input name="in2" type="float" interfacename="coat_darkening" />
</multiply>
<mix name="modulated_base_darkening" type="color3">
<input name="fg" type="color3" nodename="base_darkening" />
<input name="bg" type="color3" value="1.0, 1.0, 1.0" />
<input name="mix" type="float" nodename="coat_weight_times_coat_darkening" />
</mix>

<!--Base-->
<dot name="base" type="float">
<input name="in" type="float" interfacename="base_weight" />
</dot>
<dot name="diffuseRoughness" type="float">
<input name="in" type="float" interfacename="base_diffuse_roughness" />
</dot>
<dot name="metalness" type="float">
<input name="in" type="float" interfacename="base_metalness" />
</dot>
<multiply name="baseColor" type="color3">
<input name="in1" type="color3" interfacename="base_color" />
<input name="in2" type="color3" nodename="modulated_base_darkening" />
</multiply>

<!--Specular-->
<dot name="spec" type="float">
<input name="in" type="float" interfacename="specular_weight" />
</dot>
<dot name="specColor" type="color3">
<input name="in" type="color3" interfacename="specular_color" />
</dot>
<!--Allows override of specular_roughness by coat_roughness for materials with coat, but not for simpler materials that don't leverage coat at all.-->
<mix name="specRoughness" type="float">
<input name="fg" type="float" interfacename="coat_roughness" />
<input name="bg" type="float" interfacename="specular_roughness" />
<input name="mix" type="float" interfacename="coat_weight" />
</mix>
<dot name="specIOR" type="float">
<input name="in" type="float" interfacename="specular_ior" />
</dot>
<!--The logic for anisotropic specular is noticeably different between Standard Surface and OpenPBR, so the translation between these concepts will take more thought.-->
<dot name="specAnisotropy" type="float">
<input name="in" type="float" interfacename="specular_roughness_anisotropy" />
</dot>

<!--Transmission-->
<dot name="transmission" type="float">
<input name="in" type="float" interfacename="transmission_weight" />
</dot>
<dot name="transmissionColor" type="color3">
<input name="in" type="color3" interfacename="transmission_color" />
</dot>
<dot name="transmissionDepth" type="float">
<input name="in" type="float" interfacename="transmission_depth" />
</dot>
<dot name="transmissionScatter" type="color3">
<input name="in" type="color3" interfacename="transmission_scatter" />
</dot>
<dot name="transmissionScatterAnisotropy" type="float">
<input name="in" type="float" interfacename="transmission_scatter_anisotropy" />
</dot>
<dot name="transmissionDispersion" type="float">
<input name="in" type="float" interfacename="transmission_dispersion_scale" />
</dot>

<!--Subsurface-->
<dot name="subsurface" type="float">
<input name="in" type="float" interfacename="subsurface_weight" />
</dot>
<multiply name="subsurfaceColor" type="color3">
<input name="in1" type="color3" interfacename="subsurface_color" />
<input name="in2" type="color3" nodename="modulated_base_darkening" />
</multiply>
<dot name="subsurfaceScale" type="float">
<input name="in" type="float" interfacename="subsurface_radius" />
</dot>
<dot name="subsurfaceRadius" type="color3">
<input name="in" type="color3" interfacename="subsurface_radius_scale" />
</dot>
<dot name="subsurfaceAnisotropy" type="float">
<input name="in" type="float" interfacename="subsurface_scatter_anisotropy" />
</dot>

<!--Sheen-->
<dot name="sheen" type="float">
<input name="in" type="float" interfacename="fuzz_weight" />
</dot>
<dot name="sheenColor" type="color3">
<input name="in" type="color3" interfacename="fuzz_color" />
</dot>
<!--Sheen roughness translation is approximated by eye, and could potentially be improved with an analytic or ML-based solution.-->
<power name="sheenRoughness" type="float">
<input name="in1" type="float" interfacename="fuzz_roughness" />
<input name="in2" type="float" value="2.5" />
</power>

<!--Coat-->
<dot name="coat" type="float">
<input name="in" type="float" interfacename="coat_weight" />
</dot>
<dot name="coatColor" type="color3">
<input name="in" type="color3" interfacename="coat_color" />
</dot>
<dot name="coatRoughness" type="float">
<input name="in" type="float" interfacename="coat_roughness" />
</dot>
<dot name="coatAnisotropy" type="float">
<input name="in" type="float" interfacename="coat_roughness_anisotropy" />
</dot>
<dot name="coatIOR" type="float">
<input name="in" type="float" interfacename="coat_ior" />
</dot>
<constant name="coatAffectRoughness" type="float">
<input name="value" type="float" value="1.0" />
</constant>

<!--ThinFilm-->
<multiply name="thinFilmThicknessConversion" type="float">
<input name="in1" type="float" interfacename="thin_film_thickness" />
<input name="in2" type="float" value="1000" />
</multiply>
<ifgreater name="thinFilmThickness" type="float">
<input name="value1" type="float" interfacename="thin_film_weight" />
<input name="value2" type="float" value="0.0" />
<input name="in1" type="float" nodename="thinFilmThicknessConversion" />
<input name="in2" type="float" value="0.0" />
</ifgreater>
<dot name="thinFilmIOR" type="float">
<input name="in" type="float" interfacename="thin_film_ior" />
</dot>

<!--Emission-->
<dot name="emission" type="float">
<input name="in" type="float" interfacename="emission_luminance" />
</dot>
<dot name="emissionColor" type="color3">
<input name="in" type="color3" interfacename="emission_color" />
</dot>

<!--Geometry-->
<convert name="geometryOpacity" type="color3">
<input name="in" type="float" interfacename="geometry_opacity" />
</convert>
<dot name="geometryThinWalled" type="boolean">
<input name="in" type="boolean" interfacename="geometry_thin_walled" />
</dot>

<!--Outputs-->
<output name="base_out" type="float" nodename="base" />
<output name="base_color_out" type="color3" nodename="baseColor" />
<output name="diffuse_roughness_out" type="float" nodename="diffuseRoughness" />
<output name="metalness_out" type="float" nodename="metalness" />

<output name="specular_out" type="float" nodename="spec" />
<output name="specular_color_out" type="color3" nodename="specColor" />
<output name="specular_roughness_out" type="float" nodename="specRoughness" />
<output name="specular_IOR_out" type="float" nodename="specIOR" />
<output name="specular_anisotropy_out" type="float" nodename="specAnisotropy" />

<output name="transmission_out" type="float" nodename="transmission" />
<output name="transmission_color_out" type="color3" nodename="transmissionColor" />
<output name="transmission_depth_out" type="float" nodename="transmissionDepth" />
<output name="transmission_scatter_out" type="color3" nodename="transmissionScatter" />
<output name="transmission_scatter_anisotropy_out" type="float" nodename="transmissionScatterAnisotropy" />
<output name="transmission_dispersion_out" type="float" nodename="transmissionDispersion" />

<output name="subsurface_out" type="float" nodename="subsurface" />
<output name="subsurface_color_out" type="color3" nodename="subsurfaceColor" />
<output name="subsurface_radius_out" type="color3" nodename="subsurfaceRadius" />
<output name="subsurface_scale_out" type="float" nodename="subsurfaceScale" />
<output name="subsurface_anisotropy_out" type="float" nodename="subsurfaceAnisotropy" />

<output name="sheen_out" type="float" nodename="sheen" />
<output name="sheen_color_out" type="color3" nodename="sheenColor" />
<output name="sheen_roughness_out" type="float" nodename="sheenRoughness" />

<output name="coat_out" type="float" nodename="coat" />
<output name="coat_color_out" type="color3" nodename="coatColor" />
<output name="coat_roughness_out" type="float" nodename="coatRoughness" />
<output name="coat_anisotropy_out" type="float" nodename="coatAnisotropy" />
<output name="coat_IOR_out" type="float" nodename="coatIOR" />
<output name="coat_affect_roughness_out" type="float" nodename="coatAffectRoughness" />

<output name="thin_film_thickness_out" type="float" nodename="thinFilmThickness" />
<output name="thin_film_IOR_out" type="float" nodename="thinFilmIOR" />

<output name="emission_out" type="float" nodename="emission" />
<output name="emission_color_out" type="color3" nodename="emissionColor" />

<output name="opacity_out" type="color3" nodename="geometryOpacity" />
<output name="thin_walled_out" type="boolean" nodename="geometryThinWalled" />
</nodegraph>
</materialx>
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