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Improved open_pbr_surface to standard_surface translation (#1958)
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Integrated the logic of coat_darkening from OpenPBR into the calculations of base_color and subsurface_color.
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@mkuo-lucasfilm
mkuo-lucasfilm committed Aug 3, 2024
1 parent 1d066bb commit 1775a6d
Showing 1 changed file with 89 additions and 11 deletions.
100 changes: 89 additions & 11 deletions libraries/bxdf/translation/open_pbr_to_standard_surface.mtlx
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,6 @@
<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_color_out" type="float" />
<output name="coat_affect_roughness_out" type="float" />

<output name="thin_film_thickness_out" type="float" />
Expand All @@ -96,19 +95,101 @@

<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="baseColor" type="color3">
<input name="in" type="color3" interfacename="base_color" />
</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">
Expand Down Expand Up @@ -154,9 +235,10 @@
<dot name="subsurface" type="float">
<input name="in" type="float" interfacename="subsurface_weight" />
</dot>
<dot name="subsurfaceColor" type="color3">
<input name="in" type="color3" interfacename="subsurface_color" />
</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>
Expand Down Expand Up @@ -195,9 +277,6 @@
<dot name="coatIOR" type="float">
<input name="in" type="float" interfacename="coat_ior" />
</dot>
<dot name="coatAffectColor" type="float">
<input name="in" type="float" interfacename="coat_darkening" />
</dot>
<constant name="coatAffectRoughness" type="float">
<input name="value" type="float" value="1.0" />
</constant>
Expand Down Expand Up @@ -267,7 +346,6 @@
<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_color_out" type="float" nodename="coatAffectColor" />
<output name="coat_affect_roughness_out" type="float" nodename="coatAffectRoughness" />

<output name="thin_film_thickness_out" type="float" nodename="thinFilmThickness" />
Expand Down

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