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Shader Generator ND_mix_bsdf optimization #2499

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Shader Generator ND_mix_bsdf optimization #2499

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4f61ef8
Refactor OpenPBR nodegraph optimization in to a ShaderGenerator optim…
ld-kerley Jul 15, 2025
aa141dd
remove double underscores from node names - appears to be illegal.
ld-kerley Jul 22, 2025
33635cb
remove trailing underscores from node names - because these still mak…
ld-kerley Jul 22, 2025
06168ca
add GenOptions option to control the optimization
ld-kerley Sep 22, 2025
7724d4f
Add checkbox to MaterialXView to control bsdf mix optimization
ld-kerley Sep 22, 2025
c61991f
Add possible refactor of gltf_pbr that allows it to match the existin…
ld-kerley Sep 22, 2025
e6c2f0b
add additional stage to optimize combination of 3 bsdfs that have bee…
ld-kerley Sep 23, 2025
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55 changes: 18 additions & 37 deletions libraries/bxdf/gltf_pbr.mtlx
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Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,6 @@
<input name="color" type="color3" interfacename="base_color" />
<input name="normal" type="vector3" interfacename="normal" />
</oren_nayar_diffuse_bsdf>

<dielectric_bsdf name="transmission_bsdf" type="BSDF">
<input name="weight" type="float" value="1" />
<input name="tint" type="color3" interfacename="base_color" />
Expand All @@ -150,6 +149,11 @@
<input name="tangent" type="vector3" nodename="selected_tangent" />
<input name="scatter_mode" type="string" value="T" />
</dielectric_bsdf>
<mix name="transmission_blend" type="BSDF">
<input name="bg" type="BSDF" nodename="diffuse_bsdf" />
<input name="fg" type="BSDF" nodename="transmission_bsdf" />
<input name="mix" type="float" interfacename="transmission" />
</mix>

<generalized_schlick_bsdf name="reflection_bsdf" type="BSDF">
<input name="color0" type="color3" nodename="dielectric_f0" />
Expand All @@ -159,21 +163,6 @@
<input name="tangent" type="vector3" nodename="selected_tangent" />
<input name="scatter_mode" type="string" value="R" />
</generalized_schlick_bsdf>

<mix name="transmission_mix" type="BSDF">
<input name="bg" type="BSDF" nodename="diffuse_bsdf" />
<input name="fg" type="BSDF" nodename="transmission_bsdf" />
<input name="mix" type="float" interfacename="transmission" />
</mix>

<layer name="dielectric_bsdf" type="BSDF">
<input name="top" type="BSDF" nodename="reflection_bsdf" />
<input name="base" type="BSDF" nodename="transmission_mix" />
</layer>

<!-- Thin-film + Dielectric
Note: Due to limitations in codegen, the base layer BSDF is duplicated (#1035). -->

<generalized_schlick_bsdf name="tf_reflection_bsdf" type="BSDF">
<input name="color0" type="color3" nodename="dielectric_f0" />
<input name="color90" type="color3" nodename="dielectric_f90" />
Expand All @@ -185,32 +174,26 @@
<input name="thinfilm_ior" type="float" interfacename="iridescence_ior" />
</generalized_schlick_bsdf>


<layer name="tf_dielectric_bsdf" type="BSDF">
<input name="top" type="BSDF" nodename="tf_reflection_bsdf" />
<input name="base" type="BSDF" nodename="transmission_mix" />
</layer>

<mix name="mix_iridescent_dielectric_bsdf" type="BSDF">
<input name="bg" type="BSDF" nodename="dielectric_bsdf" />
<input name="fg" type="BSDF" nodename="tf_dielectric_bsdf" />
<mix name="reflection_blend" type="BSDF">
<input name="bg" type="BSDF" nodename="reflection_bsdf" />
<input name="fg" type="BSDF" nodename="tf_reflection_bsdf" />
<input name="mix" type="float" interfacename="iridescence" />
</mix>

<!-- Metal -->
<layer name="iridescent_dielectric_bsdf" type="BSDF">
<input name="top" type="BSDF" nodename="reflection_blend" />
<input name="base" type="BSDF" nodename="transmission_blend" />
</layer>

<!-- Metal -->
<generalized_schlick_bsdf name="metal_bsdf" type="BSDF">
<input name="color0" type="color3" interfacename="base_color" />
<input name="color90" type="color3" value="1, 1, 1" />
<input name="roughness" type="vector2" nodename="roughness_uv" />
<input name="normal" type="vector3" interfacename="normal" />
<input name="tangent" type="vector3" nodename="selected_tangent" />
</generalized_schlick_bsdf>

<!-- Thin-film + Metal
Note: Due to limitations in codegen, the base layer BSDF is duplicated (#1035). -->

<generalized_schlick_bsdf name="tf_metal_bsdf" type="BSDF">
<generalized_schlick_bsdf name="metal_bsdf_tf" type="BSDF">
<input name="color0" type="color3" interfacename="base_color" />
<input name="color90" type="color3" value="1, 1, 1" />
<input name="roughness" type="vector2" nodename="roughness_uv" />
Expand All @@ -219,18 +202,16 @@
<input name="thinfilm_thickness" type="float" interfacename="iridescence_thickness" />
<input name="thinfilm_ior" type="float" interfacename="iridescence_ior" />
</generalized_schlick_bsdf>

<mix name="mix_iridescent_metal_bsdf" type="BSDF">
<mix name="metal_blend" type="BSDF">
<input name="bg" type="BSDF" nodename="metal_bsdf" />
<input name="fg" type="BSDF" nodename="tf_metal_bsdf" />
<input name="fg" type="BSDF" nodename="metal_bsdf_tf" />
<input name="mix" type="float" interfacename="iridescence" />
</mix>

<!-- Dielectric/metal mix -->

<mix name="base_mix" type="BSDF">
<input name="bg" type="BSDF" nodename="mix_iridescent_dielectric_bsdf" />
<input name="fg" type="BSDF" nodename="mix_iridescent_metal_bsdf" />
<input name="bg" type="BSDF" nodename="iridescent_dielectric_bsdf" />
<input name="fg" type="BSDF" nodename="metal_blend" />
<input name="mix" type="float" interfacename="metallic" />
</mix>

Expand Down
7 changes: 6 additions & 1 deletion source/MaterialXGenShader/GenOptions.h
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,8 @@ class MX_GENSHADER_API GenOptions
hwNormalizeUdimTexCoords(false),
hwWriteAlbedoTable(false),
hwWriteEnvPrefilter(false),
hwImplicitBitangents(true)
hwImplicitBitangents(true),
optReplaceBsdfMixWithLinearCombination(false)
{
}
virtual ~GenOptions() { }
Expand Down Expand Up @@ -197,6 +198,10 @@ class MX_GENSHADER_API GenOptions
/// Calculate fallback bitangents from existing normals and tangents
/// inside the bitangent node.
bool hwImplicitBitangents;

/// Analyse the graph of ShaderNodes and replace any ND_mix_bsdf nodes
/// with a linear combination of their weighted inputs
bool optReplaceBsdfMixWithLinearCombination;
};

MATERIALX_NAMESPACE_END
Expand Down
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