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Clamp PBR surface opacity before shader construction #3019

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Clamp PBR surface opacity before shader construction #3019

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e9ad74f
Clamp PBR surface opacity
tdavidovicNV Jul 27, 2026
c0d0fbb
Remove GLSL surface opacity regression test
tdavidovicNV Jul 27, 2026
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2 changes: 1 addition & 1 deletion documents/Specification/MaterialX.PBRSpec.md
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Expand Up @@ -1008,7 +1008,7 @@ If the `edf` input is left unconnected, no emission will occur from the surface.
|`thin_walled`|Set to true to make the surface thin-walled |boolean |false |
|`out` |Output: the computed surface shader |surfaceshader| |

In the equations below, the `bsdf` input corresponds to $f$, the `edf` input corresponds to $L_e$, and the `opacity` input corresponds to $O$.
In the equations below, the `bsdf` input corresponds to $f$, the `edf` input corresponds to $L_e$, and the cutout opacity is $O = \mathrm{clamp}(\mathrm{opacity}, 0, 1)$. Input values below 0 are treated as 0, and input values above 1 are treated as 1, before the surface shader is constructed.

#### Surface Shading Equation

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2 changes: 1 addition & 1 deletion libraries/pbrlib/pbrlib_defs.mtlx
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Expand Up @@ -243,7 +243,7 @@
<nodedef name="ND_surface" node="surface" nodegroup="pbr" doc="A constructor node for the surfaceshader type.">
<input name="bsdf" type="BSDF" value="" doc="Distribution function for surface scattering." />
<input name="edf" type="EDF" value="" doc="Distribution function for surface emission." />
<input name="opacity" type="float" value="1.0" doc="Surface cutout opacity" />
<input name="opacity" type="float" value="1.0" uimin="0.0" uimax="1.0" doc="Surface cutout opacity, clamped to the range [0, 1]." />
<input name="thin_walled" type="boolean" value="false" uniform="true" doc="Option to make the surface thin-walled." />
<output name="out" type="surfaceshader" />
</nodedef>
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3 changes: 2 additions & 1 deletion source/MaterialXGenHw/Nodes/HwSurfaceNode.cpp
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Expand Up @@ -135,8 +135,9 @@ void HwSurfaceNode::emitFunctionCall(const ShaderNode& node, GenContext& context
if (const ShaderNode* bsdf = bsdfInput->getConnectedSibling())
{
shadergen.emitLineBegin(stage);
shadergen.emitString("float surfaceOpacity = ", stage);
shadergen.emitString("float surfaceOpacity = clamp(", stage);
shadergen.emitInput(node.getInput(getOpacityInputName()), context, stage);
shadergen.emitString(", 0.0, 1.0)", stage);
shadergen.emitLineEnd(stage);
shadergen.emitLineBreak(stage);

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2 changes: 1 addition & 1 deletion source/MaterialXGenMdl/mdl/materialx/pbrlib_1_6.mdl
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Expand Up @@ -612,7 +612,7 @@ export material mx_surface(
ior: mxp_transmission_ior > 0.0 ? color(mxp_transmission_ior) : mxp_bsdf.ior,
volume: bsdf_volume,
geometry: material_geometry(
cutout_opacity: mxp_opacity
cutout_opacity: math::clamp(mxp_opacity, 0.0, 1.0)
)
);

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2 changes: 1 addition & 1 deletion source/MaterialXGenMdl/mdl/materialx/pbrlib_1_9.mdl
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Expand Up @@ -389,6 +389,6 @@ export material mx_surface(
ior: mxp_transmission_ior > 0.0 ? color(mxp_transmission_ior) : mxp_bsdf.ior,
volume: bsdf_volume,
geometry: material_geometry(
cutout_opacity: mxp_opacity
cutout_opacity: math::clamp(mxp_opacity, 0.0, 1.0)
)
);
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