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Clarify unit-length PBR normal/tangent inputs. #2969

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Clarify unit-length PBR normal/tangent inputs. #2969

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5aee80c
Clarify unit-length PBR normal/tangent inputs.
tdavidovicNV May 15, 2026
b049f3c
Merge branch 'main' into dev/tdavidovic/mandate_unit_length_ONB
tdavidovicNV Jun 9, 2026
46ed8a7
Merge branch 'main' into dev/tdavidovic/mandate_unit_length_ONB
tdavidovicNV Jun 10, 2026
3bd2192
Merge branch 'main' into dev/tdavidovic/mandate_unit_length_ONB
tdavidovicNV Jun 12, 2026
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2 changes: 1 addition & 1 deletion documents/Specification/MaterialX.PBRSpec.md
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Expand Up @@ -114,7 +114,7 @@ In order to simplify authoring of complex materials, our model supports the noti

### Bump and Normal Mapping

The surface normal used for shading calculations is supplied as input to each BSDF that requires it. The normal can be perturbed by bump or normal mapping, before it is given to the BSDF. As a result, one can supply different normals for different BSDFs for the same shading point. When layering BSDFs, each layer can use different bump and normal maps.
The surface normal used for shading calculations is supplied as input to each BSDF that requires it. The normal can be perturbed by bump or normal mapping, before it is given to the BSDF. As a result, one can supply different normals for different BSDFs for the same shading point. When layering BSDFs, each layer can use different bump and normal maps. Normals, tangents, and bitangents used for bump or normal mapping are expected to be normalized.


## Volumes
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24 changes: 17 additions & 7 deletions documents/Specification/MaterialX.Proposals.md
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Expand Up @@ -5,7 +5,7 @@ MaterialX Proposals v1.39

# MaterialX: Proposed Additions and Changes

**Proposals for Version 1.39**
**Proposals for Version 1.39**
September 15, 2024


Expand All @@ -19,17 +19,17 @@ As such, those forward-looking proposals have been moved from the formal Specifi

## Table of Contents

**[Introduction](#introduction)**
**[Introduction](#introduction)**

**[Proposals: General](#propose-general)**
**[Proposals: General](#propose-general)**

**[Proposals: Elements](#propose-elements)**
**[Proposals: Elements](#propose-elements)**

**[Proposals: Stdlib Nodes](#propose-stdlib-nodes)**
**[Proposals: Stdlib Nodes](#propose-stdlib-nodes)**

**[Proposals: PBR Nodes](#propose-pbr-nodes)**
**[Proposals: PBR Nodes](#propose-pbr-nodes)**

**[Proposals: NPR Nodes](#propose-npr-nodes)**
**[Proposals: NPR Nodes](#propose-npr-nodes)**


<p>&nbsp;<p><hr><p>
Expand Down Expand Up @@ -393,6 +393,16 @@ Output the RGB and alpha channels of a color4 as separate outputs.

# Proposals: PBR Nodes<a id="propose-pbr-nodes"></a>

### Unit-Length Normal and Tangent-Frame Inputs

Normals, tangents, bitangent inputs should be unit-length direction vectors
in the given coordinate space. This follows from the existing math used by BSDFs
and EDFs:
- where the dot products with a normal are used a cosines.
- microfacet distributions construct local frames from the vectors.
- sampling PDFs are defined over unit (hemi)spheres.

Non-unit normals could then change energy, sampling density, reflected/transmitted directions. The alternative is to define that they do not have to be unit length, and then amend the GLSL implementations to handle this.


<p>&nbsp;<p><hr><p>
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4 changes: 2 additions & 2 deletions resources/Materials/TestSuite/libraries/metal/libraries/metal_definition.mtlx
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Expand Up @@ -6,7 +6,7 @@
<input name="SurfaceRoughness" type="float" value="0.1" uiname="Roughness" uifolder="Basic Parameters" />
<input name="SurfaceAlbedo" type="color3" value="1, 1, 1" uiname="Color" uifolder="Hilight Parameters" />
<input name="SurfaceAnisotropy" type="float" value="0.0" uiname="Anisotropy" uifolder="Hilight Parameters" />
<input name="SurfaceNormal" type="vector3" value="1, 1, 1" uiname="Relief Pattern (Bump)" uifolder="Hilight Parameters" />
<input name="SurfaceNormal" type="vector3" value="0.57735026919, 0.57735026919, 0.57735026919" uiname="Relief Pattern (Bump)" uifolder="Hilight Parameters" />
<input name="SurfaceRotation" type="float" value="0" uiname="Orientation" uifolder="Hilight Parameters" />
<input name="SurfaceCutout" type="color3" value="1, 1, 1" uiname="Image" uifolder="Cutout" />
<output name="out" type="surfaceshader" />
Expand All @@ -33,7 +33,7 @@
<input name="coat_color" type="color3" value="1, 1, 1" />
<input name="coat_roughness" type="float" value="0.1" />
<input name="coat_IOR" type="float" value="1.5" />
<input name="coat_normal" type="vector3" value="0.0, 0.0, 0.0" />
<input name="coat_normal" type="vector3" value="0.0, 0.0, 1.0" />
<input name="thin_walled" type="boolean" value="false" />
<input name="thin_film_thickness" type="float" value="0" />
<input name="thin_film_IOR" type="float" value="1.5" />
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2 changes: 1 addition & 1 deletion resources/Materials/TestSuite/locale/numericformat.mtlx
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Expand Up @@ -3,7 +3,7 @@
<standard_surface name="SR_numberformats" type="surfaceshader">
<input name="base_color" type="color3" value="0.18,0.18, 0.18" />
<input name="specular_color" type="color3" value="0.05, 0.05,0.05" />
<input name="normal" type="vector3" value="1,0.5,1" />
<input name="normal" type="vector3" value="0.666666666667,0.333333333333, 0.666666666667" />
<input name="specular_roughness" type="float" value="0.25" />
<input name="coat" type="float" value="1" />
</standard_surface>
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2 changes: 1 addition & 1 deletion resources/Materials/TestSuite/pbrlib/bsdf/add_bsdf.mtlx
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Expand Up @@ -17,7 +17,7 @@
<input name="weight" type="float" nodename="invert1" />
<input name="color" type="color3" value="0.9600, 0.1, 0.1" />
<input name="roughness" type="float" value="0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 1.0" />
</oren_nayar_diffuse_bsdf>
<dielectric_bsdf name="dielectric_brdf1" type="BSDF">
<input name="weight" type="float" nodename="clamp1" />
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2 changes: 1 addition & 1 deletion resources/Materials/TestSuite/pbrlib/bsdf/mix_bsdf.mtlx
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Expand Up @@ -22,7 +22,7 @@
<oren_nayar_diffuse_bsdf name="diffuse_brdf1" type="BSDF">
<input name="color" type="color3" value="0.96, 0.1, 0.1" />
<input name="roughness" type="float" value="0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 1.0" />
</oren_nayar_diffuse_bsdf>
<dielectric_bsdf name="dielectric_brdf1" type="BSDF">
<input name="tint" type="color3" value="1.0, 1.0, 1.0" />
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8 changes: 4 additions & 4 deletions resources/Materials/TestSuite/pbrlib/surfaceshader/surface_ops.mtlx
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Expand Up @@ -9,13 +9,13 @@
<input name="color" type="color3" value="0.18, 0.18, 0.18" />
<input name="radius" type="color3" value="1.0, 1.0, 1.0" />
<input name="anisotropy" type="float" value="0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 1.0" />
</subsurface_bsdf>
<sheen_bsdf name="sheen_brdf1" type="BSDF">
<input name="weight" type="float" value="1.0" />
<input name="color" type="color3" value="1.0, 1.0, 1.0" />
<input name="roughness" type="float" value="0.3" />
<input name="normal" type="vector3" value="0.0, 0.0, 0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 1.0" />
</sheen_bsdf>
<mix name="mix_edf1" type="EDF">
<input name="fg" type="EDF" nodename="Emission_EDF" />
Expand Down Expand Up @@ -49,7 +49,7 @@
<conductor_bsdf name="conductor_brdf1" type="BSDF">
<input name="weight" type="float" value="1.0" />
<input name="roughness" type="vector2" value="0.0, 0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 1.0" />
<input name="tangent" type="vector3" value="0.0, 0.0, 0.0" />
<input name="distribution" type="string" value="ggx" />
<input name="ior" type="color3" nodename="conductor_brdf1__artistic_ior" output="ior" />
Expand All @@ -61,7 +61,7 @@
<input name="color90" type="color3" value="1.0, 1.0, 1.0" />
<input name="exponent" type="float" value="5.0" />
<input name="roughness" type="vector2" nodename="roughness_dual1" />
<input name="normal" type="vector3" value="0.0, 0.0, 0.0" />
<input name="normal" type="vector3" value="0.0, 0.0, 1.0" />
<input name="tangent" type="vector3" value="0.0, 0.0, 0.0" />
<input name="distribution" type="string" value="ggx" />
</generalized_schlick_bsdf>
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4 changes: 2 additions & 2 deletions resources/Materials/TestSuite/stdlib/definition/definition_using_definitions.mtlx
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@@ -1,13 +1,13 @@
<?xml version="1.0"?>
<materialx version="1.39" colorspace="lin_rec709" xmlns:xi="http://www.w3.org/2001/XInclude">
<nodedef name="ND_layered" node="mylayered" version="1.0.1" isdefaultversion="true">
<input name="surface_normal" type="vector3" value="1, 1, 1" defaultgeomprop="Nworld" />
<input name="surface_normal" type="vector3" value="0.57735026919, 0.57735026919, 0.57735026919" defaultgeomprop="Nworld" />
<input name="surface_cutout" type="color3" value="1, 1, 1" />
<input name="surface_albedo" type="color3" value="1, 1, 1" />
<input name="surface_roughness" type="float" value="0" />
<input name="surface_anisotropy" type="float" value="0" />
<input name="surface_rotation" type="float" value="0" />
<input name="layered_normal" type="vector3" value="1, 1, 1" defaultgeomprop="Nworld" />
<input name="layered_normal" type="vector3" value="0.57735026919, 0.57735026919, 0.57735026919" defaultgeomprop="Nworld" />
<input name="layered_f0" type="float" value="1" />
<input name="layered_roughness" type="float" value="0" />
<input name="layered_anisotropy" type="float" value="0" />
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