Improvements to color space handling

- Add support for 'none' as a colorspace attribute, specifying that the given color should not be transformed.
- Add support for colorspace attributes on multi-output nodes (e.g. UsdUvTexture), which only affect color-typed outputs.
- Update the 'usd_normal_map.mtlx' and 'usd_uv_texture.mtlx' examples to demonstrate these new capabilities.
- Remove legacy references to colorspace 'none' for physical colors, as it's more accurate in practice to interpret these values as visible colors.

documents/Specification/MaterialX.PBRSpec.md

@@ -198,8 +198,8 @@ The PBS nodes also make use of the following standard MaterialX types:
 
 
     * `weight` (float): Weight for this BSDF’s contribution, range [0.0, 1.0]. Defaults to 1.0.
-    * `ior `(color3): Index of refraction. Default is (0.18, 0.42, 1.37) with colorspace "none" (approximate IOR for gold).
-    * `extinction` (color3): Extinction coefficient. Default is (3.42, 2.35, 1.77) with colorspace "none" (approximate extinction coefficients for gold).
+    * `ior `(color3): Index of refraction. Default is (0.18, 0.42, 1.37) (approximate IOR for gold).
+    * `extinction` (color3): Extinction coefficient. Default is (3.42, 2.35, 1.77) (approximate extinction coefficients for gold).
     * `roughness` (vector2): Surface roughness. Defaults to (0.05, 0.05).
     * `thinfilm_thickness` (float): The thickness of an iridescent thin film layer applied over the base bsdf, expressed in nanometers. Defaults to 0.0, for no thin film.
     * `thinfilm_ior` (float): The index of refraction of the thin film layer. Defaults to 1.5.

libraries/pbrlib/pbrlib_defs.mtlx

@@ -79,8 +79,8 @@
   -->
   <nodedef name="ND_conductor_bsdf" node="conductor_bsdf" bsdf="R" nodegroup="pbr" doc="A reflection BSDF node based on a microfacet model and a Fresnel curve for conductors/metals.">
     <input name="weight" type="float" value="1.0" uimin="0.0" uimax="1.0" />
-    <input name="ior" type="color3" value="0.183, 0.421, 1.373" colorspace="none" />
-    <input name="extinction" type="color3" value="3.424, 2.346, 1.770" colorspace="none" />
+    <input name="ior" type="color3" value="0.183, 0.421, 1.373" />
+    <input name="extinction" type="color3" value="3.424, 2.346, 1.770" />
     <input name="roughness" type="vector2" value="0.05, 0.05" />
     <input name="thinfilm_thickness" type="float" value="0" unittype="distance" unit="nanometer" />
     <input name="thinfilm_ior" type="float" value="1.5" />

resources/Materials/TestSuite/pbrlib/surfaceshader/usd_normal_map.mtlx

@@ -1,18 +1,23 @@
 <?xml version="1.0"?>
 <materialx version="1.39" colorspace="lin_rec709">
-  <nodegraph name="NG_usd_normal_map">
-    <tiledimage name="N_tiledimage" type="vector3" nodedef="ND_tiledimage_vector3">
-      <input name="file" type="filename" value="resources/Images/mesh_wire_norm.png" />
-      <input name="uvtiling" type="vector2" value="8.0, 8.0" />
-    </tiledimage>
-    <normalmap name="N_normalmap" type="vector3" nodedef="ND_normalmap_float">
-      <input name="in" type="vector3" nodename="N_tiledimage" />
-      <input name="space" type="string" value="object" />
-    </normalmap>
-    <output name="out" type="vector3" nodename="N_normalmap" />
-  </nodegraph>
+  <texcoord name="N_texcoord" type="vector2" />
+  <multiply name="N_multiply" type="vector2">
+    <input name="in1" type="vector2" nodename="N_texcoord" />
+    <input name="in2" type="vector2" value="8, 8" />
+  </multiply>
+  <UsdUVTexture name="N_texture_normal" type="multioutput">
+    <input name="file" type="filename" value="resources/Images/mesh_wire_norm.png" colorspace="none" />
+    <input name="st" type="vector2" nodename="N_multiply" />
+  </UsdUVTexture>
+  <convert name="N_convert" type="vector3">
+    <input name="in" type="color3" nodename="N_texture_normal" output="rgb" />
+  </convert>
+  <normalmap name="N_normalmap" type="vector3">
+    <input name="in" type="vector3" nodename="N_convert" />
+    <input name="space" type="string" value="object" />
+  </normalmap>
   <UsdPreviewSurface name="N_surface" type="surfaceshader">
-    <input name="normal" type="vector3" output="out" nodegraph="NG_usd_normal_map" />
+    <input name="normal" type="vector3" nodename="N_normalmap" />
     <input name="diffuseColor" type="color3" value="1, 1, 1" />
     <input name="metallic" type="float" value="1" />
     <input name="roughness" type="float" value="0.001" />

resources/Materials/TestSuite/pbrlib/surfaceshader/usd_uv_texture.mtlx

@@ -1,45 +1,17 @@
 <?xml version="1.0"?>
 <materialx version="1.39">
-
-  <!-- UsdUVTexture: version 2.2 test -->
-  <UsdUVTexture name="UsdUVTexture22" type="multioutput" version="2.2">
+  <UsdUVTexture name="texture_base_color" type="multioutput">
     <input name="file" type="filename" value="resources/Images/brass_color.jpg" colorspace="srgb_texture" />
   </UsdUVTexture>
-  <convert name="extractColor" type="color3">
-    <input name="in" type="color4" nodename="UsdUVTexture22" output="rgba" />
-  </convert>
-  <UsdUVTexture name="UsdUVTexture22_rough" type="multioutput" version="2.2">
+  <UsdUVTexture name="texture_roughness" type="multioutput">
     <input name="file" type="filename" value="resources/Images/brass_roughness.jpg" />
   </UsdUVTexture>
-  <extract name="extractRoughness" type="float">
-    <input name="in" type="color4" nodename="UsdUVTexture22_rough" output="rgba" />
-    <input name="index" type="integer" value="0" />
-  </extract>
-
-  <UsdPreviewSurface name="UsdPreviewSurface22" type="surfaceshader" nodedef="ND_UsdPreviewSurface_surfaceshader" version="2.3">
-    <input name="diffuseColor" type="color3" nodename="extractColor" />
-    <input name="roughness" type="float" nodename="extractRoughness" />
+  <UsdPreviewSurface name="UsdPreviewSurface" type="surfaceshader" nodedef="ND_UsdPreviewSurface_surfaceshader">
+    <input name="diffuseColor" type="color3" nodename="texture_base_color" output="rgb" />
+    <input name="roughness" type="float" nodename="texture_roughness" output="r" />
     <input name="metallic" type="float" value="1" />
   </UsdPreviewSurface>
-  <surfacematerial name="USDTexture_Tiled_Brass22" type="material">
-    <input name="surfaceshader" type="surfaceshader" nodename="UsdPreviewSurface22" />
+  <surfacematerial name="TiledBrass" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="UsdPreviewSurface" />
   </surfacematerial>
-
-  <!-- UsdUVTexture: version 2.3 test. Default is currently 2.3 so no version specifier required -->
-  <UsdUVTexture name="UsdUVTexture23_rough" type="multioutput">
-    <input name="file" type="filename" value="resources/Images/brass_roughness.jpg" />
-  </UsdUVTexture>
-  <UsdUVTexture name="UsdUVTexture23" type="multioutput">
-    <input name="file" type="filename" value="resources/Images/brass_color.jpg" colorspace="srgb_texture" />
-  </UsdUVTexture>
-
-  <UsdPreviewSurface name="UsdPreviewSurface23" type="surfaceshader" nodedef="ND_UsdPreviewSurface_surfaceshader" version="2.3">
-    <input name="diffuseColor" type="color3" nodename="UsdUVTexture23" output="rgb" />
-    <input name="roughness" type="float" nodename="UsdUVTexture23_rough" output="r" />
-    <input name="metallic" type="float" value="1" />
-  </UsdPreviewSurface>
-  <surfacematerial name="USDTexture_Tiled_Brass23" type="material">
-    <input name="surfaceshader" type="surfaceshader" nodename="UsdPreviewSurface23" />
-  </surfacematerial>
-
 </materialx>

source/MaterialXGenShader/ShaderGraph.cpp

@@ -633,14 +633,14 @@ void ShaderGraph::applyInputTransforms(ConstNodePtr node, ShaderNodePtr shaderNo
         if (input->hasValue() || input->hasInterfaceName())
         {
             string sourceColorSpace = input->getActiveColorSpace();
-            if (input->getType() == FILENAME_TYPE_STRING && node->isColorType())
+            if (input->getType() == FILENAME_TYPE_STRING && (node->isColorType() || node->isMultiOutputType()))
             {
                 // Adjust the source color space for filename interface names.
                 if (input->hasInterfaceName())
                 {
                     for (ConstNodePtr parentNode : context.getParentNodes())
                     {
-                        if (!parentNode->isColorType())
+                        if (!parentNode->isColorType() && !parentNode->isMultiOutputType())
                         {
                             InputPtr interfaceInput = parentNode->getInput(input->getInterfaceName());
                             string interfaceColorSpace = interfaceInput ? interfaceInput->getActiveColorSpace() : EMPTY_STRING;
@@ -652,9 +652,11 @@ void ShaderGraph::applyInputTransforms(ConstNodePtr node, ShaderNodePtr shaderNo
                     }
                 }
 
-                ShaderOutput* shaderOutput = shaderNode->getOutput();
-                populateColorTransformMap(colorManagementSystem, shaderOutput, sourceColorSpace, targetColorSpace, false);
-                populateUnitTransformMap(unitSystem, shaderOutput, input, targetDistanceUnit, false);
+                for (ShaderOutput* shaderOutput : shaderNode->getOutputs())
+                {
+                    populateColorTransformMap(colorManagementSystem, shaderOutput, sourceColorSpace, targetColorSpace, false);
+                    populateUnitTransformMap(unitSystem, shaderOutput, input, targetDistanceUnit, false);
+                }
             }
             else
             {
@@ -1069,7 +1071,9 @@ void ShaderGraph::populateColorTransformMap(ColorManagementSystemPtr colorManage
     if (!shaderPort ||
         sourceColorSpace.empty() ||
         targetColorSpace.empty() ||
-        sourceColorSpace == targetColorSpace)
+        sourceColorSpace == targetColorSpace ||
+        sourceColorSpace == "none" ||
+        targetColorSpace == "none")
     {
         return;
     }