From ae9f1d7b74aa49d4b895c536e8778eb013d4b8a0 Mon Sep 17 00:00:00 2001
From: JGamache-autodesk <56274617+JGamache-autodesk@users.noreply.github.com>
Date: Tue, 29 Oct 2024 16:45:15 -0400
Subject: [PATCH] Backport OpenPBR Surface to MaterialX 1.38.10 (#2082)

Backports only the minimal code necessary to render native OpenPBR surface in MaterialX in a way that has no visual impact on the existing shaders and pbr nodes present in 1.38.

Status:
- GLSL -> Fully functional
- MSL -> Fully functional. Required only backporting the inversesqrt fix on top of the GLSL code.
- OSL -> As functional as the 1.39 branch. Getting it fully functional requires OSL v1.14 features not yet released like Zeltner fuzz and compensating OrenNayar. I was not able to find any mention of a 82 deg color update on the OSL Schlick node though.
- MDL -> Compiles and validates, but no updated visuals until an updated MDL library is available.
---
 .github/workflows/main.yml                    | 105 ++-
 .github/workflows/release.yml                 |  43 ++
 libraries/CMakeLists.txt                      |  11 +-
 libraries/bxdf/mx39_open_pbr_surface.mtlx     | 679 ++++++++++++++++++
 .../pbrlib/genglsl/lib/mx39_microfacet.glsl   |  30 +
 .../genglsl/lib/mx39_microfacet_diffuse.glsl  |  88 +++
 .../genglsl/lib/mx39_microfacet_sheen.glsl    | 108 +++
 .../genglsl/lib/mx39_microfacet_specular.glsl | 419 +++++++++++
 .../genglsl/lib/mx_environment_fis.glsl       |   2 +
 .../genglsl/lib/mx_environment_none.glsl      |   2 +
 .../genglsl/lib/mx_environment_prefilter.glsl |   2 +
 .../genglsl/lib/mx_transmission_opacity.glsl  |   2 +
 .../genglsl/lib/mx_transmission_refract.glsl  |   2 +
 ..._compensating_oren_nayar_diffuse_bsdf.glsl |  42 ++
 .../genglsl/mx39_dielectric_tf_bsdf.glsl      |  92 +++
 .../mx39_generalized_schlick_tf_82_bsdf.glsl  |  98 +++
 .../genglsl/mx39_pbrlib_genglsl_impl.mtlx     |  16 +
 .../genglsl/mx39_sheen_zeltner_bsdf.glsl      |  38 +
 .../genmdl/mx39_pbrlib_genmdl_impl.mtlx       |  16 +
 .../genmsl/mx39_pbrlib_genmsl_impl.mtlx       |  16 +
 ...9_compensating_oren_nayar_diffuse_bsdf.osl |   5 +
 .../genosl/legacy/mx39_dielectric_tf_bsdf.osl |  36 +
 .../mx39_generalized_schlick_tf_82_bsdf.osl   |  38 +
 .../pbrlib/genosl/mx39_dielectric_tf_bsdf.osl |  15 +
 .../mx39_generalized_schlick_tf_82_bsdf.osl   |  15 +
 .../genosl/mx39_pbrlib_genosl_impl.legacy     |  16 +
 .../genosl/mx39_pbrlib_genosl_impl.mtlx       |  16 +
 libraries/pbrlib/pbrlib_defs.mtlx             |  74 ++
 python/Scripts/generateshader.py              |   2 -
 .../OpenPbr/open_pbr_aluminum_brushed.mtlx    |  13 +
 .../Examples/OpenPbr/open_pbr_carpaint.mtlx   |  14 +
 .../Examples/OpenPbr/open_pbr_default.mtlx    |  46 ++
 .../Examples/OpenPbr/open_pbr_glass.mtlx      |  13 +
 .../Examples/OpenPbr/open_pbr_honey.mtlx      |  14 +
 .../Examples/OpenPbr/open_pbr_ketchup.mtlx    |  14 +
 .../Examples/OpenPbr/open_pbr_lightbulb.mtlx  |  10 +
 .../Examples/OpenPbr/open_pbr_pearl.mtlx      |  20 +
 .../Examples/OpenPbr/open_pbr_soapbubble.mtlx |  15 +
 .../Examples/OpenPbr/open_pbr_velvet.mtlx     |  13 +
 resources/Materials/TestSuite/_options.mtlx   |   2 +-
 source/MaterialXGenMdl/MdlShaderGenerator.cpp |   3 +
 source/MaterialXGenShader/ShaderNode.cpp      |   3 +-
 source/MaterialXRender/CMakeLists.txt         |   3 +
 source/MaterialXTest/CMakeLists.txt           |   3 +
 .../MaterialXGenGlsl/GenGlsl.cpp              |   1 +
 .../MaterialXTest/MaterialXGenMdl/GenMdl.cpp  |   1 +
 .../MaterialXTest/MaterialXGenMsl/GenMsl.cpp  |   1 +
 .../MaterialXTest/MaterialXGenOsl/GenOsl.cpp  |   1 +
 .../MaterialXGenShader/GenShaderUtil.cpp      |   1 +
 source/MaterialXView/CMakeLists.txt           |   2 +-
 source/MaterialXView/Main.cpp                 |   2 +-
 51 files changed, 2162 insertions(+), 61 deletions(-)
 create mode 100644 .github/workflows/release.yml
 create mode 100644 libraries/bxdf/mx39_open_pbr_surface.mtlx
 create mode 100644 libraries/pbrlib/genglsl/lib/mx39_microfacet.glsl
 create mode 100644 libraries/pbrlib/genglsl/lib/mx39_microfacet_diffuse.glsl
 create mode 100644 libraries/pbrlib/genglsl/lib/mx39_microfacet_sheen.glsl
 create mode 100644 libraries/pbrlib/genglsl/lib/mx39_microfacet_specular.glsl
 create mode 100644 libraries/pbrlib/genglsl/mx39_compensating_oren_nayar_diffuse_bsdf.glsl
 create mode 100644 libraries/pbrlib/genglsl/mx39_dielectric_tf_bsdf.glsl
 create mode 100644 libraries/pbrlib/genglsl/mx39_generalized_schlick_tf_82_bsdf.glsl
 create mode 100644 libraries/pbrlib/genglsl/mx39_pbrlib_genglsl_impl.mtlx
 create mode 100644 libraries/pbrlib/genglsl/mx39_sheen_zeltner_bsdf.glsl
 create mode 100644 libraries/pbrlib/genmdl/mx39_pbrlib_genmdl_impl.mtlx
 create mode 100644 libraries/pbrlib/genmsl/mx39_pbrlib_genmsl_impl.mtlx
 create mode 100644 libraries/pbrlib/genosl/legacy/mx39_compensating_oren_nayar_diffuse_bsdf.osl
 create mode 100644 libraries/pbrlib/genosl/legacy/mx39_dielectric_tf_bsdf.osl
 create mode 100644 libraries/pbrlib/genosl/legacy/mx39_generalized_schlick_tf_82_bsdf.osl
 create mode 100644 libraries/pbrlib/genosl/mx39_dielectric_tf_bsdf.osl
 create mode 100644 libraries/pbrlib/genosl/mx39_generalized_schlick_tf_82_bsdf.osl
 create mode 100644 libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.legacy
 create mode 100644 libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_aluminum_brushed.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_carpaint.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_default.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_glass.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_honey.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_ketchup.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_lightbulb.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_pearl.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_soapbubble.mtlx
 create mode 100644 resources/Materials/Examples/OpenPbr/open_pbr_velvet.mtlx

diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 0c42bf93ad..7e01379f54 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -18,83 +18,75 @@ jobs:
       fail-fast: false
       matrix:
         include:
-        - name: Linux_GCC_9_Python37
-          os: ubuntu-20.04
+        - name: Linux_GCC_10_Python37
+          os: ubuntu-22.04
           compiler: gcc
-          compiler_version: "9"
+          compiler_version: "10"
           python: 3.7
-          cmake_config: -DMATERIALX_BUILD_SHARED_LIBS=ON
+          cmake_config: -DMATERIALX_BUILD_SHARED_LIBS=ON -DMATERIALX_BUILD_MONOLITHIC=ON
 
-        - name: Linux_GCC_12_Python311
-          os: ubuntu-22.04
+        - name: Linux_GCC_13_Python311
+          os: ubuntu-24.04
           compiler: gcc
-          compiler_version: "12"
+          compiler_version: "13"
           python: 3.11
           build_javascript: ON
 
-        - name: Linux_GCC_13_Python312
-          os: ubuntu-22.04
+        - name: Linux_GCC_14_Python312
+          os: ubuntu-24.04
           compiler: gcc
-          compiler_version: "13"
+          compiler_version: "14"
           python: 3.12
-          static_analysis: ON
-          cmake_config: -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
 
         - name: Linux_GCC_CoverageAnalysis
-          os: ubuntu-22.04
+          os: ubuntu-24.04
           compiler: gcc
           compiler_version: "None"
           python: None
           coverage_analysis: ON
           cmake_config: -DMATERIALX_COVERAGE_ANALYSIS=ON -DMATERIALX_BUILD_RENDER=OFF -DMATERIALX_BUILD_PYTHON=OFF
 
-        - name: Linux_Clang_10_Python37
-          os: ubuntu-20.04
+        - name: Linux_Clang_13_Python37
+          os: ubuntu-22.04
           compiler: clang
-          compiler_version: "10"
+          compiler_version: "13"
           python: 3.7
           cmake_config: -DMATERIALX_BUILD_SHARED_LIBS=ON
 
-        - name: Linux_Clang_15_Python312
-          os: ubuntu-22.04
+        - name: Linux_Clang_18_Python312
+          os: ubuntu-24.04
           compiler: clang
-          compiler_version: "15"
+          compiler_version: "18"
           python: 3.12
           test_render: ON
           clang_format: ON
 
-        - name: Linux_Clang_DynamicAnalysis
-          os: ubuntu-22.04
-          compiler: clang
-          compiler_version: "15"
-          python: None
-          cmake_config: -DMATERIALX_DYNAMIC_ANALYSIS=ON
-          dynamic_analysis: ON
-
-        - name: MacOS_Xcode_13_Python37
-          os: macos-12
+        - name: MacOS_Xcode_14_Python39
+          os: macos-13
           compiler: xcode
-          compiler_version: "13.1"
+          compiler_version: "14.1"
           cmake_config: -DMATERIALX_BUILD_SHARED_LIBS=ON
-          python: 3.7
+          python: 3.9
 
         - name: MacOS_Xcode_14_Python311
-          os: macos-13
+          os: macos-14
           compiler: xcode
           compiler_version: "14.3"
           python: 3.11
+          static_analysis: ON
+          cmake_config: -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
 
         - name: MacOS_Xcode_15_Python312
           os: macos-14
           compiler: xcode
-          compiler_version: "15.0"
+          compiler_version: "15.4"
           python: 3.12
           test_shaders: ON
 
         - name: iOS_Xcode_15
           os: macos-14
           compiler: xcode
-          compiler_version: "15.0"
+          compiler_version: "15.4"
           python: None
           cmake_config: -DMATERIALX_BUILD_IOS=ON -DCMAKE_OSX_SYSROOT=`xcrun --sdk iphoneos --show-sdk-path` -DCMAKE_OSX_ARCHITECTURES=arm64
 
@@ -128,14 +120,14 @@ jobs:
       if: runner.os == 'Linux'
       run: |
         sudo apt-get update
-        sudo apt-get install xorg-dev mesa-utils
+        sudo apt-get install xorg-dev
         if [ "${{ matrix.compiler_version }}" != 'None' ]; then
           if [ "${{ matrix.compiler }}" = "gcc" ]; then
-            sudo apt-get install -y g++-${{ matrix.compiler_version }} g++-${{ matrix.compiler_version }}-multilib
+            sudo apt-get install -y g++-${{ matrix.compiler_version }}
             echo "CC=gcc-${{ matrix.compiler_version }}" >> $GITHUB_ENV
             echo "CXX=g++-${{ matrix.compiler_version }}" >> $GITHUB_ENV
           else
-            sudo apt-get install -y clang-${{ matrix.compiler_version }} libc++-${{ matrix.compiler_version }}-dev libc++abi-${{ matrix.compiler_version }}-dev
+            sudo apt-get install -y clang-${{ matrix.compiler_version }}
             echo "CC=clang-${{ matrix.compiler_version }}" >> $GITHUB_ENV
             echo "CXX=clang++-${{ matrix.compiler_version }}" >> $GITHUB_ENV
           fi
@@ -198,7 +190,7 @@ jobs:
       run: find source \( -name *.h -o -name *.cpp -o -name *.mm -o -name *.inl \) ! -path "*/External/*" ! -path "*/NanoGUI/*" | xargs clang-format -i --verbose
 
     - name: CMake Generate
-      run: cmake -S . -B build -DMATERIALX_BUILD_PYTHON=ON -DMATERIALX_BUILD_VIEWER=ON -DMATERIALX_BUILD_GRAPH_EDITOR=ON -DMATERIALX_TEST_RENDER=OFF -DMATERIALX_WARNINGS_AS_ERRORS=ON ${{matrix.cmake_config}}
+      run: cmake -S . -B build -DMATERIALX_BUILD_PYTHON=ON -DMATERIALX_BUILD_VIEWER=ON -DMATERIALX_BUILD_GRAPH_EDITOR=ON -DMATERIALX_BUILD_TESTS=ON -DMATERIALX_TEST_RENDER=OFF -DMATERIALX_WARNINGS_AS_ERRORS=ON ${{matrix.cmake_config}}
 
     - name: CMake Build
       run: cmake --build build --target install --config Release --parallel 2
@@ -220,6 +212,10 @@ jobs:
         python Scripts/generateshader.py ../resources/Materials/Examples/StandardSurface --target osl
         python Scripts/generateshader.py ../resources/Materials/Examples/StandardSurface --target mdl
         python Scripts/generateshader.py ../resources/Materials/Examples/StandardSurface --target msl
+        python Scripts/generateshader.py ../resources/Materials/Examples/OpenPbr --target glsl
+        python Scripts/generateshader.py ../resources/Materials/Examples/OpenPbr --target osl
+        python Scripts/generateshader.py ../resources/Materials/Examples/OpenPbr --target mdl
+        python Scripts/generateshader.py ../resources/Materials/Examples/OpenPbr --target msl
       working-directory: python
 
     - name: Shader Validation Tests (Windows)
@@ -227,13 +223,14 @@ jobs:
       run: |
         vcpkg/vcpkg install glslang --triplet=x64-windows
         glslangValidator.exe -v
-        python python/Scripts/generateshader.py resources/Materials/Examples/StandardSurface --target glsl --validator glslangValidator.exe --vulkanGlsl True --validatorArgs="-V --aml"
-        python python/Scripts/generateshader.py resources/Materials/Examples/StandardSurface --target essl --validator glslangValidator.exe
+        python python/Scripts/generateshader.py resources/Materials/Examples --target glsl --validator glslangValidator.exe
+        python python/Scripts/generateshader.py resources/Materials/Examples --target essl --validator glslangValidator.exe
 
     - name: Shader Validation Tests (MacOS)
       if: matrix.test_shaders == 'ON' && runner.os == 'macOS'
       run: |
-        python python/Scripts/generateshader.py resources/Materials/Examples/StandardSurface --target msl --validator "xcrun metal --language=metal" --validatorArgs="-w"
+        python python/Scripts/generateshader.py resources/Materials/Examples --target msl --validator "xcrun metal --language=metal" --validatorArgs="-w"
+        python python/Scripts/generateshader.py resources/Materials/TestSuite/stdlib --target msl --validator "xcrun metal --language=metal" --validatorArgs="-w"
 
     - name: Coverage Analysis Tests
       if: matrix.coverage_analysis == 'ON'
@@ -244,10 +241,14 @@ jobs:
       working-directory: build
 
     - name: Static Analysis Tests
-      if: matrix.static_analysis == 'ON' && runner.os == 'Linux'
+      if: matrix.static_analysis == 'ON'
       run: |
-        sudo apt-get install cppcheck
-        cppcheck --project=build/compile_commands.json --error-exitcode=1 --suppress=*:*/External/* --suppress=*:*/NanoGUI/*
+        if [ "${{ runner.os }}" = "Linux" ]; then
+          sudo apt-get install cppcheck
+        else
+          brew install cppcheck
+        fi
+        cppcheck --project=build/compile_commands.json --error-exitcode=1 --suppress=normalCheckLevelMaxBranches --suppress=*:*/External/* --suppress=*:*/NanoGUI/*
 
     - name: Initialize Virtual Framebuffer
       if: matrix.test_render == 'ON' && runner.os == 'Linux'
@@ -255,7 +256,6 @@ jobs:
         Xvfb :1 -screen 0 1280x960x24 &
         echo "DISPLAY=:1" >> $GITHUB_ENV
         echo "LIBGL_ALWAYS_SOFTWARE=1" >> $GITHUB_ENV
-        echo "GALLIUM_DRIVER=llvmpipe" >> $GITHUB_ENV
 
     - name: Render Script Tests
       if: matrix.test_render == 'ON'
@@ -269,6 +269,7 @@ jobs:
       run: |
         ../installed/bin/MaterialXView --material brass_average_baked.mtlx --mesh ../../resources/Geometry/sphere.obj --screenWidth 128 --screenHeight 128 --cameraZoom 1.4 --shadowMap false --captureFilename Viewer_BrassAverage.png
         ../installed/bin/MaterialXView --material usd_preview_surface_carpaint.mtlx --mesh ../../resources/Geometry/sphere.obj --screenWidth 128 --screenHeight 128 --cameraZoom 1.4 --shadowMap false --captureFilename Viewer_CarpaintTranslated.png
+        ../installed/bin/MaterialXView --material open_pbr_carpaint.mtlx --mesh ../../resources/Geometry/sphere.obj --screenWidth 128 --screenHeight 128 --cameraZoom 1.4 --shadowMap false --captureFilename Viewer_OpenPBRCarpaintTranslated.png
         ../installed/bin/MaterialXGraphEditor --material ../../resources/Materials/Examples/StandardSurface/standard_surface_marble_solid.mtlx --viewWidth 128 --viewHeight 128 --captureFilename GraphEditor_MarbleSolid.png
       working-directory: build/render
 
@@ -331,8 +332,8 @@ jobs:
       working-directory: javascript/MaterialXView
 
     - name: Deploy Web Viewer
-      if: matrix.build_javascript == 'ON' && github.ref == 'refs/heads/main'
-      uses: JamesIves/github-pages-deploy-action@v4
+      if: matrix.build_javascript == 'ON' && github.event_name != 'pull_request'
+      uses: JamesIves/github-pages-deploy-action@v4.6.4
       with:
         branch: gh-pages
         folder: javascript/MaterialXView/dist
@@ -344,11 +345,10 @@ jobs:
       with:
         name: MaterialX_JavaScript
         path: javascript/build/installed/JavaScript/MaterialX        
-        if-no-files-found: ignore   
 
   sdist:
     name: Python SDist
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     if: github.repository == 'AcademySoftwareFoundation/MaterialX'
     outputs:
       sdist_filename: ${{ steps.generate.outputs.filename }}
@@ -383,8 +383,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-minor: ['7', '8', '9', '10', '11']
-        os: ['ubuntu-latest', 'macos-latest', 'windows-latest']
+        python-minor: ['7', '8', '9', '10', '11', '12']
+        os: ['ubuntu-22.04', 'windows-2022', 'macos-13']
 
     steps:
     - name: Sync Repository
@@ -402,7 +402,7 @@ jobs:
         path: sdist
 
     - name: Build Wheel
-      uses: pypa/cibuildwheel@v2.16.5
+      uses: pypa/cibuildwheel@v2.19.2
       with:
         package-dir: ${{ github.workspace }}/sdist/${{ needs.sdist.outputs.sdist_filename }}
       env:
@@ -413,7 +413,6 @@ jobs:
         # manylinux2014 is CentOS 7 based. Which means GCC 10 and glibc 2.17.
         CIBW_MANYLINUX_X86_64_IMAGE: manylinux2014
         CIBW_BEFORE_ALL_LINUX: yum install -y libXt-devel
-        CIBW_BEFORE_ALL_MACOS: sudo xcode-select -switch /Applications/Xcode_13.4.app
         CIBW_BUILD_VERBOSITY: 1
         CIBW_ENVIRONMENT: CMAKE_BUILD_PARALLEL_LEVEL=2
         # CIBW_BUILD_FRONTEND: build  # https://github.com/pypa/build
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
new file mode 100644
index 0000000000..6ddb62f2b4
--- /dev/null
+++ b/.github/workflows/release.yml
@@ -0,0 +1,43 @@
+name: release
+
+on:
+  release:
+    types: [published]
+
+permissions:
+  contents: read
+  
+jobs:
+
+  release:
+    name: Release Signing
+    runs-on: ubuntu-latest
+    env:
+       RELEASE_TAG: ${{ github.ref_name }}
+    permissions:
+      contents: write
+      id-token: write
+      repository-projects: write
+       
+    steps:
+      - name: Sync Repository
+        uses: actions/checkout@v4
+        with:
+          submodules: recursive
+
+      - name: Create Archive Name
+        run: echo "MATERIALX_ARCHIVE=MaterialX-${RELEASE_TAG//v}" >> $GITHUB_ENV
+
+      - name: Generate Archives
+        run: |
+          git archive --prefix ${MATERIALX_ARCHIVE}/ --output ${MATERIALX_ARCHIVE}.zip ${RELEASE_TAG}
+          git archive --prefix ${MATERIALX_ARCHIVE}/ --output ${MATERIALX_ARCHIVE}.tar.gz ${RELEASE_TAG}
+
+      - name: Sign and Upload Archives
+        uses: sigstore/gh-action-sigstore-python@v3.0.0
+        with:
+          inputs: |
+            ${{ env.MATERIALX_ARCHIVE }}.zip
+            ${{ env.MATERIALX_ARCHIVE }}.tar.gz
+          upload-signing-artifacts: true
+          release-signing-artifacts: false
diff --git a/libraries/CMakeLists.txt b/libraries/CMakeLists.txt
index d60a54cf3b..f9d7b55565 100644
--- a/libraries/CMakeLists.txt
+++ b/libraries/CMakeLists.txt
@@ -8,9 +8,13 @@ if(NOT SKBUILD)
     install(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/
             DESTINATION "${MATERIALX_INSTALL_STDLIB_PATH}"
             PATTERN "CMakeLists.txt" EXCLUDE
-            PATTERN "pbrlib_genosl_impl.*" EXCLUDE)
+            PATTERN "pbrlib_genosl_impl.*" EXCLUDE
+            PATTERN "mx39_pbrlib_genosl_impl.*" EXCLUDE)
     install(FILES "${CMAKE_CURRENT_SOURCE_DIR}/pbrlib/genosl/pbrlib_genosl_impl.${PBRLIB_SUFFIX}"
             DESTINATION "${MATERIALX_INSTALL_STDLIB_PATH}/pbrlib/genosl/" RENAME pbrlib_genosl_impl.mtlx)
+    install(FILES "${CMAKE_CURRENT_SOURCE_DIR}/pbrlib/genosl/mx39_pbrlib_genosl_impl.${PBRLIB_SUFFIX}"
+            DESTINATION "${MATERIALX_INSTALL_STDLIB_PATH}/pbrlib/genosl/" RENAME mx39_pbrlib_genosl_impl.mtlx)
+
 endif()
 
 set(MATERIALX_PYTHON_LIBRARIES_PATH "${MATERIALX_PYTHON_FOLDER_NAME}/${MATERIALX_INSTALL_STDLIB_PATH}")
@@ -22,7 +26,10 @@ if(MATERIALX_BUILD_PYTHON)
     install(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/
             DESTINATION "${MATERIALX_PYTHON_LIBRARIES_PATH}"
             PATTERN "CMakeLists.txt" EXCLUDE
-            PATTERN "pbrlib_genosl_impl.*" EXCLUDE)
+            PATTERN "pbrlib_genosl_impl.*" EXCLUDE
+            PATTERN "mx39_pbrlib_genosl_impl.*" EXCLUDE)
     install(FILES "${CMAKE_CURRENT_SOURCE_DIR}/pbrlib/genosl/pbrlib_genosl_impl.${PBRLIB_SUFFIX}"
             DESTINATION "${MATERIALX_PYTHON_LIBRARIES_PATH}/pbrlib/genosl/" RENAME pbrlib_genosl_impl.mtlx)
+    install(FILES "${CMAKE_CURRENT_SOURCE_DIR}/pbrlib/genosl/mx39_pbrlib_genosl_impl.${PBRLIB_SUFFIX}"
+            DESTINATION "${MATERIALX_PYTHON_LIBRARIES_PATH}/pbrlib/genosl/" RENAME mx39_pbrlib_genosl_impl.mtlx)
 endif()
diff --git a/libraries/bxdf/mx39_open_pbr_surface.mtlx b/libraries/bxdf/mx39_open_pbr_surface.mtlx
new file mode 100644
index 0000000000..42df378691
--- /dev/null
+++ b/libraries/bxdf/mx39_open_pbr_surface.mtlx
@@ -0,0 +1,679 @@
+<?xml version="1.0"?>
+<materialx version="1.38">
+  <!--
+    OpenPBR Surface node definition backported to MaterialX 1.38.10
+    Snapshot taken at commit f98abc43 from June 16th 2024.
+  -->
+  <nodedef name="ND_open_pbr_surface_surfaceshader" node="open_pbr_surface" nodegroup="OpenPBR" version="1.1" isdefaultversion="true"
+           doc="OpenPBR Surface Shading Model" uiname="OpenPBR Surface">
+    <input name="base_weight" type="float" value="1.0" uimin="0.0" uimax="1.0" uiname="Weight" uifolder="Base"
+           doc="Multiplier on the intensity of the reflection from the diffuse and metallic base." />
+    <input name="base_color" type="color3" value="0.8, 0.8, 0.8" uimin="0,0,0" uimax="1,1,1" uiname="Color" uifolder="Base"
+           doc="Color of the reflection from the diffuse and metallic base." />
+    <input name="base_diffuse_roughness" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Diffuse Roughness" uifolder="Base" uiadvanced="true"
+           doc="Roughness of the diffuse reflection. Higher values cause the surface to appear flatter." />
+    <input name="base_metalness" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Metalness" uifolder="Base"
+           doc="Specifies how metallic the base material appears (dials the base from pure dielectric to pure metal)." />
+    <input name="specular_weight" type="float" value="1.0" uimin="0.0" uisoftmax="1.0" uiname="Weight" uifolder="Specular"
+           doc="Multiplies the specular reflectivity." />
+    <input name="specular_color" type="color3" value="1, 1, 1" uimin="0,0,0" uimax="1,1,1" uiname="Color" uifolder="Specular"
+           doc="Color of the specular reflection (controls the physical edge-tint for metals, and a non-physical overall tint for dielectrics)." />
+    <input name="specular_roughness" type="float" value="0.3" uimin="0.0" uimax="1.0" uiname="Roughness" uifolder="Specular"
+           doc="The roughness of the specular reflection. Lower numbers produce sharper reflections, higher numbers produce blurrier reflections." />
+    <input name="specular_ior" type="float" value="1.5" uimin="0.0" uisoftmin="1.0" uisoftmax="3.0" uiname="IOR" uifolder="Specular"
+           doc="Index of refraction of the dielectric base." />
+    <input name="specular_roughness_anisotropy" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Anisotropy" uifolder="Specular" uiadvanced="true"
+           doc="The directional bias of the roughness of the metal/dielectric base, resulting in increasingly stretched highlights along the tangent direction." />
+    <input name="transmission_weight" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Weight" uifolder="Transmission" uiadvanced="true"
+           doc="Mixture weight between the transparent and opaque dielectric base. The greater the value the more transparent the material." />
+    <input name="transmission_color" type="color3" value="1, 1, 1" uimin="0,0,0" uimax="1,1,1" uiname="Color" uifolder="Transmission" uiadvanced="true"
+           doc="Controls color of the transparent base due to Beer's law volumetric absorption under the surface (reverts to a non-physical tint when transmission_depth is zero)." />
+    <input name="transmission_depth" type="float" value="0.0" uimin="0.0" uisoftmax="1.0" uiname="Depth" uifolder="Transmission" uiadvanced="true"
+           doc="Specifies the distance light travels inside the transparent base before it becomes exactly the transmission_color according to Beer's law." />
+    <input name="transmission_scatter" type="color3" value="0, 0, 0" uimin="0,0,0" uimax="1,1,1" uiname="Scatter" uifolder="Transmission" uiadvanced="true"
+           doc="Controls the color of light volumetrically scattered inside the transparent base. Suitable for materials with visually significant scattering such as honey, fruit juice, murky water, opalescent glass, or milky glass." />
+    <input name="transmission_scatter_anisotropy" type="float" value="0.0" uimin="-1.0" uimax="1.0" uiname="Anisotropy" uifolder="Transmission" uiadvanced="true"
+           doc="The amount of directional bias, or anisotropy, of the volumetric scattering in the transparent base." />
+    <input name="transmission_dispersion_scale" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Dispersion Scale" uifolder="Transmission" uiadvanced="true"
+           doc="Linearly scales the amount of dispersion." />
+    <input name="transmission_dispersion_abbe_number" type="float" value="20.0" uimin="0.0" uisoftmin="9.0" uisoftmax="91.0" uiname="Abbe Number" uifolder="Transmission" uiadvanced="true"
+           doc="Physical Abbe number of the dielectric medium, describing how much the dielectric index of refraction varies across wavelengths." />
+    <input name="subsurface_weight" type="float" value="0" uimin="0.0" uimax="1.0" uiname="Weight" uifolder="Subsurface" uiadvanced="true"
+           doc="Mixture weight which dials the opaque dielectric base between diffuse reflection and subsurface scattering. A value of 1.0 indicates full subsurface scattering and a value 0 for diffuse reflection only." />
+    <input name="subsurface_color" type="color3" value="0.8, 0.8, 0.8" uimin="0,0,0" uimax="1,1,1" uiname="Color" uifolder="Subsurface" uiadvanced="true"
+           doc="The observed reflection color of the subsurface scattering medium." />
+    <input name="subsurface_radius" type="float" value="1.0" uimin="0.0" uisoftmax="1.0" uiname="Radius" uifolder="Subsurface" uiadvanced="true"
+           doc="Length scale of the subsurface scattering mean free path." />
+    <input name="subsurface_radius_scale" type="color3" value="1.0, 0.5, 0.25" uimin="0,0,0" uimax="1,1,1" uiname="Radius Scale" uifolder="Subsurface" uiadvanced="true"
+           doc="RGB multiplier to subsurface_radius, giving the per-channel scattering mean-free-paths." />
+    <input name="subsurface_scatter_anisotropy" type="float" value="0.0" uimin="-1.0" uimax="1.0" uiname="Anisotropy" uifolder="Subsurface" uiadvanced="true"
+           doc="Controls the phase-function of subsurface scattering, where zero scatters light evenly, positive values scatter forwards, and negative values scatter backwards." />
+    <input name="fuzz_weight" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Weight" uifolder="Fuzz" uiadvanced="true"
+           doc="The presence weight of a fuzz layer that can be used to approximate microfibers, for fabrics such as velvet and satin as well as dust grains." />
+    <input name="fuzz_color" type="color3" value="1, 1, 1" uimin="0,0,0" uimax="1,1,1" uiname="Color" uifolder="Fuzz" uiadvanced="true"
+           doc="The color of the fuzz layer." />
+    <input name="fuzz_roughness" type="float" value="0.5" uimin="0.0" uimax="1.0" uiname="Roughness" uifolder="Fuzz" uiadvanced="true"
+           doc="The roughness of the fuzz layer." />
+    <input name="coat_weight" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Weight" uifolder="Coat"
+           doc="The presence weight of a reflective clear-coat layer on top of the material. Use for materials such as car paint or an oily layer." />
+    <input name="coat_color" type="color3" value="1, 1, 1" uimin="0,0,0" uimax="1,1,1" uiname="Color" uifolder="Coat"
+           doc="The color of the clear-coat layer's transparency, due to absorption in the coat." />
+    <input name="coat_roughness" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Roughness" uifolder="Coat"
+           doc="The roughness of the clear-coat reflections. The lower the value, the sharper the reflection." />
+    <input name="coat_roughness_anisotropy" type="float" value="0.0" uimin="0.0" uimax="1.0" uiname="Anisotropy" uifolder="Coat" uiadvanced="true"
+           doc="The directional bias of the roughness of the clear-coat layer, resulting in increasingly stretched highlights along the coat tangent direction." />
+    <input name="coat_ior" type="float" value="1.6" uimin="0.0" uisoftmin="1.0" uisoftmax="3.0" uiname="IOR" uifolder="Coat"
+           doc="The index of refraction of the clear-coat layer." />
+    <input name="coat_darkening" type="float" value="1.0" uimin="0.0" uimax="1.0" uiname="Darkening" uifolder="Coat"
+           doc="Modulates the physical coat darkening effect." />
+    <input name="thin_film_weight" type="float" value="0" uimin="0.0" uimax="1.0" uiname="Weight" uifolder="Thin Film" uiadvanced="true"
+           doc="Coverage weight of the thin-film. Use for materials such as multi-tone car paint or soap bubbles." />
+    <input name="thin_film_thickness" type="float" value="0.5" uimin="0.0" uisoftmax="1.0" uiname="Thickness" uifolder="Thin Film" uiadvanced="true"
+           doc="The thickness of the thin-film layer on the base (in micrometers)." />
+    <input name="thin_film_ior" type="float" value="1.4" uimin="0.0" uisoftmin="1.0" uisoftmax="3.0" uiname="IOR" uifolder="Thin Film" uiadvanced="true"
+           doc="The index of refraction of the thin-film." />
+    <input name="emission_luminance" type="float" value="0.0" uimin="0.0" uisoftmax="1000.0" uiname="Luminance" uifolder="Emission"
+           doc="The amount of emitted light, as a luminance in nits." />
+    <input name="emission_color" type="color3" value="1, 1, 1" uimin="0,0,0" uimax="1,1,1" uiname="Color" uifolder="Emission"
+           doc="The color of the emitted light." />
+    <input name="geometry_opacity" type="float" value="1" uimin="0" uimax="1" uiname="Opacity" uifolder="Geometry"
+           doc="The opacity of the entire material." />
+    <input name="geometry_thin_walled" type="boolean" value="false" uiname="Thin Walled" uifolder="Geometry" uiadvanced="true"
+           doc="If true the surface is double-sided and represents an infinitesimally thin shell. Suitable for extremely geometrically thin objects such as leaves or paper." />
+    <input name="geometry_normal" type="vector3" defaultgeomprop="Nworld" uiname="Normal" uifolder="Geometry"
+           doc="Input geometric normal" />
+    <input name="geometry_coat_normal" type="vector3" defaultgeomprop="Nworld" uiname="Coat Normal" uifolder="Geometry"
+           doc="Input normal for coat layer" />
+    <input name="geometry_tangent" type="vector3" defaultgeomprop="Tworld" uiname="Tangent" uifolder="Geometry"
+           doc="Input geometric tangent" />
+    <input name="geometry_coat_tangent" type="vector3" defaultgeomprop="Tworld" uiname="Coat Tangent" uifolder="Geometry"
+           doc="Input geometric tangent for coat layer" />
+    <output name="out" type="surfaceshader" />
+  </nodedef>
+
+  <!--
+    OpenPBR Surface graph definition
+  -->
+  <nodegraph name="NG_mx39_open_pbr_surface_surfaceshader" nodedef="ND_open_pbr_surface_surfaceshader">
+
+    <!-- Roughening due to coat-->
+    <power name="coat_roughness_to_power_4" type="float">
+      <input name="in1" type="float" interfacename="coat_roughness" />
+      <input name="in2" type="float" value="4.0" />
+    </power>
+    <multiply name="two_times_coat_roughness_to_power_4" type="float">
+      <input name="in1" type="float" nodename="coat_roughness_to_power_4" />
+      <input name="in2" type="float" value="2.0" />
+    </multiply>
+    <power name="specular_roughness_to_power_4" type="float">
+      <input name="in1" type="float" interfacename="specular_roughness" />
+      <input name="in2" type="float" value="4.0" />
+    </power>
+    <add name="add_coat_and_spec_roughnesses_to_power_4" type="float">
+      <input name="in1" type="float" nodename="two_times_coat_roughness_to_power_4" />
+      <input name="in2" type="float" nodename="specular_roughness_to_power_4" />
+    </add>
+    <min name="min_1_add_coat_and_spec_roughnesses_to_power_4" type="float">
+      <input name="in1" type="float" value="1.0" />
+      <input name="in2" type="float" nodename="add_coat_and_spec_roughnesses_to_power_4" />
+    </min>
+    <power name="coat_affected_specular_roughness" type="float">
+      <input name="in1" type="float" nodename="min_1_add_coat_and_spec_roughnesses_to_power_4" />
+      <input name="in2" type="float" value="0.25" />
+    </power>
+    <mix name="effective_specular_roughness" type="float">
+      <input name="fg" type="float" nodename="coat_affected_specular_roughness" />
+      <input name="bg" type="float" interfacename="specular_roughness" />
+      <input name="mix" type="float" interfacename="coat_weight" />
+    </mix>
+
+    <!-- Calculate main specular roughness -->
+    <open_pbr_anisotropy name="main_roughness" type="vector2">
+      <input name="roughness" type="float" nodename="effective_specular_roughness" />
+      <input name="anisotropy" type="float" interfacename="specular_roughness_anisotropy" />
+    </open_pbr_anisotropy>
+
+    <!-- Subsurface (thin-walled) -->
+    <max name="subsurface_color_nonnegative" type="color3">
+      <input name="in1" type="color3" interfacename="subsurface_color" />
+      <input name="in2" type="float" value="0.0" />
+    </max>
+    <compensating_oren_nayar_diffuse_bsdf name="subsurface_thin_walled_reflection_bsdf" type="BSDF">
+      <input name="color" type="color3" nodename="subsurface_color_nonnegative" />
+      <input name="roughness" type="float" interfacename="base_diffuse_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+    </compensating_oren_nayar_diffuse_bsdf>
+    <subtract name="one_minus_subsurface_scatter_anisotropy" type="float">
+      <input name="in1" type="float" value="1.0" />
+      <input name="in2" type="float" interfacename="subsurface_scatter_anisotropy" />
+    </subtract>
+    <multiply name="subsurface_thin_walled_brdf_factor" type="color3">
+      <input name="in1" type="color3" interfacename="subsurface_color" />
+      <input name="in2" type="float" nodename="one_minus_subsurface_scatter_anisotropy" />
+    </multiply>
+    <multiply name="subsurface_thin_walled_reflection" type="BSDF">
+      <input name="in1" type="BSDF" nodename="subsurface_thin_walled_reflection_bsdf" />
+      <input name="in2" type="color3" nodename="subsurface_thin_walled_brdf_factor" />
+    </multiply>
+    <translucent_bsdf name="subsurface_thin_walled_transmission_bsdf" type="BSDF">
+      <input name="color" type="color3" nodename="subsurface_color_nonnegative" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+    </translucent_bsdf>
+    <add name="one_plus_subsurface_scatter_anisotropy" type="float">
+      <input name="in1" type="float" value="1.0" />
+      <input name="in2" type="float" interfacename="subsurface_scatter_anisotropy" />
+    </add>
+    <multiply name="subsurface_thin_walled_btdf_factor" type="color3">
+      <input name="in1" type="color3" interfacename="subsurface_color" />
+      <input name="in2" type="float" nodename="one_plus_subsurface_scatter_anisotropy" />
+    </multiply>
+    <multiply name="subsurface_thin_walled_transmission" type="BSDF">
+      <input name="in1" type="BSDF" nodename="subsurface_thin_walled_transmission_bsdf" />
+      <input name="in2" type="color3" nodename="subsurface_thin_walled_btdf_factor" />
+    </multiply>
+    <mix name="subsurface_thin_walled" type="BSDF">
+      <input name="fg" type="BSDF" nodename="subsurface_thin_walled_reflection" />
+      <input name="bg" type="BSDF" nodename="subsurface_thin_walled_transmission" />
+      <input name="mix" type="float" value="0.5" />
+    </mix>
+
+    <!-- Subsurface (non-thin-walled) -->
+    <convert name="subsurface_radius_vector" type="vector3">
+      <input name="in" type="color3" interfacename="subsurface_radius_scale" />
+    </convert>
+    <multiply name="subsurface_radius_scaled" type="vector3">
+      <input name="in1" type="vector3" nodename="subsurface_radius_vector" />
+      <input name="in2" type="float" interfacename="subsurface_radius" />
+    </multiply>
+    <subsurface_bsdf name="subsurface_bsdf" type="BSDF">
+      <input name="color" type="color3" nodename="subsurface_color_nonnegative" />
+      <input name="radius" type="vector3" nodename="subsurface_radius_scaled" />
+      <input name="anisotropy" type="float" interfacename="subsurface_scatter_anisotropy" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+    </subsurface_bsdf>
+
+    <!-- Opaque Dielectric Base -->
+    <max name="base_color_nonnegative" type="color3">
+      <input name="in1" type="color3" interfacename="base_color" />
+      <input name="in2" type="float" value="0.0" />
+    </max>
+    <compensating_oren_nayar_diffuse_bsdf name="diffuse_bsdf" type="BSDF">
+      <input name="weight" type="float" interfacename="base_weight" />
+      <input name="color" type="color3" nodename="base_color_nonnegative" />
+      <input name="roughness" type="float" interfacename="base_diffuse_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+      <input name="energy_compensation" type="boolean" value="true" />
+    </compensating_oren_nayar_diffuse_bsdf>
+    <convert name="subsurface_selector" type="float">
+      <input name="in" type="boolean" interfacename="geometry_thin_walled" />
+    </convert>
+    <mix name="selected_subsurface" type="BSDF">
+      <input name="fg" type="BSDF" nodename="subsurface_thin_walled" />
+      <input name="bg" type="BSDF" nodename="subsurface_bsdf" />
+      <input name="mix" type="float" nodename="subsurface_selector" />
+    </mix>
+    <mix name="opaque_base" type="BSDF">
+      <input name="fg" type="BSDF" nodename="selected_subsurface" />
+      <input name="bg" type="BSDF" nodename="diffuse_bsdf" />
+      <input name="mix" type="float" interfacename="subsurface_weight" />
+    </mix>
+
+    <!-- Dielectric Base VDF -->
+    <convert name="transmission_color_vector" type="vector3">
+      <input name="in" type="color3" interfacename="transmission_color" />
+    </convert>
+    <ln name="transmission_color_ln" type="vector3">
+      <input name="in" type="vector3" nodename="transmission_color_vector" />
+    </ln>
+    <multiply name="extinction_coeff_denom" type="vector3">
+      <input name="in1" type="vector3" nodename="transmission_color_ln" />
+      <input name="in2" type="float" value="-1.0" />
+    </multiply>
+    <convert name="transmission_depth_vector" type="vector3">
+      <input name="in" type="float" interfacename="transmission_depth" />
+    </convert>
+    <divide name="extinction_coeff" type="vector3">
+      <input name="in1" type="vector3" nodename="extinction_coeff_denom" />
+      <input name="in2" type="vector3" nodename="transmission_depth_vector" />
+    </divide>
+    <convert name="transmission_scatter_vector" type="vector3">
+      <input name="in" type="color3" interfacename="transmission_scatter" />
+    </convert>
+    <divide name="scattering_coeff" type="vector3">
+      <input name="in1" type="vector3" nodename="transmission_scatter_vector" />
+      <input name="in2" type="vector3" nodename="transmission_depth_vector" />
+    </divide>
+    <subtract name="absorption_coeff" type="vector3">
+      <input name="in1" type="vector3" nodename="extinction_coeff" />
+      <input name="in2" type="vector3" nodename="scattering_coeff" />
+    </subtract>
+    <extract name="absorption_coeff_x" type="float">
+      <input name="in" type="vector3" nodename="absorption_coeff" />
+      <input name="index" type="integer" value="0" />
+    </extract>
+    <extract name="absorption_coeff_y" type="float">
+      <input name="in" type="vector3" nodename="absorption_coeff" />
+      <input name="index" type="integer" value="1" />
+    </extract>
+    <extract name="absorption_coeff_z" type="float">
+      <input name="in" type="vector3" nodename="absorption_coeff" />
+      <input name="index" type="integer" value="2" />
+    </extract>
+    <min name="absorption_coeff_min_x_y" type="float">
+      <input name="in1" type="float" nodename="absorption_coeff_x" />
+      <input name="in2" type="float" nodename="absorption_coeff_y" />
+    </min>
+    <min name="absorption_coeff_min" type="float">
+      <input name="in1" type="float" nodename="absorption_coeff_min_x_y" />
+      <input name="in2" type="float" nodename="absorption_coeff_z" />
+    </min>
+    <convert name="absorption_coeff_min_vector" type="vector3">
+      <input name="in" type="float" nodename="absorption_coeff_min" />
+    </convert>
+    <subtract name="absorption_coeff_shifted" type="vector3">
+      <input name="in1" type="vector3" nodename="absorption_coeff" />
+      <input name="in2" type="vector3" nodename="absorption_coeff_min_vector" />
+    </subtract>
+    <ifgreater name="if_absorption_coeff_shifted" type="vector3">
+      <input name="value1" type="float" value="0.0" />
+      <input name="value2" type="float" nodename="absorption_coeff_min" />
+      <input name="in1" type="vector3" nodename="absorption_coeff_shifted" />
+      <input name="in2" type="vector3" nodename="absorption_coeff" />
+    </ifgreater>
+    <ifgreater name="if_volume_absorption" type="vector3">
+      <input name="value1" type="float" interfacename="transmission_depth" />
+      <input name="value2" type="float" value="0.0" />
+      <input name="in1" type="vector3" nodename="if_absorption_coeff_shifted" />
+      <input name="in2" type="vector3" value="0.0,0.0,0.0" />
+    </ifgreater>
+    <ifgreater name="if_volume_scattering" type="vector3">
+      <input name="value1" type="float" interfacename="transmission_depth" />
+      <input name="value2" type="float" value="0.0" />
+      <input name="in1" type="vector3" nodename="scattering_coeff" />
+      <input name="in2" type="vector3" value="0.0,0.0,0.0" />
+    </ifgreater>
+    <anisotropic_vdf name="dielectric_volume" type="VDF">
+      <input name="absorption" type="vector3" nodename="if_volume_absorption" />
+      <input name="scattering" type="vector3" nodename="if_volume_scattering" />
+      <input name="anisotropy" type="float" interfacename="transmission_scatter_anisotropy" />
+    </anisotropic_vdf>
+
+    <!-- Thin-film Thickness -->
+    <multiply name="thin_film_thickness_nm" type="float">
+      <input name="in1" type="float" interfacename="thin_film_thickness" />
+      <input name="in2" type="float" value="1000.0" />
+    </multiply>
+
+    <!-- Dielectric Base -->
+      <!-- apply IOR ratio inversion method to avoid TIR artifact (as in Coat TIR section of spec) -->
+      <divide name="specular_to_coat_ior_ratio" type="float">
+         <input name="in1" type="float" interfacename="specular_ior" />
+         <input name="in2" type="float" interfacename="coat_ior" />
+      </divide>
+      <divide name="coat_to_specular_ior_ratio" type="float">
+         <input name="in1" type="float" interfacename="coat_ior" />
+         <input name="in2" type="float" interfacename="specular_ior" />
+      </divide>
+      <ifgreater name="specular_to_coat_ior_ratio_tir_fix" type="float">
+         <input name="value1" type="float" nodename="specular_to_coat_ior_ratio" />
+         <input name="value2" type="float" value="1.0" />
+         <input name="in1" type="float" nodename="specular_to_coat_ior_ratio" />
+         <input name="in2" type="float" nodename="coat_to_specular_ior_ratio" />
+      </ifgreater>
+    <mix name="eta_s" type="float">
+      <input name="fg" type="float" nodename="specular_to_coat_ior_ratio_tir_fix" />
+      <input name="bg" type="float" interfacename="specular_ior" />
+      <input name="mix" type="float" interfacename="coat_weight" />
+    </mix>
+    <subtract name="eta_s_minus_one" type="float">
+      <input name="in1" type="float" nodename="eta_s" />
+      <input name="in2" type="float" value="1.0" />
+    </subtract>
+    <add name="eta_s_plus_one" type="float">
+      <input name="in1" type="float" nodename="eta_s" />
+      <input name="in2" type="float" value="1.0" />
+    </add>
+    <divide name="specular_F0_sqrt" type="float">
+      <input name="in1" type="float" nodename="eta_s_minus_one" />
+      <input name="in2" type="float" nodename="eta_s_plus_one" />
+    </divide>
+    <multiply name="specular_F0" type="float">
+      <input name="in1" type="float" nodename="specular_F0_sqrt" />
+      <input name="in2" type="float" nodename="specular_F0_sqrt" />
+    </multiply>
+    <multiply name="scaled_specular_F0" type="float">
+      <input name="in1" type="float" interfacename="specular_weight" />
+      <input name="in2" type="float" nodename="specular_F0" />
+    </multiply>
+    <clamp name="scaled_specular_F0_clamped" type="float">
+      <input name="in" type="float" nodename="scaled_specular_F0" />
+      <input name="low" type="float" value="0.0" />
+      <input name="high" type="float" value="0.99999" />
+    </clamp>
+    <sqrt name="sqrt_scaled_specular_F0" type="float">
+      <input name="in" type="float" nodename="scaled_specular_F0_clamped" />
+    </sqrt>
+    <sign name="sign_eta_s_minus_one" type="float">
+      <input name="in" type="float" nodename="eta_s_minus_one" />
+    </sign>
+    <multiply name="modulated_eta_s_epsilon" type="float">
+      <input name="in1" type="float" nodename="sign_eta_s_minus_one" />
+      <input name="in2" type="float" nodename="sqrt_scaled_specular_F0" />
+    </multiply>
+    <subtract name="one_minus_modulated_eta_s_epsilon" type="float">
+      <input name="in1" type="float" value="1.0" />
+      <input name="in2" type="float" nodename="modulated_eta_s_epsilon" />
+    </subtract>
+    <add name="one_plus_modulated_eta_s_epsilon" type="float">
+      <input name="in1" type="float" value="1.0" />
+      <input name="in2" type="float" nodename="modulated_eta_s_epsilon" />
+    </add>
+    <divide name="modulated_eta_s" type="float">
+      <input name="in1" type="float" nodename="one_plus_modulated_eta_s_epsilon" />
+      <input name="in2" type="float" nodename="one_minus_modulated_eta_s_epsilon" />
+    </divide>
+    <ifgreater name="if_transmission_tint" type="color3">
+      <input name="value1" type="float" interfacename="transmission_depth" />
+      <input name="value2" type="float" value="0.0" />
+      <input name="in1" type="color3" value="1.0, 1.0, 1.0" />
+      <input name="in2" type="color3" interfacename="transmission_color" />
+    </ifgreater>
+    <dielectric_tf_bsdf name="dielectric_transmission" type="BSDF">
+      <input name="tint" type="color3" nodename="if_transmission_tint" />
+      <input name="ior" type="float" nodename="modulated_eta_s" />
+      <input name="roughness" type="vector2" nodename="main_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+      <input name="tangent" type="vector3" interfacename="geometry_tangent" />
+      <input name="scatter_mode" type="string" value="T" />
+    </dielectric_tf_bsdf>
+    <layer name="dielectric_volume_transmission" type="BSDF">
+      <input name="top" type="BSDF" nodename="dielectric_transmission" />
+      <input name="base" type="VDF" nodename="dielectric_volume" />
+    </layer>
+    <mix name="dielectric_substrate" type="BSDF">
+      <input name="fg" type="BSDF" nodename="dielectric_volume_transmission" />
+      <input name="bg" type="BSDF" nodename="opaque_base" />
+      <input name="mix" type="float" interfacename="transmission_weight" />
+    </mix>
+    <dielectric_tf_bsdf name="dielectric_reflection" type="BSDF">
+      <input name="tint" type="color3" interfacename="specular_color" />
+      <input name="ior" type="float" nodename="modulated_eta_s" />
+      <input name="roughness" type="vector2" nodename="main_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+      <input name="tangent" type="vector3" interfacename="geometry_tangent" />
+      <input name="scatter_mode" type="string" value="R" />
+    </dielectric_tf_bsdf>
+    <dielectric_tf_bsdf name="dielectric_reflection_tf" type="BSDF">
+      <input name="tint" type="color3" interfacename="specular_color" />
+      <input name="ior" type="float" nodename="modulated_eta_s" />
+      <input name="roughness" type="vector2" nodename="main_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+      <input name="tangent" type="vector3" interfacename="geometry_tangent" />
+      <input name="scatter_mode" type="string" value="R" />
+      <input name="thinfilm_thickness" type="float" nodename="thin_film_thickness_nm" />
+      <input name="thinfilm_ior" type="float" interfacename="thin_film_ior" />
+    </dielectric_tf_bsdf>
+    <mix name="dielectric_reflection_tf_mix" type="BSDF">
+      <input name="fg" type="BSDF" nodename="dielectric_reflection_tf" />
+      <input name="bg" type="BSDF" nodename="dielectric_reflection" />
+      <input name="mix" type="float" interfacename="thin_film_weight" />
+    </mix>
+    <layer name="dielectric_base" type="BSDF">
+      <input name="top" type="BSDF" nodename="dielectric_reflection_tf_mix" />
+      <input name="base" type="BSDF" nodename="dielectric_substrate" />
+    </layer>
+
+    <!-- Metal Layer -->
+    <multiply name="metal_reflectivity" type="color3">
+      <input name="in1" type="color3" interfacename="base_color" />
+      <input name="in2" type="float" interfacename="base_weight" />
+    </multiply>
+    <multiply name="metal_edgecolor" type="color3">
+      <input name="in1" type="color3" interfacename="specular_color" />
+      <input name="in2" type="float" interfacename="specular_weight" />
+    </multiply>
+    <generalized_schlick_tf_82_bsdf name="metal_bsdf" type="BSDF">
+      <input name="weight" type="float" interfacename="specular_weight" />
+      <input name="color0" type="color3" nodename="metal_reflectivity" />
+      <input name="color82" type="color3" nodename="metal_edgecolor" />
+      <input name="roughness" type="vector2" nodename="main_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+      <input name="tangent" type="vector3" interfacename="geometry_tangent" />
+    </generalized_schlick_tf_82_bsdf>
+    <generalized_schlick_tf_82_bsdf name="metal_bsdf_tf" type="BSDF">
+      <input name="weight" type="float" interfacename="specular_weight" />
+      <input name="color0" type="color3" nodename="metal_reflectivity" />
+      <input name="color82" type="color3" nodename="metal_edgecolor" />
+      <input name="roughness" type="vector2" nodename="main_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+      <input name="tangent" type="vector3" interfacename="geometry_tangent" />
+      <input name="thinfilm_thickness" type="float" nodename="thin_film_thickness_nm" />
+      <input name="thinfilm_ior" type="float" interfacename="thin_film_ior" />
+    </generalized_schlick_tf_82_bsdf>
+    <mix name="metal_bsdf_tf_mix" type="BSDF">
+      <input name="fg" type="BSDF" nodename="metal_bsdf_tf" />
+      <input name="bg" type="BSDF" nodename="metal_bsdf" />
+      <input name="mix" type="float" interfacename="thin_film_weight" />
+    </mix>
+    <mix name="base_substrate" type="BSDF">
+      <input name="fg" type="BSDF" nodename="metal_bsdf_tf_mix" />
+      <input name="bg" type="BSDF" nodename="dielectric_base" />
+      <input name="mix" type="float" interfacename="base_metalness" />
+    </mix>
+
+    <!-- Coat darkening calculation  -->
+    <!-- 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>
+    <multiply name="darkened_base_substrate" type="BSDF">
+      <input name="in1" type="BSDF" nodename="base_substrate" />
+      <input name="in2" type="color3" nodename="modulated_base_darkening" />
+    </multiply>
+
+    <!-- Coat Layer -->
+    <mix name="coat_attenuation" type="color3">
+      <input name="fg" type="color3" interfacename="coat_color" />
+      <input name="bg" type="color3" value="1.0, 1.0, 1.0" />
+      <input name="mix" type="float" interfacename="coat_weight" />
+    </mix>
+    <multiply name="coat_substrate_attenuated" type="BSDF">
+      <input name="in1" type="BSDF" nodename="darkened_base_substrate" />
+      <input name="in2" type="color3" nodename="coat_attenuation" />
+    </multiply>
+
+    <open_pbr_anisotropy name="coat_roughness_vector" type="vector2">
+      <input name="roughness" type="float" interfacename="coat_roughness" />
+      <input name="anisotropy" type="float" interfacename="coat_roughness_anisotropy" />
+    </open_pbr_anisotropy>
+    <dielectric_tf_bsdf name="coat_bsdf" type="BSDF">
+      <input name="weight" type="float" interfacename="coat_weight" />
+      <input name="ior" type="float" interfacename="coat_ior" />
+      <input name="roughness" type="vector2" nodename="coat_roughness_vector" />
+      <input name="normal" type="vector3" interfacename="geometry_coat_normal" />
+      <input name="tangent" type="vector3" interfacename="geometry_coat_tangent" />
+      <input name="scatter_mode" type="string" value="R" />
+    </dielectric_tf_bsdf>
+    <layer name="coat_layer" type="BSDF">
+      <input name="top" type="BSDF" nodename="coat_bsdf" />
+      <input name="base" type="BSDF" nodename="coat_substrate_attenuated" />
+    </layer>
+
+    <!-- Fuzz Layer -->
+    <sheen_zeltner_bsdf name="fuzz_bsdf" type="BSDF">
+      <input name="weight" type="float" interfacename="fuzz_weight" />
+      <input name="color" type="color3" interfacename="fuzz_color" />
+      <input name="roughness" type="float" interfacename="fuzz_roughness" />
+      <input name="normal" type="vector3" interfacename="geometry_normal" />
+    </sheen_zeltner_bsdf>
+    <layer name="fuzz_layer" type="BSDF">
+      <input name="top" type="BSDF" nodename="fuzz_bsdf" />
+      <input name="base" type="BSDF" nodename="coat_layer" />
+    </layer>
+
+    <!-- Emission Layer -->
+    <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>
+    <multiply name="emission_weight" type="color3">
+      <input name="in1" type="color3" interfacename="emission_color" />
+      <input name="in2" type="float" interfacename="emission_luminance" />
+    </multiply>
+    <uniform_edf name="uncoated_emission_edf" type="EDF">
+      <input name="color" type="color3" nodename="emission_weight" />
+    </uniform_edf>
+    <multiply name="coat_tinted_emission_edf" type="EDF">
+      <input name="in1" type="EDF" nodename="uncoated_emission_edf" />
+      <input name="in2" type="color3" interfacename="coat_color" />
+    </multiply>
+    <convert name="one_minus_coat_F0_color" type="color3">
+      <input name="in" type="float" nodename="one_minus_coat_F0" />
+    </convert>
+    <generalized_schlick_edf name="coated_emission_edf" type="EDF">
+      <input name="color0" type="color3" nodename="one_minus_coat_F0_color" />
+      <input name="color90" type="color3" value="0.0, 0.0, 0.0" />
+      <input name="exponent" type="float" value="5.0" />
+      <input name="base" type="EDF" nodename="coat_tinted_emission_edf" />
+    </generalized_schlick_edf>
+    <mix name="emission_edf" type="EDF">
+      <input name="fg" type="EDF" nodename="coated_emission_edf" />
+      <input name="bg" type="EDF" nodename="uncoated_emission_edf" />
+      <input name="mix" type="float" interfacename="coat_weight" />
+    </mix>
+
+    <!-- Surface Construction -->
+    <surface name="shader_constructor" type="surfaceshader">
+      <input name="bsdf" type="BSDF" nodename="fuzz_layer" />
+      <input name="edf" type="EDF" nodename="emission_edf" />
+      <input name="opacity" type="float" interfacename="geometry_opacity" />
+    </surface>
+
+    <!-- Output -->
+    <output name="out" type="surfaceshader" nodename="shader_constructor" />
+
+  </nodegraph>
+
+  <!--
+    OpenPBR Anisotropy node definition
+  -->
+  <nodedef name="ND_open_pbr_anisotropy" node="open_pbr_anisotropy" nodegroup="OpenPBR" ldx_hide="true"
+           doc="Computes anisotropic surface roughness as defined in the OpenPBR specification.">
+    <input name="roughness" type="float" value="0.0" />
+    <input name="anisotropy" type="float" value="0.0" />
+    <output name="out" type="vector2" />
+  </nodedef>
+
+  <!--
+    OpenPBR Anisotropy graph definition
+  -->
+  <nodegraph name="NG_open_pbr_anisotropy" nodedef="ND_open_pbr_anisotropy">
+    <invert name="aniso_invert" type="float">
+      <input name="in" type="float" interfacename="anisotropy" />
+    </invert>
+    <multiply name="aniso_invert_sq" type="float">
+      <input name="in1" type="float" nodename="aniso_invert" />
+      <input name="in2" type="float" nodename="aniso_invert" />
+    </multiply>
+    <add name="denom" type="float">
+      <input name="in1" type="float" nodename="aniso_invert_sq" />
+      <input name="in2" type="float" value="1.0" />
+    </add>
+    <divide name="fraction" type="float">
+      <input name="in1" type="float" value="2.0" />
+      <input name="in2" type="float" nodename="denom" />
+    </divide>
+    <sqrt name="sqrt" type="float">
+      <input name="in" type="float" nodename="fraction" />
+    </sqrt>
+    <multiply name="rough_sq" type="float">
+      <input name="in1" type="float" interfacename="roughness" />
+      <input name="in2" type="float" interfacename="roughness" />
+    </multiply>
+    <multiply name="alpha_x" type="float">
+      <input name="in1" type="float" nodename="rough_sq" />
+      <input name="in2" type="float" nodename="sqrt" />
+    </multiply>
+    <multiply name="alpha_y" type="float">
+      <input name="in1" type="float" nodename="aniso_invert" />
+      <input name="in2" type="float" nodename="alpha_x" />
+    </multiply>
+    <combine2 name="result" type="vector2">
+      <input name="in1" type="float" nodename="alpha_x" />
+      <input name="in2" type="float" nodename="alpha_y" />
+    </combine2>
+    <output name="out" type="vector2" nodename="result" />
+  </nodegraph>
+
+</materialx>
diff --git a/libraries/pbrlib/genglsl/lib/mx39_microfacet.glsl b/libraries/pbrlib/genglsl/lib/mx39_microfacet.glsl
new file mode 100644
index 0000000000..5637f388a0
--- /dev/null
+++ b/libraries/pbrlib/genglsl/lib/mx39_microfacet.glsl
@@ -0,0 +1,30 @@
+#include "mx_microfacet.glsl"
+
+float mx39_pow6(float x)
+{
+    float x2 = mx_square(x);
+    return mx_square(x2) * x2;
+}
+
+// Generate a cosine-weighted sample on the unit hemisphere.
+vec3 mx39_cosine_sample_hemisphere(vec2 Xi)
+{
+    float phi = 2.0 * M_PI * Xi.x;
+    float cosTheta = sqrt(Xi.y);
+    float sinTheta = sqrt(1.0 - Xi.y);
+    return vec3(cos(phi) * sinTheta,
+                sin(phi) * sinTheta,
+                cosTheta);
+}
+
+// Construct an orthonormal basis from a unit vector.
+// https://graphics.pixar.com/library/OrthonormalB/paper.pdf
+mat3 mx39_orthonormal_basis(vec3 N)
+{
+    float sign = (N.z < 0.0) ? -1.0 : 1.0;
+    float a = -1.0 / (sign + N.z);
+    float b = N.x * N.y * a;
+    vec3 X = vec3(1.0 + sign * N.x * N.x * a, sign * b, -sign * N.x);
+    vec3 Y = vec3(b, sign + N.y * N.y * a, -N.y);
+    return mat3(X, Y, N);
+}
diff --git a/libraries/pbrlib/genglsl/lib/mx39_microfacet_diffuse.glsl b/libraries/pbrlib/genglsl/lib/mx39_microfacet_diffuse.glsl
new file mode 100644
index 0000000000..c7ef22b78a
--- /dev/null
+++ b/libraries/pbrlib/genglsl/lib/mx39_microfacet_diffuse.glsl
@@ -0,0 +1,88 @@
+#include "mx39_microfacet.glsl"
+#include "mx_microfacet_diffuse.glsl"
+
+const float FUJII_CONSTANT_1 = 0.5 - 2.0 / (3.0 * M_PI);
+const float FUJII_CONSTANT_2 = 2.0 / 3.0 - 28.0 / (15.0 * M_PI);
+
+// Qualitative Oren-Nayar diffuse with simplified math:
+// https://www1.cs.columbia.edu/CAVE/publications/pdfs/Oren_SIGGRAPH94.pdf
+float mx39_oren_nayar_diffuse(float NdotV, float NdotL, float LdotV, float roughness)
+{
+    float s = LdotV - NdotL * NdotV;
+    float stinv = (s > 0.0) ? s / max(NdotL, NdotV) : 0.0;
+
+    float sigma2 = mx_square(roughness);
+    float A = 1.0 - 0.5 * (sigma2 / (sigma2 + 0.33));
+    float B = 0.45 * sigma2 / (sigma2 + 0.09);
+
+    return A + B * stinv;
+}
+
+// Rational quadratic fit to Monte Carlo data for Oren-Nayar directional albedo.
+float mx39_oren_nayar_diffuse_dir_albedo_analytic(float NdotV, float roughness)
+{
+    vec2 r = vec2(1.0, 1.0) +
+             vec2(-0.4297, -0.6076) * roughness +
+             vec2(-0.7632, -0.4993) * NdotV * roughness +
+             vec2(1.4385, 2.0315) * mx_square(roughness);
+    return r.x / r.y;
+}
+
+float mx39_oren_nayar_diffuse_dir_albedo(float NdotV, float roughness)
+{
+    float dirAlbedo = mx39_oren_nayar_diffuse_dir_albedo_analytic(NdotV, roughness);
+    return clamp(dirAlbedo, 0.0, 1.0);
+}
+
+// Improved Oren-Nayar diffuse from Fujii:
+// https://mimosa-pudica.net/improved-oren-nayar.html
+float mx39_oren_nayar_fujii_diffuse_dir_albedo(float cosTheta, float roughness)
+{
+    float A = 1.0 / (1.0 + FUJII_CONSTANT_1 * roughness);
+    float B = roughness * A;
+    float Si = sqrt(max(0.0, 1.0 - mx_square(cosTheta)));
+    float G = Si * (acos(clamp(cosTheta, -1.0, 1.0)) - Si * cosTheta) +
+              2.0 * ((Si / cosTheta) * (1.0 - Si * Si * Si) - Si) / 3.0;
+    return A + (B * G * M_PI_INV);
+}
+
+float mx39_oren_nayar_fujii_diffuse_avg_albedo(float roughness)
+{
+    float A = 1.0 / (1.0 + FUJII_CONSTANT_1 * roughness);
+    return A * (1.0 + FUJII_CONSTANT_2 * roughness);
+}   
+
+// Energy-compensated Oren-Nayar diffuse from OpenPBR Surface:
+// https://academysoftwarefoundation.github.io/OpenPBR/
+vec3 mx39_oren_nayar_compensated_diffuse(float NdotV, float NdotL, float LdotV, float roughness, vec3 color)
+{
+    float s = LdotV - NdotL * NdotV;
+    float stinv = (s > 0.0) ? s / max(NdotL, NdotV) : s;
+
+    // Compute the single-scatter lobe.
+    float A = 1.0 / (1.0 + FUJII_CONSTANT_1 * roughness);
+    vec3 lobeSingleScatter = color * A * (1.0 + roughness * stinv);
+
+    // Compute the multi-scatter lobe.
+    float dirAlbedoV = mx39_oren_nayar_fujii_diffuse_dir_albedo(NdotV, roughness);
+    float dirAlbedoL = mx39_oren_nayar_fujii_diffuse_dir_albedo(NdotL, roughness);
+    float avgAlbedo = mx39_oren_nayar_fujii_diffuse_avg_albedo(roughness);
+    vec3 colorMultiScatter = mx_square(color) * avgAlbedo /
+                             (vec3(1.0) - color * max(0.0, 1.0 - avgAlbedo));
+    vec3 lobeMultiScatter = colorMultiScatter *
+                            max(M_FLOAT_EPS, 1.0 - dirAlbedoV) *
+                            max(M_FLOAT_EPS, 1.0 - dirAlbedoL) /
+                            max(M_FLOAT_EPS, 1.0 - avgAlbedo);
+
+    // Return the sum.
+    return lobeSingleScatter + lobeMultiScatter;
+}
+
+vec3 mx39_oren_nayar_compensated_diffuse_dir_albedo(float cosTheta, float roughness, vec3 color)
+{
+    float dirAlbedo = mx39_oren_nayar_fujii_diffuse_dir_albedo(cosTheta, roughness);
+    float avgAlbedo = mx39_oren_nayar_fujii_diffuse_avg_albedo(roughness);
+    vec3 colorMultiScatter = mx_square(color) * avgAlbedo /
+                             (vec3(1.0) - color * max(0.0, 1.0 - avgAlbedo));
+    return mix(colorMultiScatter, color, dirAlbedo);
+}
diff --git a/libraries/pbrlib/genglsl/lib/mx39_microfacet_sheen.glsl b/libraries/pbrlib/genglsl/lib/mx39_microfacet_sheen.glsl
new file mode 100644
index 0000000000..4f94e9e0e1
--- /dev/null
+++ b/libraries/pbrlib/genglsl/lib/mx39_microfacet_sheen.glsl
@@ -0,0 +1,108 @@
+#include "mx39_microfacet.glsl"
+#include "mx_microfacet_sheen.glsl"
+
+float mx_inversesqrt(float x)
+{
+#ifdef __METAL_VERSION__
+    return ::rsqrt(x);
+#else
+    return inversesqrt(x);
+#endif
+}
+
+// The following functions are adapted from https://github.com/tizian/ltc-sheen.
+// "Practical Multiple-Scattering Sheen Using Linearly Transformed Cosines", Zeltner et al.
+
+// Gaussian fit to directional albedo table.
+float mx39_zeltner_sheen_dir_albedo(float x, float y)
+{
+    float s = y*(0.0206607 + 1.58491*y)/(0.0379424 + y*(1.32227 + y));
+    float m = y*(-0.193854 + y*(-1.14885 + y*(1.7932 - 0.95943*y*y)))/(0.046391 + y);
+    float o = y*(0.000654023 + (-0.0207818 + 0.119681*y)*y)/(1.26264 + y*(-1.92021 + y));
+    return exp(-0.5*mx_square((x - m)/s))/(s*sqrt(2.0*M_PI)) + o;
+}
+
+// Rational fits to LTC matrix coefficients.
+float mx39_zeltner_sheen_ltc_aInv(float x, float y)
+{
+    return (2.58126*x + 0.813703*y)*y/(1.0 + 0.310327*x*x + 2.60994*x*y);
+}
+
+float mx39_zeltner_sheen_ltc_bInv(float x, float y)
+{
+    return sqrt(1.0 - x)*(y - 1.0)*y*y*y/(0.0000254053 + 1.71228*x - 1.71506*x*y + 1.34174*y*y);
+}
+
+// V and N are assumed to be unit vectors.
+mat3 mx39_orthonormal_basis_ltc(vec3 V, vec3 N, float NdotV)
+{
+    // Generate a tangent vector in the plane of V and N.
+    // This required to correctly orient the LTC lobe.
+    vec3 X = V - N*NdotV;
+    float lenSqr = dot(X, X);
+    if (lenSqr > 0.0)
+    {
+        X *= mx_inversesqrt(lenSqr);
+        vec3 Y = cross(N, X);
+        return mat3(X, Y, N);
+    }
+
+    // If lenSqr == 0, then V == N, so any orthonormal basis will do.
+    return mx39_orthonormal_basis(N);
+}
+
+// Multiplication by directional albedo is handled by the calling function.
+float mx39_zeltner_sheen_brdf(vec3 L, vec3 V, vec3 N, float NdotV, float roughness)
+{
+    mat3 toLTC = transpose(mx39_orthonormal_basis_ltc(V, N, NdotV));
+    vec3 w = toLTC * L;
+
+    float aInv = mx39_zeltner_sheen_ltc_aInv(NdotV, roughness);
+    float bInv = mx39_zeltner_sheen_ltc_bInv(NdotV, roughness);
+
+    // Transform w to original configuration (clamped cosine).
+    //                 |aInv    0 bInv|
+    // wo = M^-1 . w = |   0 aInv    0| . w
+    //                 |   0    0    1|
+    vec3 wo = vec3(aInv*w.x + bInv*w.z, aInv * w.y, w.z);
+    float lenSqr = dot(wo, wo);
+
+    // D(w) = Do(M^-1.w / ||M^-1.w||) . |M^-1| / ||M^-1.w||^3
+    //      = Do(M^-1.w) . |M^-1| / ||M^-1.w||^4
+    //      = Do(wo) . |M^-1| / dot(wo, wo)^2
+    //      = Do(wo) . aInv^2 / dot(wo, wo)^2
+    //      = Do(wo) . (aInv / dot(wo, wo))^2
+    return max(wo.z, 0.0) * M_PI_INV * mx_square(aInv / lenSqr);
+}
+
+vec3 mx39_zeltner_sheen_importance_sample(vec2 Xi, vec3 V, vec3 N, float roughness, out float pdf)
+{
+    float NdotV = clamp(dot(N, V), 0.0, 1.0);
+    roughness = clamp(roughness, 0.01, 1.0); // Clamp to range of original impl.
+
+    vec3 wo = mx39_cosine_sample_hemisphere(Xi);
+
+    float aInv = mx39_zeltner_sheen_ltc_aInv(NdotV, roughness);
+    float bInv = mx39_zeltner_sheen_ltc_bInv(NdotV, roughness);
+
+    // Transform wo from original configuration (clamped cosine).
+    //              |1/aInv      0 -bInv/aInv|
+    // w = M . wo = |     0 1/aInv          0| . wo
+    //              |     0      0          1|    
+    vec3 w = vec3(wo.x/aInv - wo.z*bInv/aInv, wo.y / aInv, wo.z);
+
+    float lenSqr = dot(w, w);
+    w *= mx_inversesqrt(lenSqr);
+
+    // D(w) = Do(wo) . ||M.wo||^3 / |M|
+    //      = Do(wo / ||M.wo||) . ||M.wo||^4 / |M| 
+    //      = Do(w) . ||M.wo||^4 / |M| (possible because M doesn't change z component)
+    //      = Do(w) . dot(w, w)^2 * aInv^2
+    //      = Do(w) . (aInv * dot(w, w))^2
+    pdf = max(w.z, 0.0) * M_PI_INV * mx_square(aInv * lenSqr);
+
+    mat3 fromLTC = mx39_orthonormal_basis_ltc(V, N, NdotV);
+    w = fromLTC * w;
+
+    return w;
+}
diff --git a/libraries/pbrlib/genglsl/lib/mx39_microfacet_specular.glsl b/libraries/pbrlib/genglsl/lib/mx39_microfacet_specular.glsl
new file mode 100644
index 0000000000..fa4badc7e5
--- /dev/null
+++ b/libraries/pbrlib/genglsl/lib/mx39_microfacet_specular.glsl
@@ -0,0 +1,419 @@
+#include "mx39_microfacet.glsl"
+#include "mx_microfacet_specular.glsl"
+
+const int MX39_FRESNEL_MODEL_DIELECTRIC = 0;
+const int MX39_FRESNEL_MODEL_CONDUCTOR = 1;
+const int MX39_FRESNEL_MODEL_SCHLICK = 2;
+
+// Parameters for Fresnel calculations
+struct Mx39FresnelData
+{
+    // Fresnel model
+    int model;
+    bool airy;
+
+    // Physical Fresnel
+    vec3 ior;
+    vec3 extinction;
+
+    // Generalized Schlick Fresnel
+    vec3 F0;
+    vec3 F82;
+    vec3 F90;
+    float exponent;
+
+    // Thin film
+    float tf_thickness;
+    float tf_ior;
+
+    // Refraction
+    bool refraction;
+};
+
+// Convert a real-valued index of refraction to normal-incidence reflectivity.
+float mx39_ior_to_f0(float ior)
+{
+    return mx_square((ior - 1.0) / (ior + 1.0));
+}
+
+// Convert normal-incidence reflectivity to real-valued index of refraction.
+float mx39_f0_to_ior(float F0)
+{
+    float sqrtF0 = sqrt(clamp(F0, 0.01, 0.99));
+    return (1.0 + sqrtF0) / (1.0 - sqrtF0);
+}
+vec3 mx39_f0_to_ior(vec3 F0)
+{
+    vec3 sqrtF0 = sqrt(clamp(F0, 0.01, 0.99));
+    return (vec3(1.0) + sqrtF0) / (vec3(1.0) - sqrtF0);
+}
+
+// https://renderwonk.com/publications/wp-generalization-adobe/gen-adobe.pdf
+vec3 mx39_fresnel_hoffman_schlick(float cosTheta, Mx39FresnelData fd)
+{
+    const float COS_THETA_MAX = 1.0 / 7.0;
+    const float COS_THETA_FACTOR = 1.0 / (COS_THETA_MAX * pow(1.0 - COS_THETA_MAX, 6.0));
+
+    float x = clamp(cosTheta, 0.0, 1.0);
+    vec3 a = mix(fd.F0, fd.F90, pow(1.0 - COS_THETA_MAX, fd.exponent)) * (vec3(1.0) - fd.F82) * COS_THETA_FACTOR;
+    return mix(fd.F0, fd.F90, pow(1.0 - x, fd.exponent)) - a * x * mx39_pow6(1.0 - x);
+}
+
+// https://seblagarde.wordpress.com/2013/04/29/memo-on-fresnel-equations/
+float mx39_fresnel_dielectric(float cosTheta, float ior)
+{
+    float c = cosTheta;
+    float g2 = ior*ior + c*c - 1.0;
+    if (g2 < 0.0)
+    {
+        // Total internal reflection
+        return 1.0;
+    }
+
+    float g = sqrt(g2);
+    return 0.5 * mx_square((g - c) / (g + c)) *
+                (1.0 + mx_square(((g + c) * c - 1.0) / ((g - c) * c + 1.0)));
+}
+
+// https://seblagarde.wordpress.com/2013/04/29/memo-on-fresnel-equations/
+vec2 mx39_fresnel_dielectric_polarized(float cosTheta, float ior)
+{
+    float cosTheta2 = mx_square(clamp(cosTheta, 0.0, 1.0));
+    float sinTheta2 = 1.0 - cosTheta2;
+
+    float t0 = max(ior * ior - sinTheta2, 0.0);
+    float t1 = t0 + cosTheta2;
+    float t2 = 2.0 * sqrt(t0) * cosTheta;
+    float Rs = (t1 - t2) / (t1 + t2);
+
+    float t3 = cosTheta2 * t0 + sinTheta2 * sinTheta2;
+    float t4 = t2 * sinTheta2;
+    float Rp = Rs * (t3 - t4) / (t3 + t4);
+
+    return vec2(Rp, Rs);
+}
+
+// https://seblagarde.wordpress.com/2013/04/29/memo-on-fresnel-equations/
+void mx39_fresnel_conductor_polarized(float cosTheta, vec3 n, vec3 k, out vec3 Rp, out vec3 Rs)
+{
+    float cosTheta2 = mx_square(clamp(cosTheta, 0.0, 1.0));
+    float sinTheta2 = 1.0 - cosTheta2;
+    vec3 n2 = n * n;
+    vec3 k2 = k * k;
+
+    vec3 t0 = n2 - k2 - vec3(sinTheta2);
+    vec3 a2plusb2 = sqrt(t0 * t0 + 4.0 * n2 * k2);
+    vec3 t1 = a2plusb2 + vec3(cosTheta2);
+    vec3 a = sqrt(max(0.5 * (a2plusb2 + t0), 0.0));
+    vec3 t2 = 2.0 * a * cosTheta;
+    Rs = (t1 - t2) / (t1 + t2);
+
+    vec3 t3 = cosTheta2 * a2plusb2 + vec3(sinTheta2 * sinTheta2);
+    vec3 t4 = t2 * sinTheta2;
+    Rp = Rs * (t3 - t4) / (t3 + t4);
+}
+
+vec3 mx39_fresnel_conductor(float cosTheta, vec3 n, vec3 k)
+{
+    vec3 Rp, Rs;
+    mx39_fresnel_conductor_polarized(cosTheta, n, k, Rp, Rs);
+    return 0.5 * (Rp  + Rs);
+}
+
+// https://belcour.github.io/blog/research/publication/2017/05/01/brdf-thin-film.html
+void mx39_fresnel_conductor_phase_polarized(float cosTheta, float eta1, vec3 eta2, vec3 kappa2, out vec3 phiP, out vec3 phiS)
+{
+    vec3 k2 = kappa2 / eta2;
+    vec3 sinThetaSqr = vec3(1.0) - cosTheta * cosTheta;
+    vec3 A = eta2*eta2*(vec3(1.0)-k2*k2) - eta1*eta1*sinThetaSqr;
+    vec3 B = sqrt(A*A + mx_square(2.0*eta2*eta2*k2));
+    vec3 U = sqrt((A+B)/2.0);
+    vec3 V = max(vec3(0.0), sqrt((B-A)/2.0));
+
+    phiS = atan(2.0*eta1*V*cosTheta, U*U + V*V - mx_square(eta1*cosTheta));
+    phiP = atan(2.0*eta1*eta2*eta2*cosTheta * (2.0*k2*U - (vec3(1.0)-k2*k2) * V),
+                mx_square(eta2*eta2*(vec3(1.0)+k2*k2)*cosTheta) - eta1*eta1*(U*U+V*V));
+}
+
+// A Practical Extension to Microfacet Theory for the Modeling of Varying Iridescence
+// https://belcour.github.io/blog/research/publication/2017/05/01/brdf-thin-film.html
+vec3 mx39_fresnel_airy(float cosTheta, Mx39FresnelData fd)
+{
+    // XYZ to CIE 1931 RGB color space (using neutral E illuminant)
+    const mat3 XYZ_TO_RGB = mat3(2.3706743, -0.5138850, 0.0052982, -0.9000405, 1.4253036, -0.0146949, -0.4706338, 0.0885814, 1.0093968);
+
+    // Assume vacuum on the outside
+    float eta1 = 1.0;
+    float eta2 = max(fd.tf_ior, eta1);
+    vec3 eta3 = (fd.model == MX39_FRESNEL_MODEL_SCHLICK) ? mx39_f0_to_ior(fd.F0) : fd.ior;
+    vec3 kappa3 = (fd.model == MX39_FRESNEL_MODEL_SCHLICK) ? vec3(0.0) : fd.extinction;
+    float cosThetaT = sqrt(1.0 - (1.0 - mx_square(cosTheta)) * mx_square(eta1 / eta2));
+
+    // First interface
+    vec2 R12 = mx39_fresnel_dielectric_polarized(cosTheta, eta2 / eta1);
+    if (cosThetaT <= 0.0)
+    {
+        // Total internal reflection
+        R12 = vec2(1.0);
+    }
+    vec2 T121 = vec2(1.0) - R12;
+
+    // Second interface
+    vec3 R23p, R23s;
+    if (fd.model == MX39_FRESNEL_MODEL_SCHLICK)
+    {
+        vec3 f = mx39_fresnel_hoffman_schlick(cosThetaT, fd);
+        R23p = 0.5 * f;
+        R23s = 0.5 * f;
+    }
+    else
+    {
+        mx39_fresnel_conductor_polarized(cosThetaT, eta3 / eta2, kappa3 / eta2, R23p, R23s);
+    }
+
+    // Phase shift
+    float cosB = cos(atan(eta2 / eta1));
+    vec2 phi21 = vec2(cosTheta < cosB ? 0.0 : M_PI, M_PI);
+    vec3 phi23p, phi23s;
+    if (fd.model == MX39_FRESNEL_MODEL_SCHLICK)
+    {
+        phi23p = vec3((eta3[0] < eta2) ? M_PI : 0.0,
+                      (eta3[1] < eta2) ? M_PI : 0.0,
+                      (eta3[2] < eta2) ? M_PI : 0.0);
+        phi23s = phi23p;
+    }
+    else
+    {
+        mx39_fresnel_conductor_phase_polarized(cosThetaT, eta2, eta3, kappa3, phi23p, phi23s);
+    }
+    vec3 r123p = max(sqrt(R12.x*R23p), 0.0);
+    vec3 r123s = max(sqrt(R12.y*R23s), 0.0);
+
+    // Iridescence term
+    vec3 I = vec3(0.0);
+    vec3 Cm, Sm;
+
+    // Optical path difference
+    float distMeters = fd.tf_thickness * 1.0e-9;
+    float opd = 2.0 * eta2 * cosThetaT * distMeters;
+
+    // Iridescence term using spectral antialiasing for Parallel polarization
+
+    // Reflectance term for m=0 (DC term amplitude)
+    vec3 Rs = (mx_square(T121.x) * R23p) / (vec3(1.0) - R12.x*R23p);
+    I += R12.x + Rs;
+
+    // Reflectance term for m>0 (pairs of diracs)
+    Cm = Rs - T121.x;
+    for (int m=1; m<=2; m++)
+    {
+        Cm *= r123p;
+        Sm  = 2.0 * mx_eval_sensitivity(float(m) * opd, float(m)*(phi23p+vec3(phi21.x)));
+        I  += Cm*Sm;
+    }
+
+    // Iridescence term using spectral antialiasing for Perpendicular polarization
+
+    // Reflectance term for m=0 (DC term amplitude)
+    vec3 Rp = (mx_square(T121.y) * R23s) / (vec3(1.0) - R12.y*R23s);
+    I += R12.y + Rp;
+
+    // Reflectance term for m>0 (pairs of diracs)
+    Cm = Rp - T121.y;
+    for (int m=1; m<=2; m++)
+    {
+        Cm *= r123s;
+        Sm  = 2.0 * mx_eval_sensitivity(float(m) * opd, float(m)*(phi23s+vec3(phi21.y)));
+        I  += Cm*Sm;
+    }
+
+    // Average parallel and perpendicular polarization
+    I *= 0.5;
+
+    // Convert back to RGB reflectance
+    I = clamp(XYZ_TO_RGB * I, 0.0, 1.0);
+
+    return I;
+}
+
+Mx39FresnelData mx39_init_fresnel_dielectric(float ior, float tf_thickness, float tf_ior)
+{
+    Mx39FresnelData fd;
+    fd.model = MX39_FRESNEL_MODEL_DIELECTRIC;
+    fd.airy = tf_thickness > 0.0;
+    fd.ior = vec3(ior);
+    fd.extinction = vec3(0.0);
+    fd.F0 = vec3(0.0);
+    fd.F82 = vec3(0.0);
+    fd.F90 = vec3(0.0);
+    fd.exponent = 0.0;
+    fd.tf_thickness = tf_thickness;
+    fd.tf_ior = tf_ior;
+    fd.refraction = false;
+    return fd;
+}
+
+Mx39FresnelData mx39_init_fresnel_conductor(vec3 ior, vec3 extinction, float tf_thickness, float tf_ior)
+{
+    Mx39FresnelData fd;
+    fd.model = MX39_FRESNEL_MODEL_CONDUCTOR;
+    fd.airy = tf_thickness > 0.0;
+    fd.ior = ior;
+    fd.extinction = extinction;
+    fd.F0 = vec3(0.0);
+    fd.F82 = vec3(0.0);
+    fd.F90 = vec3(0.0);
+    fd.exponent = 0.0;
+    fd.tf_thickness = tf_thickness;
+    fd.tf_ior = tf_ior;
+    fd.refraction = false;
+    return fd;
+}
+
+Mx39FresnelData mx39_init_fresnel_schlick(vec3 F0, vec3 F82, vec3 F90, float exponent, float tf_thickness, float tf_ior)
+{
+    Mx39FresnelData fd;
+    fd.model = MX39_FRESNEL_MODEL_SCHLICK;
+    fd.airy = tf_thickness > 0.0;
+    fd.ior = vec3(0.0);
+    fd.extinction = vec3(0.0);
+    fd.F0 = F0;
+    fd.F82 = F82;
+    fd.F90 = F90;
+    fd.exponent = exponent;
+    fd.tf_thickness = tf_thickness;
+    fd.tf_ior = tf_ior;
+    fd.refraction = false;
+    return fd;
+}
+
+vec3 mx39_compute_fresnel(float cosTheta, Mx39FresnelData fd)
+{
+    if (fd.airy)
+    {
+         return mx39_fresnel_airy(cosTheta, fd);
+    }
+    else if (fd.model == MX39_FRESNEL_MODEL_DIELECTRIC)
+    {
+        return vec3(mx39_fresnel_dielectric(cosTheta, fd.ior.x));
+    }
+    else if (fd.model == MX39_FRESNEL_MODEL_CONDUCTOR)
+    {
+        return mx39_fresnel_conductor(cosTheta, fd.ior, fd.extinction);
+    }
+    else
+    {
+        return mx39_fresnel_hoffman_schlick(cosTheta, fd);
+    }
+}
+
+#ifdef MX39_USING_ENVIRONMENT_NONE
+vec3 mx39_environment_radiance(vec3 N, vec3 V, vec3 X, vec2 alpha, int distribution, Mx39FresnelData fd)
+{
+    return vec3(0.0);
+}
+#endif
+
+#ifdef MX39_USING_ENVIRONMENT_PREFILTER
+vec3 mx39_environment_radiance(vec3 N, vec3 V, vec3 X, vec2 alpha, int distribution, Mx39FresnelData fd)
+{
+    N = mx_forward_facing_normal(N, V);
+    vec3 L = fd.refraction ? mx_refraction_solid_sphere(-V, N, fd.ior.x) : -reflect(V, N);
+
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+
+    float avgAlpha = mx_average_alpha(alpha);
+    vec3 F = mx39_compute_fresnel(NdotV, fd);
+    float G = mx_ggx_smith_G2(NdotV, NdotV, avgAlpha);
+    vec3 FG = fd.refraction ? vec3(1.0) - (F * G) : F * G;
+
+    vec3 Li = mx_latlong_map_lookup(L, $envMatrix, mx_latlong_alpha_to_lod(avgAlpha), $envRadiance);
+    return Li * FG * $envLightIntensity;
+}
+#endif
+
+#ifdef MX39_USING_ENVIRONMENT_FIS
+vec3 mx39_environment_radiance(vec3 N, vec3 V, vec3 X, vec2 alpha, int distribution, Mx39FresnelData fd)
+{
+    // Generate tangent frame.
+    X = normalize(X - dot(X, N) * N);
+    vec3 Y = cross(N, X);
+    mat3 tangentToWorld = mat3(X, Y, N);
+
+    // Transform the view vector to tangent space.
+    V = vec3(dot(V, X), dot(V, Y), dot(V, N));
+
+    // Compute derived properties.
+    float NdotV = clamp(V.z, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(alpha);
+    float G1V = mx_ggx_smith_G1(NdotV, avgAlpha);
+    
+    // Integrate outgoing radiance using filtered importance sampling.
+    // http://cgg.mff.cuni.cz/~jaroslav/papers/2008-egsr-fis/2008-egsr-fis-final-embedded.pdf
+    vec3 radiance = vec3(0.0);
+    int envRadianceSamples = $envRadianceSamples;
+    for (int i = 0; i < envRadianceSamples; i++)
+    {
+        vec2 Xi = mx_spherical_fibonacci(i, envRadianceSamples);
+
+        // Compute the half vector and incoming light direction.
+        vec3 H = mx_ggx_importance_sample_VNDF(Xi, V, alpha);
+        vec3 L = fd.refraction ? mx_refraction_solid_sphere(-V, H, fd.ior.x) : -reflect(V, H);
+        
+        // Compute dot products for this sample.
+        float NdotL = clamp(L.z, M_FLOAT_EPS, 1.0);
+        float VdotH = clamp(dot(V, H), M_FLOAT_EPS, 1.0);
+
+        // Sample the environment light from the given direction.
+        vec3 Lw = tangentToWorld * L;
+        float pdf = mx_ggx_NDF(H, alpha) * G1V / (4.0 * NdotV);
+        float lod = mx_latlong_compute_lod(Lw, pdf, float($envRadianceMips - 1), envRadianceSamples);
+        vec3 sampleColor = mx_latlong_map_lookup(Lw, $envMatrix, lod, $envRadiance);
+
+        // Compute the Fresnel term.
+        vec3 F = mx39_compute_fresnel(VdotH, fd);
+
+        // Compute the geometric term.
+        float G = mx_ggx_smith_G2(NdotL, NdotV, avgAlpha);
+
+        // Compute the combined FG term, which is inverted for refraction.
+        vec3 FG = fd.refraction ? vec3(1.0) - (F * G) : F * G;
+
+        // Add the radiance contribution of this sample.
+        // From https://cdn2.unrealengine.com/Resources/files/2013SiggraphPresentationsNotes-26915738.pdf
+        //   incidentLight = sampleColor * NdotL
+        //   microfacetSpecular = D * F * G / (4 * NdotL * NdotV)
+        //   pdf = D * G1V / (4 * NdotV);
+        //   radiance = incidentLight * microfacetSpecular / pdf
+        radiance += sampleColor * FG;
+    }
+
+    // Apply the global component of the geometric term and normalize.
+    radiance /= G1V * float(envRadianceSamples);
+
+    // Return the final radiance.
+    return radiance * $envLightIntensity;
+}
+#endif
+
+#ifdef MX39_USING_TRANSMISSION_OPACITY
+vec3 mx39_surface_transmission(vec3 N, vec3 V, vec3 X, vec2 alpha, int distribution, Mx39FresnelData fd, vec3 tint)
+{
+    return tint;
+}
+#endif
+
+#ifdef MX39_USING_TRANSMISSION_REFRACT
+vec3 mx39_surface_transmission(vec3 N, vec3 V, vec3 X, vec2 alpha, int distribution, Mx39FresnelData fd, vec3 tint)
+{
+    // Approximate the appearance of surface transmission as glossy
+    // environment map refraction, ignoring any scene geometry that might
+    // be visible through the surface.
+    fd.refraction = true;
+    if ($refractionTwoSided)
+    {
+        tint = mx_square(tint);
+    }
+    return mx39_environment_radiance(N, V, X, alpha, distribution, fd) * tint;
+}
+#endif
diff --git a/libraries/pbrlib/genglsl/lib/mx_environment_fis.glsl b/libraries/pbrlib/genglsl/lib/mx_environment_fis.glsl
index 0b28f3645f..6bfc64571e 100644
--- a/libraries/pbrlib/genglsl/lib/mx_environment_fis.glsl
+++ b/libraries/pbrlib/genglsl/lib/mx_environment_fis.glsl
@@ -67,3 +67,5 @@ vec3 mx_environment_irradiance(vec3 N)
     vec3 Li = mx_latlong_map_lookup(N, $envMatrix, 0.0, $envIrradiance);
     return Li * $envLightIntensity;
 }
+
+#define MX39_USING_ENVIRONMENT_FIS
diff --git a/libraries/pbrlib/genglsl/lib/mx_environment_none.glsl b/libraries/pbrlib/genglsl/lib/mx_environment_none.glsl
index f0a1da5989..f535c84757 100644
--- a/libraries/pbrlib/genglsl/lib/mx_environment_none.glsl
+++ b/libraries/pbrlib/genglsl/lib/mx_environment_none.glsl
@@ -9,3 +9,5 @@ vec3 mx_environment_irradiance(vec3 N)
 {
     return vec3(0.0);
 }
+
+#define MX39_USING_ENVIRONMENT_NONE
diff --git a/libraries/pbrlib/genglsl/lib/mx_environment_prefilter.glsl b/libraries/pbrlib/genglsl/lib/mx_environment_prefilter.glsl
index 778742c449..89e898a1e1 100644
--- a/libraries/pbrlib/genglsl/lib/mx_environment_prefilter.glsl
+++ b/libraries/pbrlib/genglsl/lib/mx_environment_prefilter.glsl
@@ -28,3 +28,5 @@ vec3 mx_environment_irradiance(vec3 N)
     vec3 Li = mx_latlong_map_lookup(N, $envMatrix, 0.0, $envIrradiance);
     return Li * $envLightIntensity;
 }
+
+#define MX39_USING_ENVIRONMENT_PREFILTER
diff --git a/libraries/pbrlib/genglsl/lib/mx_transmission_opacity.glsl b/libraries/pbrlib/genglsl/lib/mx_transmission_opacity.glsl
index 2861d06194..54bef92ff4 100644
--- a/libraries/pbrlib/genglsl/lib/mx_transmission_opacity.glsl
+++ b/libraries/pbrlib/genglsl/lib/mx_transmission_opacity.glsl
@@ -4,3 +4,5 @@ vec3 mx_surface_transmission(vec3 N, vec3 V, vec3 X, vec2 alpha, int distributio
 {
     return tint;
 }
+
+#define MX39_USING_TRANSMISSION_OPACITY
diff --git a/libraries/pbrlib/genglsl/lib/mx_transmission_refract.glsl b/libraries/pbrlib/genglsl/lib/mx_transmission_refract.glsl
index 64e496a384..4493321b4b 100644
--- a/libraries/pbrlib/genglsl/lib/mx_transmission_refract.glsl
+++ b/libraries/pbrlib/genglsl/lib/mx_transmission_refract.glsl
@@ -12,3 +12,5 @@ vec3 mx_surface_transmission(vec3 N, vec3 V, vec3 X, vec2 alpha, int distributio
     }
     return mx_environment_radiance(N, V, X, alpha, distribution, fd) * tint;
 }
+
+#define MX39_USING_TRANSMISSION_REFRACT
diff --git a/libraries/pbrlib/genglsl/mx39_compensating_oren_nayar_diffuse_bsdf.glsl b/libraries/pbrlib/genglsl/mx39_compensating_oren_nayar_diffuse_bsdf.glsl
new file mode 100644
index 0000000000..b93b5b8cd0
--- /dev/null
+++ b/libraries/pbrlib/genglsl/mx39_compensating_oren_nayar_diffuse_bsdf.glsl
@@ -0,0 +1,42 @@
+#include "lib/mx39_microfacet_diffuse.glsl"
+
+void mx39_compensating_oren_nayar_diffuse_bsdf_reflection(vec3 L, vec3 V, vec3 P, float occlusion, float weight, vec3 color, float roughness, vec3 normal, bool energy_compensation, inout BSDF bsdf)
+{
+    bsdf.throughput = vec3(0.0);
+
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    normal = mx_forward_facing_normal(normal, V);
+
+    float NdotV = clamp(dot(normal, V), M_FLOAT_EPS, 1.0);
+    float NdotL = clamp(dot(normal, L), M_FLOAT_EPS, 1.0);
+    float LdotV = clamp(dot(L, V), M_FLOAT_EPS, 1.0);
+
+    vec3 diffuse = energy_compensation ?
+                   mx39_oren_nayar_compensated_diffuse(NdotV, NdotL, LdotV, roughness, color) :
+                   mx39_oren_nayar_diffuse(NdotV, NdotL, LdotV, roughness) * color;
+    bsdf.response = diffuse * occlusion * weight * NdotL * M_PI_INV;
+}
+
+void mx39_compensating_oren_nayar_diffuse_bsdf_indirect(vec3 V, float weight, vec3 color, float roughness, vec3 normal, bool energy_compensation, inout BSDF bsdf)
+{
+    bsdf.throughput = vec3(0.0);
+
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    normal = mx_forward_facing_normal(normal, V);
+
+    float NdotV = clamp(dot(normal, V), M_FLOAT_EPS, 1.0);
+
+    vec3 diffuse = energy_compensation ?
+                   mx39_oren_nayar_compensated_diffuse_dir_albedo(NdotV, roughness, color) :
+                   mx39_oren_nayar_diffuse_dir_albedo(NdotV, roughness) * color;
+    vec3 Li = mx_environment_irradiance(normal);
+    bsdf.response = Li * diffuse * weight;
+}
diff --git a/libraries/pbrlib/genglsl/mx39_dielectric_tf_bsdf.glsl b/libraries/pbrlib/genglsl/mx39_dielectric_tf_bsdf.glsl
new file mode 100644
index 0000000000..3dc668c4fa
--- /dev/null
+++ b/libraries/pbrlib/genglsl/mx39_dielectric_tf_bsdf.glsl
@@ -0,0 +1,92 @@
+#include "lib/mx39_microfacet_specular.glsl"
+
+void mx39_dielectric_tf_bsdf_reflection(vec3 L, vec3 V, vec3 P, float occlusion, float weight, vec3 tint, float ior, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+
+    X = normalize(X - dot(X, N) * N);
+    vec3 Y = cross(N, X);
+    vec3 H = normalize(L + V);
+
+    float NdotL = clamp(dot(N, L), M_FLOAT_EPS, 1.0);
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+    float VdotH = clamp(dot(V, H), M_FLOAT_EPS, 1.0);
+
+    vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+    vec3 Ht = vec3(dot(H, X), dot(H, Y), dot(H, N));
+
+    vec3 safeTint = max(tint, 0.0);
+    Mx39FresnelData fd = mx39_init_fresnel_dielectric(ior, thinfilm_thickness, thinfilm_ior);
+    vec3  F = mx39_compute_fresnel(VdotH, fd);
+    float D = mx_ggx_NDF(Ht, safeAlpha);
+    float G = mx_ggx_smith_G2(NdotL, NdotV, avgAlpha);
+
+    float F0 = mx39_ior_to_f0(ior);
+    vec3 comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+    vec3 dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, F0, 1.0) * comp;
+    bsdf.throughput = 1.0 - dirAlbedo * weight;
+
+    // Note: NdotL is cancelled out
+    bsdf.response = D * F * G * comp * safeTint * occlusion * weight / (4.0 * NdotV);
+}
+
+void mx39_dielectric_tf_bsdf_transmission(vec3 V, float weight, vec3 tint, float ior, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+
+    vec3 safeTint = max(tint, 0.0);
+    Mx39FresnelData fd = mx39_init_fresnel_dielectric(ior, thinfilm_thickness, thinfilm_ior);
+    vec3 F = mx39_compute_fresnel(NdotV, fd);
+
+    vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+
+    float F0 = mx39_ior_to_f0(ior);
+    vec3 comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+    vec3 dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, F0, 1.0) * comp;
+    bsdf.throughput = 1.0 - dirAlbedo * weight;
+
+    if (scatter_mode != 0)
+    {
+        bsdf.response = mx39_surface_transmission(N, V, X, safeAlpha, distribution, fd, safeTint) * weight;
+    }
+}
+
+void mx39_dielectric_tf_bsdf_indirect(vec3 V, float weight, vec3 tint, float ior, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+
+    vec3 safeTint = max(tint, 0.0);
+    Mx39FresnelData fd = mx39_init_fresnel_dielectric(ior, thinfilm_thickness, thinfilm_ior);
+    vec3 F = mx39_compute_fresnel(NdotV, fd);
+
+    vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+
+    float F0 = mx39_ior_to_f0(ior);
+    vec3 comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+    vec3 dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, F0, 1.0) * comp;
+    bsdf.throughput = 1.0 - dirAlbedo * weight;
+
+    vec3 Li = mx39_environment_radiance(N, V, X, safeAlpha, distribution, fd);
+    bsdf.response = Li * safeTint * comp * weight;
+}
diff --git a/libraries/pbrlib/genglsl/mx39_generalized_schlick_tf_82_bsdf.glsl b/libraries/pbrlib/genglsl/mx39_generalized_schlick_tf_82_bsdf.glsl
new file mode 100644
index 0000000000..512245784a
--- /dev/null
+++ b/libraries/pbrlib/genglsl/mx39_generalized_schlick_tf_82_bsdf.glsl
@@ -0,0 +1,98 @@
+#include "lib/mx39_microfacet_specular.glsl"
+
+void mx39_generalized_schlick_tf_82_bsdf_reflection(vec3 L, vec3 V, vec3 P, float occlusion, float weight, vec3 color0, vec3 color82, vec3 color90, float exponent, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+
+    X = normalize(X - dot(X, N) * N);
+    vec3 Y = cross(N, X);
+    vec3 H = normalize(L + V);
+
+    float NdotL = clamp(dot(N, L), M_FLOAT_EPS, 1.0);
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+    float VdotH = clamp(dot(V, H), M_FLOAT_EPS, 1.0);
+
+    vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+    vec3 Ht = vec3(dot(H, X), dot(H, Y), dot(H, N));
+
+    vec3 safeColor0 = max(color0, 0.0);
+    vec3 safeColor82 = max(color82, 0.0);
+    vec3 safeColor90 = max(color90, 0.0);
+    Mx39FresnelData fd = mx39_init_fresnel_schlick(safeColor0, safeColor82, safeColor90, exponent, thinfilm_thickness, thinfilm_ior);
+    vec3  F = mx39_compute_fresnel(VdotH, fd);
+    float D = mx_ggx_NDF(Ht, safeAlpha);
+    float G = mx_ggx_smith_G2(NdotL, NdotV, avgAlpha);
+
+    vec3 comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+    vec3 dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, safeColor0, safeColor90) * comp;
+    float avgDirAlbedo = dot(dirAlbedo, vec3(1.0 / 3.0));
+    bsdf.throughput = vec3(1.0 - avgDirAlbedo * weight);
+
+    // Note: NdotL is cancelled out
+    bsdf.response = D * F * G * comp * occlusion * weight / (4.0 * NdotV);
+}
+
+void mx39_generalized_schlick_tf_82_bsdf_transmission(vec3 V, float weight, vec3 color0, vec3 color82, vec3 color90, float exponent, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+
+    vec3 safeColor0 = max(color0, 0.0);
+    vec3 safeColor82 = max(color82, 0.0);
+    vec3 safeColor90 = max(color90, 0.0);
+    Mx39FresnelData fd = mx39_init_fresnel_schlick(safeColor0, safeColor82, safeColor90, exponent, thinfilm_thickness, thinfilm_ior);
+    vec3 F = mx39_compute_fresnel(NdotV, fd);
+
+    vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+
+    vec3 comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+    vec3 dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, safeColor0, safeColor90) * comp;
+    float avgDirAlbedo = dot(dirAlbedo, vec3(1.0 / 3.0));
+    bsdf.throughput = vec3(1.0 - avgDirAlbedo * weight);
+
+    if (scatter_mode != 0)
+    {
+        float avgF0 = dot(safeColor0, vec3(1.0 / 3.0));
+        fd.ior = vec3(mx39_f0_to_ior(avgF0));
+        bsdf.response = mx39_surface_transmission(N, V, X, safeAlpha, distribution, fd, safeColor0) * weight;
+    }
+}
+
+void mx39_generalized_schlick_tf_82_bsdf_indirect(vec3 V, float weight, vec3 color0, vec3 color82, vec3 color90, float exponent, vec2 roughness, float thinfilm_thickness, float thinfilm_ior, vec3 N, vec3 X, int distribution, int scatter_mode, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+
+    vec3 safeColor0 = max(color0, 0.0);
+    vec3 safeColor82 = max(color82, 0.0);
+    vec3 safeColor90 = max(color90, 0.0);
+    Mx39FresnelData fd = mx39_init_fresnel_schlick(safeColor0, safeColor82, safeColor90, exponent, thinfilm_thickness, thinfilm_ior);
+    vec3 F = mx39_compute_fresnel(NdotV, fd);
+
+    vec2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+    vec3 comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+    vec3 dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, safeColor0, safeColor90) * comp;
+    float avgDirAlbedo = dot(dirAlbedo, vec3(1.0 / 3.0));
+    bsdf.throughput = vec3(1.0 - avgDirAlbedo * weight);
+
+    vec3 Li = mx39_environment_radiance(N, V, X, safeAlpha, distribution, fd);
+    bsdf.response = Li * comp * weight;
+}
diff --git a/libraries/pbrlib/genglsl/mx39_pbrlib_genglsl_impl.mtlx b/libraries/pbrlib/genglsl/mx39_pbrlib_genglsl_impl.mtlx
new file mode 100644
index 0000000000..3626896222
--- /dev/null
+++ b/libraries/pbrlib/genglsl/mx39_pbrlib_genglsl_impl.mtlx
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<materialx version="1.38">
+
+  <!-- <compensating_oren_nayar_diffuse_bsdf> -->
+  <implementation name="IM_compensating_oren_nayar_diffuse_bsdf_genglsl" nodedef="ND_compensating_oren_nayar_diffuse_bsdf" file="mx39_compensating_oren_nayar_diffuse_bsdf.glsl" function="mx39_compensating_oren_nayar_diffuse_bsdf" target="genglsl" />
+
+  <!-- <dielectric_tf_bsdf> -->
+  <implementation name="IM_dielectric_tf_bsdf_genglsl" nodedef="ND_dielectric_tf_bsdf" file="mx39_dielectric_tf_bsdf.glsl" function="mx39_dielectric_tf_bsdf" target="genglsl" />
+
+  <!-- <generalized_schlick_tf_82_bsdf> -->
+  <implementation name="IM_generalized_schlick_tf_82_bsdf_genglsl" nodedef="ND_generalized_schlick_tf_82_bsdf" file="mx39_generalized_schlick_tf_82_bsdf.glsl" function="mx39_generalized_schlick_tf_82_bsdf" target="genglsl" />
+
+  <!-- <sheen_zeltner_bsdf> -->
+  <implementation name="IM_sheen_zeltner_bsdf_genglsl" nodedef="ND_sheen_zeltner_bsdf" file="mx39_sheen_zeltner_bsdf.glsl" function="mx39_sheen_zeltner_bsdf" target="genglsl" />
+
+</materialx>
diff --git a/libraries/pbrlib/genglsl/mx39_sheen_zeltner_bsdf.glsl b/libraries/pbrlib/genglsl/mx39_sheen_zeltner_bsdf.glsl
new file mode 100644
index 0000000000..c6a874a5da
--- /dev/null
+++ b/libraries/pbrlib/genglsl/mx39_sheen_zeltner_bsdf.glsl
@@ -0,0 +1,38 @@
+#include "lib/mx39_microfacet_sheen.glsl"
+
+void mx39_sheen_zeltner_bsdf_reflection(vec3 L, vec3 V, vec3 P, float occlusion, float weight, vec3 color, float roughness, vec3 N, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+
+    roughness = clamp(roughness, 0.01, 1.0); // Clamp to range of original impl.
+
+    vec3 fr = color * mx39_zeltner_sheen_brdf(L, V, N, NdotV, roughness);
+    float dirAlbedo = mx39_zeltner_sheen_dir_albedo(NdotV, roughness);
+    bsdf.throughput = vec3(1.0 - dirAlbedo * weight);
+    bsdf.response = dirAlbedo * fr * occlusion * weight;
+}
+
+void mx39_sheen_zeltner_bsdf_indirect(vec3 V, float weight, vec3 color, float roughness, vec3 N, inout BSDF bsdf)
+{
+    if (weight < M_FLOAT_EPS)
+    {
+        return;
+    }
+
+    N = mx_forward_facing_normal(N, V);
+    float NdotV = clamp(dot(N, V), M_FLOAT_EPS, 1.0);
+
+    float dirAlbedo;
+    roughness = clamp(roughness, 0.01, 1.0); // Clamp to range of original impl.
+    dirAlbedo = mx39_zeltner_sheen_dir_albedo(NdotV, roughness);
+
+    vec3 Li = mx_environment_irradiance(N);
+    bsdf.throughput = vec3(1.0 - dirAlbedo * weight);
+    bsdf.response = Li * color * dirAlbedo * weight;
+}
diff --git a/libraries/pbrlib/genmdl/mx39_pbrlib_genmdl_impl.mtlx b/libraries/pbrlib/genmdl/mx39_pbrlib_genmdl_impl.mtlx
new file mode 100644
index 0000000000..f2dc8c184d
--- /dev/null
+++ b/libraries/pbrlib/genmdl/mx39_pbrlib_genmdl_impl.mtlx
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<materialx version="1.38">
+
+  <!-- <compensating_oren_nayar_diffuse_bsdf> -->
+  <implementation name="IM_compensating_oren_nayar_diffuse_bsdf_genmdl" nodedef="ND_compensating_oren_nayar_diffuse_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_oren_nayar_diffuse_bsdf(mxp_weight:{{weight}}, mxp_color:{{color}}, mxp_roughness:{{roughness}}, mxp_normal:{{normal}})" target="genmdl" />
+
+  <!-- <dielectric_tf_bsdf> -->
+  <implementation name="IM_dielectric_tf_bsdf_genmdl" nodedef="ND_dielectric_tf_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_dielectric_bsdf(mxp_weight:{{weight}}, mxp_tint:{{tint}}, mxp_ior:{{ior}}, mxp_roughness:{{roughness}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}}, mxp_scatter_mode:{{scatter_mode}}, mxp_base:{{base}})" target="genmdl" />
+
+  <!-- <generalized_schlick_tf_82_bsdf> -->
+  <implementation name="IM_generalized_schlick_tf_82_bsdf_genmdl" nodedef="ND_generalized_schlick_tf_82_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_generalized_schlick_bsdf(mxp_weight:{{weight}}, mxp_color0:{{color0}}, mxp_color90:{{color90}}, mxp_exponent:{{exponent}},mxp_roughness:{{roughness}}, mxp_thinfilm_thickness:{{thinfilm_thickness}}, mxp_thinfilm_ior:{{thinfilm_ior}}, mxp_normal:{{normal}}, mxp_tangent:{{tangent}}, mxp_distribution:{{distribution}}, mxp_scatter_mode:{{scatter_mode}}, mxp_base:{{base}})" target="genmdl" />
+
+  <!-- <sheen_zeltner_bsdf> -->
+  <implementation name="IM_sheen_zeltner_bsdf_genmdl" nodedef="ND_sheen_zeltner_bsdf" sourcecode="materialx::pbrlib_{{MDL_VERSION_SUFFIX}}::mx_sheen_bsdf(mxp_weight:{{weight}}, mxp_color:{{color}}, mxp_roughness:{{roughness}}, mxp_normal:{{normal}}, mxp_base:{{base}})" target="genmdl" />
+
+</materialx>
diff --git a/libraries/pbrlib/genmsl/mx39_pbrlib_genmsl_impl.mtlx b/libraries/pbrlib/genmsl/mx39_pbrlib_genmsl_impl.mtlx
new file mode 100644
index 0000000000..93fe12e647
--- /dev/null
+++ b/libraries/pbrlib/genmsl/mx39_pbrlib_genmsl_impl.mtlx
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<materialx version="1.38">
+
+  <!-- <compensating_oren_nayar_diffuse_bsdf> -->
+  <implementation name="IM_compensating_oren_nayar_diffuse_bsdf_genmsl" nodedef="ND_compensating_oren_nayar_diffuse_bsdf" file="../genglsl/mx39_compensating_oren_nayar_diffuse_bsdf.glsl" function="mx39_compensating_oren_nayar_diffuse_bsdf" target="genmsl" />
+
+  <!-- <dielectric_tf_bsdf> -->
+  <implementation name="IM_dielectric_tf_bsdf_genmsl" nodedef="ND_dielectric_tf_bsdf" file="../genglsl/mx39_dielectric_tf_bsdf.glsl" function="mx39_dielectric_tf_bsdf" target="genmsl" />
+
+  <!-- <generalized_schlick_tf_82_bsdf> -->
+  <implementation name="IM_generalized_schlick_tf_82_bsdf_genmsl" nodedef="ND_generalized_schlick_tf_82_bsdf" file="../genglsl/mx39_generalized_schlick_tf_82_bsdf.glsl" function="mx39_generalized_schlick_tf_82_bsdf" target="genmsl" />
+
+  <!-- <sheen_zeltner_bsdf> -->
+  <implementation name="IM_sheen_zeltner_bsdf_genmsl" nodedef="ND_sheen_zeltner_bsdf" file="../genglsl/mx39_sheen_zeltner_bsdf.glsl" function="mx39_sheen_zeltner_bsdf" target="genmsl" />
+
+</materialx>
diff --git a/libraries/pbrlib/genosl/legacy/mx39_compensating_oren_nayar_diffuse_bsdf.osl b/libraries/pbrlib/genosl/legacy/mx39_compensating_oren_nayar_diffuse_bsdf.osl
new file mode 100644
index 0000000000..2ce4dd07b1
--- /dev/null
+++ b/libraries/pbrlib/genosl/legacy/mx39_compensating_oren_nayar_diffuse_bsdf.osl
@@ -0,0 +1,5 @@
+void mx39_compensating_oren_nayar_diffuse_bsdf(float weight, color _color, float roughness, normal N, int energy_compensation, output BSDF bsdf)
+{
+    bsdf.response = _color * weight * oren_nayar(N, roughness);
+    bsdf.throughput = color(0.0);
+}
diff --git a/libraries/pbrlib/genosl/legacy/mx39_dielectric_tf_bsdf.osl b/libraries/pbrlib/genosl/legacy/mx39_dielectric_tf_bsdf.osl
new file mode 100644
index 0000000000..5d6c81fd36
--- /dev/null
+++ b/libraries/pbrlib/genosl/legacy/mx39_dielectric_tf_bsdf.osl
@@ -0,0 +1,36 @@
+#include "../lib/mx_microfacet_specular.osl"
+
+void mx39_dielectric_tf_bsdf(float weight, color tint, float ior, vector2 roughness, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
+{
+    if (scatter_mode == "T")
+    {
+        bsdf.response = tint * weight * microfacet(distribution, N, U, roughness.x, roughness.y, ior, 1);
+        bsdf.throughput = tint * weight;
+        return;
+    }
+
+    float NdotV = clamp(dot(N,-I), M_FLOAT_EPS, 1.0);
+    float F0 = mx_ior_to_f0(ior);
+    float F = mx_fresnel_schlick(NdotV, F0);
+
+    // Calculate compensation for multiple scattering.
+    // This should normally be done inside the closure
+    // but since vanilla OSL doesen't support this we
+    // add it here in shader code instead.
+    vector2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+    float comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+
+    // Calculate throughput from directional albedo.
+    float dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, ior) * comp;
+    bsdf.throughput = 1.0 - dirAlbedo * weight;
+
+    if (scatter_mode == "R")
+    {
+        bsdf.response = tint * weight * comp * microfacet(distribution, N, U, safeAlpha.x, safeAlpha.y, ior, 0);
+    }
+    else
+    {
+        bsdf.response = tint * weight * comp * microfacet(distribution, N, U, safeAlpha.x, safeAlpha.y, ior, 2);
+    }
+}
diff --git a/libraries/pbrlib/genosl/legacy/mx39_generalized_schlick_tf_82_bsdf.osl b/libraries/pbrlib/genosl/legacy/mx39_generalized_schlick_tf_82_bsdf.osl
new file mode 100644
index 0000000000..ac0e3928e5
--- /dev/null
+++ b/libraries/pbrlib/genosl/legacy/mx39_generalized_schlick_tf_82_bsdf.osl
@@ -0,0 +1,38 @@
+#include "../lib/mx_microfacet_specular.osl"
+
+void mx39_generalized_schlick_tf_82_bsdf(float weight, color color0, color color82, color color90, float exponent, vector2 roughness, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
+{
+    float avgF0 = dot(color0, color(1.0 / 3.0));
+    float ior = mx_f0_to_ior(avgF0);
+
+    if (scatter_mode == "T")
+    {
+        bsdf.response = weight * microfacet(distribution, N, U, roughness.x, roughness.y, ior, 1);
+        bsdf.throughput = weight;
+        return;
+    }
+
+    float NdotV = fabs(dot(N,-I));
+    color F = mx_fresnel_schlick(NdotV, color0, color90, exponent);
+
+    // Calculate compensation for multiple scattering.
+    // This should normally be done inside the closure
+    // but since vanilla OSL doesen't support this we
+    // add it here in shader code instead.
+    vector2 safeAlpha = clamp(roughness, M_FLOAT_EPS, 1.0);
+    float avgAlpha = mx_average_alpha(safeAlpha);
+    color comp = mx_ggx_energy_compensation(NdotV, avgAlpha, F);
+
+    // Calculate throughput from directional albedo.
+    color dirAlbedo = mx_ggx_dir_albedo(NdotV, avgAlpha, color0, color90) * comp;
+    float avgDirAlbedo = dot(dirAlbedo, color(1.0 / 3.0));
+    bsdf.throughput = 1.0 - avgDirAlbedo * weight;
+
+    // Calculate the reflection response, setting IOR to zero to disable internal Fresnel.
+    bsdf.response = F * comp * weight * microfacet(distribution, N, U, safeAlpha.x, safeAlpha.y, 0.0, 0);
+
+    if (scatter_mode == "RT")
+    {
+        bsdf.response += bsdf.throughput * microfacet(distribution, N, U, safeAlpha.x, safeAlpha.y, ior, 1);
+    }
+}
diff --git a/libraries/pbrlib/genosl/mx39_dielectric_tf_bsdf.osl b/libraries/pbrlib/genosl/mx39_dielectric_tf_bsdf.osl
new file mode 100644
index 0000000000..5b4243506c
--- /dev/null
+++ b/libraries/pbrlib/genosl/mx39_dielectric_tf_bsdf.osl
@@ -0,0 +1,15 @@
+void mx39_dielectric_tf_bsdf(float weight, color tint, float ior, vector2 roughness, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
+{
+    if (scatter_mode == "R")
+    {
+        bsdf = weight * dielectric_bsdf(N, U, tint, color(0.0), roughness.x, roughness.y, ior, distribution, "thinfilm_thickness", thinfilm_thickness, "thinfilm_ior", thinfilm_ior);
+    }
+    else if (scatter_mode == "T")
+    {
+        bsdf = weight * dielectric_bsdf(N, U, color(0.0), tint, roughness.x, roughness.y, ior, distribution, "thinfilm_thickness", thinfilm_thickness, "thinfilm_ior", thinfilm_ior);
+    }
+    else
+    {
+        bsdf = weight * dielectric_bsdf(N, U, tint, tint, roughness.x, roughness.y, ior, distribution, "thinfilm_thickness", thinfilm_thickness, "thinfilm_ior", thinfilm_ior);
+    }
+}
diff --git a/libraries/pbrlib/genosl/mx39_generalized_schlick_tf_82_bsdf.osl b/libraries/pbrlib/genosl/mx39_generalized_schlick_tf_82_bsdf.osl
new file mode 100644
index 0000000000..4fb9eac0c3
--- /dev/null
+++ b/libraries/pbrlib/genosl/mx39_generalized_schlick_tf_82_bsdf.osl
@@ -0,0 +1,15 @@
+void mx39_generalized_schlick_tf_82_bsdf(float weight, color color0, color color82, color color90, float exponent, vector2 roughness, float thinfilm_thickness, float thinfilm_ior, normal N, vector U, string distribution, string scatter_mode, output BSDF bsdf)
+{
+    if (scatter_mode == "R")
+    {
+        bsdf = weight * generalized_schlick_bsdf(N, U, color(1.0), color(0.0), roughness.x, roughness.y, color0, color90, exponent, distribution, "thinfilm_thickness", thinfilm_thickness, "thinfilm_ior", thinfilm_ior);
+    }
+    else if (scatter_mode == "T")
+    {
+        bsdf = weight * generalized_schlick_bsdf(N, U, color(0.0), color(1.0), roughness.x, roughness.y, color0, color90, exponent, distribution, "thinfilm_thickness", thinfilm_thickness, "thinfilm_ior", thinfilm_ior);
+    }
+    else
+    {
+        bsdf = weight * generalized_schlick_bsdf(N, U, color(1.0), color(1.0), roughness.x, roughness.y, color0, color90, exponent, distribution, "thinfilm_thickness", thinfilm_thickness, "thinfilm_ior", thinfilm_ior);
+    }
+}
diff --git a/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.legacy b/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.legacy
new file mode 100644
index 0000000000..95af5056f4
--- /dev/null
+++ b/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.legacy
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<materialx version="1.38">
+
+  <!-- <compensating_oren_nayar_diffuse_bsdf> -->
+  <implementation name="IM_compensating_oren_nayar_diffuse_bsdf_genosl" nodedef="ND_compensating_oren_nayar_diffuse_bsdf" file="legacy/mx39_compensating_oren_nayar_diffuse_bsdf.osl" function="mx39_compensating_oren_nayar_diffuse_bsdf" target="genosl" />
+
+  <!-- <dielectric_tf_bsdf> -->
+  <implementation name="IM_dielectric_tf_bsdf_genosl" nodedef="ND_dielectric_tf_bsdf" file="legacy/mx39_dielectric_tf_bsdf.osl" function="mx39_dielectric_tf_bsdf" target="genosl" />
+
+  <!-- <generalized_schlick_tf_82_bsdf> -->
+  <implementation name="IM_generalized_schlick_tf_82_bsdf_genosl" nodedef="ND_generalized_schlick_tf_82_bsdf" file="legacy/mx39_generalized_schlick_tf_82_bsdf.osl" function="mx39_generalized_schlick_tf_82_bsdf" target="genosl" />
+
+  <!-- <sheen_zeltner_bsdf> -->
+  <implementation name="IM_sheen_zeltner_bsdf_genosl" nodedef="ND_sheen_zeltner_bsdf" file="legacy/mx_sheen_bsdf.osl" function="mx_sheen_bsdf" target="genosl" />
+
+</materialx>
diff --git a/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.mtlx b/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.mtlx
new file mode 100644
index 0000000000..df8d6a59e9
--- /dev/null
+++ b/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.mtlx
@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<materialx version="1.38">
+
+  <!-- <compensating_oren_nayar_diffuse_bsdf> -->
+  <implementation name="IM_compensating_oren_nayar_diffuse_bsdf_genosl" nodedef="ND_compensating_oren_nayar_diffuse_bsdf" sourcecode="{{weight}} * oren_nayar_diffuse_bsdf({{normal}}, {{color}}, {{roughness}})" target="genosl" />
+
+  <!-- <dielectric_tf_bsdf> -->
+  <implementation name="IM_dielectric_tf_bsdf_genosl" nodedef="ND_dielectric_tf_bsdf" file="mx39_dielectric_tf_bsdf.osl" function="mx39_dielectric_tf_bsdf" target="genosl" />
+
+  <!-- <generalized_schlick_tf_82_bsdf> -->
+  <implementation name="IM_generalized_schlick_tf_82_bsdf_genosl" nodedef="ND_generalized_schlick_tf_82_bsdf" file="mx39_generalized_schlick_tf_82_bsdf.osl" function="mx39_generalized_schlick_tf_82_bsdf" target="genosl" />
+
+  <!-- <sheen_zeltner_bsdf> -->
+  <implementation name="IM_sheen_zeltner_bsdf_genosl" nodedef="ND_sheen_zeltner_bsdf" sourcecode="{{weight}} * sheen_bsdf({{normal}}, {{color}}, {{roughness}})" target="genosl" />
+
+</materialx>
diff --git a/libraries/pbrlib/pbrlib_defs.mtlx b/libraries/pbrlib/pbrlib_defs.mtlx
index e63625a45d..5fe6a6a773 100644
--- a/libraries/pbrlib/pbrlib_defs.mtlx
+++ b/libraries/pbrlib/pbrlib_defs.mtlx
@@ -417,4 +417,78 @@
     <output name="extinction" type="color3" />
   </nodedef>
 
+  <!-- ======================================================================== -->
+  <!-- OpenPBR Surface Nodes backported from 1.39                               -->
+  <!--                                                                          -->
+  <!-- PLEASE DO NOT USE THESE NODES IN YOUR SHADERS. DCCs, PLEASE HIDE THEM.   -->
+  <!--   Otherwise we will have to provide upgrade paths in 1.39.               -->
+  <!-- ======================================================================== -->
+
+  <!--
+    Node: <compensating_oren_nayar_diffuse_bsdf>
+    A BSDF node for diffuse reflection.
+    This node acquired energy compensation in 1.39.
+  -->
+  <nodedef name="ND_compensating_oren_nayar_diffuse_bsdf" node="compensating_oren_nayar_diffuse_bsdf" bsdf="R" nodegroup="OpenPBR" uivisible="false" doc="A BSDF node for diffuse reflections.">
+    <input name="weight" type="float" value="1.0" uimin="0.0" uimax="1.0" />
+    <input name="color" type="color3" value="0.18, 0.18, 0.18" />
+    <input name="roughness" type="float" value="0.0" />
+    <input name="normal" type="vector3" defaultgeomprop="Nworld" />
+    <input name="energy_compensation" type="boolean" value="false" uniform="true" />
+    <output name="out" type="BSDF" />
+  </nodedef>
+
+  <!--
+    Node: <dielectric_tf_bsdf>
+    A reflection/transmission BSDF node based on a microfacet model and a Fresnel curve for dielectrics.
+    This node became thin-film aware in 1.39
+  -->
+  <nodedef name="ND_dielectric_tf_bsdf" node="dielectric_tf_bsdf" nodegroup="OpenPBR" uivisible="false" doc="A reflection/transmission BSDF node based on a microfacet model and a Fresnel curve for dielectrics.">
+    <input name="weight" type="float" value="1.0" uimin="0.0" uimax="1.0" />
+    <input name="tint" type="color3" value="1.0, 1.0, 1.0" />
+    <input name="ior" type="float" value="1.5" />
+    <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" />
+    <input name="normal" type="vector3" defaultgeomprop="Nworld" />
+    <input name="tangent" type="vector3" defaultgeomprop="Tworld" />
+    <input name="distribution" type="string" value="ggx" enum="ggx" uniform="true" />
+    <input name="scatter_mode" type="string" value="R" enum="R,T,RT" uniform="true" />
+    <output name="out" type="BSDF" />
+  </nodedef>
+
+  <!--
+    Node: <generalized_schlick_tf_82_bsdf>
+    A reflection/transmission BSDF node based on a microfacet model and a generalized Schlick Fresnel curve.
+    This node gained a 82 degree color and thin film awareness in 1.39
+  -->
+  <nodedef name="ND_generalized_schlick_tf_82_bsdf" node="generalized_schlick_tf_82_bsdf" nodegroup="OpenPBR" uivisible="false" doc="A reflection/transmission BSDF node based on a microfacet model and a generalized Schlick Fresnel curve.">
+    <input name="weight" type="float" value="1.0" uimin="0.0" uimax="1.0" />
+    <input name="color0" type="color3" value="1.0, 1.0, 1.0" />
+    <input name="color82" type="color3" value="1.0, 1.0, 1.0" />
+    <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" 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" />
+    <input name="normal" type="vector3" defaultgeomprop="Nworld" />
+    <input name="tangent" type="vector3" defaultgeomprop="Tworld" />
+    <input name="distribution" type="string" value="ggx" enum="ggx" uniform="true" />
+    <input name="scatter_mode" type="string" value="R" enum="R,T,RT" uniform="true" />
+    <output name="out" type="BSDF" />
+  </nodedef>
+
+  <!--
+    Node: <sheen_zeltner_bsdf>
+    A microfacet BSDF for the back-scattering properties of cloth-like materials.
+    This node gained a Zeltner mode in MaterialX 1.39. We split the code to only expose Zeltner case.
+  -->
+  <nodedef name="ND_sheen_zeltner_bsdf" node="sheen_zeltner_bsdf" bsdf="R" nodegroup="OpenPBR" uivisible="false" doc="A microfacet BSDF for the back-scattering properties of cloth-like materials.">
+    <input name="weight" type="float" value="1.0" uimin="0.0" uimax="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" defaultgeomprop="Nworld" />
+    <output name="out" type="BSDF" />
+  </nodedef>
+
 </materialx>
diff --git a/python/Scripts/generateshader.py b/python/Scripts/generateshader.py
index f6158d270a..65b628d733 100644
--- a/python/Scripts/generateshader.py
+++ b/python/Scripts/generateshader.py
@@ -143,8 +143,6 @@ def main():
         nodes = mx_gen_shader.findRenderableElements(doc)
         if not nodes:
             nodes = doc.getMaterialNodes()
-            if not nodes:
-                nodes = doc.getNodesOfType(mx.SURFACE_SHADER_TYPE_STRING)
 
         pathPrefix = ''
         if opts.outputPath and os.path.exists(opts.outputPath):
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_aluminum_brushed.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_aluminum_brushed.mtlx
new file mode 100644
index 0000000000..7f7072d416
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_aluminum_brushed.mtlx
@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Aluminum_Brushed" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="base_color" type="color3" value="0.912, 0.914, 0.920" />
+    <input name="base_metalness" type="float" value="1.0" />
+    <input name="specular_color" type="color3" value="0.970, 0.979, 0.988" />
+    <input name="specular_roughness" type="float" value="0.2" />
+    <input name="specular_roughness_anisotropy" type="float" value="0.9" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_carpaint.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_carpaint.mtlx
new file mode 100644
index 0000000000..fd42fdf48d
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_carpaint.mtlx
@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Car_Paint" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="base_color" type="color3" value="0.1, 0.6, 0.9" />
+    <input name="specular_ior" type="float" value="1.6" />
+    <input name="specular_roughness" type="float" value="0.3" />
+    <input name="coat_weight" type="float" value="1" />
+    <input name="coat_roughness" type="float" value="0.02" />
+    <input name="coat_ior" type="float" value="1.6" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_default.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_default.mtlx
new file mode 100644
index 0000000000..8125541a99
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_default.mtlx
@@ -0,0 +1,46 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Default" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+    <input name="displacementshader" type="displacementshader" value="" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="base_weight" type="float" value="1.0" />
+    <input name="base_color" type="color3" value="0.8, 0.8, 0.8" />
+    <input name="base_diffuse_roughness" type="float" value="0.0" />
+    <input name="base_metalness" type="float" value="0.0" />
+    <input name="specular_weight" type="float" value="1.0" />
+    <input name="specular_color" type="color3" value="1, 1, 1" />
+    <input name="specular_roughness" type="float" value="0.3" />
+    <input name="specular_ior" type="float" value="1.5" />
+    <input name="specular_roughness_anisotropy" type="float" value="0.0" />
+    <input name="transmission_weight" type="float" value="0.0" />
+    <input name="transmission_color" type="color3" value="1, 1, 1" />
+    <input name="transmission_depth" type="float" value="0.0" />
+    <input name="transmission_scatter" type="color3" value="0, 0, 0" />
+    <input name="transmission_scatter_anisotropy" type="float" value="0.0" />
+    <input name="transmission_dispersion_scale" type="float" value="0.0" />
+    <input name="transmission_dispersion_abbe_number" type="float" value="20.0" />
+    <input name="subsurface_weight" type="float" value="0" />
+    <input name="subsurface_color" type="color3" value="0.8, 0.8, 0.8" />
+    <input name="subsurface_radius" type="float" value="1.0" />
+    <input name="subsurface_radius_scale" type="color3" value="1.0, 0.5, 0.25" />
+    <input name="subsurface_scatter_anisotropy" type="float" value="0.0" />
+    <input name="fuzz_weight" type="float" value="0.0" />
+    <input name="fuzz_color" type="color3" value="1, 1, 1" />
+    <input name="fuzz_roughness" type="float" value="0.5" />
+    <input name="coat_weight" type="float" value="0.0" />
+    <input name="coat_color" type="color3" value="1, 1, 1" />
+    <input name="coat_roughness" type="float" value="0.0" />
+    <input name="coat_roughness_anisotropy" type="float" value="0.0" />
+    <input name="coat_ior" type="float" value="1.6" />
+    <input name="coat_darkening" type="float" value="1.0" />
+    <input name="thin_film_weight" type="float" value="0" />
+    <input name="thin_film_thickness" type="float" value="0.5" />
+    <input name="thin_film_ior" type="float" value="1.4" />
+    <input name="emission_luminance" type="float" value="0.0" />
+    <input name="emission_color" type="color3" value="1, 1, 1" />
+    <input name="geometry_opacity" type="float" value="1" />
+    <input name="geometry_thin_walled" type="boolean" value="false" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_glass.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_glass.mtlx
new file mode 100644
index 0000000000..a661b9d1f6
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_glass.mtlx
@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Glass" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="specular_roughness" type="float" value="0.0" />
+    <input name="specular_ior" type="float" value="1.52" />
+    <input name="transmission_weight" type="float" value="1.0" />
+    <input name="transmission_dispersion_abbe_number" type="float" value="64" />
+    <input name="transmission_dispersion_scale" type="float" value="1.0" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_honey.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_honey.mtlx
new file mode 100644
index 0000000000..41e076d231
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_honey.mtlx
@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Honey" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="specular_roughness" type="float" value="0.0" />
+    <input name="specular_ior" type="float" value="1.504" />
+    <input name="transmission_weight" type="float" value="1.0" />
+    <input name="transmission_color" type="color3" value="0.83, 0.4, 0.04" />
+    <input name="transmission_depth" type="float" value="2" />
+    <input name="transmission_scatter" type="color3" value="0.9, 0.9, 0.9" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_ketchup.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_ketchup.mtlx
new file mode 100644
index 0000000000..cda2ebdf7e
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_ketchup.mtlx
@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Ketchup" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="base_color" type="color3" value="0.164, 0.006, 0.002" />
+    <input name="specular_roughness" type="float" value="0" />
+    <input name="specular_ior" type="float" value="1.3" />
+    <input name="subsurface_weight" type="float" value="1.0" />
+    <input name="subsurface_color" type="color3" value="0.164, 0.006, 0.002" />
+    <input name="subsurface_radius_scale" type="color3" value="0.476, 0.058, 0.039" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_lightbulb.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_lightbulb.mtlx
new file mode 100644
index 0000000000..a915f842a4
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_lightbulb.mtlx
@@ -0,0 +1,10 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Light_Bulb" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="emission_color" type="color3" value="1.000, 0.415, 0.099" />
+    <input name="emission_luminance" type="float" value="10000" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_pearl.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_pearl.mtlx
new file mode 100644
index 0000000000..83db774b8e
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_pearl.mtlx
@@ -0,0 +1,20 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Pearl" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="base_color" type="color3" value="0.8, 0.75, 0.7" />
+    <input name="specular_roughness" type="float" value="0.35" />
+    <input name="specular_ior" type="float" value="1.5" />
+    <input name="subsurface_weight" type="float" value="1.0" />
+    <input name="subsurface_color" type="color3" value="0.8, 0.75, 0.7" />
+    <input name="subsurface_radius_scale" type="color3" value="0.3, 0.5, 0.3" />
+    <input name="coat_weight" type="float" value="1" />
+    <input name="coat_roughness" type="float" value="0.15" />
+    <input name="coat_ior" type="float" value="1.68" />
+    <input name="thin_film_weight" type="float" value="1.0" />
+    <input name="thin_film_thickness" type="float" value="0.420" />
+    <input name="thin_film_ior" type="float" value="2" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_soapbubble.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_soapbubble.mtlx
new file mode 100644
index 0000000000..af0faccb2a
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_soapbubble.mtlx
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Soap_Bubble" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="specular_roughness" type="float" value="0" />
+    <input name="specular_ior" type="float" value="1.0" />
+    <input name="transmission_weight" type="float" value="1.0" />
+    <input name="thin_film_weight" type="float" value="1.0" />
+    <input name="thin_film_thickness" type="float" value="0.5" />
+    <input name="thin_film_ior" type="float" value="1.4" />
+    <input name="geometry_thin_walled" type="boolean" value="true" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/Examples/OpenPbr/open_pbr_velvet.mtlx b/resources/Materials/Examples/OpenPbr/open_pbr_velvet.mtlx
new file mode 100644
index 0000000000..6fbc907f3d
--- /dev/null
+++ b/resources/Materials/Examples/OpenPbr/open_pbr_velvet.mtlx
@@ -0,0 +1,13 @@
+<?xml version="1.0"?>
+<materialx version="1.38" colorspace="lin_rec709">
+  <surfacematerial name="Velvet" type="material">
+    <input name="surfaceshader" type="surfaceshader" nodename="open_pbr_surface_surfaceshader" />
+  </surfacematerial>
+  <open_pbr_surface name="open_pbr_surface_surfaceshader" type="surfaceshader">
+    <input name="base_color" type="color3" value="0.02, 0.02, 0.02" />
+    <input name="specular_roughness" type="float" value="0.8" />
+    <input name="fuzz_weight" type="float" value="1" />
+    <input name="fuzz_color" type="color3" value="0.4, 0.4, 0.4" />
+    <input name="fuzz_roughness" type="float" value="0.5" />
+  </open_pbr_surface>
+</materialx>
diff --git a/resources/Materials/TestSuite/_options.mtlx b/resources/Materials/TestSuite/_options.mtlx
index 99db2a9f50..e12a5b564b 100644
--- a/resources/Materials/TestSuite/_options.mtlx
+++ b/resources/Materials/TestSuite/_options.mtlx
@@ -74,7 +74,7 @@
     <input name="extraLibraryPaths" type="string" value="" />
 
     <!-- List of document paths for render tests -->
-    <input name="renderTestPaths" type="string" value="resources/Materials/Examples/StandardSurface,resources/Materials/TestSuite/stdlib/color_management,resources/Materials/TestSuite/stdlib/convolution,resources/Materials/TestSuite/stdlib/geometric,resources/Materials/TestSuite/stdlib/procedural,resources/Materials/TestSuite/pbrlib,resources/Materials/TestSuite/nprlib" />
+    <input name="renderTestPaths" type="string" value="resources/Materials/Examples/OpenPbr,resources/Materials/Examples/StandardSurface,resources/Materials/TestSuite/stdlib/color_management,resources/Materials/TestSuite/stdlib/convolution,resources/Materials/TestSuite/stdlib/geometric,resources/Materials/TestSuite/stdlib/procedural,resources/Materials/TestSuite/pbrlib,resources/Materials/TestSuite/nprlib" />
 
     <!-- Enable reference quality rendering. Default is false. -->
     <input name="enableReferenceQuality" type="boolean" value="false" />
diff --git a/source/MaterialXGenMdl/MdlShaderGenerator.cpp b/source/MaterialXGenMdl/MdlShaderGenerator.cpp
index 5a1f39f48d..57c653bc83 100644
--- a/source/MaterialXGenMdl/MdlShaderGenerator.cpp
+++ b/source/MaterialXGenMdl/MdlShaderGenerator.cpp
@@ -192,15 +192,18 @@ MdlShaderGenerator::MdlShaderGenerator() :
 
     // <!-- <dielectric_bsdf> -->
     registerImplementation("IM_dielectric_bsdf_" + MdlShaderGenerator::TARGET, ThinFilmReceiverNodeMdl::create);
+    registerImplementation("IM_dielectric_tf_bsdf_" + MdlShaderGenerator::TARGET, LayerableNodeMdl::create);
 
     // <!-- <conductor_bsdf> -->
     registerImplementation("IM_conductor_bsdf_" + MdlShaderGenerator::TARGET, ThinFilmReceiverNodeMdl::create);
 
     // <!-- <generalized_schlick_bsdf> -->
     registerImplementation("IM_generalized_schlick_bsdf_" + MdlShaderGenerator::TARGET, ThinFilmReceiverNodeMdl::create);
+    registerImplementation("IM_generalized_schlick_tf_82_bsdf_" + MdlShaderGenerator::TARGET, LayerableNodeMdl::create);
 
     // <!-- <sheen_bsdf> -->
     registerImplementation("IM_sheen_bsdf_" + MdlShaderGenerator::TARGET, LayerableNodeMdl::create);
+    registerImplementation("IM_sheen_zeltner_bsdf_" + MdlShaderGenerator::TARGET, LayerableNodeMdl::create);
 
     // <!-- <image> -->
     registerImplementation("IM_image_float_" + MdlShaderGenerator::TARGET, ImageNodeMdl::create);
diff --git a/source/MaterialXGenShader/ShaderNode.cpp b/source/MaterialXGenShader/ShaderNode.cpp
index 6e951b06e6..adcf71566b 100644
--- a/source/MaterialXGenShader/ShaderNode.cpp
+++ b/source/MaterialXGenShader/ShaderNode.cpp
@@ -235,7 +235,8 @@ ShaderNodePtr ShaderNode::create(const ShaderGraph* parent, const string& name,
     }
     else if (*primaryOutput->getType() == *Type::SURFACESHADER)
     {
-        if (nodeDefName == "ND_surface_unlit")
+        if (nodeDefName == "ND_surface_unlit" ||
+            (stringStartsWith(nodeDefName, "ND_convert_") && stringEndsWith(nodeDefName, "_surfaceshader")))
         {
             newNode->_classification = Classification::SHADER | Classification::SURFACE | Classification::UNLIT;
         }
diff --git a/source/MaterialXRender/CMakeLists.txt b/source/MaterialXRender/CMakeLists.txt
index 52d07e688e..654a9648bb 100644
--- a/source/MaterialXRender/CMakeLists.txt
+++ b/source/MaterialXRender/CMakeLists.txt
@@ -18,6 +18,9 @@ assign_source_group("Header Files" ${materialx_headers})
 
 if(UNIX)
     add_compile_options(-Wno-unused-function)
+    if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+        add_compile_options(-Wno-stringop-overflow)
+    endif()
 endif()
 
 add_library(${MATERIALX_MODULE_NAME} ${materialx_source} ${materialx_headers} ${materialx_inlined})
diff --git a/source/MaterialXTest/CMakeLists.txt b/source/MaterialXTest/CMakeLists.txt
index 862a176b50..9d2bd578dd 100644
--- a/source/MaterialXTest/CMakeLists.txt
+++ b/source/MaterialXTest/CMakeLists.txt
@@ -98,6 +98,9 @@ if(MATERIALX_OSL_LEGACY_CLOSURES)
     add_custom_command(TARGET MaterialXTest POST_BUILD
         COMMAND ${CMAKE_COMMAND} -E rename
         ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/libraries/pbrlib/genosl/pbrlib_genosl_impl.legacy ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/libraries/pbrlib/genosl/pbrlib_genosl_impl.mtlx)
+    add_custom_command(TARGET MaterialXTest POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E rename
+        ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.legacy ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/libraries/pbrlib/genosl/mx39_pbrlib_genosl_impl.mtlx)
 endif()
 
 if(MATERIALX_BUILD_GEN_MDL)
diff --git a/source/MaterialXTest/MaterialXGenGlsl/GenGlsl.cpp b/source/MaterialXTest/MaterialXGenGlsl/GenGlsl.cpp
index 2cc4d7ccf4..e2857f1eb2 100644
--- a/source/MaterialXTest/MaterialXGenGlsl/GenGlsl.cpp
+++ b/source/MaterialXTest/MaterialXGenGlsl/GenGlsl.cpp
@@ -158,6 +158,7 @@ static void generateGlslCode(GlslType type = GlslType::Glsl400)
     mx::FilePathVec testRootPaths;
     testRootPaths.push_back(searchPath.find("resources/Materials/TestSuite"));
     testRootPaths.push_back(searchPath.find("resources/Materials/Examples/StandardSurface"));
+    testRootPaths.push_back(searchPath.find("resources/Materials/Examples/OpenPbr"));
 
     const mx::FilePath logPath("genglsl_" + GlslTypeToString(type) + "_generate_test.txt");
 
diff --git a/source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp b/source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp
index 8da7e22fe5..2cd48dd4c4 100644
--- a/source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp
+++ b/source/MaterialXTest/MaterialXGenMdl/GenMdl.cpp
@@ -357,6 +357,7 @@ TEST_CASE("GenShader: MDL Shader Generation", "[genmdl]")
     mx::FilePathVec testRootPaths;
     testRootPaths.push_back(searchPath.find("resources/Materials/TestSuite"));
     testRootPaths.push_back(searchPath.find("resources/Materials/Examples/StandardSurface"));
+    testRootPaths.push_back(searchPath.find("resources/Materials/Examples/OpenPbr"));
 
     const mx::FilePath logPath("genmdl_mdl_generate_test.txt");
 
diff --git a/source/MaterialXTest/MaterialXGenMsl/GenMsl.cpp b/source/MaterialXTest/MaterialXGenMsl/GenMsl.cpp
index 03dbcbde69..62c108deca 100644
--- a/source/MaterialXTest/MaterialXGenMsl/GenMsl.cpp
+++ b/source/MaterialXTest/MaterialXGenMsl/GenMsl.cpp
@@ -124,6 +124,7 @@ static void generateMslCode()
     mx::FilePathVec testRootPaths;
     testRootPaths.push_back(searchPath.find("resources/Materials/TestSuite"));
     testRootPaths.push_back(searchPath.find("resources/Materials/Examples/StandardSurface"));
+    testRootPaths.push_back(searchPath.find("resources/Materials/Examples/OpenPbr"));
 
     const mx::FilePath logPath("genmsl_msl23_layout_generate_test.txt");
 
diff --git a/source/MaterialXTest/MaterialXGenOsl/GenOsl.cpp b/source/MaterialXTest/MaterialXGenOsl/GenOsl.cpp
index 13a8b5ffdf..28156a41fe 100644
--- a/source/MaterialXTest/MaterialXGenOsl/GenOsl.cpp
+++ b/source/MaterialXTest/MaterialXGenOsl/GenOsl.cpp
@@ -183,6 +183,7 @@ static void generateOslCode()
     mx::FilePathVec testRootPaths;
     testRootPaths.push_back(searchPath.find("resources/Materials/TestSuite"));
     testRootPaths.push_back(searchPath.find("resources/Materials/Examples/StandardSurface"));
+    testRootPaths.push_back(searchPath.find("resources/Materials/Examples/OpenPbr"));
 
     const mx::FilePath logPath("genosl_vanilla_generate_test.txt");
 
diff --git a/source/MaterialXTest/MaterialXGenShader/GenShaderUtil.cpp b/source/MaterialXTest/MaterialXGenShader/GenShaderUtil.cpp
index 5aa1d7aa2d..3ed23848e6 100644
--- a/source/MaterialXTest/MaterialXGenShader/GenShaderUtil.cpp
+++ b/source/MaterialXTest/MaterialXGenShader/GenShaderUtil.cpp
@@ -355,6 +355,7 @@ void shaderGenPerformanceTest(mx::GenContext& context)
     // Read mtlx documents
     mx::FilePathVec testRootPaths;
     testRootPaths.push_back("resources/Materials/Examples/StandardSurface");
+    testRootPaths.push_back("resources/Materials/Examples/OpenPbr");
 
     std::vector<mx::DocumentPtr> loadedDocuments;
     mx::StringVec documentsPaths;
diff --git a/source/MaterialXView/CMakeLists.txt b/source/MaterialXView/CMakeLists.txt
index 1d9a329e46..e3e81a4b09 100644
--- a/source/MaterialXView/CMakeLists.txt
+++ b/source/MaterialXView/CMakeLists.txt
@@ -70,7 +70,7 @@ else()
     elseif(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
         add_compile_options(-Wno-deprecated)
     elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
-        add_compile_options(-Wno-format-truncation -Wno-use-after-free)
+        add_compile_options(-Wno-format-truncation -Wno-stringop-overflow -Wno-use-after-free)
     endif()
 
     # Disable NanoGUI compiler modifications for Clang
diff --git a/source/MaterialXView/Main.cpp b/source/MaterialXView/Main.cpp
index 904466c065..b2a9403f0f 100644
--- a/source/MaterialXView/Main.cpp
+++ b/source/MaterialXView/Main.cpp
@@ -72,7 +72,7 @@ int main(int argc, char* const argv[])
         tokens.emplace_back(argv[i]);
     }
 
-    std::string materialFilename = "resources/Materials/Examples/StandardSurface/standard_surface_default.mtlx";
+    std::string materialFilename = "resources/Materials/Examples/OpenPbr/open_pbr_default.mtlx";
     std::string meshFilename = "resources/Geometry/shaderball.glb";
     std::string envRadianceFilename = "resources/Lights/san_giuseppe_bridge_split.hdr";
     mx::FileSearchPath searchPath = mx::getDefaultDataSearchPath();