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glTF / MaterialX Translation Library
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kwokcb/glTF_MaterialX
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This repo contains utilities to support glTF bidirectional MaterialX data model conversion for workflows first described in theASWF 2022 Open Source dayspresentation.
The supported targets are:
- glTF version2.0.1
- Corresponding MaterialX version which supports this. The current target release is1.38.8..
Any future specification changes will go into MaterialX core as noted by issues loggedhere
AKhronos integration using this library is being reviewed for integration into main. Thiscurrently includes additional features such as integration in the MaterialXViewer andMaterialX GraphEditor, and Python support. Note that no pipeline tools are integrated there (such as baking) hence export expects the target nodegraph denoted in the next section.
 |  |
For further documentation on interop and workflows seeMaterialX Learning Site.
The glTF documentation covers:
- The target MaterialX representation, which includes theglTF PBR node
- Details about glTF support nodes which are part of the core MaterialX distribution.
- Key glTF<->MaterialX mapping information.
- Node implementations. (Filter nodes which start with gltf).
Real world distance units are not explicitly used but can be added in on top of the supplemental nodes. An integration can set a target unit tometer to match glTF if using code generation.
The default input color space is assumed linear / raw except for color input images whih by default match glTF (srgb_texture = sRGB), and "render space" for uniforms and varying geometric color by default.
The current target for MaterialX material assignments is basic<materialassign> nodes as part of one or more<look>s. For simplicity and the ability to beparsable by MaterialX integrations such as USD an assignment which uses explicitgeom specifiers is recommended. Thus assignments which use regular expressions is not supported.
Conversely for glTF assignments direct assignment are supported at any transform or leaf depth. Variants are not supported at this time.
This is the main module containing core logic for bi-directional mapping.This module can be used directly.
This is a sample C++ program which uses the MaterialxglTF module to allow command line conversion. RunglTF2Mtlx --help for command line options.
This contains unit testing for the MaterialXglTF module. It performs bidirectional conversion from and to glTF for the set of input files specified in theresources direction. Currently this contains a basic set ofglTF Sample model files.
SeeDeveloper Docs for more details.
The basic import from glTF to MaterialX and MaterialX to glTF for shading models: gltf_pbr orunlit_surface (if the material is marked as being unit`. Texture mapping including sampler and transform is supported bidirectionally.
Color per vertex associated alpha blending is supported. Import detectionuses a heuristic of checking if the assigned geometry has a color channel to add a default color channel binding to the input on the graph node.
| Flght Helmet | Alpha Blend Test | Vertex Color Test |
|---|---|---|
 |  |  |
Thecurrent "Boombox" asset which is distributed as part of MaterialX is generated using the glTF to MaterialX utility.
Sample Results
Note that all renders are generated as part of unit tests using the coreMaterialXView program.
| Asset | MaterialX from glTF | glTF from MaterialX | Render |
|---|---|---|---|
| glTF Logo | MaterialX | GLTF |  |
| Chess Set | MaterialX | GLTF |  |
| Damaged Helmet | MaterialX | GLTF |  |
| Boombox with Axes | MaterialX | GLTF |  |
| Iridescence Lamp | MaterialX | GLTF |  |
| Texture Transform Test | MaterialX | GLTF |  |
| Unlit Test | MaterialX | GLTF |  |
Sample Results
Conversion from "stock" MaterialX materials to glTF is available for "distillation".
Metallic-roughness-occlusion (ORM) maps are generated based on whether there are any graph connections forocclusion,metallic androughness inputs on a<gtlf_pbr> instance. If metallic and or roughness are mapped to different inputs then the upstream image(s) or uniform input(s) are merged. This allows for (re)import to<gltf_colorimage> which supports channel splitting of the merged image.
| Asset | MaterialX to glTF | glTF to MaterialX | Render | Notes |
|---|---|---|---|---|
| Jade | glTF | MTLX |  | |
| Marble | glTF | MTLX |  | Fidelity and control lost in baking |
| Plastic | glTF | MTLX |  | |
| Wood | glTF | MTLX |  | ORM map created |
| Brass | glTF | MTLX |  | ORM map created |
| Chess Piece | glTF | MTLX |  | ORM map created |
| Brick | glTF | MTLX |  | ORM map created |
| Calibration | glTF | MTLX |  | |
| Velvet | glTF | MTLX |  |
The setup uses theshader translation graphfoundhere to accomplish the workflow as presented in the ASWF presentation:
|
An expanded example is shown here for tiled brass.
Shader translation graph inserted
<?xml version="1.0"?><materialxversion="1.38"colorspace="lin_rec709"fileprefix="../../../Images/"> <nodegraphname="NG_brass1"> <tiledimagename="image_color"type="color3"> <inputname="file"type="filename"value="brass_color.jpg"colorspace="srgb_texture" /> <inputname="uvtiling"type="vector2"value="1.0, 1.0" /> </tiledimage> <tiledimagename="image_roughness"type="float"> <inputname="file"type="filename"value="brass_roughness.jpg" /> <inputname="uvtiling"type="vector2"value="1.0, 1.0" /> </tiledimage> <standard_surface_to_gltf_pbrname="node1"type="multioutput"nodedef="ND_standard_surface_to_gltf_pbr"> <inputname="base"type="float"value="1" /> <inputname="base_color"type="color3"value="1, 1, 1" /> <inputname="specular_roughness"type="float"nodename="image_roughness" /> <inputname="metalness"type="float"value="1" /> <inputname="coat"type="float"value="1" /> <inputname="coat_color"type="color3"nodename="image_color" /> <inputname="coat_roughness"type="float"nodename="image_roughness" /> </standard_surface_to_gltf_pbr> <outputname="base_color_out"type="color3"nodename="node1"output="base_color_out" /> <outputname="metallic_out"type="float"nodename="node1"output="metallic_out" /> <outputname="roughness_out"type="float"nodename="node1"output="roughness_out" /> <outputname="transmission_out"type="float"nodename="node1"output="transmission_out" /> <outputname="thickness_out"type="float"nodename="node1"output="thickness_out" /> <outputname="attenuation_color_out"type="color3"nodename="node1"output="attenuation_color_out" /> <outputname="sheen_color_out"type="color3"nodename="node1"output="sheen_color_out" /> <outputname="sheen_roughness_out"type="float"nodename="node1"output="sheen_roughness_out" /> <outputname="clearcoat_out"type="float"nodename="node1"output="clearcoat_out" /> <outputname="clearcoat_roughness_out"type="float"nodename="node1"output="clearcoat_roughness_out" /> <outputname="emissive_out"type="color3"nodename="node1"output="emissive_out" /> </nodegraph> <gltf_pbrname="SR_brass1"type="surfaceshader"> <inputname="base_color"type="color3"output="base_color_out"nodegraph="NG_brass1" /> <inputname="metallic"type="float"output="metallic_out"nodegraph="NG_brass1" /> <inputname="roughness"type="float"output="roughness_out"nodegraph="NG_brass1" /> <inputname="transmission"type="float"output="transmission_out"nodegraph="NG_brass1" /> <inputname="thickness"type="float"output="thickness_out"nodegraph="NG_brass1" /> <inputname="attenuation_color"type="color3"output="attenuation_color_out"nodegraph="NG_brass1" /> <inputname="sheen_color"type="color3"output="sheen_color_out"nodegraph="NG_brass1" /> <inputname="sheen_roughness"type="float"output="sheen_roughness_out"nodegraph="NG_brass1" /> <inputname="clearcoat"type="float"output="clearcoat_out"nodegraph="NG_brass1" /> <inputname="clearcoat_roughness"type="float"output="clearcoat_roughness_out"nodegraph="NG_brass1" /> <inputname="emissive"type="color3"output="emissive_out"nodegraph="NG_brass1" /> </gltf_pbr> <surfacematerialname="Tiled_Brass"type="material"> <inputname="surfaceshader"type="surfaceshader"nodename="SR_brass1" /> </surfacematerial></materialx>
Results of baking of graph
<?xml version="1.0"?><materialxversion="1.38"colorspace="lin_rec709"> <nodegraphname="NG_baked"colorspace="srgb_texture"> <imagename="base_color_baked"type="color3"> <inputname="file"type="filename"value="D:\Work\materialx\glTF_MaterialX\build\bin\resources\glTF_export\Materials\Examples\StandardSurface\Tiled_Brass_gltf_pbr_base_color.png" /> </image> <outputname="base_color_output"type="color3"nodename="base_color_baked" /> <imagename="roughness_baked"type="float"> <inputname="file"type="filename"value="D:\Work\materialx\glTF_MaterialX\build\bin\resources\glTF_export\Materials\Examples\StandardSurface\Tiled_Brass_gltf_pbr_roughness.png" /> </image> <outputname="roughness_output"type="float"nodename="roughness_baked" /> <imagename="clearcoat_baked"type="float"> <inputname="file"type="filename"value="D:\Work\materialx\glTF_MaterialX\build\bin\resources\glTF_export\Materials\Examples\StandardSurface\Tiled_Brass_gltf_pbr_clearcoat.png" /> </image> <outputname="clearcoat_output"type="float"nodename="clearcoat_baked" /> <imagename="clearcoat_roughness_baked"type="float"> <inputname="file"type="filename"value="D:\Work\materialx\glTF_MaterialX\build\bin\resources\glTF_export\Materials\Examples\StandardSurface\Tiled_Brass_gltf_pbr_clearcoat_roughness.png" /> </image> <outputname="clearcoat_roughness_output"type="float"nodename="clearcoat_roughness_baked" /> </nodegraph> <gltf_pbrname="SR_brass1_baked"type="surfaceshader"> <inputname="base_color"type="color3"output="base_color_output"nodegraph="NG_baked" /> <inputname="roughness"type="float"output="roughness_output"nodegraph="NG_baked" /> <inputname="clearcoat"type="float"output="clearcoat_output"nodegraph="NG_baked" /> <inputname="clearcoat_roughness"type="float"output="clearcoat_roughness_output"nodegraph="NG_baked" /> </gltf_pbr> <surfacematerialname="Tiled_Brass_baked"type="material"> <inputname="surfaceshader"type="surfaceshader"nodename="SR_brass1_baked" /> </surfacematerial></materialx>
Converted to glTF
ORM map merging occurs during this step to create the "combined" BGRA image created and referenced.
{"asset": {"copyright":"Created via glTF translation utilities found here: https://github.com/kwokcb/glTF_MaterialX","generator":"MaterialX 1.38.7 to glTF 2.0 generator","version":"2.0" },"images": [ {"name":"NG_baked/base_color_baked","uri":"D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_base_color.png" }, {"name":"NG_baked/roughness_baked","uri":"D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_roughness_combined.png" }, {"name":"NG_baked/clearcoat_baked","uri":"D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_clearcoat.png" }, {"name":"NG_baked/clearcoat_roughness_baked","uri":"D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_clearcoat_roughness.png" } ],"materials": [ {"name":"SR_brass1_baked","pbrMetallicRoughness": {"baseColorTexture": {"index":0 },"metallicRoughnessTexture": {"index":1 } },"extensions": {"KHR_materials_clearcoat": {"clearcoatTexture": {"index":2,"scale":0 },"clearcoatRoughnessTexture": {"index":3,"scale":0 },"clearcoatFactor":1,"clearcoatRoughnessFactor":1 },"KHR_materials_ior": { },"KHR_materials_specular": { },"KHR_materials_transmission": { },"KHR_materials_sheen": { },"KHR_materials_emissive_strength": { },"KHR_materials_iridescence": {"iridescenceIor":1,"iridescenceThicknessMinimum":0,"iridescenceThicknessMaximum":0 } } } ],"textures": [ {"name":"NG_baked/base_color_baked","source":0 }, {"name":"NG_baked/roughness_baked","source":1 }, {"name":"NG_baked/clearcoat_baked","source":2 }, {"name":"NG_baked/clearcoat_roughness_baked","source":3 } ],"extensionsUsed": ["KHR_materials_clearcoat","KHR_materials_ior","KHR_materials_specular","KHR_materials_transmission","KHR_materials_sheen","KHR_materials_emissive_strength","KHR_materials_iridescence" ]}Re-imported back to MaterialX
<?xml version="1.0"?><materialxversion="1.38"> <gltf_pbrname="SHD_SR_brass1_baked"type="surfaceshader"> <inputname="base_color"type="color3"nodename="NG_baked_base_color_baked" /> <inputname="metallic"type="float"value="1"nodename="NG_baked_roughness_baked"channels="z" /> <inputname="roughness"type="float"value="1"nodename="NG_baked_roughness_baked"channels="y" /> <inputname="occlusion"type="float"value="1"nodename="NG_baked_roughness_baked"channels="x" /> <inputname="sheen_color"type="color3"value="0, 0, 0" /> <inputname="sheen_roughness"type="float"value="0" /> <inputname="iridescence"type="float"value="0" /> <inputname="iridescence_ior"type="float"value="1" /> <inputname="iridescence_thickness"type="float"value="100" /> <inputname="clearcoat"type="float"nodename="image_clearcoat" /> <inputname="clearcoat_roughness"type="float"nodename="image_clearcoat_roughness" /> <inputname="transmission"type="float"value="0" /> <inputname="specular_color"type="color3"value="1, 1, 1" /> <inputname="specular"type="float"value="1" /> <inputname="ior"type="float"value="1.5" /> <inputname="emissive"type="color3"value="0, 0, 0" /> <inputname="emissive_strength"type="float"value="1" /> </gltf_pbr> <surfacematerialname="MAT_SR_brass1_baked"type="material"> <inputname="surfaceshader"type="surfaceshader"nodename="SHD_SR_brass1_baked" /> </surfacematerial> <gltf_imagename="NG_baked_base_color_baked"type="color3"> <inputname="file"type="filename"value="D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_base_color.png"colorspace="srgb_texture" /> </gltf_image> <gltf_imagename="NG_baked_roughness_baked"type="vector3"> <inputname="file"type="filename"value="D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_roughness_combined.png" /> </gltf_image> <gltf_imagename="image_clearcoat"type="float"> <inputname="file"type="filename"value="D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_clearcoat.png" /> </gltf_image> <gltf_imagename="image_clearcoat_roughness"type="float"> <inputname="file"type="filename"value="D:/Work/materialx/glTF_MaterialX/build/bin/resources/glTF_export/Materials/Examples/StandardSurface/Tiled_Brass_gltf_pbr_clearcoat_roughness.png" /> </gltf_image> <lookname="look1" /></materialx>
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glTF / MaterialX Translation Library