guc
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pablode
glTF to USD converter with MaterialX support
guc
guc is a glTF to Universal Scene Description (USD) converter.
Unlike...
- gltf2usd, it aims to be more than a PoC
- usd_from_gltf, it is not AR Quick Look centric
- Apple's USDZ Tools, it is open-source and freely available
guc furthermore supports near-lossless material translation via the MaterialX standard. Shading networks can be encoded as UsdShade and flattened for backwards compatibility.
All glTF features except animation and skinning are implemented and have been tested on Khronos's sample and validation models.
Wayfair's Iridescent Dish with Olives (CC BY) converted to USD+MaterialX with guc and rendered in hdStorm (left). The same model in Khronos's glTF Sample Viewer (right).
Build
You need USD 22.08 with MaterialX and OpenImageIO support enabled.
Do a recursive clone of the repository and set up a build folder:
git clone https://github.com/pablode/guc --recursive
mkdir guc/build && cd guc/build
Pass following parameters in the CMake generation phase:
cmake .. -Wno-dev \
-DUSD_ROOT=<USD_INSTALL_DIR> \
-DCMAKE_BUILD_TYPE=Release
Build the executable:
cmake --build . -j8 --target guc --config Release
Note: If you're using MSVC, be sure to select a 64-bit generator.
Usage
Usage: guc <gltf_path> <usd_path> [params]
Available params:
--emit-mtlx Emit MaterialX materials in addition to UsdPreviewSurfaces
--mtlx-as-usdshade Convert and inline MaterialX materials with UsdMtlx
--flatten-nodes Flatten MaterialX glTF PBR nodes to stdlib and pbrlib nodes
--explicit-colorspace-transforms Explicitly transform colorspaces using MaterialX nodes
--hdstorm-compat Apply compatibility tweaks for the USD hdStorm renderer
Both .gltf and .glb file types are valid input. .usda and .usdc USD formats can be written.
Debug logging can be enabled by defining the TF_DEBUG="GUC" environment variable.
Extension support
| Name | Status |
|---|---|
| KHR_draco_mesh_compression | ❌ Not supported |
| KHR_lights_punctual | ✅ Partial 1 |
| KHR_materials_clearcoat | ✅ Complete |
| KHR_materials_ior | ✅ Complete |
| KHR_materials_sheen | ✅ Complete |
| KHR_materials_specular | ✅ Complete |
| KHR_materials_transmission | ✅ Complete |
| KHR_materials_unlit | 🚧 Planned |
| KHR_materials_variants | 🚧 Planned |
| KHR_materials_volume | ✅ Partial 2 |
| KHR_mesh_quantization | ❌ Not supported |
| KHR_texture_basisu | ❌ Not supported |
| KHR_texture_transform | 🚧 Planned |
| KHR_xmp_json_ld | ❌ Not supported |
[1] Spotlight cone falloff is ignored.
[2] Thickness is not supported by the MaterialX glTF PBR implementation.
Apple AR Quick Look compatibility
I have no intention of implementing workarounds for Apple's incomplete USD support. usd_from_gltf or Apple's USDZ Tools should be used instead.
License
Copyright 2022 Pablo Delgado Krämer
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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