HdCycles

A USD/Hydra RenderDelegate plugin that adds support for the Cycles renderer (Blender's physically based path tracer) to any client.

Its goal is to render a one-to-one representation of a USD scene with Cycles.

This requires three components:

• hdCycles (Cycles Hydra Delegate)
• ndrCycles (Cycles Node Definition Registry)
• usdCycles (Cycles USD Schema)

The first two of which are implemented in this repository.

Building

Requirements

• Cycles standalone libraries and headers Source
• USD 19.xx+
  • Most of the USD requirements need to be available (OpenSubdiv, PNG, OpenImageIO, OpenVDB ...)

Linux

Make sure to build cycles with -DCMAKE_POSITION_INDEPENDENT_CODE=ON

mkdir build
cd build

cmake -DUSD_ROOT=/path/to/usd/root               \
  -DCYCLES_ROOT=/path/to/cycles                  \
  -DCYCLES_LIBRARY_DIR=/path/to/cycles/build/lib \
  -DCYCLES_INCLUDE_DIRS=/path/to/cycles/src      \
  ..

Windows

mkdir build
cd build

cmake -DUSD_ROOT=C:/path/to/usd/root               \
  -DCYCLES_ROOT=C:/path/to/cycles                  \
  -DCYCLES_LIBRARY_DIR=C:/path/to/cycles/build/lib \
  -DCYCLES_INCLUDE_DIRS=C:/path/to/cycles/src      \
  ..

Installation

Both the hdCycles plugin and the ndrCycles plugin must be added to the PXR_PLUGINPATH_NAME environment variable.

For example:

PXR_PLUGINPATH_NAME = %HDCYCLES_INSTALL_DIR%/plugin/usd/ndrCycles/resources;%HDCYCLES_INSTALL_DIR%/plugin/usd/hdCycles/resources

Notes

usdCycles schema

To allow a full 1:1 representation of a Blender Cycles scene, we need to store Cycles specific settings in USD. To do this, we created usdCycles. More information can be found in that repo.

To prevent DCC's and tooling to not have to implement the full dependency chain of hdCycles, the usdCycles schema definition has been split into it's own repo (and rez package). Found Here!.

Building hdCycles without usdCycles is possible, but results in a very limited subsection of Cycles settings.

For full usdCycles schema support, please build with usdCycles.

Stability & Performance

The codebase is in active development and should be deemed as unstable.

The primary priority is feature-completness. Stability and performance will be addressed in the future.

Please file issues for any question or problem.

Materials

Currently Cycles materials are exported through custom additions to the Blender USD Exporter.

Of note, hdCycles expects a flattened Cycles Material graph, with no groups or reroute nodes. It also does not use the Material Output node. Instead it favours the USD/Hydra material binding inputs.

For now only BSDF nodes are registered in the ndr plugin.

Lights

Currently light node networks are unsupported via USD Lux. A proposal from Pixar plans to fix these limitations. It is planned to support proper world and light materials once the proposal is accepted.

Feature Set

Currently supported features:

License

This project is licensed under the Apache 2 license.

For a full list of third-party licenses see: LICENSE-THIRDPARTY

Attribution

This could not have been made without the help and reference of the following open source projects:

• USD - Copyright 2016 Pixar Animation Studios - Apache 2.0 License
• arnold-usd - Copyright 2020 Autodesk - Apache 2.0 License
• arnold-usd - Copyright 2019 Luma Pictures - Apache 2.0 License
• RadeonProRenderUSD - Copyright 2020 Advanced Micro Devices, Inc - Apache 2.0 License
• Mikktspace - Copyright 2011 Morten S. Mikkelsen - Zlib
• GafferCycles - Copyright 2018 Alex Fuller - BSD 3-Clause License