Arnold USD

This repository contains a set of components and tools to use the Arnold renderer with Pixar's Universal Scene Description. Notably, the following components are included:

• Hydra render delegate
• Arnold procedural for USD
• Schemas to describe an Arnold scene in USD

Contributions are welcome! Please make sure to read the contribution guidelines.

Building and installation

Please follow the building instructions. To use the components, provided you installed in <arnold-usd_dir>, set the following environment variables:

• Add <arnold-usd_dir>/procedural to ARNOLD_PLUGIN_PATH for the Arnold usd procedural.
• Add <arnold-usd_dir>/lib/python to PYTHONPATH for the Python schema bindings.
• Add <arnold-usd_dir>/plugin to PXR_PLUGINPATH_NAME for the Hydra render delegate and the Node Registry plugin.
• Add <arnold-usd_dir>/lib/usd to PXR_PLUGINPATH_NAME for the USD schemas.
• Add <arnold-usd_dir>/lib to LD_LIBRARY_PATH on Linux, PATH on Windows and DYLD_LIBRARY_PATH on Mac.

Hydra Render Delegate

The render delegate currently supports the following features:

• RPrim Support
  • Mesh
    • All primvars are supported, st/uv is accessible through the built-in uv attribute on the mesh
    • Normal primvars are translated to Arnold built-in attributes
    • Support for the displayColor primvar
    • Subdivision settings
  • Volume
  • Points
• SPrim Support
  • Materials
    • Arnold shaders are supported, the info:id attribute is used to determine the shader type
    • UsdPreviewSurface is translated to Arnold shaders
  • Lights
    • Distant Light
    • Sphere Light
    • Disk Light
    • Rect Light
    • Cylinder Light
    • Dome Light
• BPrim Support
  • Render Buffer
  • OpenVDB Asset
• Point Instancer, including nesting of Point Instancers and instancing Volumes
• Selection in USD View and other applications using the primId AOV
• Displaying the Color, Depth and PrimID AOVs
• Motion Blur
  • Deformation
  • Transformation
• USD Skel support
• HdExtComputation support for polymeshes
• Render Settings via the Render Delegate
  • Sampling parameters
  • Threading parameters
  • Ignore parameters
  • Profiling and logging parameters
  • Switching between CPU and GPU mode seamlessly
  • Default values are configurable through environment variables for most of these parameters

Limitations

• Crash on linux at startup with usdview : Currently, the arnold library needs to be ld-preloaded to avoid the crash, e.g. LD_PRELOAD=/path_to_arnold/bin/libai.so usdview scene.usda
• No motion blur support for the Point Instancer attributes
• Can’t preview arbitrary primvar AOVs
• No basisCurves
• No field3d volume grids
• Not all the parameters are accessible through the render settings
  • Texture Cache size
  • Texture generation parameters (automip, autotile)
• No normal maps on the UsdPreviewSurface
• Only converging renders are supported (ie. it’s not possible to block the viewport until the render finishes)
• No of physical camera parameters
• No coordsys support
• No per face material assigments
• Can't open textures from usdz files
• Only 8 bit precision for the rendered buffers

Node Registry Plugin

The Node Registry plugin supports the current features:

• Registering Sdr nodes for every built-in shader and custom shader
  • Setting up the asset URI either to <built-in> or to the path of the shader library providing the shader.
  • Creating all parameters.

Limitations

• No nodes registered for
  • Shapes
  • Lights
  • Filters
  • Drivers
• No node is registered for the options node
• Metadata is not converted for any node

Arnold USD Procedural

The procedural supports the following features:

• USD shapes
  • UsdGeomMesh
  • UsdGeomCurves
  • UsdGeomBasisCurves
  • UsdGeomPoints
  • UsdGeomCube
  • UsdGeomSphere
  • UsdGeomCone
  • UsdGeomCylinder
  • UsdPointInstancer
  • UsdVolume
  • primvars are translated as user data
• USD Lights
  • UsdLuxDistantLight
  • UsdLuxDomeLight
  • UsdLuxDiskLight
  • UsdLuxSphereLight
  • UsdLuxRectLight
  • UsdLuxGeometryLight
  • Support for textured lights (dome and rectangle)
• USD native shaders
  • UsdPreviewSurface
  • UsdPrimVar*
  • UsdUVTexture
• Arnold shaders supported as UsdShade nodes (where info:id gives the shader type)
• Support for any additional Arnold parameter in USD nodes (e.g. attribute primvars:arnold:subdiv_iterations in a UsdGeomMesh)
• Support for any Arnold node type (e.g. USD type ArnoldSetParameter gets rendered as arnold set_parameter node)
• Support for multi-threaded parsing of a USD file

Limitations Currently unsupported:

• Nurbs
• Cameras
• Connections to input attribute channels

Acknowledgments

• Luma Pictures' usd-arnold
• RodeoFX's OpenWalter
• Ben Asher
• Sebastien Blaineau-Ortega
• Chad Dombrova
• Guillaume Laforge
• Julian Hodgson
• Thiago Ize
• Pal Mezei
• Paul Molodowitch
• Nathan Rusch
• Frederic Servant
• Charles Flèche