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
    • UsdTransform nodes
    • Per-face material assignments
  • Lights
    • Distant Light
    • Sphere Light
    • Disk Light
    • Rect Light
    • Cylinder Light
    • Dome Light
    • Shaping Parameters
  • Light and Shadow Linking
  • ExtComputation
  • HdCamera
    • Perspective projection
• 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
  • Using motion vectors on Points
• Rendervar support
  • Raw Rendervars
  • Primvar Rendervars
  • LPE Rendervars
  • SourceName parameter
  • DataType parameter
  • Setting up Arnold filters via "arnold:filter_type"
    • Filtering parameters via "arnold:param_name"
    • Filtering parameters via "arnold:filter_node_entry:param_name"
• 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
• Deep render products
• Basis Curves support
  • Remapping uv/st to uvs
  • Remapping normals to orientations
• Pause and Resume API
• Half and Double types

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
• Ignoring primvars:arnold:basis on curves
• No support for periodic or pinned curves
• No field3d volume grids
• 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 coordsys support
• Can't open textures from usdz files
• No support for orthographic cameras
• Face-varying primvars are not correctly interpolated
• Possible flicker when using cryptomatte: this is due to the prototypes not being named in a deterministic way. Setting the environment variable USD_ASSIGN_PROTOTYPES_DETERMINISTICALLY should fix this issue.

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 Geom primitives
  • UsdGeomMesh
  • UsdGeomCurves
  • UsdGeomBasisCurves
  • UsdGeomPoints
  • UsdGeomCube
  • UsdGeomSphere
  • UsdGeomCone
  • UsdGeomCylinder
  • UsdPointInstancer
  • UsdVolume
  • UsdGeomCamera
  • primvars are translated as user data
• USD Lux primitives
  • UsdLuxDistantLight
  • UsdLuxDomeLight
  • UsdLuxDiskLight
  • UsdLuxSphereLight
  • UsdLuxRectLight
  • UsdLuxGeometryLight
  • Support for textured lights (dome, rectangle and geometry)
• USD native shaders
  • UsdPreviewSurface
  • UsdPrimVar*
  • UsdUVTexture
  • Per channel connections via adapter nodes
  • UsdTransform nodes
• UsdSkel support
• 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
• UsdRender schema support
• Half and Double types
• Usd Purpose
• Light Linking
• Multiple frames in a single file

Limitations Currently unsupported:

• Nurbs

Arnold USD Procedural

The scene delegate supports the following features:

• Arnold built-in shapes
• Render time procedurals shipped with the core

Limitations Currently unsupported:

• Custom procedurals
• Lights
• Displaying Arnold schemas with non-Arnold render delegates

Testsuite

Running the arnold-usd testsuite requires the latest version of Arnold, that can be downloaded at https://www.arnoldrenderer.com/arnold/download/ It is not supported for older versions of Arnold.

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