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

Building and installation

Please follow the building instructions. To use the components, provided you installed in , set the following environment variables:

• Add /procedural to ARNOLD_PLUGIN_PATH for the Arnold usd procedural.
• Add /lib/python to PYTHONPATH for the Python schema bindings.
• Add /plugin to PXR_PLUGINPATH_NAME for the Hydra render delegate and the Node Registry plugin.
• Add /lib/usd to PXR_PLUGINPATH_NAME for the USD schemas.
• Add /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

• SPrim Support

• BPrim Support

• 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

• Rendervar support

• USD Skel support
• HdExtComputation support for polymeshes
• Render Settings via the Render Delegate

• Deep render products
• Basis Curves support

• Pause and Resume API
• Half and Double types

• 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
• 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

Limitations

• No nodes registered for

• 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

• USD Lux primitives

• USD native shaders

• 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

• Nurbs

Scene delegate

The scene delegate supports the following features:

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

• 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 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
• Raymond Kreppene
• Julien Deboise
• Jerry Gamache
• Tom Minor
• Cyril Pichard
• Libby O'Meara