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>/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

All primvars are supported, st/uv is accessible through the built-in uv attribute on the mesh
Support for the displayColor primvar
Subdivision settings
Mesh
Volume
Points

SPrim Support

Distant Light
Sphere Light
Disk Light
Rect Light
Cylinder Light
Dome Light
Arnold shaders are supported, the info:id attribute is used to determine the shader type
UsdPreviewSurface is translated to Arnold shaders
Materials
Lights

BPrim Support

Render Buffer
OpenVDB Asset

Point Instancer, including nesting of Point Instancers
Selection in USD View and other applications using the primId AOV
Displaying the Color, Depth and PrimID AOVs
Motion Blur

Deformation
Transformation

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 HdExtComputation and UsdSkel computation via the render delegate
No of physical camera parameters
No coordsys support

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
UsdGeomPoints
UsdGeomCube
UsdGeomSphere
UsdGeomCone
UsdGeomCylinder
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 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