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This repository contains a set of components and tools to use theArnold renderer with Pixar'sUniversal 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 thecontribution guidelines.

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

• Add<arnold-usd_dir>/procedural toARNOLD_PLUGIN_PATH for the Arnoldusd procedural.
• Add<arnold-usd_dir>/lib/python toPYTHONPATH for the Python schema bindings.
• Add<arnold-usd_dir>/plugin toPXR_PLUGINPATH_NAME for the Hydra render delegate and the Node Registry plugin.
• Add<arnold-usd_dir>/lib/usd toPXR_PLUGINPATH_NAME for the USD schemas.
• Add<arnold-usd_dir>/lib toLD_LIBRARY_PATH on Linux,PATH on Windows andDYLD_LIBRARY_PATH on Mac.

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, theinfo: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 theprimId 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 variableUSD_ASSIGN_PROTOTYPES_DETERMINISTICALLY should fix this issue.

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

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. attributeprimvars:arnold:subdiv_iterations in a UsdGeomMesh)
• Support for any Arnold node type (e.g. USD type ArnoldSetParameter gets rendered as arnoldset_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

LimitationsCurrently unsupported:

• Nurbs

The scene delegate supports the following features:

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

LimitationsCurrently unsupported:

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

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

• Luma Pictures'usd-arnold
• RodeoFX'sOpenWalter
• 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