usdOpenAssetIOResolver

A USD AR2 plugin that hosts OpenAssetIO.

Note: This project is in a proof-of-concept phase, to explore compatibility between the two ecosystems. It is in no way feature complete or optimized for performance.

Provides the capability to resolve entity references through any OpenAssetIO enabled manager without the need for USD specific programming.

Special attention has been made to ensure that this plugin can be used in existing USD documents, preserving the ArDefaultResolver search-path based resolution behaviour for path based references.

Example

def "ParkingLot"
{
    def "ParkingLot_Floor_1" (
        references = @bal:///floor@</ParkingLot_Floor>
    )
    {
    }
}

An asset management system's OpenAssetIO entity reference can be used anywhere the @<ref>@ syntax is supported. In this case, a reference to an asset managed by our test manager, the Basic Asset Library is used.

How entities are resolved

When USD creates an instance of the resolver, The default OpenAssetIO manager will be initialized - see the docs for more on this mechanism.

The plugin then resolves the LocatableContentTrait for each string that the configured manager claims as a reference, and passes this path on for loading.

Note: The LocatableContentTrait dictates that the resolved location should be an absolute path, and so the default USD search path mechanism will have no effect on the resolved result.

Asset variation based on the parent asset (anchorAssetPath) has not yet been implemented, but will be added at a later date.

Project status

This resolver is currently in prototype stage, it has several key limitations.

• Python is currently required whilst the remaining work porting the core OpenAssetIO API to C++ is completed.

• managementPolicy is not checked, and so the configured manager will always be queried for each reference during stage composition.

• Only the LocatableContentTrait is resolved. File extensions and file modification times will are based on file-based fallbacks if possible, and return sensible defaults if not. Many potentially expected structures (ie, AssetInfo), will be empty.

• There is no USD locale set in the OpenAssetIO context.

• Only read workflows are supported. Methods related to writing data fall back to the ArDefaultResolver.

• Error handling is as yet quite primitive, an incomplete configuration may provide cryptic and hard to understand errors. You are advised to be extra sure all your environment variables are setup correctly.

• The implementation has in not been optimized for performance.

Dependencies

OpenAssetIO (1.0.0-beta.2.0)

The OpenAssetIO libary is available pre-built for some common platforms. These are available here.

Alternatively, OpenAssetIO can be built from source. The steps to do this can be found here.

USD (22.11)

Install USD by whatever means, the most straightforward being to check out the repo and use the provided build_usd.py script. If you elect to install USD to a custom location, remember to take a note of it, so you can pass it to CMAKE_PREFIX_PATH below.

The specific versions listed for these dependencies are simply the versions that the resolver was tested against during development, it's possible other versions will function.

Building

cmake -S . -B build -DCMAKE_PREFIX_PATH=/path/to/openassetio/dist/;/path/to/USD
cmake --build build
cmake --install build

Running

To enable the resolver, before running any USD application, you must set the PXR_PLUGINPATH_NAME environment variable to point to plugInfo.json.

You also need to configure OpenAssetIO with a manager. Use the OPENASSETIO_DEFAULT_CONFIG variable.

export PXR_PLUGINPATH_NAME=$(pwd)/build/dist/resources/plugInfo.json
export OPENASSETIO_DEFAULT_CONFIG=path/to/config/openassetio.conf
usdcat yourUsdFile.usd

Note

Depending on you install mechanism, you may also need to extend your system paths (eg LD_LIBRARY_PATH and PYTHONPATH) to reference OpenAssetIO and Usd.

For an example of this, and a whole build/run configuration, see test.yml, which utilizes the openassetio-build and ci-vfxall Docker containers to manage dependencies and install/run the resolver.

Debug logging

Before running any USD application

export TF_DEBUG=OPENASSETIO_RESOLVER
export OPENASSETIO_LOGGING_SEVERITY=1

To enable debug logging from the resolver.

Testing

To run tests, once built, from the project root:

python -m pip install -r requirements.txt
python -m pytest

Note

Refer to the Running section for the environmental prerequisites to run these tests. The tests will set OPENASSETIO_DEFAULT_CONFIG appropriately, and unless otherwise defined, attempt to set PXR_PLUGINPATH_NAME if the standard build directory was used.

A note on Python

One of the goals of OpenAssetIO is to provide a flexible API surface for a variety of production use cases. We have seen many situations where asset management code is only present in interpreted languages such as Python.

Python however, has a huge performance impact due to its use of the GIL.

There has been significant interest in the ability to use Python-based code within the USD context. OpenAssetIO allows managers to write their code in either Python, or C/C++ depending on the performance characteristics required.

This plugin facilitates code in either language to be used within USD.

We fully understand the concerns this may bring, especially in the content of real-world production at scale, and plan to tackle this on several fronts:

• OpenAssetIO operates without Python in the case that C/C++ implementations of required methods are provided.
• OpenAssetIO will provide an (optional) out-of-process Python interpreter to avoid UI thread locking when the host tool uses python for its user interface.
• OpenAssetIO allows for mixed implementations, such that high call volume methods such as resolve can be written in C++, and low volume methods (eg: register) can be implemented in Python.