UsdQt

Qt components for building custom USD tools

Current Branch Compatibility

• master : USD 19.07
  • Should be compatible with the post-19.07 USD dev branch up to and including b6ccb4e5
• dev : USD 19.11+

Project Goals

The UI components that make up usdview are good reference for functionality, but they’re purpose-built for the application, and are implemented in ways that make them difficult to decouple from it.

This project is meant to provide application components that can provide similar (as well as new) functionality, to allow for ad-hoc use in custom tools.

Longer-term, we hope this project will grow to the point that it can be used to build a fully-functional usdview application.

Contents

This project contains a mixture of pure Python and wrapped C++ code. All Qt code is written in pure Python to avoid the need to link against Qt and get moc involved in the build process. This may change in the future if deemed beneficial/necessary.

The compiled extension module provides a set of helper classes that interface with the USD C++ API to accelerate certain USD queries, operations, etc.

Installed Python Packages

• pxr.UsdQt: Contains various Qt item data models, helper classes for building UIs, and some other USD and Qt utility code. The _bindings module currently contains all of the wrapped classes from the compiled extension module.
• pxr.UsdQtEditors: Contains various Qt UI elements. These range from purpose-built display/editor widgets to an extensible outliner UI that also serves as a good usage example for many of the utilities in pxr.UsdQt.
• treemodel: Contains a generic item tree and a Qt item model mixin that uses it, which are used by some of the classes in pxr.UsdQt.

Building/Installation

The recommended (and currently only tested) way to build the project is using CMake. A setup.py file is provided as well, but it has not been tested with the most recent updates.

Build Requirements

• Boost Python
• USD
• TBB

CMake Options

• INSTALL_PURE_PYTHON (BOOL): Whether to install the pure Python code in addition to the compiled extension module. This defaults to ON.

A note about UsdQt.py and UsdQtEditors.py

You may notice that the source contains UsdQt.py and UsdQtEditors.py files alongside the package source directories. These are "shim" modules that we've found to be very useful during the development of this project, as they enable us to do more rapid editing and testing on the pure Python code without needing to run a CMake build and install between each minor edit. They are not installed with the project.

Using UsdQt with the USD Python bindings

UsdQt uses pkg_resources (or pkgutil if the former is not available) to declare pxr as a "namespace package" at runtime. This allows it to overlay its sub-packages onto the same pxr package used by the USD Python bindings, so that the two projects can be installed in separate locations and still work together.

However, the USD Python bindings do not currently declare pxr as a namespace package in a symmetrical way, which unfortunately means that if the USD Python bindings are listed before UsdQt on the module search path, you will not be able to import pxr.UsdQt. Thus, unless/until the USD Python bindings are updated to declare pxr as a namespace package, you will need to make sure UsdQt is listed before the USD Python bindings on the module search path.

More information on namespace packages in Python can be found in the docs for pkg_resources and pkgutil:

https://setuptools.readthedocs.io/en/latest/pkg_resources.html#namespace-package-support

https://docs.python.org/2/library/pkgutil.html

Using an alternate Qt API

UsdQt expects its underlying Qt API to adhere to the Qt5 module layout, and uses the PySide2 API.

By default, it will attempt to import and use PySide2. This can be overridden by setting the PXR_QT_PYTHON_BINDING environment variable to the name of the API package/module you wish to use instead.

This works with the popular Qt.py project.

Planned Future Additions

Here are some of the ideas we've had for future additions to the project. We're happy to consider new suggestions as well.

• UI components for authoring and working with USD variant sets.
• An adaptor class to translate USD notices to Qt signals.
• A QSyntaxHighlighter class for .usda syntax.
• A Hydra viewport widget.