Qt 5.11 Brings New Accessibility Backend on Windows

Accessibility technology encompasses assistive tools such as screen readers, magnifiers and braille displays, as well as APIs and frameworks that allow applications to expose elements of their UI to such tools.

While some UI widgets provided by the operating system may already be prepared to provide content and metadata to assistive tools, Qt renders UI elements itself. This approach requires a way to expose information about these elements to accessibility frameworks, which would otherwise perceive the applications as sets of empty windows.

To expose information about UI elements on Windows, Qt relied on the legacy Microsoft Active Accessibility framework (MSAA), until Qt 5.10. However, proper framework support was lacking in some areas, and nowadays MSAA has been superseded by a new framework and its use is no longer recommended for new applications.

With release 5.11 we will replace the MSAA accessibility backend with a new implementation based on the more modern Microsoft UI Automation, which superseded MSAA as the de facto standard for accessibility on the Windows platform. UI Automation has been available in all Windows releases since RTM versions of Windows 7 and Server 2008, as well as provided with system updates on Windows XP, Vista and Server 2003.

Since the accessibility changes in Qt 5.11 are internal, existing accessible applications are not expected to require any changes to utilize the improved functionality provided by UI Automation. Compatibility with MSAA-only assistive tools is maintained by bridge components built in the UI Automation framework itself.

One area where immediate improvement resulting from the new approach can be perceived is in the control of Qt-based applications using the built-in virtual keyboard in touchscreen-based Windows computers, like the Microsoft Surface line. In Qt 5.10, compatibility with some UI widgets was limited and events like the automatic showing and hiding of the virtual keyboard were not supported. With Qt 5.11, the same level of functionality available to applications based on native Windows widgets should be expected.

Also, the new UI Automation support in Qt may become useful for application testing, since it can provide metadata and programmatic control of UI elements, which can be leveraged by automated test suites and other tools.

We invite users to test the new accessibility functionality, and to give us feedback by writing to the mailing lists and reporting bugs.