Changes to Qt OpenGL

Qt 6 is a result of the conscious effort to make the framework more efficient and easy to use.

We try to maintain binary and source compatibility for all the public APIs in each release. But some changes were inevitable in an effort to make Qt a better framework.

In this topic we summarize those changes in Qt OpenGL, and provide guidance to handle them.

Deprecated classes removed

The Qt OpenGL module was deprecated for the life time of Qt 5, and the classes it contained have been removed in Qt 6.

This refers specifically to the classes prefixed by QGL.

QOpenGL classes migrated

In Qt 5, a replacement set of OpenGL-support classes were added to Qt Gui. This was in order to support OpenGL as the cross-platform graphics API that served as foundation for graphics in Qt.

In Qt 6, these have been migrated to the Qt OpenGL module. They are still usable and fully supported for applications depending on OpenGL directly. However, they are no longer considered foundational, since Qt has been extended to support other graphics APIs in its foundation, such as Direct3D, Metal and Vulkan.

Existing application code will largely continue working, but should now include Qt OpenGL in project files, as well as include the headers if these were previously included indirectly through Qt Gui.

Note: A notable exception is QOpenGLContext, which still resides in Qt Gui.

QOpenGLWidgets

Another exception is the QOpenGLWidget class. This has been moved to a new module named Qt OpenGL Widgets and should be included from there.

Selecting the OpenGL backend for RHI

In addition to adjusting project files and including headers, the application should also manually set the rendering backend to OpenGL in order to use this functionality when working with Qt Quick. By default, Qt will use the most appropriate graphics API on the target platform. See the RHI rendering documentation for more details.

Removal of ANGLE

On Windows, ANGLE, a third-party OpenGL ES to Direct 3D translator, is no longer included in Qt 6. This means Qt::AA_UseOpenGLES and the environment variable QT_OPENGL=angle no longer has any effect. In dynamic OpenGL builds there is no automatic fallback to ANGLE in case OpenGL-proper fails to initialize. For QWindow or QWidget based applications using OpenGL directly, for example via QOpenGLWidget, this means that OpenGL-proper is the only option at runtime. However, the use of a pure software OpenGL implementation, such as Mesa llvmpipe that is shipped with the pre-built Qt packages, is still available.

For Qt Quick and Qt Quick 3D applications, Qt 6 introduces support for Direct 3D 11, Vulkan, and Metal, in addition to OpenGL. On Windows, Qt 6 defaults to Direct 3D, therefore the effect of the removal of ANGLE is lessened by the addition of support to other graphics APIs.

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