Changes to Qt GUI
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 GUI, and provide guidance to handle them.
Implicit construction of a QBitmap from a QPixmap is no longer supported. The constructor and assignment operator have been made explicit and marked as deprecated. Use the new static factory function fromPixmap instead.
QKeyCombination is a new class for storing a combination of a key with an optional modifier. It should be used as a replacement for combining values from the Qt::Key enum with a modifier in a type-safe way.
We recommend migrating code that currently uses operator+() to combine a key and modifiers, as future C++ standards are likely to declare arithmetic operations between unrelated enumeration types as illegal. Use operator|(), and change APIs that expect an
int to expect a QKeyCombination instead.
Existing APIs that expect an
int for a key combination can be called using QKeyCombination::toCombined().
The QFontDatabase class has now only static member functions. The constructor has been deprecated. Instead of e.g.
The numerical values of the QFont::Weight enumerator have been changed to be in line with OpenType weight values. QFont::setWeight() expects an enum value instead of an
int, and code that calls the setter with an integer will fail to compile. To continue to use old integer values, use QFont::setLegacyWeight().
The setRange() method is no longer marked as virtual.
With the introduction of Qt RHI as the rendering foundation in Qt, most classes prefixed by
QOpenGL have been moved into the Qt OpenGL module.
More details can be found in the Qt OpenGL porting guide.
One notable exception is the class QOpenGLContext, which still resides in Qt GUI.
In addition, the class QOpenGLWidget has been moved to a new module, named Qt OpenGL Widgets.
On Windows, ANGLE, a third-party OpenGL ES to Direct 3D translator, is no longer included in Qt. This means Qt::AA_UseOpenGLES and the environment variable
QT_OPENGL=angle no longer have 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 run time. However, the alternative of using 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 the default choice is Direct 3D, therefore the removal of ANGLE is alleviated by having support for graphics APIs other than OpenGL as well.
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