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// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\page opengl-changes-qt6.html
\title Changes to Qt OpenGL
\ingroup changes-qt-5-to-6
\brief QOpenGL classes migrated, QOpenGLWidget class has been moved to Qt OpenGL Widgets.
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 \l{Qt OpenGL}, and provide
guidance to handle them.
\section1 Deprecated classes removed
The \l{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 \c{QGL}.
\section1 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 \l{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 \l{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 \l QOpenGLContext, which still resides in
Qt Gui.
\section1 The QOpenGLWidgets class
Another exception is the \l QOpenGLWidget class. This has been moved to a new
module named \c{Qt OpenGL Widgets} and should be included from there.
\section1 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
\l{Rendering via the Qt Rendering Hardware Interface}{RHI rendering documentation}
for more details.
\section1 Removal of ANGLE
On Windows, ANGLE, a third-party OpenGL ES to Direct 3D translator, is no
longer included in Qt 6. This means \c Qt::AA_UseOpenGLES and the
environment variable \c{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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