// 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 Migrate Qt OpenGL to Qt 6.

    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.
*/
