/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \module QtGui
    \title Qt GUI C++ Classes
    \ingroup modules
    \qtvariable gui

    \brief The Qt GUI module provides the basic enablers for graphical
    applications written with Qt.

    The Qt GUI module provides classes for windowing system
    integration, event handling, OpenGL and OpenGL ES integration,
    Vulkan integration, 2D graphics, imaging, fonts and typography.
    These classes are used internally by Qt's user interface technologies
    and can also be used directly, for instance to write applications using
    low-level OpenGL ES graphics APIs.

    To include the definitions of the module's classes, use the
    following directive:

    \snippet code/doc_src_qtgui.pro 0

    If you use \l qmake to build your projects, \l{Qt GUI} is included by
    default. To disable Qt GUI, add the following line to your \c .pro file:

    \snippet code/doc_src_qtgui.pro 1

*/

/*!
    \page qtgui-index.html
    \title Qt GUI

    The Qt GUI module provides classes for windowing system
    integration, event handling, OpenGL and OpenGL ES integration, 2D
    graphics, basic imaging, fonts and text. These classes are used
    internally by Qt's user interface technologies and can also be
    used directly, for instance to write applications using low-level
    OpenGL ES graphics APIs.

    For application developers writing user interfaces, Qt provides
    higher level API's, like Qt Quick, that are much more suitable
    than the enablers found in the Qt GUI module.

    \section1 Getting Started

    To include the definitions of the module's classes, use the
    following directive:

    \snippet code/doc_src_qtgui.pro 0

    If you use \l qmake to build your projects, Qt GUI is included by
    default. To disable Qt GUI, add the following line to your \c .pro file:

    \snippet code/doc_src_qtgui.pro 1

    \section1 Application Windows

    The most important classes in the Qt GUI module are
    QGuiApplication and QWindow. A Qt application that wants to show
    content on screen, will need to make use of these. QGuiApplication
    contains the main event loop, where all events from the window
    system and other sources are processed and dispatched. It also
    handles the application's initialization and finalization.

    The \l QWindow class represents a window in the underlying
    windowing system. It provides a number of virtual functions to
    handle events (\l {QEvent}) from the windowing system, such as
    touch-input, exposure, focus, key strokes and geometry changes.



    \section1 2D Graphics

    The Qt GUI module contains classes for 2D graphics, imaging, fonts
    and advanced typography.

    A \l QWindow created with the surface type \l
    {QSurface::RasterSurface} can be used in combination with \l
    {QBackingStore} and \l {QPainter}, Qt's highly optimized 2D vector
    graphics API. QPainter supports drawing lines, polygons, vector
    paths, images and text. For more information, see \l{Paint
    System} and \l {Raster Window Example}.

    Qt can load and save images using the \l QImage and \l QPixmap
    classes. By default, Qt supports the most common image formats
    including JPEG and PNG among others. Users can add support for
    additional formats via the \l QImageIOPlugin class. For more
    information, see \l {Reading and Writing Image Files}

    Typography in Qt is done with \l QTextDocument which uses the \l
    QPainter API in combination with Qt's font classes, primarily
    QFont. Applications that prefer more low-level APIs  to text
    and font handling, classes like QRawFont and QGlyphRun can be
    used.



    \section1 OpenGL and OpenGL ES Integration

    QWindow supports rendering using OpenGL and OpenGL ES, depending
    on what the platform supports. OpenGL rendering is enabled by
    setting the QWindow's surface type to QSurface::OpenGLSurface,
    choosing the format attributes with QSurfaceFormat, and then
    creating a QOpenGLContext to manage the native OpenGL context. In
    addition, Qt has QOpenGLPaintDevice, which enables the use of
    OpenGL accelerated QPainter rendering, as well as convenience
    classes that simplify the writing of OpenGL code and hides the
    complexities of extension handling and the differences between
    OpenGL ES 2 and desktop OpenGL. The convenience classes include
    QOpenGLFunctions that lets an application use all the OpenGL ES 2
    functions on desktop OpenGL without having to manually resolve the
    OpenGL function pointers, thus allowing cross-platform development
    of applications targeting mobile or embedded devices, and some
    classes that wrap native OpenGL functionality in a simpler Qt API:

    \list
    \li QOpenGLBuffer
    \li QOpenGLFramebufferObject
    \li QOpenGLShaderProgram
    \li QOpenGLTexture
    \li QOpenGLDebugLogger
    \li QOpenGLTimerQuery
    \li QOpenGLVertexArrayObject
    \endlist

    Finally, in order to provide better support for the newer versions
    (3.0 and higher) of OpenGL, a versioned function wrapper mechanism
    is also available: The QOpenGLFunction_N_N family of classes
    expose all the functions in a given OpenGL version and profile,
    allowing easy development of desktop applications relying on
    modern, desktop-only OpenGL features.

    For more information, see the \l {OpenGL Window Example}.

    The Qt GUI module also contains a few math classes to aid with the
    most common mathmatical operations related to 3D graphics. These
    classes include \l {QMatrix4x4}, \l {QVector4D} and \l {QQuaternion}

    A \l {QWindow} created with the \l {QSurface::OpenGLSurface} can
    be used in combination with \l QPainter and \l QOpenGLPaintDevice
    to have OpenGL hardware accelerated 2D graphics, by sacrificing
    some of the visual quality.



    \section1 Vulkan Integration

    Qt 5.10 added support for \l {Vulkan}. This requires
    the presence of the \l{LunarG Vulkan SDK}.

    On Windows, the SDK sets the environment variable \c {VULKAN_SDK},
    which will be detected by the \c {configure} script.

    On Android, Vulkan headers were added in API level 24 of the NDK.

    Relevant classes:

    \list
    \li QVulkanDeviceFunctions
    \li QVulkanExtension
    \li QVulkanFunctions
    \li QVulkanInfoVector
    \li QVulkanInstance
    \li QVulkanWindow
    \li QVulkanWindowRenderer
    \endlist

    For more information, see the \l{Hello Vulkan Widget Example}
    and the \l {Hello Vulkan Window Example}.

    \section1 Qt GUI Prior to Qt 5.0

    Prior to Qt 5.0, the Qt GUI module was the monolithic container
    for all things relating to graphical user interfaces in Qt, and
    included the Qt widget set, the item views, the graphics view
    framework and also printing. Starting Qt 5, these classes have
    been moved to the Qt Widgets module. Printing has been
    moved to the Qt Print Support module.  Please note that these
    modules can be excluded from a Qt installation.

    Qt GUI now contains only a small set of enablers, which are generally
    useful for all graphical applications.

    \section1 Drag and Drop

    More info in \l{Drag and Drop}

    \section1 Licenses and Attributions

    Qt GUI is available under commercial licenses from \l{The Qt Company}.
    In addition, it is available under free software licenses. Since Qt 5.4,
    these free software licenses are
    \l{GNU Lesser General Public License, version 3}, or
    the \l{GNU General Public License, version 2}.
    See \l{Qt Licensing} for further details.

    Furthermore, Qt GUI in Qt \QtVersion may contain third-party
    modules under following permissive licenses:

    \generatelist{groupsbymodule attributions-qtgui}

    \section1 Reference
    \list
    \li \l{Qt GUI C++ Classes}
        \list
        \li \l{Event Classes}
        \li \l{Painting Classes}
        \li \l{Rendering in 3D}
        \endlist
    \endlist
 */
