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/****************************************************************************
**
** Copyright (C) 2022 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
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** 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.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page qtgui-overview.html
\title Qt GUI Overview
\brief An overview of the Qt GUI module.
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 but can also be used directly, for example to write
applications using low-level OpenGL ES graphics APIs.
For application developers writing user interfaces, Qt provides higher level
APIs, like Qt Quick, that are much more suitable than the enablers found in
the Qt GUI module.
\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 has to use
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 can use classes
like QRawFont and QGlyphRun.
\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. This enables
cross-platform development of applications targeting mobile or embedded
devices, and provides 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, 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 that rely 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 mathematical 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 GUI has support for the \l {Vulkan} API. Qt applications require 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 Drag and Drop
Qt GUI includes support for drag and drop. The \l{Drag and Drop} overview
has more information.
*/
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