// Copyright (C) 2019 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
\page qpa.html
\title Qt Platform Abstraction

The Qt Platform Abstraction (QPA) is the main platform abstraction layer in Qt.

The API can be identified by the \c QPlatform* class prefix, and is used
for implementing higher level classes typically found in \l{Qt GUI}, e.g.
\c QPlatformWindow for window system integration exposed through QWindow,
or \c QPlatformTheme for deeper platform theming and integration, exposed
through QStyleHint and QStyle.

There are no source or binary compatibility guarantees for the QPA classes,
meaning that the API is only guaranteed to work with the Qt version
it was developed against. API changes will however only be made in minor
releases. (5.1, 5.2, and so on.)

\section1 API Overview

\list
\li Window system integration
    \list
    \li QPlatformIntegration
    \li QPlatformAccessibility
    \li QPlatformBackingStore
    \li QPlatformClipboard
    \li QPlatformCursor
    \li QPlatformDrag
    \li QPlatformFontDatabase
    \li QPlatformGraphicsBuffer
    \li QPlatformInputContext
    \li QPlatformOffscreenSurface
    \li QPlatformOpenGLContext
    \li QPlatformScreen
    \li QPlatformServices
    \li QPlatformSharedGraphicsCache
    \li QPlatformSurface
    \li QPlatformWindow
    \endlist

\li Style/theming
    \list
    \li QPlatformTheme
    \li platform palettes
    \li platform fonts
    \li theme hints
    \endlist

\li Native dialogs and menus
    \list
    \li QPlatformDialogHelper
    \li QPlatformMenu
    \li QPlatformMenuBar
    \li QPlatformMenuItem
    \endlist
\endlist

\note In addition to the QPA APIs, there are many other platform abstractions
in Qt, for example the event dispatcher abstractions in \l{Qt Core} and the
rendering hardware abstractions in RHI.
The QPA APIs are mostly focused on window system integration and related support.

\section1 QPA Plugins

Concrete implementations of the interfaces listed above live in QPA plugins,
or platform plugins, adding support for the various platforms Qt runs on.
QPA plugins are implemented by subclassing the \c QPlatform* classes.

The following table summarizes the platform plugins available:

\table
\header
    \li Plugin Name
    \li Plugin Class Name
    \li Description
\row
    \li \c qandroid
    \li QAndroidPlatformIntegration
    \li \l{Qt for Android}{Android support}
\row
    \li \c qbsdfb
    \li QBsdFbIntegration
    \li BsdFb support
\row
    \li \c qcocoa
    \li QCocoaIntegrationPlugin
    \li \l{Qt for macOS}{macOS support}
\row
    \li \c qdirect2d
    \li QWindowsDirect2DIntegrationPlugin
    \li Similar to the \c qwindows plugin, but replaces the raster paint engine
        with a Direct2D-based paint engine for QPixmap and QBackingStore.
\row
    \li \c qdirectfb
    \li QDirectFbIntegrationPlugin
    \li DirectFB is centered around \e surfaces, which are the equivalent of a
        QPaintDevice.
\row
    \li \c qeglfs
    \li QEglFSIntegrationPlugin
    \li \l{embedded eglfs}{EGLFS} support for embedded Linux devices.
\row
    \li \c qhaiku
    \li QHaikuIntegration
    \li Haiku support
\row
    \li \c qios
    \li QIOSIntegrationPlugin
    \li \l{Qt for iOS}{iOS support}
\row
    \li \c qlinuxfb
    \li QLinuxFbIntegrationPlugin
    \li \l LinuxFB support for embedded Linux devices.
\row
    \li \c qvnc
    \li QVncIntegration
    \li VNC support
\row
    \li \c qwayland
    \li \list
            \li QWaylandIntegrationPlugin
            \li QWaylandBrcmEglPlatformIntegrationPlugin
            \li QWaylandEglPlatformIntegrationPlugin
            \li QWaylandXCompositeEglPlatformIntegrationPlugin
            \li QWaylandXCompositeGlxPlatformIntegrationPlugin
        \endlist
    \li \l{Wayland and Qt}{Wayland support}
\row
    \li \c qwindows
    \li QWindowsIntegrationPlugin
    \li \l{Qt for Windows}{Windows support}
\row
    \li \c qxcb
    \li QXcbIntegrationPlugin
    \li \l{Qt for Linux/X11}{X Window System (X11) support}
\endtable

\section2 Selecting a QPA plugin

Qt will select a default QPA plugin, depending on the platform.
The \c{QT_QPA_PLATFORM} environment variable and the \c{-platform}
command line argument allow you to override this default.
See \l QGuiApplication for more details.

You can pass a semicolon-separated list to install a plugin. In this case,
the installer will go through the items in the list and install the first
available plugin.

Example:
\badcode
-qpa xcb;wayland
\endcode

The above line checks whether the \c xcb plugin is available, if it isn't,
it then checks for the wayland plugin.

\section2 Writing a QPA plugin

There is no detailed tutorial documentation for writing QPA plugins at this
time. However, there are two minimal plugins shipped with Qt for testing and
other special purposes that you can use as examples:

\list
\li \c{qtbase/src/plugins/platforms/minimal/}
\li \c{qtbase/src/plugins/platforms/minimalegl/}
\endlist

The \c qminimal plugin is used for tools that link against \l{Qt GUI}, but do
not require window system integration (for example, \c qmlplugindump).
It also has diagnostic support for dumping window contents to image files
as determined by environment variables.

*/
