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// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
* \title Qt Wayland Compositor Examples - Spanning Screens
* \example spanning-screens
* \brief Spanning Screens is an example that demonstrates how to let Wayland clients span multiple screens.
* \ingroup qtwaylandcompositor-examples
*
* \section1 Introduction
*
* Spanning screens is a Wayland compositor example that maximizes clients across a top and a bottom
* screen.
*
* \image spanning-screens.jpg
*
* For an introduction to the basic principles of creating a \l{Qt Wayland Compositor} with Qt,
* see the \l{Qt Wayland Compositor Examples - Minimal QML}{Minimal QML example}.
*
* \section1 Supporting Multiple Screens
*
* In \l{Qt Wayland Compositor} a screen is represented by a \l{WaylandOutput}, and a \l Window is
* used to contain the \l{Qt Quick} scene representing both clients and the compositor's UI.
*
* In this example, a multi-screen setup is emulated by creating two windows on the primary screen,
* but the code can easily be modified to target multiple physical screens.
*
* \snippet spanning-screens/main.qml enable screens
*
* Since each \l Window represents an isolated \l{Qt Quick} scene, this means we need a trick to
* have the same client content display inside both windows. The way to do this in
* \l{Qt Wayland Compositor} is to create two views of the same client content: One for the "top"
* window and one for the "bottom". The views share a reference to the same underlying graphics buffer.
* This allows us to copy different areas of the client's surface onto each of the windows.
*
* \snippet spanning-screens/main.qml create items
*
* When the client connects to the \l{Shell Extensions - Qt Wayland Compositor}{shell extension}
* \l{XdgShell}, we create two references to the surface. One of them is added to the "top" output,
* and the second to the "bottom". The item on the bottom output also gets an offset corresponding
* to the height of the top output. This ensures that the part of the client surface showing on
* the bottom output starts where the top output ends.
*
* \snippet spanning-screens/main.qml size
*
* In addition, we tell the client to resize its surface so that it fills both the top and bottom
* window. The end result is a client that spans two windows, or "screens".
*
* Referencing the same client surface from multiple items is a tool which can be used for many
* things. For a demonstration of a desktop-style compositor where windows can be moved from screen
* to screen, take a look at the
* \l{Qt Wayland Compositor Examples - Multi Screen}{Multi Screen example}.
*
* The \l{Qt Wayland Compositor Examples - Multi Output}{Multi Output example} shows how client
* surfaces can be displayed on multiple outputs with different sizes and other properties.
*
* \note In order to support multiple Wayland outputs in the same compositor, the
* \l Qt::AA_ShareOpenGLContexts attribute must be set before the \l QGuiApplication
* object is constructed.
*/
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