// 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
 * \meta category {Embedded}
 * \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.
 */