// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only

/*!
 * \title QtShell Compositor
 * \example qtshell
 * \examplecategory {Embedded}
 * \brief QtShell Compositor shows how to use the QtShell shell extension.
 * \ingroup qtwaylandcompositor-examples
 *
 * QtShell Compositor is a desktop-style Wayland compositor example implementing a
 * complete Qt Wayland Compositor which uses the specialized
 * \l{Shell Extensions - Qt Wayland Compositor}{shell extension protocol} called \l{QtShell}.
 *
 * \image qtshell.jpg {QtShell compositor with two client windows}
 *
 * The compositor is implemented with Qt Quick and QML.
 *
 * \section1 Making the Connection
 *
 * The example lists QtShell as the only extension to the WaylandCompositor object. This means that
 * any client connecting to the server must also support this extension, thus they should be Qt
 * applications running against the same version of Qt as the compositor.
 *
 * \snippet qtshell/qml/main.qml shell
 *
 * When a client connects to the QtShell interface, it creates a \l{QtShellSurface}. The compositor
 * is notified of this by the emission of the
 * \l [QML] {QtShell::}{qtShellSurfaceCreated} signal. The
 * example then adds the shell surface to a ListModel for easy access later.
 *
 * \snippet qtshell/qml/CompositorScreen.qml handleShellSurface
 *
 * The ListModel is used as the model for a \l{Repeater} which creates the Qt Quick items required
 * to display the client contents on screen.
 *
 * \snippet qtshell/qml/CompositorScreen.qml repeater
 *
 * It uses the local \c Chrome type, which handles window states and decorations.
 *
 * \section1 Chrome
 *
 * The \c Chrome is the type that ensures the client contents are visible and also handles window
 * state, position, size, and so on. It uses the built-in QtShellChrome as a basis, which
 * automatically handles window state (maximized, minimized, fullscreen) and window activation
 * (ensuring that only a single window is active at the time).
 *
 * Its behavior can be customized to some extent, but it is also possible to write the \c Chrome
 * functionality from scratch, building from a basic \l{Item} type instead. QtShellChrome is a
 * convenience class which provides typical compositor behavior, and saves us the time of
 * implementing this logic in the example.
 *
 * However the \c Chrome is written, it should have a ShellSurfaceItem to hold the client contents.
 *
 * \snippet qtshell/qml/Chrome.qml shellsurfaceitem
 *
 * The ShellSurfaceItem is the visual representation of the client's contents in the Qt Quick scene.
 * Its size should usually match the size of the client's buffer, otherwise it may look stretched or
 * squeezed. QtShellChrome will automatically be sized to the \l{QtShellSurface}'s
 * \l{QtShellSurface::windowGeometry}{windowGeometry}, which is the size of the
 * client's buffer plus the size of the frame margins. The frame margins are reserved areas on the
 * sides of the \c Chrome which can be used to contain window decorations.
 *
 * The ShellSurfaceItem is therefore anchored to the window decorations to fill the area reserved
 * for the client buffer.
 *
 * \section1 Window Decorations
 *
 * The window decoration is usually a frame around a client's contents which adds information
 * (such as a window title) and the possibility of user interaction (such as resizing, closing,
 * moving the window, and so on.)
 *
 * With \l{QtShell}, window decorations are always drawn by the compositor and not by the client.
 * In order for sizes and positions to be communicated correctly, QtShell also needs to know how
 * much of the window is reserved for these decorations. This can be handled automatically by
 * QtShellChrome, or manually, by setting
 * \l{QtShellChrome::frameMarginLeft}{frameMarginLeft},
 * \l{QtShellChrome::frameMarginRight}{frameMarginRight},
 * \l{QtShellChrome::frameMarginTop}{frameMarginTop} and
 * \l{QtShellChrome::frameMarginBottom}{frameMarginBottom}.
 *
 * For typical cases where there are resize handles around the window and a title bar at the top,
 * it is more convenient to rely on the default frame margins. The QtShell Compositor example
 * does this.
 *
 * First, we create Qt Quick items to represent the different parts of the window's decorations.
 * On the left side, for example, there should be a resize handle that the user can grab and drag in
 * order to resize the window.
 *
 * \snippet qtshell/qml/Chrome.qml leftResizeHandle
 *
 * We simply make this a five-pixel wide rectangle in the example, anchored to the top, bottom and
 * left side of the \c Chrome.
 *
 * Similarly, we add Qt Quick items that represent the right, top, bottom, top-left, top-right,
 * bottom-left and bottom-right resize handles. We also add a title bar. When the decorations have
 * been created and anchored correctly to the sides of the \c{Chrome}, we set corresponding
 * properties in QtShellChrome.
 *
 * \snippet qtshell/qml/Chrome.qml decorations
 *
 * When the decoration properties are set, the default resizing and repositioning behavior will be
 * added automatically. The user will be able to interact with the resize handles in order to resize
 * the window, and drag the title bar to reposition it. The frame margins of the QtShellSurface will
 * also be set automatically to account for the size of the decorations (as long as none of the
 * frame margins properties have been set explicitly.)
 *
 * The visibility of the decorations will be handled automatically by the QtShellChrome based on
 * the window flags of the QtShellSurface.
 *
 * \section1 Window Management
 *
 * As part of the decorations, it is common to have tool buttons which manage the window state
 * and life span. In the example, these are added to the title bar.
 *
 * \snippet qtshell/qml/Chrome.qml buttons
 *
 * The visibility of each button is conditional on the window flag for that button, and when each
 * of them is clicked, we simply call the corresponding method in QtShellChrome. The exception is
 * the "close" button, which calls the
 * \l{QtWaylandCompositor::QtShellSurface::sendClose()}{sendClose()} method in QtShellSurface.
 * This instructs the client to close itself, and ensures a graceful shutdown of the application.
 *
 * \snippet qtshell/qml/CompositorScreen.qml taskbar
 *
 * As an additional window management tool, the example has a "task bar". This is just a row of
 * tool buttons at the bottom with the window titles. The buttons can be clicked to de-minimize
 * applications and bring them to the front if they are obscured by other windows. Similarly
 * to the \c{Chrome}, we use a \l{Repeater} for creating the tool buttons and use the shell surface
 * list as model for this. For simplicity, the example does not have any handling of overflow (when
 * there are too many applications for the task bar), but in a proper compositor, this is also
 * something that should be considered.
 *
 * Finally, to avoid maximized applications expanding to fill the area covered by the task bar, we
 * create a special item to manage the parts of the WaylandOutput real estate that is available to
 * client windows.
 *
 * \snippet qtshell/qml/CompositorScreen.qml usableArea
 *
 * It is simply anchored to the sides of the WaylandOutput, but its bottom anchor is at the top
 * of the task bar.
 *
 * In the \c{Chrome}, we use this area to define the \l{QtShellChrome::maximizedRect}{maximizedRect}
 * of the window.
 *
 * \snippet qtshell/qml/Chrome.qml maximizedRect
 *
 * By default, this property will match the full WaylandOutput. In our case, however, we do not want
 * to include the task bar in the available area, so we override the default.
 */
