// 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 - Server Side Decoration Compositor
 * \example server-side-decoration
 * \brief Server Side Decoration Compositor is a simple example that demonstrates server side window decorations on xdg-shell.
 * \ingroup qtwaylandcompositor-examples
 *
 * \image server-side-decoration.png
 *
 * \section1 Introduction
 *
 * Server Side Decoration Compositor is a desktop-style Wayland compositor example implementing
 * server-side window decorations.
 *
 * 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 Decorations
 *
 * The term \e{window decorations} refers to the additional UI that accompanies most windows in the
 * windowing system. Examples of this are:
 *
 * \list
 *   \li The graphical frame around the window surface, which a user can click and drag to resize
 *       the window.
 *   \li The title bar of the window, which might be used to move the window.
 *   \li The system tool buttons for maximizing, minimizing and closing a window.
 * \endlist
 *
 * Traditionally in Wayland, it has been the client's task to render these decorations. At the same
 * time, the position, size and state of the window is the compositor's domain.
 * Some \l{Shell Extensions - Qt Wayland Compositor}{shell extensions} optionally support
 * \e{server-side decorations}. This enables a compositor to communicate to clients that they should
 * not draw their own window decorations.  Instead, the compositor is responsible for drawing the
 * window decorations.  This corresponds to how decorations are handled on other windowing systems,
 * such as macOS, Windows and X11.  It is worth noting that certain clients may not support this at
 * all. If the system is expected to run such applications, then this should also be taken into
 * account.
 *
 * Benefits of server-side decorations:
 * \list
 *   \li Clients do not have to reserve space for system UI in their Wayland buffers.
 *   \li Qt Quick and OpenGL-based clients do not have to render into a separate FBO and copy
 *       the content into their Wayland buffers.
 *   \li Client windows will have a consistent appearance, independent of which UI toolkit is in
 *       use.
 *   \li System functionality, such as resizing, closing and changing window state, is centralized
 *       in the server instead of being shared between the server and client.
 * \endlist
 *
 * \section1 The Code
 *
 * The example compositor only supports the \l{XdgShell} extension. It initializes the extension in
 * the usual way and adds surfaces to a \l ListModel in order to access them later.
 *
 * \snippet server-side-decoration/main.qml XdgShell
 *
 * In addition, the example initializes the \l XdgDecorationManagerV1 extension. This allows it
 * to communicate to the client that it prefers server-side decorations.
 *
 * Since the interface is optional, it could be that the client does not support it and will always
 * draw its own decorations. Therefore, the mode is only "preferred" and we need to check the actual
 * mode of the top-level window before we decorate it.
 *
 * \snippet server-side-decoration/main.qml decoration
 *
 * For each window, we create a simple title bar above it. The title bar has a gradient, some text,
 * a \l DragHandler which manages its position, and a close button.
 *
 * The image shows a client which supports the decoration manager extensions on the upper left-hand
 * side, and the same client with client-side decorations on the lower, right-hand side.
 */