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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 Minimal QML
++ * \example minimal-qml
++ * \examplecategory {Embedded}
++ * \brief Minimal QML is a simple example that demonstrates how to write a Wayland compositor in QML.
++ * \ingroup qtwaylandcompositor-examples
++ *
++ * Minimal QML is a desktop-style Wayland compositor example implementing a
++ * complete Qt Wayland Compositor with as little code as possible. The compositor is implemented
++ * with Qt Quick and QML.
++ *
++ * \image minimal-qml.png {Minimal QML compositor with client window}
++ *
++ * \section1 The WaylandCompositor Object
++ *
++ * The top-level item of the compositor is a \l WaylandCompositor. This represents the Wayland
++ * server itself and manages the connections to clients as they come in.
++ *
++ * \snippet minimal-qml/main.qml compositor
++ *
++ * By default, the server supports the core Wayland protocol for communicating with clients.
++ * Usually, though, you will also want to support one or more extensions to the protocol. This
++ * gives the client more tools to influence its role in the windowing system.
++ *
++ * Qt supports several standard and common extensions. In addition, it is easy to create and support
++ * custom extensions, as long as support can be added in both the client and server code.
++ *
++ * \section1 Shell Extensions
++ *
++ * Typically, a compositor will support at least one
++ * \l{Shell Extensions - Qt Wayland Compositor}{shell extension}. Extensions are added to
++ * the compositor by instantiating them as direct children of the \l WaylandCompositor object. They
++ * will automatically be added to its \c extensions property and broadcast to clients when they
++ * connect.
++ *
++ * \snippet minimal-qml/main.qml shells
++ *
++ * The \e{Minimal QML} example supports three different shells: \l{WlShell}, \l{XdgShell} and
++ * \l{IviApplication}.
++ *
++ * A client can connect to either of these and it will be used as a channel for communicating
++ * about certain things between the client and compositor, such as creating new windows,
++ * negotiating size, and so on.
++ *
++ * When a client creates a new surface, its active extension will receive a signal of this. The
++ * signal contains a \l ShellSurface argument. Depending on which extension received the signal,
++ * this argument will be of a subclass of \l{ShellSurface}: \l{WlShellSurface}, \l{XdgSurface}
++ * or \l{IviSurface} respectively.
++ *
++ * The \l ShellSurface can be used to access features of the shell extension for the specific
++ * surface. In the \e{Minimal QML} example, we simply want to add the client to our scene. To
++ * record existence of the new window, we add it to a simple \l ListModel for safe-keeping.
++ *
++ * \snippet minimal-qml/main.qml model
++ *
++ * \section1 Creating the Scene
++ *
++ * Most of the necessary compositor code is already ready. The final step is to make sure
++ * applications are actually visible on the screen.
++ *
++ * For all compositors, we have to define at least one output. This is done by instantiating
++ * a \l WaylandOutput object as the direct child of the \l WaylandCompositor. If there is only
++ * a single output, this will represent the primary screen on the system. (You may also create
++ * multiple \l WaylandOutput objects to address multiple screens if they are available. See
++ * the \l{Multi Screen}{Multi Screen example} for more details
++ * about this.)
++ *
++ * \snippet minimal-qml/main.qml output
++ *
++ * Inside the \l{WaylandOutput}, we create a \l Window that serves as the container for
++ * our scene. In the example, we give this a size. The size used if the compositor is running as
++ * an application inside another windowing system which supports custom-sized windows. In a
++ * typical use case on an embedded device, where the compositor is the only display server running,
++ * it will probably be running on a full-screen platform plugin (such as \c{eglfs}) and the size
++ * set here will not matter.
++ *
++ * The final step is to create items for each of the \l ShellSurface objects that have been created.
++ * For this, we can use the \l ShellSurfaceItem class.
++ *
++ * \snippet minimal-qml/main.qml shell surface item
++ *
++ * We create a \l ShellSurfaceItem for each of the shell surfaces in our model, and assign them
++ * to the \c shellSurface property. In addition, we make sure the model is updated when the shell
++ * surface is destroyed. This can happen when a client manually closes a window, and if it exits
++ * or crashes.
++ *
++ * And this is all the code needed to create a functional Wayland compositor using Qt Quick and
++ * QML. For another example of a compositor written in QML but which has a few more features, take
++ * a look at the \l{Fancy Compositor}{Fancy Compositor example}.
++ */