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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 IVI Compositor
++ * \example ivi-compositor
++ * \examplecategory {Embedded}
++ * \brief IVI Compositor is an example that demonstrates how to use the IviApplication extension.
++ * \ingroup qtwaylandcompositor-examples
++ *
++ * \section1 Introduction
++ *
++ * This example demonstrates using the \l IviApplication shell extension in a Wayland display
++ * server (also known as a Wayland compositor).
++ *
++ * For an introduction to the basic principles of creating a \l{Qt Wayland Compositor} with Qt,
++ * see the \l{Minimal QML}{Minimal QML example}.
++ *
++ * \section1 The Protocol
++ *
++ * \l IviApplication is a \l{Shell Extensions - Qt Wayland Compositor}{shell extension} that was
++ * designed specifically for making In-vehice Infotainment systems.
++ *
++ * It is a minimalistic protocol, and only provides the following functionality:
++ *
++ * \list 1
++ * \li The client can identify itself with an \e{IVI-id}.
++ * \li The server can request that the client resizes itself.
++ * \endlist
++ *
++ * \section2 The Identification Numbers
++ *
++ * In a typical \l IviApplication setup, you will have a predefined set of applications that can
++ * connect to the server. Since these applications are already known when the system is designed,
++ * they can be assigned hardcoded numbers that identify them. Given that the client and server
++ * agree on these numbers ahead of time, semantics can be built into the ID numbers.
++ *
++ * For instance, if a client identifies itself as the navigation application, the server can
++ * recognize this and allocate a large, centered part of the screen for its window. An application
++ * identifying itself as a clock, on the other hand, might be delegated to a smaller area in the
++ * margins of the screen.
++ *
++ * By default, Qt applications will advertise their system PIDs ("process IDs") as the \e{IVI-id}.
++ * The client can override this by setting \c{QT_IVI_SURFACE_ID} in its environment before
++ * connecting to the server.
++ *
++ * \section1 The Example
++ *
++ * A Qt Wayland Compositor may support multiple shell extensions at once, but the
++ * \e{IVICompositor example} only supports the \l IviApplication protocol. This means that the
++ * clients have to also support this shell extension in order to connect to the server.
++ *
++ * The compositor window in the example is split into two horizontally: A left area which is
++ * designated for a specialized application with the id "1337", and a right area which is for all
++ * other applications.
++ *
++ * \image ivi-compositor-1.png {Compositor window split horizontally with
++ * left area for application ID "1337" and right area for other
++ * applications}
++ *
++ * \section2 Creating the Layout
++ *
++ * The layout of the window is created inside a \l WaylandOutput. This typically corresponds to
++ * a physical screen available to the compositor. If a single \l WaylandOutput is created, as in
++ * the \e{IVICompositor example}, it will usually correspond to the primary screen.
++ *
++ * \snippet ivi-compositor/main.qml wayland output
++ *
++ * The code creates a \l WaylandOutput for the screen and creates a \l Window on this as the top
++ * level container of all compositor contents. Inside this window, it creates two rectangles that
++ * will serve as containers for applications as they connect.
++ *
++ * \section2 Connecting Clients
++ *
++ * If no additional configuration has been done, a Qt application will connect with an \e{IVI-id}
++ * equal to its process ID. For instance, if we run another Qt example application with
++ * \c{-platform wayland}, it will be delegated to the right-hand side of the layout, granted that
++ * its ID is different from "1337".
++ *
++ * \image ivi-compositor-2.png {Compositor window with label and text field
++ * on the right side}
++ *
++ * However, if we set the \c{QT_IVI_SURFACE_ID} environment variable to "1337" before starting
++ * the example, it will be delegated to the left-hand side of the layout.
++ *
++ * \image ivi-compositor-3.png {Compositor window with label and text field
++ * on the left side}
++ *
++ * When a client connects to the \c IVIApplication interface, it will emit the \c{iviSurfaceCreated}
++ * signal. This is where the positioning of the application's surface is handled.
++ *
++ * \snippet ivi-compositor/main.qml connecting
++ *
++ * The \c{iviSurfaceCreated} signal receives an \l IviSurface argument which can be used to access
++ * the client's ID. The compositor then creates a \l ShellSurfaceItem for the surface (as defined by
++ * the \c chromeComponent). \c ShellSurfaceItem is the class used for placing shell surfaces into
++ * the Qt Quick scene, and you will see this same pattern in all the Qt Wayland Compositor examples.
++ *
++ * What makes the \e{IVICompositor example} special is that it checks the \c iviId property of the
++ * incoming shell surface and decides on a parent for the \l ShellSurfaceItem depending on what
++ * this is. If the ID is equal to "1337" it will be parented to the \c leftArea, and if not it will
++ * be in the \c rightArea.
++ *
++ * The implementation of the \l ShellSurfaceItem handles resizing by informing the client whenever
++ * the size changes (which can happen if the compositor is running inside a desktop-style windowing
++ * system and its window is resized).
++ *
++ * \snippet ivi-compositor/main.qml resizing
++ *
++ * The \c{sendConfigure()} method is defined in \l IviSurface and will send an event to the client.
++ * The client will receive a resize event with the new size, so it can relayout its contents.
++ *
++ * If multiple applications connect to the same area in the layout, they will simply be stacked
++ * according to normal Qt Quick ordering rules. There are no built-in mechanisms for closing
++ * applications or managing state, but this can easily be added as ordinary Qt Quick code.
++ */