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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 Qt Wayland Compositor Examples - Pure QML
\example pure-qml
\brief Pure QML is an example that demonstrates how to write a Wayland compositor in pure QML.
\ingroup qtwaylandcompositor-examples
\section1 Introduction
Pure QML is a small desktop-style Wayland compositor example that demonstrates the power and
ease of the \l{Qt Wayland Compositor} QML APIs.
The Pure QML example is similar to the
\l{Qt Wayland Compositor Examples - Minimal QML}{Minimal QML example}, in that it is a
full-blown Wayland compositor, implemented only using QML code.
\section1 Initializing the Compositor
Like the \l{Qt Wayland Compositor Examples - Minimal QML}{Minimal QML example}, Pure QML
supports the main \l{Shell Extensions - Qt Wayland Compositor}{shell extensions} that are
supported by Qt.
\snippet pure-qml/qml/main.qml shell extensions
These are instantiated as children of the \l{WaylandCompositor} which automatically adds
them to the list of supported interfaces which is broadcasted to clients from the server.
When a connected client creates a surface and binds it to one of the shell extensions, the
corresponding signal is emitted. This then calls a method inside our custom \l WaylandOutput
class, which appends the \l ShellSurface to a \l{ListModel}.
\snippet pure-qml/qml/CompositorScreen.qml handleShellSurface
This model is used as the source for a \l Repeater which creates
\l{ShellSurfaceItem}{ShellSurfaceItems} inside the compositor's \l WaylandOutput. This adds a
view of the surface in the Qt Quick scene. Since it is a \l{ShellSurfaceItem}, it also has
certain interaction options for the user of the compositor, depending on which shell extension
is in use.
\snippet pure-qml/qml/CompositorScreen.qml repeater
\section1 Keyboard
In addition to the basic windowing system functions, the Pure QML compositor also supports an
optional on-screen keyboard running in-process. This uses the \l{Qt Virtual Keyboard} module,
and will be enabled if the module is available.
\snippet pure-qml/qml/Keyboard.qml keyboard
The code is simple. We instantiate an \l InputPanel in the bottom of the output, and make sure
it is visible if and only if it is currently active.
\snippet pure-qml/qml/CompositorScreen.qml keyboard
The keyboard is then added to the \l WaylandOutput using a \l Loader element. The \l Loader is
used here to avoid having a hard dependency on the \l{Qt Virtual Keyboard} module. If loading
fails, then the compositor will continue operating normally, but without support for an
on-screen keyboard.
Finally, we need a way for the compositor to communicate the text input to its clients. This
is done via a \c{text-input} extension. The Pure QML example only supports the
\c{qt_text_input_method_unstable_v1} protocol.
\snippet pure-qml/qml/main.qml text input
The extension is added to the compositor by instantiating the \l QtTextInputMethodManager as
a child of the \l{WaylandCompositor}.
In order for the on-screen keyboard to work, this protocol must also be supported by the client.
Therefore, the \l QtTextInputMethodManager is most useful if the clients are also Qt
applications.
\note Qt also supports \l{TextInputManager}, which is an implementation of the
\c{text_input_unstable_v2} protocol.
\section1 Transitions
In addition to the basic functionality, the Pure QML example also demonstrates animated
transitions between states.
The first of these is the \e{activation} transition. This is only supported on the \l{XdgShell},
since this is the only shell extension which has an \l{XdgToplevel::}{activated} state.
\snippet pure-qml/qml/Chrome.qml activation
When a client window becomes activated under the \l XdgShell protocol, we trigger an animation
which makes the window "pop out" for 200 ms.
The Pure QML compositor also supports a \e{destruction} animation. This triggers whenever the
window closes and surface is destroyed, whether this was because the client gracefully closed
its window, or even if it crashes.
\snippet pure-qml/qml/Chrome.qml destruction
To ensure that the content exists for the duration of the animation, we start by locking the
buffer. This means the final frame rendered by the client will remain in memory until we are
done with it.
Again, we trigger an animation on the scale of the item. The animation in question imitates
turning off the power on a CRT screen, giving a visual clue to the user that the window is
closing, and didn't just vanish into thin air.
Any sort of animated effect may be used for state changes such as these, with the full range
of Qt Quick at your disposal.
*/
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