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// Copyright (C) 2021 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\page qtwaylandcompositor-shellextensions.html
\title Shell Extensions - Qt Wayland Compositor
In Wayland, \e{shells} are extensions which provide \e{surface semantics}. This means that they
provide ways for the server and client to communicate about surfaces. Surfaces, in this context,
are often also referred to as "windows", which is typically the representation of the surface in
the compositor.
Shell extensions provide tools for the client and server to communicate about certain things:
\list
\li They can provide a way for the client to inform the server about the purpose of a surface:
Is it a tool-tip, a pop-up menu, or a regular application window, for instance? Based on
this, the server can decide on the geometry of the window and how the user can interact
with it.
\li They can also provide protocols for manipulating the surface, such as resizing, moving,
and hiding them.
\endlist
Like other extensions, support for shells is added to a compositor by instantiating them
as direct children of the \l WaylandCompositor top-level object. The shell extensions supported
by Qt are: \l{WlShell}, \l{XdgShell} and \l{IviApplication}.
\list
\li \l XdgShell is an appropriate shell for desktop-style systems, where any number of
applications can connect and where windows can be manually resized and repositioned by
the user.
\li \l IviApplication is a minimalistic protocol, originally intended for In-vehicle
Infotainment systems. It is useful for embedded systems, where a pre-defined set of
applications can run, often with pre-assigned screen real estate. For some more details
on this protocol, see the \l{IVI Compositor}{IVI Compositor example}.
\li \l QtShell is a specialized shell for Qt applications which supports the window management
features available in Qt. It may be suitable on a platform where both the compositor and
client applications are written with Qt, and where applications are trusted not to abuse
features such as manual window positioning and "bring-to-front".
\li \l WlShell is mostly useful for compatibility with third-party applications. This is also
a desktop-style shell, but it has been deprecated and replaced by \l XdgShell.
\endlist
When designing an embedded system from the bottom up, there are no rules determining which
shell extension to use. It will typically be either \l XdgShell or \l{IviApplication}. The
decision should be influenced by what features the system will need, and whether there are
applications involved which are not written in Qt and which have their own requirements.
A Qt Wayland Compositor can also support multiple shell extensions at once. See the
\l{Minimal QML}{Minimal QML example} for an example where all three shell extensions listed
above are supported.
*/
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