QtWayland

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What is QtWayland?

QtWayland is a Qt 5 module that wraps the functionality of Wayland. QtWayland is separated into a client and server side. The client side is the wayland platform plugin, and provides a way to run Qt applications as Wayland clients. The server side is the Qt Wayland Compositor API, and allows users to write their own Wayland compositors.

What is Wayland

Wayland is a protocol for a compositor to talk to its clients as well as a C library implementation of that protocol. For more detailed information you should visit the Wayland project homepage

How can I get binaries for Qt Wayland?

The Qt installer does unfortunately not include binaries for Qt Wayland. You can however build it from source yourself if you want to use the latest stable version (see below).

If you are using Qt provided by your Linux distribution there is most likely a separate package for Qt Wayland, i.e. qt5-wayland (Arch Linux), or two separate packages, i.e. qtwaylandclient5 and qtwaylandcompositor5-dev (Ubuntu 17.10). Beware that distros may ship really old versions of Qt though, and the compositor API was first released as stable with Qt 5.8.

Where can I find the code for QtWayland?

Qt Wayland Repo

How do I build QtWayland?

Ubuntu 14.04

Ubuntu 14.04 contains all necessary dependencies, so it is no longer necessary to build Wayland yourself. The old instructions are available below.

The following packages are required (list may be incomplete)

• libwayland-dev
• libwayland-egl1-mesa
• libwayland-server0
• libgles2-mesa-dev
• libxkbcommon-dev

qtbase needs to be configured with OpenGL ES2

configure -developer-build -opengl es2 [...]

The compositor API is still experimental, and not built by default. To enable it, add wayland-compositor to the configuration:

cd qtwayland
qmake CONFIG+=wayland-compositor

Setup build environment Ubuntu 12.04

The first step is to start with a reasonably modern Linux distribution. I use Ubuntu 12.04, so anything newer is just gravy. The following instructions are based off of the tips on: http://wayland.freedesktop.org/building.html

The first thing I do is start by creating an install directory for my Wayland dependencies and create an environment file to source:

So if I wanted to install my Wayland dependencies into the folder $HOME/Apps/Wayland I would create the folder, and then create the file:
~/Apps/Wayland/wayland.sourceme_

#wayland.sourceme
WLD=$HOME/Apps/Wayland # change this to another location if you prefer
LD_LIBRARY_PATH=$WLD/lib
PKG_CONFIG_PATH=$WLD/lib/pkgconfig/:$WLD/share/pkgconfig/
ACLOCAL="aclocal -I $WLD/share/aclocal"
PATH=$WLD/bin:$PATH
XDG_RUNTIME_DIR=/tmp

export WLD LD_LIBRARY_PATH PKG_CONFIG_PATH ACLOCAL PATH XDG_RUNTIME_DIR

So then source that file to set up your work environment:
source~/Apps/Wayland/wayland.sourceme

Qt dependency

Currently, you need to build the latest Qt (stable branch) (see http://lists.qt-project.org/pipermail/development/2013-December/014789.html ) WITHOUT using the wayland.sourceme environment. The modules you need at the very least are:
qtbase
qtdeclarative

If you face linker errors related to libGL and undefined references, it may be necessary to compile Qt5 and link it with the self compiled mesa. Maybe due to the way that mesa was compiled and installed, the configure script will require to explicitly define the version of OpenGL to be used with: ./configure -opengl es2

Building the QtWayland module

Once you have a working build of Qt 5, then pull down the latest QtWayland module code and configure with "qmake" this time using the wayland.sourceme environment. Make sure that you use the version of qmake that you get with Qt 5 here. This will make sure that the Wayland platform plugin and QtCompositor API are build using your special versions of OpenGL and Wayland.

source ~/Apps/Wayland/wayland.sourceme
git clone git://code.qt.io/qt/qtwayland.git
cd qtwayland
qmake
make
make install

How do I use QtWayland?

Run Qt applications as Wayland clients

When you build the QtWayland module, you should get a new platform plugin for wayland. To use it you must first already have a Wayland compositor running. This could be either the Weston reference compositor provided by the Wayland project, or a Qt example compositor provided by QtWayland. Regardless the only thing you need to do as an application developer to run your GUI application as a wayland client is:

source~/Apps/Wayland/wayland.sourceme
./application -platform wayland

Create and Run your own Wayland Compositor with Qt5

Running example compositors

The QtWayland module provides a couple of example compositors that demonstrate how the QtCompositor API works. These are built in the examples folder of the QtWayland module if you add "wayland-compositor" to the CONFIG variable when starting qmake, as in :

qmake CONFIG+=wayland-compositor

These examples represent the server side of Wayland, so they do not use the wayland platform plugin, but rather whatever platform you need to run on. Generally this is going to be either eglfs, kms, or if you want to run in X11 xcb.

If you wanted to run the qml-compositor in X11 you would run the following:

source ~/Apps/Wayland/wayland.sourceme
cd qtwayland/examples/qml-compositor
./qml-compositor -platform xcb

And now that you have a Wayland compositor running, you can connect and display Wayland clients.

Creating your own compositor

The API to create a Wayland compositor and control associated events (e.g. a new client connected) is exposed through the QtWayland class WaylandCompositor. Its constructor expects as the primary parameter a pointer to a QWindow object, which allows some flexibility when implementing your compositor.

Thanks to this, there are 3 different approaches while implementing a compositor:

• QWindow based: the instance will be used to setup the WaylandCompositor object.

• QWidget based: in this case, the base widget window handle will be used.

• QML based: your C++ application will use a QQuickView object to setup the WaylandCompositor. At the time of writing, there is no way to create a compositor using only QML.

WaylandCompositor is a pure abstract virtual class, which means that it is not possible to create instances of it. A common pattern while implementing a compositor is inherit from WaylandCompositor and implement the function method *void surfaceCreated(WaylandSurface surface).

This method will be executed every time a new client connects (i.e. an application was started and requests the services of the compositor), being represented as a WaylandSurface object. There are some signals that this object can generate and must be treated by the compositor, namely:

• mapped(): emitted when the client has connected to the compositor.

• damaged(): TODO

• destroyed(): emitted when the client quits (i.e. the application has exited)

• unmapped(): TODO

• extendedSurfaceReady(): TODO

The project file will need to use the compositor module (i.e. add in the .pro file QT += compositor). It is interesting to comment that at time of writing, there are some QML related APIs only available by adding a define in the project file (i.e. DEFINES += QT_COMPOSITOR_QUICK).