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Weston
======
Weston is the reference implementation of a Wayland compositor, and a
useful compositor in its own right. Weston has various backends that
lets it run on Linux kernel modesetting and evdev input as well as
under X11. Weston ships with a few example clients, from simple
clients that demonstrate certain aspects of the protocol to more
complete clients and a simplistic toolkit. There is also a quite
capable terminal emulator (weston-terminal) and an toy/example desktop
shell. Finally, weston also provides integration with the Xorg server
and can pull X clients into the Wayland desktop and act as a X window
manager.
Refer to http://wayland.freedesktop.org/building.html for building
weston and its dependencies.
The test suite can be invoked via `make check`; see
http://wayland.freedesktop.org/testing.html for additional details.
Libweston
=========
Libweston is an effort to separate the re-usable parts of Weston into
a library. Libweston provides most of the boring and tedious bits of
correctly implementing core Wayland protocols and interfacing with
input and output systems, so that people who just want to write a new
"Wayland window manager" (WM) or a small desktop environment (DE) can
focus on the WM part.
Libweston was first introduced in Weston 1.9, and is expected to
continue evolving through many Weston releases before it achieves a
stable API and feature completeness.
API (in)stability and parallel installability
---------------------------------------------
As libweston's API surface is huge, it is impossible to get it right
in one go. Therefore developers reserve the right to break the API
between every 1.x.0 Weston release (minor version bumps), just like
Weston's plugin API does. For git snapshots of the master branch, the
API can break any time without warning or version bump.
Libweston API or ABI will not be broken between Weston's stable
releases 1.x.0 and 1.x.y, where y < 90.
To make things tolerable for libweston users despite ABI breakages,
libweston is designed to be perfectly parallel-installable. An
ABI-version is defined for libweston, and it is bumped for releases as
needed. Different ABI-versions of libweston can be installed in
parallel, so that external projects can easily depend on a particular
ABI-version, and they do not have to fight over which ABI-version is
installed in a user's system. This allows a user to install many
different compositors each requiring a different libweston ABI-version
without tricks or conflicts.
Note, that versions of Weston itself will not be parallel-installable,
only libweston is.
For more information about parallel installability, see
http://ometer.com/parallel.html
Libweston design goals
----------------------
The high-level goal of libweston is that what used to be shell plugins
will be main executables. Instead of launching 'weston' with various
arguments to choose the shell, one would be launching
'weston-desktop', 'weston-ivi', 'orbital', etc. The main executable
(the hosting program) links to libweston for a fundamental compositor
implementation. Libweston is also intended for use by other projects
who want to create new "Wayland WMs".
The libweston API/ABI will be separating the shell logic and main
program from the rest of the "Weston compositor" (libweston
internals).
Details:
- All configuration and user interfaces will be outside of libweston.
This includes command line parsing, configuration files, and runtime
(graphical) UI.
- The hosting program (main executable) will be in full control of all
libweston options. Libweston should not have user settable options
that would work behind the hosting program's back, except perhaps
debugging features and such.
- Signal handling will be outside of libweston.
- Child process execution and management will be outside of libweston.
- The different backends (drm, fbdev, x11, etc) will be an internal
detail of libweston. Libweston will not support third party
backends. However, hosting programs need to handle
backend-specific configuration due to differences in behaviour and
available features.
- Renderers will be libweston internal details too, though again the
hosting program may affect the choice of renderer if the backend
allows, and maybe set renderer-specific options.
- plugin design ???
- xwayland ???
There are still many more details to be decided.
For packagers
-------------
Always build Weston with --with-cairo=image.
The Weston project is (will be) intended to be split into several
binary packages, each with its own dependencies. The maximal split
would be roughly like this:
- libweston (minimal dependencies):
+ headless backend
+ wayland backend
- gl-renderer (depends on GL libs etc.)
- drm-backend (depends on libdrm, libgbm, libudev, libinput, ...)
- x11-backend (depends of X11/xcb libs)
- xwayland (depends on X11/xcb libs)
- rpi-backend (depends on DispmanX, libudev, ...)
- fbdev-backend (depends on libudev...)
- rdp-backend (depends on freerdp)
+ screen-share
- weston (the executable, not parallel-installable):
+ desktop shell
+ ivi-shell
+ fullscreen shell
+ weston-info, weston-terminal, etc. we install by default
- weston demos (not parallel-installable)
+ weston-simple-* programs
+ possibly all the programs we build but do not install by
default
- and possibly more...
Everything should be parallel-installable across libweston
ABI-versions, except those explicitly mentioned.
Weston's build may not sanely allow this yet, but this is the
intention.
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