288 lines
11 KiB
Markdown
288 lines
11 KiB
Markdown
Weston
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======
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Weston is the reference implementation of a Wayland compositor, as well as a
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useful environment in and of itself.
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Out of the box, Weston provides a very basic desktop, or a full-featured
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environment for non-desktop uses such as automotive, embedded, in-flight,
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industrial, kiosks, set-top boxes and TVs. It also provides a library allowing
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other projects to build their own full-featured environments on top of Weston's
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core.
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The core focus of Weston is correctness and reliability. Weston aims to be lean
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and fast, but more importantly, to be predictable. Whilst Weston does have known
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bugs and shortcomings, we avoid unknown or variable behaviour as much as
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possible, including variable performance such as occasional spikes in frame
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display time.
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A small suite of example or demo clients are also provided: though they can be
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useful in themselves, their main purpose is to be an example or test case for
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others building compositors or clients.
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If you are after a more mainline desktop experience, the
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[GNOME](https://www.gnome.org) and [KDE](https://www.kde.org) projects provide
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full-featured desktop environments built on the Wayland protocol. Many other
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projects also exist providing Wayland clients and desktop environments: you are
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not limited to just what you can find in Weston.
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Reporting issues and contributing
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=================================
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Weston's development is
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[hosted on freedesktop.org GitLab](https://gitlab.freedesktop.org/wayland/weston/).
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Please also see [the contributing document](CONTRIBUTING.md), which details how
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to make code or non-technical contributions to Weston.
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Building Weston
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===============
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Weston is built using autotools, with `autogen.sh` and `make`. It often depends
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on the current release versions of
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[Wayland](https://gitlab.freedesktop.org/wayland/wayland) and
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[wayland-protocols](https://cgit.freedesktop.org/wayland/wayland-protocols).
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Every push to the Weston master repository and its forks is built using GitLab
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CI. [Reading the configuration](.gitlab-ci.yml) may provide a useful example of
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how to build and install Weston.
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More [detailed documentation on building Weston](https://wayland.freedesktop.org/building.html)
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is available on the Wayland site. There are also more details on
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[how to run and write tests](https://wayland.freedesktop.org/testing.html).
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Running Weston
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==============
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Once Weston is installed, most users can simply run it by typing `weston`. This
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will launch Weston inside whatever environment you launch it from: when launched
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from a text console, it will take over that console. When launched from inside
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an existing Wayland or X11 session, it will start a 'nested' instance of Weston
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inside a window in that session.
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Help is available by running `weston --help`, or `man weston`, which will list
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the available configuration options and display backends. It can also be
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configured through a file on disk; more information on this can be found through
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`man weston.ini`.
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In some special cases, such as when running remotely or without logind's session
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control, Weston may not be able to run directly from a text console. In these
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situations, you can instead execute the `weston-launch` helper, which will gain
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privileged access to input and output devices by running as root, then granting
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access to the main Weston binary running as your user. Running Weston this way
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is not recommended unless necessary.
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Libweston
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=========
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Libweston is an effort to separate the re-usable parts of Weston into
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a library. Libweston provides most of the boring and tedious bits of
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correctly implementing core Wayland protocols and interfacing with
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input and output systems, so that people who just want to write a new
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"Wayland window manager" (WM) or a small desktop environment (DE) can
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focus on the WM part.
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Libweston was first introduced in Weston 1.12, and is expected to
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continue evolving through many Weston releases before it achieves a
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stable API and feature completeness.
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API/ABI (in)stability and parallel installability
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-------------------------------------------------
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As libweston's API surface is huge, it is impossible to get it right
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in one go. Therefore developers reserve the right to break the API/ABI and bump
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the major version to signify that. For git snapshots of the master branch, the
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API/ABI can break any time without warning.
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Libweston major can be bumped only once during a development cycle. This should
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happen on the first patch that breaks the API or ABI. Further breaks before the
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next Weston major.0.0 release do not cause a bump. This means that libweston
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API and ABI are allowed to break also after an alpha release, up to the final
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release. However, breaks after alpha should be judged by the usual practices
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for allowing minor features, fixes only, or critical fixes only.
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To make things tolerable for libweston users despite API/ABI breakages,
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different libweston major versions are designed to be perfectly
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parallel-installable. This way external projects can easily depend on a
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particular API/ABI-version. Thus they do not have to fight over which
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ABI-version is installed in a user's system. This allows a user to install many
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different compositors each requiring a different libweston ABI-version without
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tricks or conflicts.
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Note, that versions of Weston itself will not be parallel-installable,
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only libweston is.
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For more information about parallel installability, see
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http://ometer.com/parallel.html
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Versioning scheme
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-----------------
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In order to provide consistent, easy to use versioning, libweston
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follows the rules in the Apache Portable Runtime Project
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http://apr.apache.org/versioning.html.
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The document provides the full details, with the gist summed below:
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- Major - backward incompatible changes.
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- Minor - new backward compatible features.
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- Patch - internal (implementation specific) fixes.
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Weston and libweston have separate version numbers in configure.ac. All
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releases are made by the Weston version number. Libweston version number
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matches the Weston version number in all releases except maybe pre-releases.
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Pre-releases have the Weston micro version 91 or greater.
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A pre-release is allowed to install a libweston version greater than the Weston
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version in case libweston major was bumped. In that case, the libweston version
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must be Weston major + 1 and with minor and patch versions zero.
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Pkg-config files are named after libweston major, but carry the Weston version
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number. This means that Weston pre-release 2.1.91 may install libweston-3.pc
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for the future libweston 3.0.0, but the .pc file says the version is still
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2.1.91. When a libweston user wants to depend on the fully stable API and ABI
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of a libweston major, he should use (e.g. for major 3):
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PKG_CHECK_MODULES(LIBWESTON, [libweston-3 >= 3.0.0])
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Depending only on libweston-3 without a specific version number still allows
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pre-releases which might have different API or ABI.
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Forward compatibility
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---------------------
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Inspired by ATK, Qt and KDE programs/libraries, libjpeg-turbo, GDK,
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NetworkManager, js17, lz4 and many others, libweston uses a macro to restrict
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the API visible to the developer - REQUIRE_LIBWESTON_API_VERSION.
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Note that different projects focus on different aspects - upper and/or lower
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version check, default to visible/hidden old/new symbols and so on.
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libweston aims to guard all newly introduced API, in order to prevent subtle
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breaks that a simple recompile (against a newer version) might cause.
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The macro is of the format 0x$MAJOR$MINOR and does not include PATCH version.
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As mentioned in the Versioning scheme section, the latter does not reflect any
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user visible API changes, thus should be not considered part of the API version.
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All new symbols should be guarded by the macro like the example given below:
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#if REQUIRE_LIBWESTON_API_VERSION >= 0x0101
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bool
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weston_ham_sandwich(void);
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#endif
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In order to use the said symbol, the one will have a similar code in their
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configure.ac:
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PKG_CHECK_MODULES(LIBWESTON, [libweston-1 >= 1.1])
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AC_DEFINE(REQUIRE_LIBWESTON_API_VERSION, [0x0101])
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If the user is _not_ interested in forward compatibility, they can use 0xffff
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or similar high value. Yet doing so is not recommended.
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Libweston design goals
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----------------------
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The high-level goal of libweston is to decouple the compositor from
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the shell implementation (what used to be shell plugins).
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Thus, instead of launching 'weston' with various arguments to choose the
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shell, one would launch the shell itself, e.g. 'weston-desktop',
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'weston-ivi', 'orbital', etc. The main executable (the hosting program)
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will implement the shell, while libweston will be used for a fundamental
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compositor implementation.
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Libweston is also intended for use by other project developers who want
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to create new "Wayland WMs".
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Details:
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- All configuration and user interfaces will be outside of libweston.
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This includes command line parsing, configuration files, and runtime
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(graphical) UI.
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- The hosting program (main executable) will be in full control of all
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libweston options. Libweston should not have user settable options
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that would work behind the hosting program's back, except perhaps
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debugging features and such.
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- Signal handling will be outside of libweston.
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- Child process execution and management will be outside of libweston.
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- The different backends (drm, fbdev, x11, etc) will be an internal
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detail of libweston. Libweston will not support third party
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backends. However, hosting programs need to handle
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backend-specific configuration due to differences in behaviour and
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available features.
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- Renderers will be libweston internal details too, though again the
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hosting program may affect the choice of renderer if the backend
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allows, and maybe set renderer-specific options.
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- plugin design ???
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- xwayland ???
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- weston-launch is still with libweston even though it can only launch
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Weston and nothing else. We would like to allow it to launch any compositor,
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but since it gives by design root access to input devices and DRM, how can
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we restrict it to intended programs?
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There are still many more details to be decided.
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For packagers
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-------------
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Always build Weston with --with-cairo=image.
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The Weston project is (will be) intended to be split into several
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binary packages, each with its own dependencies. The maximal split
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would be roughly like this:
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- libweston (minimal dependencies):
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+ headless backend
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+ wayland backend
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- gl-renderer (depends on GL libs etc.)
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- drm-backend (depends on libdrm, libgbm, libudev, libinput, ...)
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- x11-backend (depends of X11/xcb libs)
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- xwayland (depends on X11/xcb libs)
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- fbdev-backend (depends on libudev...)
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- rdp-backend (depends on freerdp)
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- weston (the executable, not parallel-installable):
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+ desktop shell
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+ ivi-shell
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+ fullscreen shell
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+ weston-info, weston-terminal, etc. we install by default
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+ screen-share
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- weston demos (not parallel-installable)
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+ weston-simple-* programs
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+ possibly all the programs we build but do not install by
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default
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- and possibly more...
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Everything should be parallel-installable across libweston major
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ABI-versions (libweston-1.so, libweston-2.so, etc.), except those
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explicitly mentioned.
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Weston's build may not sanely allow this yet, but this is the
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intention.
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