Editing Windowing system (section)

==Display server communications protocols==

===X11===
{{Main|X Window System core protocol|X Window System}}

[[File:X11 display server protocol.svg|thumb|350px|The [[X.Org Server]] communicates with its clients, e.g. [[Amarok (software)|Amarok]], over the X11 protocol.]]
{{stack|[[File:X11.svg|right|60px|X Window System logo]]}}

One example of a display server is the [[X.Org Server]], which runs on top of the kernel (usually a [[Unix]]-like kernel, such as [[Linux]] or [[BSD]]). It receives user input data (e.g. from [[evdev]] on Linux) and passes it to one of its clients. The display server also receives data from its clients; it processes the data, it does the compositing and on Linux it passes the data to one of three kernel components &ndash; [[Direct Rendering Manager|DRM]], [[Graphics Execution Manager|gem]] or [[KMS driver]]. The component writes the data into the [[framebuffer]] and content of the framebuffer is transmitted to the connected screen and displayed. X relies on [[GLX]].

One of the implementations of display server concept is [[X Window System]], in particular its actually used version &ndash; [[X.Org Server]] and [[Xlib]] and [[XCB]] client libraries. The X.Org Server is a display server, but in its current implementation it relies on a second program, the [[compositing window manager]], to do the compositing. Examples are [[Mutter (window manager)|Mutter]] or [[KWin]].

Notable examples of display servers implementing the X11 display server protocol are [[X.Org Server]], [[XFree86]], [[XQuartz]] and [[Cygwin/X]], while client libraries implementing the X11 display server protocol are [[Xlib]] and [[XCB]].

===Wayland===
{{Main|Wayland (protocol)}}

[[File:Wayland display server protocol.svg|thumb|300px|The Wayland display server protocol]]
{{stack|[[File:Wayland Logo.svg|right|60px|Wayland logo]]}}

Display servers that implement the Wayland display server protocol are called [[Wayland compositor]]s. Like any display server, a Wayland compositor is responsible for handling input and output for its clients and, in contrast to X11, the [[compositing]] as well. Examples are [[Weston (software)|Weston]], [[Mutter (software)|Mutter]], [[KWin]] or [[Enlightenment (software)|Enlightenment]].

Wayland compositors communicate with Wayland clients over the [[Wayland (protocol)|Wayland display server protocol]]. This protocol defines that clients can directly write data into the framebuffer using the [[EGL (OpenGL)|EGL]] [[rendering API]]. The display server still gets to decide which window is on top and thus visible to the user and also still is responsible for passing data regarding input devices from [[evdev]] to its clients.

Wayland is used to a certain degree in some Linux desktop distributions, such as [[Fedora (operating system)|Fedora]]. It is also well suited for mobile computing and has been adopted, for example, by the smartphone- and tablet-focused projects [[Tizen]], [[Sailfish OS]] and [[AsteroidOS]].

An implementation of Wayland is available under the [[MIT License]], the [[libwayland-client]] and libwayland-server libraries.

There is an ongoing effort to add Wayland support to [[ChromeOS]].<ref>{{cite web | url = https://chromium.googlesource.com/chromium/src/+/master/docs/ozone_overview.md | title = Ozone Overview | access-date = 2017-08-20}}</ref>

===Mir===
{{Main|Mir (software)}}

The [[Mir (software)|Mir display server]] comes with its own Mir display server protocol which is different from those used by X11 and Wayland. Mir additionally supports the X11 protocol. It was developed by [[Canonical Ltd.|Canonical]] and was intended to be the display server of choice for [[Ubuntu (operating system)|Ubuntu]]. As of 2017, it has been replaced with the Wayland display server for desktop editions of Ubuntu.

There are implementations of the Mir display server, the libmir-server and the libmir-client libraries available under the [[GPLv3]].