computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, a windowing system (or window system) is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the

WIMP Wimp, WIMP, or Wimps may refer to: Science and technology * Weakly interacting massive particle, a hypothetical particle of dark matter * WIMP (computing), the "window, icon, menu, pointer" paradigm * WIMP (software bundle), the web stack of Windo ...

( windows, icons,

menu In a restaurant, the menu is a list of food and beverages offered to customers and the prices. A menu may be à la carte – which presents a list of options from which customers choose – or table d'hôte, in which case a pre-established seque ...

s, pointer) paradigm for a user interface. Each currently running

application Application may refer to: Mathematics and computing * Application software, computer software designed to help the user to perform specific tasks ** Application layer, an abstraction layer that specifies protocols and interface methods used in a c ...

is assigned a usually resizable and usually rectangular surface of the display to present its GUI to the user; these windows may overlap each other, as opposed to a tiling interface where they are not allowed to overlap. Usually a

window decoration In computing, a window is a graphical control element. It consists of a visual area containing some of the graphical user interface of the program it belongs to and is framed by a window decoration. It usually has a rectangular shape that can ...

is drawn around each window. The programming of both the window decoration and of available widgets inside of the window, which are graphical elements for direct user interaction, such as sliders, buttons, etc., is eased and simplified through the use of widget toolkits.

Technical details

The main component of any windowing system is usually called the

display server In computing, a windowing system (or window system) is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the WIMP ( windows, icons, menus, pointer) paradigm ...

, although alternative denominations such as window server or compositor are also in use. Any application that runs and presents its GUI in a window, is a client of the display server. The display server and its clients communicate with each other over a communications protocol, which is usually called display server protocol, the display server being the mediator between the clients and the user. It receives all the input from the kernel, that the kernel receives from all attached input devices, such as

keyboard Keyboard may refer to: Text input * Keyboard, part of a typewriter * Computer keyboard ** Keyboard layout, the software control of computer keyboards and their mapping ** Keyboard technology, computer keyboard hardware and firmware Music * Mu ...

, pointing devices, or touchscreen and transmits it to the correct client. The display server is also responsible for the output of the clients to the computer monitor. The output of sound is usually not managed by the display server, but the sound volume is usually handled through GUI applets and it is the display server who decides which applications are on top. A windowing system enables the computer user to work with several programs at the same time. Each program presents its GUI in its own window, which is generally a rectangular area of the screen. From a programmer's point of view, a windowing system implements graphical primitives. For example: rendering fonts or drawing a line on the screen. It provides an abstraction of the graphics hardware for use by higher-level elements of the graphical interface such as a window manager. A display server protocol can be network capable or even network transparent, facilitating the implementation of thin clients.

Display server

Schema of the layers of the graphical user interface

A display server or window server is a program whose primary task is to coordinate the input and output of its clients to and from the rest of the operating system, the hardware, and each other. The display server communicates with its clients over the display server protocol, a communications protocol, which can be network-transparent or simply network-capable. The display server is a key component in any graphical user interface, specifically the windowing system.

Display server communications protocols

X11

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 Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...

or BSD). It receives user input data (e.g. from

evdev evdev (short for 'event device') is a generic input event interface in the Linux kernel and FreeBSD. It generalizes raw input events from device drivers and makes them available through character devices in the /dev/input/ directory. The user-s ...

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 – DRM,

gem A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, an ...

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 GLX (initialism for "OpenGL Extension to the X Window System") is an extension to the X Window System core protocol providing an interface between OpenGL and the X Window System as well as extensions to OpenGL itself. It enables programs wishi ...

. One of the implementations of display server concept is X Window System, in particular its actually used version – X.Org Server and Xlib and

XCB XCB (''X protocol C-language Binding'') is a library implementing the client-side of the X11 display server protocol. XCB is written in the C programming language and distributed under the MIT License. The project was started in 2001 by ...

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 or KWin. Notable examples of display servers implementing the X11 display server protocol are X.Org Server, XFree86,

XQuartz XQuartz is an open-source version of the X.Org X server, a component of the X Window System (X11, or shortened to simply X, and sometimes informally X-Windows) that runs on macOS. It formally replaced Apple's internal X11 app. The name "XQuart ...

and

Cygwin/X Cygwin/X is an implementation of the X Window System that runs under Microsoft Windows. It is part of the Cygwin project, and is installed using Cygwin's standard setup system. Cygwin/X is free software, licensed under the X11 License. Cygwin/ ...

, while client libraries implementing the X11 display server protocol are Xlib and

Wayland

Display servers that implement the Wayland display server protocol are called

Wayland compositor Wayland is a communication protocol that specifies the communication between a display server and its clients, as well as a C library implementation of that protocol. A display server using the Wayland protocol is called a '' 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 – additionally for the compositing. Examples are Weston, Mutter, KWin or Enlightenment. Wayland compositors communicate with Wayland clients over the Wayland display server protocol. This protocol defines that clients can directly write data into the framebuffer using the 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 to input devices from

to its clients. Wayland is used to a certain degree in some Linux desktop distributions, such as 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.

Mir

The 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 and was intended to be the display server of choice for 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 The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general u ...

SurfaceFlinger

Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...

developed a display server called SurfaceFlinger for Android (another Linux kernel-based operating system primarily for mobile devices): Everything in Android is rendered to a "surface"; "surfaces" are produced by applications and placed into a queue that is managed by SurfaceFlinger. Yet another Android-specific solution is "Gralloc". Gralloc handles device memory i.e. it does allocation, arbitration, it handles synchronization via Android/Linux fence file descriptors. Gralloc competes with other solutions like e.g. Mesa's

Generic Buffer Management Mesa, also called Mesa3D and The Mesa 3D Graphics Library, is an open-source software, open source implementation of OpenGL, Vulkan, and other computer graphics, graphics Application programming interface, API specifications. Mesa translates the ...

(GBM) or Nvidia's EGLStreams. The Gralloc hardware abstraction layer (HAL) is used to allocate the buffers that underlie "surfaces". For compositing in Android, Surfaces are sent to SurfaceFlinger, which uses OpenGL ES to do the compositing. Hardware Composer HAL (HWC) was introduced in Android 3.0 and has evolved steadily over the years. Its primary purpose is to determine the most efficient way to composite buffers with the available hardware. As a HAL, its implementation is device-specific and usually done by the display hardware OEM.

Quartz Compositor

For Apple's macOS family of operating systems,

Quartz Compositor Quartz Compositor is the display server (and at the same time the compositing window manager) in macOS. It is responsible for presenting and maintaining rasterized, rendered graphics from the rest of the Core Graphics framework and other rend ...

fulfils the tasks of a display server and of a window manager in the windowing system.

Desktop Window Manager

For

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...

, from Windows Vista onward,

Desktop Window Manager Desktop Window Manager (DWM, previously Desktop Compositing Engine or DCE) is the compositing window manager in Microsoft Windows since Windows Vista that enables the use of hardware acceleration to render the graphical user interface of Windows ...

enables the use of hardware acceleration to render the graphical user interface. It was originally created to enable portions of the new "Windows Aero" user experience, which allowed for effects such as transparency, 3D window switching and more. It is also included with Windows Server 2008, but requires the "Desktop Experience" feature and compatible graphics drivers to be installed. From Windows 8 onwards DWM can't be disabled and is software rendered if no suitable graphics card is installed.

List of windowing systems

For Unix-like operating systems

* 8½ and

rio Rio or Río is the Portuguese, Spanish, Italian, and Maltese word for "river". When spoken on its own, the word often means Rio de Janeiro, a major city in Brazil. Rio or Río may also refer to: Geography Brazil * Rio de Janeiro * Rio do Sul, a ...

for Plan 9 * FramebufferUI in-kernel windowing system * ''HP Windows/9000'' (on early versions of HP-UX) * Sapphire for the PERQ * ManaGeR (MGR) *

Metisse Metisse is a 2.5D X window manager with many features that set it apart from the traditional 3D "cube" workspace. Windows can be turned three-dimensionally in any direction, enabling the user to fit more windows onto a screen, and they can be sc ...

* Mir * NeWS / OpenWindows * NeXT DPS * Orbital ( Redox) *

Qt Extended Qt Extended (named Qtopia before September 30, 2008) is an application platform for embedded Linux-based mobile computing devices such as personal digital assistants, video projectors and mobile phones. It was initially developed by Qt Software, ...

( Mac OS X) *

SunView SunView (Sun Visual Integrated Environment for Workstations, originally SunTools) is a discontinued windowing system from Sun Microsystems developed in the early 1980s. It was included as part of SunOS, Sun's UNIX implementation; unlike lat ...

* Twin (Text WINdows) *

W Window System The W window system is a discontinued windowing system and precursor in name and concept to the modern X Window System window system. W was originally developed at Stanford University by Paul Asente and Brian Reid for the V operating system. In ...

* Wayland * X Window System * XFast * Xynth

For Windows NT-family operating systems

(DWM) in

( Vista and later) * ReactOS Explorer *

Classic Shell Classic Shell is a computer program for Microsoft Windows that provides user interface elements intended to restore familiar features from past versions of Windows. It focuses on the Start menu, File Explorer and Internet Explorer — three maj ...

* Pokki * RetroUI *

Talisman Desktop Talisman Desktop is a Windows shell replacement introduced in 1997 by Lighttek Software, designed to allow the user to configure its interface. It is available in a number of languages including English, French, Spanish, Swedish, Portuguese, Russi ...

Web Web most often refers to: * Spider web, a silken structure created by the animal * World Wide Web or the Web, an Internet-based hypertext system Web, WEB, or the Web may also refer to: Computing * WEB, a literate programming system created by ...
windowing systems

* Dojo *

ExtJS Ext JS is a JavaScript application framework for building interactive cross-platform web applications using techniques such as Ajax, DHTML and DOM scripting. It can be used as a simple component framework (for example, to create dynamic grids on ...

* TIBCO General Interface * Web Window Manager

Other

* DM *

GEM A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, an ...

* Intuition * Microwindows * MiniGUI * OOHG * Visi On * VWS (VAX Workstation Software) Some systems such as

( XP, 9x and earlier), the classic Mac OS (version 9 and earlier), and Palm OS, contain a windowing system which is integrated with the OS.

References

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