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In computing, a windowing system (or window system) is a software suite that manages separately different parts of display screens. [1] It is a type of graphical user interface (GUI) which implements the WIMP (windows, icons, menus, pointer) paradigm for a user interface.
Each currently running application 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 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.
The main component of any windowing system is usually called the display server, 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 an application programming interface (API) or 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, 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.[ citation needed ]
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.[ citation needed ]
A display server protocol can be network capable or even network transparent, facilitating the implementation of thin clients.[ citation needed ]
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.
The server/client relationship of a standalone display server is somewhat counterintuitive in that a "server" is usually thought of as a large, remote machine, whereas a standalone "display server" is a small local system, with most clients being executed on a larger central machine. The explanation is that a display server provides the services of a display and input devices.
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 – DRM, 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 – 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 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.
Display servers that implement the Wayland display server protocol are called Wayland compositors. 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, 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 evdev 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. [2]
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.
Google developed a display server called SurfaceFlinger [3] 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. [4] [5]
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 (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.
For Apple's macOS family of operating systems, Quartz Compositor fulfils the tasks of a display server and of a window manager in the windowing system.
For Microsoft Windows, from Windows Vista onward, Desktop Window Manager 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.
Some systems such as Microsoft Windows (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.[ citation needed ]
A graphical user interface, or GUI, is a form of user interface that allows users to interact with electronic devices through graphical icons and visual indicators such as secondary notation. In many applications, GUIs are used instead of text-based UIs, which are based on typed command labels or text navigation. GUIs were introduced in reaction to the perceived steep learning curve of command-line interfaces (CLIs), which require commands to be typed on a computer keyboard.
The X Window System is a windowing system for bitmap displays, common on Unix-like operating systems.
An X window manager is a window manager that runs on top of the X Window System, a windowing system mainly used on Unix-like systems.
Virtual Network Computing (VNC) is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another computer. It transmits the keyboard and mouse input from one computer to another, relaying the graphical-screen updates, over a network.
XQuartz is an open-source version of the X.Org X server, a display server for the X Window System that runs on macOS. It formally replaced Apple's internal X11 app. The name "XQuartz" derives from Quartz, part of the macOS Core Graphics framework, to which XQuartz connects these applications. XQuartz allows cross-platform applications using X11 for the GUI to run on macOS, many of which are not specifically designed for macOS. This includes numerous scientific and academic software projects.
freedesktop.org (fd.o), formerly X Desktop Group (XDG), is a project to work on interoperability and shared base technology for free-software desktop environments for the X Window System (X11) and Wayland on Linux and other Unix-like operating systems. Although freedesktop.org produces specifications for interoperability, it is not a formal standards body.
X.Org Server is the free and open-source implementation of the X Window System (X11) display server stewarded by the X.Org Foundation.
GLX 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 wishing to use OpenGL to do so within a window provided by the X Window System. GLX distinguishes two "states": indirect state and direct state.
A window manager is system software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment. They work in conjunction with the underlying graphical system that provides required functionality—support for graphics hardware, pointing devices, and a keyboard—and are often written and created using a widget toolkit.
In computing, a virtual desktop is a term used with respect to user interfaces, usually within the WIMP paradigm, to describe ways in which the virtual space of a computer's desktop environment is expanded beyond the physical limits of the screen's display area through the use of software. This compensates limits of the desktop area and is helpful in reducing clutter of running graphical applications.
In computing, a shell is a computer program that exposes an operating system's services to a human user or other programs. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation. It is named a shell because it is the outermost layer around the operating system.
In computing, a tiling window manager is a window manager with an organization of the screen into mutually non-overlapping frames, as opposed to the more common approach of coordinate-based stacking of overlapping objects (windows) that tries to fully emulate the desktop metaphor.
A compositing manager, or compositor, is software that provides applications with an off-screen buffer for each window. The compositing manager composites the window buffers into an image representing the screen and writes the result into the display memory. A compositing window manager is a window manager that is also a compositing manager.
Linux 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 (distro), which includes the kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses and recommends the name "GNU/Linux" to emphasize the use and importance of GNU software in many distributions, causing some controversy.
In computing, Nano-X is a windowing system which is full featured enough to be used on a PC, an embedded system or a PDA. It is an Open Source project aimed at bringing the features of modern graphical windowing environments to smaller devices and platforms. The project was renamed from Microwindows due to legal threats from Microsoft regarding the Windows trademark.
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, because it additionally performs the task of a compositing window manager.
Mir is a computer display server and, recently, a Wayland compositor for the Linux operating system that is under development by Canonical Ltd. It was planned to replace the currently used X Window System for Ubuntu; however, the plan changed and Mutter was adopted as part of GNOME Shell.
Windows Subsystem for Linux (WSL) is a feature of Microsoft Windows that allows developers to run a Linux environment without the need for a separate virtual machine or dual booting. There are two versions of WSL: WSL 1 and WSL 2. WSL is not available to all Windows 10 users by default. It can be installed either by joining the Windows Insider program or manually via Microsoft Store or Winget.
Client-side decoration (CSD) is the concept of allowing a graphical application software to be responsible for drawing its own window decorations, historically the responsibility of the window manager.