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Compositing window manager

compositing window manager, how to write a compositing window manager
A compositing window manager, or compositor, is a window manager that provides applications with an off-screen buffer for each window The window manager composites the window buffers into an image representing the screen and writes the result into the display memory12

Compositing window managers may perform additional processing on buffered windows, applying 2D and 3D animated effects such as blending, fading, scaling, rotation, duplication, bending and contortion, shuffling, blurring, redirecting applications, and translating windows into one of a number of displays and virtual desktops Computer graphics technology allows for visual effects to be rendered in real time such as drop shadows, live previews, and complex animation34 Since the screen is double buffered, it does not flicker during updates

The most commonly used compositing window managers include:

  • Linux, FreeBSD and OpenSolaris—Compiz, KWin, Xfwm, Enlightenment and Mutter
  • Windows—the Desktop Window Manager
  • macOS—the Quartz Compositor


  • 1 Comparison with stacking window managers
  • 2 History
  • 3 Compositing and 3D effects in operating systems
    • 31 Linux
    • 32 Java
    • 33 AmigaOS 4 and MorphOS
    • 34 Microsoft Windows
  • 4 Usability and eye candy
    • 41 Magnifiers
    • 42 Live preview
    • 43 Window switching
      • 431 Flip switching
      • 432 Cover switching
      • 433 Ring switching
      • 434 Grouping
      • 435 Exposé
      • 436 Mission Control
    • 44 Widget engines
    • 45 Transitions and other effects
    • 46 User Interface Façades
  • 5 List of compositing window managers
  • 6 List of standalone compositing managers
  • 7 Operating systems with compositing window managers
  • 8 See also
  • 9 References
  • 10 External links

Comparison with stacking window managersedit

The window manager sends each window a message to repaint itself whenever appropriate such as when it is resized, or when another window passes in front of it With a stacking manager, the repainting process can become corrupted when a program that is slow, unresponsive or buggy does not respond to messages in a timely manner56 A malicious program can cause the system to appear unstable by simply neglecting to repaint its window Then, one or more of the following conditions may result:

  • a clipped window does not repaint uncovered regions, resulting in either blank spaces or a "trail" left behind from another window
  • portions of windows such as decorative drop shadows are left behind and not properly painted over
  • the mouse pointer is corrupted7unreliable source
  • screen updates become unbearably slow8
  • the entire screen freezes until the program either responds or is terminated9

With a compositing manager, if a window stops repainting itself when requested by the window manager, its last repaint will remain displayed and the window might be dimmed Often the title changes to reflect the status of the window as unresponsive A program may prevent its window from being moved or unmapped, but generally will not cause repainting problems


One of the first systems with a compositing windowing system was the Commodore Amiga, released in 1985 Applications could first request a region of memory outside the current display region for use as bitmap The Amiga windowing system would then use a series of bit blits using the system's hardware blitter to build a composite of these applications' bitmaps, along with buttons and sliders, in display memory, without requiring these applications to redraw any of their bitmaps10

Metacity window manager, part of GNOME

On March 24, 2001, Mac OS X v100 became the first mainstream operating system to feature software-based 3D compositing and effects, provided by its Quartz component With the release of Mac OS X v102 and Quartz Extreme, the job of compositing could be moved to dedicated graphics hardware211

Sun Microsystems developed an ambitious 3D graphics system to layer on top of its Swing toolkit, which was called Project Looking Glass It was first demonstrated at the 2003 LinuxWorld Expo Although Apple threatened to sue Sun for breach of intellectual property rights, some of the functionality in Looking Glass has been implemented in other window managers A few years into its development, it was discontinued by Sun, whose primary business was selling enterprise mainframes

The Desktop Window Manager in Project Longhorn was first presented to the 2003 Windows Hardware Engineering Conference demonstrating wobbly windows12 Severe delays in the development of Longhorn caused Microsoft not to debut its 3D compositing window manager until the release of Windows Vista in January 200713

Compositing under the X Window System required some redesign, which took place incrementally14 Metacity 284 was released in August 200415 However, the first widely publicized compositing window manager for X was Xfwm, released in January 200516 On 26 January 2005, Compiz was released, introducing fully accelerated 3D compositing to the Linux platform17 KDE's KWin also supports compositing

Compositing and 3D effects in operating systemsedit

In compositing, 3D effects could be applied on windows to provide 3D desktop effects Modern compositing window managers use 3D hardware acceleration Compositing window manager software communicates with graphics hardware via programming interfaces such as OpenGL or Direct3D

The earliest widespread implementations using this technique were released for the Mac in Mac OS X 102, and for Linux in a Luminocity prototype Currently, window managers using OpenGL include Compiz, KWin, and the Quartz Compositor, while Desktop Window Manager currently uses DirectX 9 OpenGL is still not fully supported in hardware, so performance of OpenGL-based compositing should continue to improve as hardware improvescitation needed


Stacking window managers running on X server required a chroma keying or green screening extension Compositing was introduced by way of the "Composite" extension Compositing managers use hardware acceleration through this extension, if available

Further information: AIGLX Ubuntu 804 Hardy Heron running Compiz's Shift Switcher in Flip mode

Under Linux and UNIX, the ability to do full 3D-accelerated compositing required fundamental changes to X11 in order to use hardware acceleration Originally, a number of modified X11 implementations designed around OpenGL began to appear, including Xgl The introduction of AIGLX would eliminate the need to use Xgl, and allow window managers to do 3D accelerated compositing on a standard X server, while still allowing for direct rendering Currentlywhen NVIDIA, Intel and ATI cards support AIGLX

Compiz introduced a cube effect, which allows the user to see up to 6 virtual desktops at once Each desktop is converted into a surface texture of the cube, which can be rotated at will Compiz displays a wide array of 2D and 3D effects and has relatively low hardware requirements18 Compiz used to bewhen included in Ubuntu Linux, and is enabled automatically when supported hardware and drivers are available

Mutter Metacity + Clutter has replaced Metacity as the default window manager for GNOME It is featured in the GNOME Shell component of GNOME 30 It uses the display engine Clutter, which has been ported to all major operating systems, netbooks and smartphones

Since version 4, KDE's window manager KWin has compositing capabilities KWin features much of the same functionality also present in Compiz


Main article: Project Looking Glass

Project Looking Glass was a window manager combining 3D rendering and the cross-platform Java programming language It is now inactive and released under the GNU General Public License The Granular Linux live CD distribution includes Looking Glass as an optional window manager

In the aftermath of it being discontinued, some of its features, such as cover switching and thumbnail live previews, have found their way onto other window managers Its more original features included window tilting, two-sided window frames and parallax scrolling backgrounds

AmigaOS 4 and MorphOSedit

While they are able to run on 3D-capable hardware, AmigaOS and MorphOS are designed to run on old legacy Amiga computers, starting with the Amiga 1200 As such, their window managers have mostly planar rendering capabilities that include composite layering, alpha blending, gradients, high resolution and multiple desktops "screens" that can partially clip one another

Microsoft Windowsedit

While the window manager in Windows 2000 does perform compositing, it does not perform transformations such as a per-pixel alpha Few commercial applications took advantage of alpha blending; freeware programs were among the first to experiment with it, albeit through optional settings1920 Compositing was introduced with Desktop Window Manager in Windows Vista1

Windows Vista and Windows 7 allow the user to disable Desktop Window Manager by selecting the Windows Basic appearance settings In addition, it is automatically disabled by Windows in order to perform hardware overlay through the Overlay Mixer Filter

Usability and eye candyedit

The compositing approach makes it easier to implement a number of features that make the user interface more accessible, simpler to use or with eye candy elements


The magnification effect in Compiz click image to view in scale

Vector graphics, such as TrueType fonts and 3D-accelerated elements, can be expanded without degradation usually due to aliasing A screen magnifier enlarges an area of the screen, making portions of text easier to read – whether to prevent eye strain, for the visually impaired, or simply at a distance Zoom effects such as the fish eye magnifier and zoom desktop effects provide this functionality

Live previewedit

A preview of a window can be displayed in a pop-up thumbnail when the user hovers its associated taskbar button This allows the user to identify and manage several concurrently running programs

Window switchingedit

Basic window switching in Xgl

Windows with similar names and icons tend to cause confusion, especially when their title bars overlap; the position of every such window on the taskbar has to be memorized When there are many open windows in this manner, the user often has to resort to trial and error—clicking each taskbar button one-by-one—before proceeding Window switching allows one to quickly preview several windows at once by temporarily rearranging them against a decorative background After a selection is made, the windows are then restored to their original arrangement

Selection begins when the user either enters a hotkey combination, moves the mouse pointer to a hotspot on the screen, or, in some situations, uses the mouse's scroll wheel Items are navigated using the keyboard or mouse An item is selected by either releasing the hotkey, hitting the Enter key or clicking on it with the mouse

Flip switchingedit

Flip switching in Compiz

The flip switcher is an enhancement to the Alt-Tab switching feature Running windows are arranged into a stack – similar to a flip-style selector in a 1950s jukebox, or a Rolodex In some systems, the user can press Alt-Shift-Tab to navigate backwards Visual transitions are applied to each item while navigating

Common implementations of flip switching include Flip 3D in Windows and Shift Switcher in Compiz

Cover switchingedit

Cover Switch in KWin

Cover switching is like flip switching with a few, mostly visual, differences Instead of one stack with the selection at the top, two symmetrical stacks are shown with the current selection front and center similar to the window tilting feature in Looking Glass

Cover Flow is an implementation of cover switching in macOS More recent versions use blurring to de-emphasize non-selected items Cover Flow has also been implemented in other software published by Apple such as iTunes

This is also referred to as "flick-book view"

Ring switchingedit

Ring switching in Compiz Fusion

Ring switching is like flip switching, except the windows move in a circle, with the current selection in front, usually at the bottom Most compositing window managers include this feature out of the box, and third-party applications, such as 3d-desktop, are also available


The user can group windows together, such that only one window at a time is visible in each group In Compiz, the window frame is flipped to indicate when the active window in its group has been changed


Main article: Exposé macOS

macOS displays a preview of every window on the screen by tiling them Other systems with similar functionality Microsoft Windows, Compiz, KWin, third-party applications are referred to as Exposé clones The hotkey to activate Exposé is not Alt-Tab, but rather F3

Mission Controledit

Mac OS X 107 combines several other compositing features developed by Apple—such as Exposé, Dashboard, and Spaces—into a larger program called Mission Control

Widget enginesedit

Main article: Software widget

On macOS, "widgets" single-purpose applets such as a clock, note pad, and calculator can appear by pressing a hotkey Widget engines speed work by keeping commonly used widgets accessible while unobtrusive They are handled by the Dashboard program in macOS

Compiz starts with a blank Widget Layer, allowing the user to add applications by clicking on them A variety of widgets are supported, including Screenlets, gDesklets and SuperKaramba21

Windows Vista provides gadgets that the user can place on the Windows Sidebar Sidebar gadgets, a Windows Live start page Web gadgets, or an external display, such as the user's mobile phone SideShow gadgets The Windows Sidebar was a visible partition in Windows Vista, and was eliminated in Windows 7, along with Sidebar gadgets which were changed to Desktop Gadgets

Transitions and other effectsedit

Before compositing window managers were developed, windows would instantly jump in and out of view, which is incongruent with the interface metaphor and with a physical office setting The sudden appearance and disappearance of GUI elements may seem confusing or even chaotic to inexperienced userscitation needed Visual transitions provide context and help distinguish the causal relationships of GUI elements Instead of just disappearing, a window may fade away, or visibly shrink to the taskbar A pull-down menu that has been clicked may smoothly radiate outward from the menu bar, making it easier to determine its origin and purpose

Gradual and natural transitions may beoriginal research especially helpful for elderly or visually impaired users who notice changes to the screen more slowly and with less clarity For example, an inexperienced user may impulsively click on a menu that was activated by accident, causing him or her to lose work The short delay necessary to display a visual transition may give the user enough time to make a conscious decision, and avoid such mistakes

User Interface Façadesedit

Metisse implements user interface façades, a system that provides users with simple ways to adapt, reconfigure, and recombine existing graphical interfaces, through the use of direct manipulation techniques22

List of compositing window managersedit

  • 3Dwm, a three-dimensional workspace manager23 and general-purpose platform for 3D user interfaces242526 As of June 2006 this project is inactive
  • Desktop Window Manager and the Windows Aero theme on Windows
  • Quartz Compositor on macOS
  • Compiz
  • KWin since version 33
  • Mutter
  • Xfwm from within Xfce since version 42
  • Metisse window system

List of standalone compositing managersedit

  • xcompmgr—a minimal alternative to Compiz
  • Compton–A bug-fixed fork of dcompmgr, which is a fork of xcompmgr
  • Cairo Compmgr Cairo Composite Manager—a compositing add-on for existing window managers It uses Cairo, a vector graphics library also used in GTK+
  • Unagi Compositing Manager—a compositing manager which can be used along with an existing window manager It uses the XCB library
  • MCompositor—used on MeeGo handsets

Operating systems with compositing window managersedit

  • Mac OS X 100 and later
  • any Unix-like OS using XOrg/AIGLX or Xgl
  • AmigaOS 4
  • MorphOS 20 and later
  • Windows Vista and later

See alsoedit

  • Window manager
  • Tiling window manager
  • Stacking window manager
  • Re-parenting window manager
  • Retained mode
  • Zooming user interface
  • Computer graphics


  1. ^ a b "Desktop Window Manager" Msdn2microsoftcom Retrieved 2008-11-21 
  2. ^ a b "Mac OS X 104 Tiger: Page 13" Arstechnicacom Retrieved 2008-11-21 
  3. ^ "Compizorg :: Home/Start – Compiz" Compizorg Retrieved 2008-11-21 
  4. ^ "Blueprint: "Compositing window management compiz/beryl"" Blueprintslaunchpadnet Retrieved 2008-11-21 
  5. ^ "Multiple Internet Explorer Instances Do Not Redraw Screen Correctly" Microsoft 2003-10-09 Retrieved 2010-12-17 
  6. ^ "PHOTOSCORE SUPPORT FAQ" Retrieved 2010-12-17 
  7. ^ "Mouser cursor corruption on xinerama" Canonical Ltd 2006-08-02 Retrieved 2010-12-17 
  8. ^ "Archived from groups: microsoftpublicwindowsxpvideo" Bestofmedia Group 2004-07-18 Retrieved 2010-12-17 
  9. ^ "Mustang: Swing apps freeze then painting corrupt" Oracle 2006-05-01 Retrieved 2010-12-17 
  10. ^ "Amiga RKM Libraries Manual" 
  11. ^ "A Brief History of Mac OS X" Kernelthreadcom Retrieved 2008-11-21 
  12. ^ "Microsoft's Longhorn 3D UI– More Info Emerges" ExtremeTech 
  13. ^ "Microsoft Windows History" Computerhopecom Retrieved 2008-11-21 
  14. ^ "The ReArchitecture of the X Window System" Keithpcom Retrieved 2008-11-21 
  15. ^ "pkgsrcse | The NetBSD package collection" Pkgsrcse Retrieved 2008-11-21 
  16. ^ "Xfce 420 released!" foo-projectsorg 2005-01-16 Retrieved 2009-02-25 
  17. ^ "Version History – Preferences Hide and Seek" Hideseeksourceforgenet Retrieved 2008-11-21 
  18. ^ "Installing/running Compiz on GeForce2 MX/MX 400" 
  19. ^ "Example alpha transparency utility" 
  20. ^ "Alpha Blending Transparent Windows" CodeGuru 
  21. ^ "Plugins/Widget - Compiz Wiki" Compiz Retrieved 2010-12-26 
  22. ^ "Metisse: User Interface Façades" Metisse Retrieved 2011-08-03 
  23. ^ 3Dwm - About, 2004-01-23, archived from the original on 2004-02-06, retrieved 2010-02-04 
  24. ^ 3Dwm - About - FAQ - About the Project, 2003-12-03, archived from the original on 2004-02-24, retrieved 2010-02-04 
  25. ^ 3D window manager, retrieved 2010-12-16 
  26. ^ Yeargin, Ray 2005-03-31, 3DWM: A screenshot look at the 3D desktop, retrieved 2010-12-16 

External linksedit

  • Various effects in Compiz on YouTube
  • Comparison between Windows Aero and Compiz on YouTube
  • Mac OS X and the Quartz Compositor on YouTube
  • Drop shadows and transparency in xcompmgr on YouTube
  • Desktop switching using 3d-desktop on YouTube
  • Desktop switching using the cube effect on YouTube
  • Official demonstration video for Project Looking Glass on YouTube
  • Background and windowing effects in Looking Glass on YouTube

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