Composition manager
A composition manager is a window manager that enables compositing techniques to be used for computer screen outputs. Composition managers play a special role in the use of hardware accelerated effects on normal desktops . The eye-candy effects used there, such as transparency, 3D display, stepless zooming and live previews of videos or animated sequences, are only possible with the help of the composition manager.
The X.Org server , like the X extensions or modifications Xgl and AIGLX Composition Manager, uses OpenGL to accelerate various effects. The composition managers used are kompmgr, xcompmgr, Compiz , KWin and Metacity (with extensions). Compiz, KWin and Metacity are also window managers . Such a combination of composition manager and window manager is also known as a composition window manager.
Purpose of Composition Managers
With the classic X without composition manager, the windows are simply drawn onto the desktop background using 2D graphics functions (in software or hardware, i.e. via CPU or 2D graphics processor). This meant that windows, if they were completely or partially covered by other windows, but become visible (e.g. because the upper windows are moved), have to be redrawn (referred to as damage ). Composition managers, on the other hand, fulfill the task of graphically combining the windows of running applications before they are displayed. This is usually done by the 3D hardware (the graphics card or the graphics unit in the chipset), i.e. the windows are converted into textures and combined by the graphics unit to form the overall screen content. This eliminates the need to manually handle the invalid areas, and this technique enables various effects when combining the windows, such as B. transparency or animation.