Quartz Compositor

Quartz Compositor is the windowing system that is responsible for the user interface in Mac OS X. On a Mac OS X system, the Quartz Compositor can be seen in a process list as Window Manager or, in more recent versions, WindowServer.

Quartz Compositor performs two main functions:
 * maintaining and compositing windows
 * event routing

Each window in Mac OS X is stored as a bitmap associated with positioning (including z-index positioning), transparency and anti-aliasing information. The application that owns the window draws the window contents to the appropriate bitmap, using any of the supported drawing modes (for example Quartz 2D, QuickDraw, OpenGL). Quartz Compositor then takes each window bitmap and composites them together using the associated information to create a display.

This allows the Mac OS X windowing system to be "agnostic in terms of a drawing model" and gives it the ability to create impressive visual effects, such as the genie effect as a window is minimised to the Dock.

Quartz Compositor in its role as window manager, also has an event queue which receives events (key strokes, mouse clicks, etc) from the I/O Kit. The Quartz Compositor takes the events from the queue, determines which process owns the window where the event occurred and passes the event on to the processes own event queue.

Quartz Extreme
See: Quartz Extreme

Starting with Mac OS X 10.2, Quartz Compositor was extended by Quartz Extreme.