Quartz Compositor

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Quartz Compositor

Developer:	Apple Computer
OS:	Mac OS X
Use:	Windowing system
License:	Proprietary
Website:	www.apple.com/…/quartzextreme/

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's two main functions are maintaining and compositing windows, and routing events.

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 (such as Quartz 2D, QuickDraw, or 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 minimized to the Dock.

In its role as window manager, Quartz Compositor also has an event queue which receives events, such as key strokes and mouse clicks. 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 process's own event queue.

[edit] Quartz Extreme

Starting with Mac OS X v10.2, Quartz Compositor was extended by Quartz Extreme, which uses OpenGL to render screen displays faster by presenting them as textures within a 3D OpenGL context. This permits faster compositing of screen images using 3D hardware acceleration.

To use Quartz Extreme, the Macintosh must have a graphics card with support for arbitrary texture dimensions and a minimum of 16 MB of VRAM. In practice, this means either an NVIDIA GeForce2 MX (or higher) or an ATI Radeon (or higher), using an AGP or PCI Express slot. With the advent of the Intel Macs support for the Intel GMA950 graphics card has also been added.

In Mac OS X v10.4, Apple introduced Quartz 2D Extreme (Q2DE), increasing the speed of the actual drawing operations as well, so that as much of the compositing and drawing was taken over by the graphics card as possible. Note that Q2DE is not enabled by default due to bugs in a number of the graphic card drivers for Mac OS X. In order to enable Q2DE, one may use the Quartz Debug tool included with Apple's Xcode 2.0 developer tools, however, the change will not survive a reboot. To make the change permanent across reboots, one must edit the plist file that controls this feature directly. This file is located in /Library/Preferences, and it's named com.apple.windowserver.plist. Change the Quartz2DExtremeEnabled value to YES. If the Macintosh doesn't contain a GPU that supports Quartz 2D Extreme, the file will not exist.