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Quartz Compositor is the window server in Mac OS X. It is responsible for presenting and maintaining rasterized, rendered graphics from the rest of the Core Graphics framework and other renderers in the Quartz technologies family.

Quartz Compositor is the sole facilitator for the placement of rendered bitmaps into the memory of the graphics card. The bitmap output from Quartz 2D, OpenGL, Core Image, QuickTime, or other process is written to a specific memory location, or backing store. The Compositor then reads the data from the backing stores and assembles each into one image for the display, writing that image to the frame buffer memory of the graphics card. Quartz Compositor only accepts raster data, and is the only process that can directly access the graphics frame buffer.^[1]

In managing individual windows, Quartz Compositor accepts a bitmap image of the window's contents from its renderer, along with its position. The choice of the renderer is up to the individual application, although most use Quartz 2D. Quartz Compositor then acts as a "visual mixing board," by adding the given window to the whole scene for the display. This model makes the Mac OS X window server unique, as individual processes are not allowed to claim ownership on the display.^[2]

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.^[3]

Mac OS X v10.2 introduced Quartz Extreme: graphics processor (GPU) acceleration for the Quartz Compositor. With Quartz Extreme, no central processor (CPU) cycles are utilized for scene composition. Quartz Compositor runs using the graphics processor (GPU) by encapsulating each rendered backing store in an OpenGL texture map or surface. The GPU then composes the surfaces and maps to provide the final image, which is delivered to its frame buffer.

Quartz Extreme only uses OpenGL commands, and requires a graphics card connected to an AGP 2X or faster bus (including AGP 4X, 8X, and PCI Express), supporting textures and maps of arbitrary size, since many of the renderers have no size limitation (Quartz 2D for example).^[4] It is automatically enabled on Mac systems with one of the following types of graphics cards:^[5]

• ATI Radeon, AGP-based, 16MB VRAM minimum, or newer
• NVIDIA GeForce2 MX, 16MB VRAM minimum, or newer

Quartz Extreme is not the same as Quartz 2D Extreme, which is optional GPU acceleration for the Quartz 2D renderer. Further, any GPU that is capable of rendering Core Image instructions is also capable of Quartz Extreme.

• Quartz (graphics layer)
• Quartz Composer
• Desktop Window Manager
• Compositing window manager on X Window System
• Compiz

• Quartz Extreme (apple.com)
• The Graphics and Windowing Environment - from Apple's Mac OS X Documentation
• Quartz Services Reference