Quartz Compositor is the windowing system 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. Internally, it is also known as WindowServer.
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.
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.
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.
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). It is automatically enabled on Mac systems with one of the following types of graphics cards:
- AMD (ATI) Radeon, AGP-based, 16MB VRAM minimum, or better
- NVIDIA GeForce2 MX, 16MB VRAM minimum, or better
QuartzGL (called Quartz 2D Extreme when it was introduced in Mac OS X Tiger) is GPU acceleration for the Quartz 2D API. As of Mac OS X Snow Leopard, it is still not enabled by default. However, it has been possible to enable it, using the Quartz Debug application included in the Apple Developer Tools. QuartzGL will be disabled once again upon quitting the Quartz Debug utility. A workaround is to force quit the Quartz Debug application, which will leave QuartzGL enabled system-wide.
All graphics cards capable of supporting Core Image also support QuartzGL.
As of August 2011, no non Apple web browser fully support GPU hardware acceleration based QuartzGL for rendering contents.  Firefox 13.0 and later supports hardware acceleration on OSX 10.8/10.7/10.6.  Mac OS X 10.7, however, includes an edition of the Safari browser with full hardware acceleration support.
- Russell, Matthew. "What Is Quartz (or Why Can't Windows Do That)". O'Reilly Mac DevCenter. O'Reilly Media. Retrieved 17 November 2011.
- John Siracusa (2005-04-28). "Mac OS X 10.4 Tiger". ArsTechnica. Retrieved 2010-01-15.
- "Apple - Developer - Mac OS X Technology Overview: Graphics, Imaging, and Multimedia". Retrieved 2007-04-18.
- "Apple - Mac OS X 10.4: Requirements for Quartz Extreme and Core Image graphics". Retrieved 2007-02-12.
- Firefox 4: hardware acceleration ✩ Mozilla Hacks – the Web developer blog
- 692879 – Implement CoreGraphics Azure backend
- The Graphics and Windowing Environment - from Apple's Mac OS X Documentation
- Quartz Services Reference