Quartz Compositor

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, QuickTimes, 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.

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.