What is the window compositing engine used by macOS?

The window compositing engine used by macOS is Quartz Compositor.

Quartz Compositor is both macOS’s display server and its compositing window manager. It assembles the visible desktop by combining rendered images from individual application windows, then sends the resulting scene to the display. Each window typically provides a bitmap or backing store containing its current contents; the compositor places those surfaces at the correct positions and layers them with effects such as transparency and animation.

The name is easy to confuse with related graphics technologies. Quartz 2D is a drawing API within Apple’s Quartz graphics family, while Core Graphics is the framework commonly used to access that 2D drawing functionality. OpenGL and Metal are rendering technologies that applications or system components may use to produce graphics, but neither is the macOS window compositor itself.

Quartz Extreme, introduced with Mac OS X 10.2 Jaguar, accelerated final scene composition using the graphics processor. This distinction matters: Quartz Compositor is the system component responsible for assembling windows, whereas Quartz Extreme describes hardware-accelerated composition. Later macOS releases continued evolving the graphics stack while retaining the compositor’s central role.