The APIs for drawing used in this chapter are commonly referred to as AppKit drawing APIs. Behind the scenes, the AppKit drawing APIs are implemented using a framework called Core Graphics, which is colloquially referred to as Quartz.
If you are serious about custom drawing you will want to look into Core Graphics. The concepts are very similar, except it is a C API, and it is much more explicit about the graphics context (almost every Core Graphics API takes a CGContextRef, essentially a pointer to the context, as its first parameter). Core Graphics provides somewhat lower-level access to drawing and, in some cases, much finer control than is possible in AppKit.