Drawing with Core Graphics
Every application we’ve built so far has been constructed from views and controls that are part of the UIKit framework. You can do a lot with UIKit, and a great many applications can be constructed using only its predefined objects. Some visual elements, however, can’t be fully realized without going beyond what the UIKit stock components offer.
For example, sometimes an application needs to be able to do custom drawing. Fortunately, iOS includes the Core Graphics framework which allows us to do a wide array of drawing tasks. In this chapter, we’ll explore this powerful graphics environment. We’ll also build sample applications that demonstrate key features of Core Graphics and explain its main concepts. ...