Multi-Touch
iOS supports both single- and Multi-Touch interfaces. Single-touch GUIs handle just one touch at any time. This relieves you of any responsibility to determine which touch you were tracking. The one touch you receive is the only one you need to work with. You look at its data, respond to it, and wait for the next event.
When working with Multi-Touch—that is, when you respond to multiple onscreen touches at once—you receive an entire set of touches. It is up to you to order and respond to that set. You can, however, track each touch separately and see how it changes over time, which enables you to provide a richer set of possible user interaction. Recipes for both single-touch and Multi-Touch interaction follow in this chapter.
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