Touchscreen technology has been available for many years now, but until recently, it was quite uncommon to find it used on a computer, especially a mobile one. Instead, you were more likely to find it in places such as airports and museums, providing a way to interact with exhibits or browse associated information. Those touchscreens were quite primitive and generally responded only to a single touch location at one time. As technology has improved, we now see far more advanced touchscreens everywhere, and using them is becoming the normal way to work with the latest smartphones. Newer screens also have a major advantage over the old ones: they can respond to multiple points of interaction simultaneously. This is known as multitouch.

Multitouch enables complex interaction, as combinations of touchpoints can do more interesting things than multiple single touchpoints. With multitouch, you can combine two or more points of interaction into complex gestures, such as pinching or rotating, that are impossible with a single touchpoint. Some gestures can be simpler, such as swiping a finger across the screen, so they don't always require multitouch, but multitouch extends the possibilities dramatically. Some applications, such as playing with a virtual piano keyboard, don't require multitouch interaction. Others, such as web browsing and photo manipulation, rely on it.

In this section, you'll look at what is possible and how you can respond to multitouch events and gestures ...

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