Touchable area of a UIButton

Is there any way to define which area of a UIButton is clickable? In my case I would like to have开发者_StackOverflow中文版 PNGs with an alpha channel overlapping. These PNGs should act as buttons - but only where alpha is > 0. Is there a way?

Best Stefan

Don't do that. According to the Apple Human Interface Guidelines, all UI elements should behave in a consistent manner.

OBShapedButton is an awesome project that will give you a button that will only respond to taps that are in the images area. I've messed with Irregularly Shaped UIButtons and I think OBShapedButton is a little more accurate. Not trying to bash on the other one at all. I've used the other and it works just fine. I've just seen a more accurate hit area with this one.