iPhone - Curved UISlider or Similar Functionality

I am trying to implement a curved UISlider (around a half or quarter circle) or an interactive ?UIView? that would create a similar effect. The reason for the slider (or similar) is so that the user can interact with an object, but the interaction must be limited to the round portions of the semi-circle. The im开发者_开发技巧age inside the circle changes based on the interactive object's location.

Can anyone point to me towards example code or other references?

Thank you!