Objective c : link two points with the touch by drawing

Question

Hi,

I have two points. The user can be able to join a point from the other. With the touch moved action, a straigth is created incrementaly and during the dragging on the screen.

I have created a method to retrieve the equation of the straigth and then the point of intersection with the finger and this straigth. After, I redraw a new straigth on each move which start from the first point to the intersection ti finally reach the point.

But this is not really reactive due to the number of computation I think... Is there a way to do that with a UISlider or UIProgress Bar?

I tried to do it with a UISlider but when I touch the screen and the Slider is created, then I must retouch the screen to drag it... is there a way to directly drag even if it's created at the same time?

Thanks a lot!