So the curve will be moving smoothly.

When the user hit on the curve should be appear a point and from it a pendulum which will be deformed the curve in that point.

So this is the reason because a need to find a point on the curve.

there is anyway to find the t parameter of the curve?

thanks again

best

C.

perhaps you can borrow from this: http://www.openprocessing.org/visuals/?visualID=12768

it's just an approximation though, because an exact analytical solution is tough -- a second-order distance equation against a third-order curve implies solving a sixth-order equation in the general case.