curve editor

Can you be more specific? Do you just want to draw a curve and save it as an image? Do you want to know the equation of the curve, or the polynormial of best fit of a given degree? Do you want Bézier control points?

Or taking, a step back, what is this for? If you just want a 'spline editor' for example, I'd guess that searching on that term might get some useful results.

It's for giving the user a way to indicate how some results must be filtered. So on a Cartesian coordinate system (excluding the negative values) where the curve is drawn, I need to be able to know the ordinate value for each abscissa. I hope it's clear. And I would like to be able to give the user a way to change the type of curve : Bézier, b-spline, Hermite, ... and to choose the number of control points.