如何在给定一组点的情况下计算平滑路径的控制点？

I am using UIBezierPath, but this question concerns control points for the paths, not the drawing. Given a set of points, I can render a path. However, I have not been able to figure out how to calculate the control points to have a smooth line like in a photo curves editor ( I am using UIBezierPath, but this question conc