I raised this requirement long long ago and Walter gave me a partial solution, but so far we haven't done anything with this. I'm just curious if in the latest release of GoDiagram there is an option for curve links going through the control points. As you know, in the version we are using, GoDiagram 2.5, the control points for curve links are not on the links.
In Graphics class of .net, there are methods for drawing such curves, i.e. DrawCurve. I guess the one used in GoDiagram is DrawBezier.
The Curves.cs code is dependent on the System.Drawing.Drawing2D.GraphicsPath AddCurve method. This method automatically calculates a "cardinal spline", where the curve travels directly through each point that defines the spline.
Unfortunately, there is no equivalent class/method available in the standard Java libraries. It might be possible to calculate an equivalent set of cubic curves between each of the points in the spline, but doing so would be complex and involve significant computation. We will consider adding this feature in a future release of JGo, but no promises.