Bezier Curve is another promising formula / curve that could potentially be used in the project.
It is generated by having 4 points on the graph: one for the start, one for the end and two control points for creating the curve. There is another variation of the Bezier curve with only one control point called quadratic Bezier curve, but the version with two provides more flexibility, variability.
Although it is not possible to achieve sharp edges, Bezier curve brings more variations of curves comparing to Super Ellipse. Because of that, I believe it could be used for generating Stained Glass design inner lines.
Here is a Cubic Bezier Curve plotted on the graph.
Generative Design Of Stained-Glass Windows 