compute method
Implementation
Face2 compute() {
// todo test ???
var triangle = Triangle(null, null, null);
var a = edge!.tail()!;
var b = edge!.head();
var c = edge!.next!.head();
triangle.set(a.point, b.point, c.point);
triangle.getNormal(normal);
triangle.getMidpoint(midpoint);
area = triangle.getArea();
constant = normal.dot(midpoint);
return this;
}