Feature: EdgePainter paint between node widgets' edge

[PatrickStar125]

Why need this feature

Hi, cupofme. I wanna thank for your work that helps me a lot. Now I am wodering how to draw lines not from the center position but node widgets' edge, but I find it hard to implement this with only a paint method in EdgePainter.
Effect example:

My workaround

(Offset, Offset) _toEdgePosition(
    Offset src,
    Offset dest,
    double srcSize,
    double destSize,
  ) {
    final delta = dest - src;
    final mu = delta / delta.distance;
    final destEdgeOffset = mu * destSize / 2;
    final srcEdgeOffset = mu * srcSize / 2;
    return (src + srcEdgeOffset, dest - destEdgeOffset);
  }

Providing source and destination size I can calculate the offset.

@override
void paint(Canvas canvas, Size size) {
  if (!controller.canLayout) {
    return;
  }

  final layout = controller.layout;
  final edges = controller.edges;

  for (final edge in edges) {
    var src = layout.getPosition(edge.source);
    var dest = layout.getPosition(edge.destination);
    if (configuration.isEdgePositioned) {
      (src, dest) = _toEdgePosition(
        src,
        dest,
        edge.source.size,
        edge.destination.size,
      );
    }
    configuration.edgePainter.paint(
      canvas,
      edge,
      src,
      dest,
    );
  }
}

Then I can achieve the effect above. But I don't think my workaround is a good idea, this function is only for circle container.

My thought

Maybe a more custom EdgePainter like NodeViewBuilder can do more effects such as MoreRegion or GestureDectector. And I am trying for it.