Parameters
- startFrom
- this point will already have been added to the stroke by ComputePoints before calling this method
- fromDir
- normally 0, 90, 180, or 270 degrees
- endTo
- ComputePoints will add this point after calling this method
- toDir
- normally 0, 90, 180, or 270 degrees
- fromnode
- the Node that the link is coming from
- tonode
- the Node that the link is going to