How to create a parabola link between two ports?

GoDiagram (6 and previous)
1

In our application, we need to create a parabola link between two ports.

We also need draw the arrowhead in the middle of a curve link(not straight line) and the arrowhead can be dragged as a selection handle of link.
How to do ?
2

Look at what the StateCharter sample does…

at startup, it sets the default link class for a GoView to create:

  InitializeComponent();
  this.goView1.NewLinkClass = typeof(Transition);

The Transition class (GoLabeledLink) is set up as Bezier:

public Transition() {
  this.Style = GoStrokeStyle.Bezier;

and when a link is created, it sets curviness based on the number of links between the 2 nodes:

// when a link is drawn, make sure it has a text label at the middle
// and appears as a curved arrow
private void goView1_LinkCreated(object sender, Northwoods.Go.GoSelectionEventArgs e) {
  GoLabeledLink l = e.GoObject as GoLabeledLink;
  if (l != null) {
    l.Curviness = 20*this.Doc.NumLinksBetween(l.FromPort, l.ToPort);
    l.CalculateRoute();
  }
}

and the final bit is the setting of AdjustingStyle if the Transition is “Resized”

this.AdjustingStyle = GoLinkAdjustingStyle.Scale;

so that the link keeps the curviness when a node is moved.

3

ok, so you also want an arrowhead on the midpoint, and also to drag the curviness by dragging the arrowhead?

4

Jake, Thanks.

Yes, we also need to draw an arrowhead on the midpoint and to drag the curviness by dragging the arrowhead.
5

ok… this is a big part of what you need then (finding the midpoint)

http://www.nwoods.com/forum/forum_posts.asp?TID=1579

and TwoColorLink in NodeLinkDemo shows how to draw an arrowhead…

which just leaves the problem of what angle to draw the arrowhead to match the link, and I think that problem is solved by looking at the angle of two vectors… you’ve got 4 points in the link (from port, 2 control points and to port). If you draw a line from from port to first control point and a line from the second control point to the to port… then average the slope of those two lines… I’m pretty sure you get the right answer.

But I don’t think I have an example of that.

stackoverflow to the rescue (maybe… haven’t checked the math here)

http://stackoverflow.com/questions/12357200/angle-of-a-given-point-on-a-bezier-curve