Code

public class MyBehavior : DrawShapesBehavior
{
	public MyBehavior(Diagram diagram) : base(diagram) { }

	public override InteractionState StartDraw(Point point)
	{
		var node = Diagram.GetNodeAt(point, true);
		if (node != null)
		{
			if (GetAnchorAt(node, point) != null)
			{
				var link = CreateLink(node, point);
				Diagram.Links.Add(link);
				return new InteractionState(link, Action.Create, link.ControlPoints.Count - 1, point);
			}

			return new InteractionState(node, Action.Modify, 8, point);
		}

		return base.StartDraw(point);
	}

	static AnchorPoint GetAnchorAt(DiagramNode node, Point point)
	{
		foreach (AnchorPoint ap in node.AnchorPattern.Points)
		{
			Rect r = node.Bounds;
			Point p = new Point(
				r.Width * ap.X / 100 + r.X,
				r.Height * ap.Y / 100 + r.Y);

			if (p.Distance(point) < 10)
				return ap;
		}

		return null;
	}
}