Re: graphs with labelled edges

> From: "Tim Bradshaw" <tfb@cley.com>
> Sent: Tuesday, April 30, 2002 10:54 PM
> Subject: graphs with labelled edges
>
> I would like to be able to draw graphs which have labels on their
> edges.  There are two problems I don't know how to solve:
>
> 1. Is there any easy way using CAPI:GRAPH-PANE to label edges in the
>    graph?  I guess I need to do something with :EDGE-PINBOARD-CLASS,
>    but I'm not sure what!

Since the labels may extend beyond the bounding rectangle of the
edge, I think you need to create a separate pinboard object for
the label.

The following code might get you started:

_________________________________________________________________

(defun node-children (node)
  (when (< node 16)
    (list (* node 2)
          (1+ (* node 2)))))

(defvar *edges*) ; a list of triplets of the form
                 ; (from-data to-data line-pinboard-object)

(defun my-make-edge (pinboard from to)
  (let* ((edge (make-instance 'capi:line-pinboard-object)))
    (push (list from to edge) *edges*)
    edge))

(defun make-labelled-graph ()
  (let* ((*edges* '())
         (graph (capi:contain
                 (make-instance 'capi:graph-pane
                                :roots '(1)
                                :edge-pane-function 'my-make-edge
                                :children-function 'node-children)
                 :best-width 300
                 :best-height 400
                 :process nil ; so that dynamic binding of *edges* is
not lost
                 )))
    (loop for x in *edges*
          do (let* ((label (capi:with-geometry (third x)
                             (make-instance
                              'capi:item-pinboard-object
                              :text (format nil "~S-~S"
                                            (first x)
                                            (second x))
                              :x (+ capi:%x%
                                    (/ capi:%width% 2))
                              :y (+ capi:%y%
                                    (/ capi:%height% 2))))))
               (capi:manipulate-pinboard graph
                                         label
                                         :add-top)))))

(make-labelled-graph)

_________________________________________________________________


> 2. Is there any way to make it be so that if there are two edges
>    between a pair of nodes (so the same node appears twice in the
>    children) that two edges are drawn?  This seems to me to be very
>    hard as they need to avoid each other, and I can live without
>    this
>    by preprocessing the graph to make there just be one child with a
>    the edge having label which is all the labels combined.
>
> Is there any other grapher anyone knows of which could do (2)?

No ideas here.

>
> Thanks
>
> --tim

Simon.