drawing graphs with dia

[Grégoire Dooms <dooms info ucl ac be>]

Hi,
I often need to draw graphs and the best tool I have come around up to 
now is dia.
With the aspect ratio and central connection point of ellipses dia is a 
great tool to draw undirected graphs.

But when it comes to directed graphs, things get a little more difficult.

There have been some discussions on this list about features that could 
improve dia for drawing directed graphs:
- The line gap code from David Hoover :
http://mail.gnome.org/archives/dia-list/2002-November/msg00097.html
- The curve/line intersection:
http://mail.gnome.org/archives/dia-list/2004-August/msg00086.html
- The "virtual" and "edge"  in the chickenpox  discussion:
http://mail.gnome.org/archives/dia-list/2004-March/msg00098.html

I cannot find the line gap UI in dia v0.94 and cannot compile from CVS 
(see below).

So here is my question:
I would like to implement some kind of support for radial arcs in a 
graph (the end of the arrow touches the  edge of the ellipse while the 
arrow points to and is connected to the central CP).

How should I do this ?
- An auto-gap option on lines (only working when connected with central 
CP of circles at first)
- A programmed object for graph_node/arc (with lots of code copy-pasted 
from ellipse.c and line.c)
- any other way ?

PS: I tried to compile CVS HEAD on 2005-03-11 and got this error:
widgets.c:30:27: dia-lib-icons.h: No such file or directory
(I did cvs up -d to update my cvs tree) should I check-out from scratch ?

--
Grégoire Dooms