## Auto-layout of Graph Components

From: "andrew cooke" <andrew@...>

Date: Thu, 19 Mar 2009 09:43:18 -0400 (CLT)

One of the projects I work on (at my paid job, ISTI) is a simple GUI
front-end to software that manages data for seismic detectors.  I don't
understand the underlying system completely, but it's component-based,
with many different processes, each configured separately, communicating
in real time via shared buffers.  Each installation is different, and some
rather complex, so can be a bit of a nightmare to configure, or to
understand an existing system.

Hence a GUI front end, although there are obvious limitations on what is
possible when you are layering on top of a system like that, especially
when the top layer must be as tolerant as possible to different deployment
scenarios.

Anyway, I wrote the code a while back (which is itself based on an earlier
system) and one thing we tried to add was a graphical display, showing the
interconnected processes and buffers.  The main problem (after inferring
what the connections are, which means reading each process's configuration
file) is providing a clear, flexible layout.

Originally I hoped to use a "springs" layout engine, which simulates the
physics of connecting the nodes with springs - if you're interested in
this kind of problem you've probably seen libraries like this.  However, I
couldn't find a good implementation for Python and was worried that
implementing my own would be too expensive.

So I went with a simpler option, which was to constrain the geometry to
two concentric circles, with the buffers on the inner circle and the
processes outside.  The exact ordering was calculated using simulated
annealing.  This seemed to produce reasonable results for my test system
(with a handful of buffers and maybe 10 or so processes), but I was unsure
how it would scale (I guessed at how various things would vary with graph
size and made the layout engine auto-adapt the parameters, but didn't have
another system to test it on).

Anyway, yesterday we finally used it on a larger client system.  The
result is here - http://www.acooke.org/ewfe-graph.png - and I am really
pleased.  Sure, there are more beautiful programs in the world, but for
the tradeoffs made I think this is a great result.  It should be a huge
help to the end user (clicking on the different components lets you edit
their configurations, stop/start them. etc etc).

Andrew