Visualization using observer pattern

Konrad Hinsen
Tue, 28 Oct 1997 19:01:32 +0100

> I just discovered a lightweight visualization package called Flex
> (, which can act as a
> visualization server via TCP/IP sockets. I hust hacked a little MMTK

I also discovered it a while ago, but wasn't impressed by its graphical
representation, so I dropped it. The TCP/IP stuff is neat though...

> Now my question: How could molecules notify the observer upon coordinate
> change, _without_ the user invoking special notify() methods explicitly in
> the interpreter? As I don't want to mess with the existing class structure
> for ChemicalObjects, but still want to make my standard collections
> viewable, I decided to override the __getattr__ and __setattr__ methods at
> the Atom or ChemicalObjects class or at the Atom instance level. None
> worked though. 

You'd have to override the setPosition() method for atoms, have it
call the old version, and send the notification you need.

However, there are a couple of problems:
1) You wouldn't catch coordinate changes made by C modules (i.e. MD).
2) You would get a notification per atom, which could be much more than
   you want.
3) Doing it is a bit messy, because the only solution I can think of
   is to assign a new function to Atom.setPosition.

I think the "right" solution is to build a notification framework
into MMTK. But before doing that, the important question is what
exactly it should do. I suppose implementation is a much smaller
Konrad Hinsen                          | E-Mail:
Laboratoire de Dynamique Moleculaire   | Tel.: +33-
Institut de Biologie Structurale       | Fax:  +33-
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