I came across exactly this issue recently when I was starting to write a simulator. It has essentially 3 parts.

• Computation - calculation of changes for each iteration
• Setup & control - input data on what is being modelled and drive the simluation
• Graphics - Representation of data

I was particularly looking for the ability to strip out/replace either the computation (to allow a different model to be simulated), or a different Graphics package (in case the original isn't high performance enough).

I spent a long time deciding what graphical system to use, and settled on Gtk+ for the display and Glade for the visual UI building.

The computation model was written as a separate module.

This combination allowed almost complete separation between the computation, the control and the grpahics, with just a few object references passed between the modules, allowing easy replacement of one of the modules.

I plan to publicise the code when it is a bit more advanced.
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Brovnik