[Chart] Device coordinates to plot coordinates

[Sacha Sokoloski]

I have another question related to the last.

I'm continuing to build up more machinery for running animations using 
Chart and GTK, and one thing which I would like to do is to register 
mouse clicks from a GTK window, and transfer them into the coordinates 
of the plot. The principle reason for this, as an example, is that I 
have some physical system that I'm simulating, and it would be nice to 
be able to click on the system to set the initial coordinates. It seems 
like PickFn is somehow the key, but I thought I would ask before I dive 
into the guts of Chart.

It would also be helpful to be able to do this in the context of a grid 
renderable, but I'm not sure how possible that would be.

At some point I can also upload my various animation tools, once we 
figure out a good way to integrate it. I've noticed that Diagrams people 
also has an 'active' package for running animations, but I'm not sure 
how to fit it in. Maybe some kind of GTK backend option for animations?

Thanks,

  - Sacha