Processing is excellent and I have used it extensively. I have also used Nodebox, which is something similar but in Python: http://nodebox.net Most recently however I have switched to using Field. I'm not a huge fan of Java syntax, so being able to write Processing apps in Python/Jython via Field is a big win for me. http://openendedgroup.com/field There are lots of features I haven't even touched in Field yet...
This is the kind of thing I read HNN for - stuff I never even knew I needed. Do I understand correctly that Field lets you build graphical representations of your code ? Kind of like ... graphical literate programming? This is where my wife would say "Jézus Mária és minden szentek". It's ... full of stars ...
You can also embed sliders and colour-pickers etc. directly in your code to give you even more ways to modify things.
Yes, this is as amazing as it sounds!