I’ve just finished a fairly long introductory class on object-oriented programming in Processing. Yes, there are other classes in the oven that I'll serve up when they're ready. Here's the link: Programmation orientée-objet, version sympathique. There is also source code for a silly little program called Bestioles that you can play with in your browser from the following address: Bestioles. This program is used at the end of the class and synthesizes quite a few concepts that are explored throughout the entire series of classes on Processing.
As usual, the text is in French, but you can always copy the many code examples and see what they do. I get many requests asking for translations of these classes. Unfortunately, I'm only paid to teach in French, and I don't have the time anyway to write these classes, so it's really just a question of what has become absolutely indispensable to our work within the Atelier.
I'll come back to this question of object-oriented programming later, but it has become quite clear to me over the past year that you cannot reach any acceptable level in Processing if you do not teach object-oriented programming as a basis for most work. And although we've been using objects within the Atelier since day one, I noticed that too many students at the end of last year were still creating their projects with linear structures that were stifling their work. So this year we've moved into objects from the get-go, hence this on-line class which I hope to use as a starting point for a more robust exploration of code, as well as artwork using richer algorithms.