Wow, that is some very nifty canvas manipulation. Well in terms of difficulty I think to create that level of interactivity would be a huge challenge even for a pro like myself. There is a lot of advanced mathematical calculations in doing that. Perhaps there is a plugin or library but failing that looks like a lot of head banging mathematics. I’ve done things similar in flash using actionscript but that was aeons ago. Though I suppose the trig is similar.

I can’t recommend anything more recent but this book does a good job of going over the mathematical concepts to create that level of interactivity. Though if you’re not familiar with Actiionscript and JavaScript not to mention canvas manipulation it might be a stretch. Though it does do a good job of breaking down the mathematics of creating such behavior.

Thank you very much oddz for your clear assessment!
If we look “just” at the last stage where you get the circle. Is this also that much work? Would it be much easier if I create the circle in 2D?