Perhaps, Processing just isn't the right language to write multi-window applications?

It depends on what you want to do in the seperate winodws, if you want each own to show a movie or complex animation then it is probably not the best tool for the job.

I have used the G4P library to successfully create many multi-window applications. Although each window is effectively a seperate sketch (each with its own PApplet object) I can reduce the framerate for inactive windows and then increase it again when they get focus.

I used this technique with the Mandelbrot example that comes with the library and have had over 20 windows open at the same time with this app.

Thanks for your reply, quarks.

I just stumbled over your G4P lib and also saw the mandelbrot example.
This lib and the examples look great and i will check it out sooner or later for sure!

My current project is an animation movie editor with 4 windows: movie, timeline and two controller windows. It is quite a complex task i think. Besides the performance problems, it seems to me that writing it in a multi-sketch style will throw away many of the comforts processing offers compared against plain java. Apart from that, i have to use the Minim lib, which caused hard crashes when launched from a "sub-sketch". So I'd be forced to place it in the "main-sketch", which seems to be not reasonable, because the main-sketch should be responsible for displaying the animation.

So i decided to try it with a "pseudo-window-class", which will manage to draw at partiular sections of the window, map mouseclicks etc...