@yedefei About the multi threading part: I also used to think this would just be fine, but clearly, it isn't. None of Greenfoot APIs are thread safe, so you have to do much work to let it be safe. Davmac told me this, and has a useful scenario: http://www.greenfoot.org/scenarios/1963 to show the amount of code for thread safety. If you want to do more with threads, you should really dive into the books. Just some big advice from me

@mjrb4 I already said that being the fastest wasn't my first goal, but it would be fun if it turned out te be (which will be impossible for me, because as you said, the AWT graphics use hardware). But anyway, thanks for the comment!

It is the same code, and I'm still wondering why you see difference. I know where it is, but when I remove it, you get a less ice effect. But anyway, I'll fix the detection 'bug'

For those of you who have wanted the code of Jump!, I've posted the engine with source code. Please give credit when you use it: http://www.greenfoot.org/scenarios/5764

After testing (my above comment), I discovered already that Graphics uses the GPU. And about using the awt Image of a GreenfootImage, 2 things: -I created this scenario to show people some algoritms, being the fastest would be fun, but wasn't my first goal. -I've looked at the code of GreenfootImage, and they use a Graphics2D instance to draw.

I couldn't find the course, since the doc folder is re-created when you look at documentation. What you need to do, is create a new folder (in the same folder as images and sounds), and put the course in there.