Hello Danpost, this is really great stuff, I'm going to use it for a project I've been working on for the last months (see a version of the project in a very early stage on http://www.greenfoot.org/scenarios/12057). Keep up the great work!

Thanks for your feedback! Concerning the performance problem: I share your suspicion and it might also be related to my laptop that works only with Intel HD Graphics (though I've never suspected that a simple program could bring down my laptop so quickly...) And thanks for your compliment! I will definitely keep improving it, starting with using vector movements for the projectiles and adding more weapons.