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This is a Greenfoot version of the well-known 2d physics engine "Box2D" by Erin Catto. More specificly this is actually a port from "JBox2D", a java port for the Box2D engine which is written in C++.
> Box2D website: box2d.org
> JBox2D website: jbox2d.org
Box2D features precise collisions for any convex chaped polygon, circles and more. Additionally it fearures joints like springs. Most importantly though: Its performance is incredible.
Note that due to its independent nature Box2D can't draw its shapes so that is something you will have to do. It's not hard though.
What I actually did is simply move some folders and creating some helping classes that simplify the structure to create and work with the engine.
You can easily reuse these classes and the whole engine in your scenarios by copying the "org", the "rccookie" folder and the license file over into your scenario's folder.
Below you find a simple demo showing of some simple parts of the Box2D engine. Left-click to add circles, which can be adjusted using the ui. Middle-cling to add boxes and right-click to add static walls.