void makeBody(float x, float y) { BodyDef bd = new BodyDef(); bd.type = BodyType.DYNAMIC; bd.position.set(box2d.coordPixelsToWorld(x, y)); body = box2d.createBody(bd); body.setUserData(this); // This is important PolygonShape sd = new PolygonShape(); float box2dW = box2d.scalarPixelsToWorld(w/2); float box2dH = box2d.scalarPixelsToWorld(h/2); sd.setAsBox(box2dW, box2dH); FixtureDef fd = new FixtureDef(); fd.setUserData("box"); // Attach Fixture to Body body.createFixture(fd);