cocos2d-iphone - Ring and Pole - Box2d

Question

How I can make a b2Body in box2d so that it could form a ring which does not collide from the center just like a ring. like when we flick the object and there's another body (like pole), the pole can go inside from the ring.

like this:

Answer 1

you can make a joint of two circle bodies like this

o o  ->

          ||
          ||
         o||o
          ||  

Answer 2

首先想到的是倒置杆，即杆本身只是一个孔，它周围的空间是盒子。然后在它上面放置一个倒置的图像（看起来像一根杆子），然后让环落入孔中。只是一个愚弄眼睛的问题。