相关定义：射线以及射线碰撞体结构

　　Ray , RaycastHit , 

ray:就是点跟方向

raycastHit:

 

       

发射线：1，physics   2，Camera

 

 

 

Ray ray = new Ray(Vector3.zero, Vector3.forward);

        RaycastHit hit = new RaycastHit();

        Physics.Raycast(ray, out hit);

        Camera.main.ScreenPointToRay(new Vector3(2, 2, 2));

        //Camera.main.ViewportPointToRay