camera.ScreenPointToRay()，camera.ScreenToWorldPoint()与Raycast()

 1 Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
 2             RaycastHit hit;
 3
 4             if (Physics.Raycast(ray,out hit,layermask))
 5             {
 6                 Vector3 dir = hit.point - Camera.main.transform.position;                   //dir为由摄像机指向摄像机到射线打到的点的向量
 7                 Vector3 forward = Camera.main.transform.forward;                            //指向摄像机正前方的单位向量
 8                 Debug.Log("Camera.main.ScreenToWorldPoint(Input.mousePosition) "
 9                     + Camera.main.ScreenToWorldPoint(Input.mousePosition)
10                     + new Vector3(0, 0, (Vector3.Dot(dir, forward))));                      //Vector3.Dot(dir, forward)为dir与forward的点乘，几何意义为dir在forward上的投影
11                 Debug.Log("hit.point " + hit.point);
12             }