Quaternion turntodirection(Vector3 targetpt, Vector3 originalPt)
    {
        float y = targetpt.y - originalPt.y;
        float h = targetpt.x - originalPt.x;
        float aa = Mathf.Atan2(y, h) * (-180) / 3.1415926f + 90; // 此處注意的是： Mathf.Atan2(y軸座標值,x軸座標值); 是自y軸開始的角度（即順時針方向），如果是Mathf.Atan2(x,y),則是自x軸開始的角度（即逆時針方向）
    
        //===================
        float angle = Mathf.Atan2(vDir.x, vDir.y) * Mathf.Rad2Deg;//用這種方式更高效！
        //====================
        Quaternion angle = Quaternion.Euler(0f, 0f, -aa);

        Debug.Log("angle" + aa);
        return angle;
        //curRole.transform.rotation = angle;
    }
 

Update函式中       

Vector2 mousePositionOnScreen = Input.mousePosition;        //讓場景中的Z=滑鼠座標的Z        
        Vector2  mousePositionInWorld = Camera.main.ScreenToWorldPoint(mousePositionOnScreen);
        s_head.rotation = turntodirection(mousePositionInWorld, s_head.position);