Unity3d 拖拽物体

 void OnMouseDrag()    {        //屏幕空间拖拽        //float distance_to_screen = Camera.main.WorldToScreenPoint(gameObject.transform.position).z;        //transform.position = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, distance_to_screen));        //float distance_to_screen = Camera.main.WorldToScreenPoint(gameObject.transform.position).z;        //Vector3 pos_move = Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, distance_to_screen));        //transform.position = new Vector3(pos_move.x, transform.position.y, pos_move.z);        ///立体空间拖拽        // Bit shift the index of the layer (8) to get a bit mask        int layerMask = 1 << 9;        // This would cast rays only against colliders in layer 8.        // But instead we want to collide against everything except layer 8. The ~ Operator does this, it inverts a bitmask.        layerMask = ~layerMask;        RaycastHit hit;        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);        if (Physics.Raycast(ray, out hit, Mathf.Infinity, layerMask))        {            transform.position = new Vector3(hit.point.x, transform.position.y, hit.point.z);        }    }