//从这开始是Debug代码,删掉不影响功能
    //绘制四叉树节点的范围
    void DrawField()
    {
        if (DontHaveChildren())
        {
            Vector3 upperRight = new Vector3(_field.right, _field.top, 0);
            Vector3 lowerRight = new Vector3(_field.right, _field.bottom, 0);
            Vector3 lowerLeft  = new Vector3(_field.left, _field.bottom, 0);
            Vector3 upperLeft  = new Vector3(_field.left, _field.top, 0);

            Debug.DrawLine(upperRight, lowerRight, Color.blue * 0.8f, 0);
            Debug.DrawLine(lowerRight, lowerLeft, Color.blue * 0.8f, 0);
            Debug.DrawLine(lowerLeft, upperLeft, Color.blue * 0.8f, 0);
            Debug.DrawLine(upperLeft, upperRight, Color.blue * 0.8f, 0);
        }
        else
        {
            _upperRightChild.DrawField();
            _lowerRightChild.DrawField();
            _lowerLeftChild.DrawField();
            _upperLeftChild.DrawField();
        }
    }