code: function ( rx, ry ) {
              var radx = this.DEG_TO_RAD * rx,
                  rady = this.DEG_TO_RAD * ry,
              //mtx = new $B.geom.Matrix( 1, rady, radx, 1, 0, 0 );
                  mtx = new $B.geom.Matrix( 1, Math.tan(rady), Math.tan(radx), 1, 0, 0 );
              return this.concat( mtx );
          }
docs: Matrix 객체에 기울이기 또는 시어링 변형을 적용
  @param	{Number}	rx	Degree
  @param	{Number}	ry	Degree
  @return {Matrix}