code: function(deg, ox, oy, cos, sin) {
          var x2, y2;
          x2 =
              (this._x + this._origin.x - ox) * cos +
              (this._y + this._origin.y - oy) * sin +
              (ox - this._origin.x);
          y2 =
              (this._y + this._origin.y - oy) * cos -
              (this._x + this._origin.x - ox) * sin +
              (oy - this._origin.y);
          this._setter2d("_rotation", this._rotation - deg);
          this._setter2d("_x", x2);
          this._setter2d("_y", y2);
      }
docs: Method for rotation rather than through a setter
  
  Pass in degree amount, origin coordinate and precalculated cos/sin