code: function(current) {
          var center = this.getCenter(current);
          var width  = 1.0 / this.getZoom(current);
          var height = width / this.getAspectRatio();
  
          return new $.Rect(
              center.x - (width / 2.0),
              center.y - (height / 2.0),
              width,
              height
          );
      }
docs: Returns the bounds of the visible area in viewport coordinates.
  This method ignores the viewport rotation. Use
  {@link OpenSeadragon.Viewport#getBounds} to take it into account.
  @function
  @param {Boolean} current - Pass true for the current location; defaults to false (target location).
  @returns {OpenSeadragon.Rect} The location you are zoomed/panned to, in viewport coordinates.