code: function(viewport) {
              $.console.assert(viewport,
                  'A viewport must now be passed to Overlay.getBounds.');
              var width = this.width;
              var height = this.height;
              if (width === null || height === null) {
                  var size = viewport.deltaPointsFromPixelsNoRotate(this.size, true);
                  if (width === null) {
                      width = size.x;
                  }
                  if (height === null) {
                      height = size.y;
                  }
              }
              var location = this.location.clone();
              this.adjust(location, new $.Point(width, height));
              return this._adjustBoundsForRotation(
                  viewport, new $.Rect(location.x, location.y, width, height));
          }
docs: Returns the current bounds of the overlay in viewport coordinates
  @function
  @param {OpenSeadragon.Viewport} viewport the viewport
  @returns {OpenSeadragon.Rect} overlay bounds