code: function( pixel ) {
          var viewerCoordinates = this.imageToViewerElementCoordinates( pixel );
          return viewerCoordinates.plus(
                  OpenSeadragon.getElementPosition( this.viewer.element ));
      }
docs: Convert image coordinates to pixel coordinates relative to the window.
  @param {OpenSeadragon.Point} pixel
  @returns {OpenSeadragon.Point}