code: function(point) {
          $.console.assert(this.viewer,
              "[Viewport.viewportToWindowCoordinates] the viewport must have a viewer.");
          var viewerCoordinates = this.viewportToViewerElementCoordinates(point);
          return viewerCoordinates.plus(
                  $.getElementPosition(this.viewer.element));
      }
docs: Convert viewport coordinates to pixel coordinates relative to the window.
  @param {OpenSeadragon.Point} point
  @returns {OpenSeadragon.Point}