code: function(pixel) {
          $.console.assert(this.viewer,
              "[Viewport.imageToWindowCoordinates] the viewport must have a viewer.");
          var viewerCoordinates = this.imageToViewerElementCoordinates(pixel);
          return viewerCoordinates.plus(
                  $.getElementPosition(this.viewer.element));
      }
docs: Convert image coordinates to pixel coordinates relative to the window.
  Note: not accurate with multi-image.
  @param {OpenSeadragon.Point} pixel
  @returns {OpenSeadragon.Point}