code: function(viewerX, viewerY, current) {
          var point;
          if (viewerX instanceof $.Point) {
              //they passed a point instead of individual components
              current = viewerY;
              point = viewerX;
          } else {
              point = new $.Point(viewerX, viewerY);
          }
  
          point = point.rotate(-this.getRotation(current), this._getRotationPoint(current));
          return current ?
              this._viewportToImageDelta(
                  point.x - this._xSpring.current.value,
                  point.y - this._ySpring.current.value) :
              this._viewportToImageDelta(
                  point.x - this._xSpring.target.value,
                  point.y - this._ySpring.target.value);
      }
docs: Translates from OpenSeadragon viewer coordinate system to image coordinate system.
  This method can be called either by passing X,Y coordinates or an {@link OpenSeadragon.Point}.
  @param {Number|OpenSeadragon.Point} viewerX - The X coordinate or point in viewport coordinate system.
  @param {Number} [viewerY] - The Y coordinate in viewport coordinate system.
  @param {Boolean} [current=false] - Pass true to use the current location; false for target location.
  @return {OpenSeadragon.Point} A point representing the coordinates in the image.