function() {
    this.deltaX =  window.pageXOffset
                || document.documentElement.scrollLeft
                || document.body.scrollLeft
                || 0;
    this.deltaY =  window.pageYOffset
                || document.documentElement.scrollTop
                || document.body.scrollTop
                || 0;
  }
function() {
    this.deltaX =  window.pageXOffset
                || document.documentElement.scrollLeft
                || document.body.scrollLeft
                || 0;
    this.deltaY =  window.pageYOffset
                || document.documentElement.scrollTop
                || document.body.scrollTop
                || 0;
  }
function ( ) { this . deltaX = window . pageXOffset || document . documentElement . scrollLeft || document . body . scrollLeft || 0 ; this . deltaY = window . pageYOffset || document . documentElement . scrollTop || document . body . scrollTop || 0 ; }
must be called before calling withinIncludingScrolloffset, every time the page is scrolled
must be called before calling withinIncludingScrolloffset every time the page is scrolled
This is the function that is called when the page is scrolled.