1  
   2    /** This is high-level function; REPLACE IT WITH YOUR CODE.
   3   * It must react to delta being more/less than zero.
   4   */
   5  function zoomInOut(delta) {
   6  	if (delta >= 0)
   7  		zoomIn()
   8  	else
   9  		zoomOut()
  10  }
  11  
  12  function wheel(event){
  13  	var delta = 0;
  14  	if (!event) event = window.event;
  15  	if (event.wheelDelta) {
  16  		delta = event.wheelDelta/120; 
  17  		if (window.opera) delta = -delta;
  18  	} else if (event.detail) {
  19  		delta = -event.detail/3;
  20  	}
  21  	if (delta)
  22  		zoomInOut(delta);
  23          if (event.preventDefault)
  24                  event.preventDefault();
  25          event.returnValue = false;
  26  }
  27  
  28  /* Initialization code. */
  29  if (window.addEventListener)
  30  	window.addEventListener('DOMMouseScroll', wheel, false);
  31  window.onmousewheel = document.onmousewheel = wheel;