/**
 * Event handler for mouse wheel event.
 */
function wheel(event){
	var delta = 0;
	if (!event) /* For IE. */
		event = window.event;
	if (event.wheelDelta) { /* IE/Opera. */
		delta = event.wheelDelta/120;
	/**
	 * In Opera 9, delta differs in sign as compared to IE.
	 */
	if (window.opera)
		delta = -delta;
	} else if (event.detail) { /** Mozilla case. */
		/**
		 * In Mozilla, sign of delta is different than in IE. Also,
		 * delta is multiple of 3.
		 */
        delta = -event.detail/3;
	}
	/**
	 * If delta is nonzero, handle it. Basically, delta is now positive if
	 * wheel was scrolled up, and negative, if wheel was scrolled down.
	 */
	if (delta)
		handleMouseWheel(delta);
	/**
	 * Prevent default actions caused by mouse wheel. That might be ugly,
	 * but we handle scrolls somehow anyway, so don't bother here..
	 */
	if (event.preventDefault)
		event.preventDefault();
	event.returnValue = false;
}

/**
 * Initialization code. If you use your own event management code, change it as
 * required.
 */
if (window.addEventListener)
	/** DOMMouseScroll is for mozilla. */
    window.addEventListener('DOMMouseScroll', wheel, false);

/** IE/Opera. */
window.onmousewheel = document.onmousewheel = wheel;