// http://adomas.org/javascript-mouse-wheel/
function WheelHelper() {
    this.delegate = Silverlight.createDelegate(this, this.handleMouseWheel);
    if (window.addEventListener) {
        // DOMMouseScroll is for mozilla.
        window.addEventListener('DOMMouseScroll', this.delegate, false);
    }
    window.onmousewheel = document.onmousewheel = this.delegate;
}

WheelHelper.prototype.wheelScrolled = null;
WheelHelper.prototype.delegate = null;

WheelHelper.prototype.handleMouseWheel = function(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;
        //Sign is only reversed in windows FF
        if(navigator.userAgent.indexOf("Macintosh") != -1)
            delta=-delta;
    }

    //alert(delta);
    // 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 && this.wheelScrolled)
        this.wheelScrolled(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();
        
    //alert(delta);
    event.returnValue = false;
}

WheelHelper.prototype.detach = function() {
    if (this.delegate != null) {
        if (window.removeEventListener) {
            window.removeEventListener('DOMMouseScroll', this.delegate, false);
        }
        
        // IE/Opera.
        window.onmousewheel = document.onmousewheel = null;
        
        this.delegate = null;
    }
}