mxGraph画图区域使用鼠标滚轮实现放大/缩小

// 重写鼠标滚轮事件
mxEvent.addMouseWheelListener = function (funct) {
  
}

// 添加初次载入事件
window.onload = function () {
    var element= document.getElementById('graph');
    addScrollListener(element, wheelHandle);
}

function addScrollListener(element, wheelHandle) {
    if (typeof element != 'object') return;
    if (typeof wheelHandle != 'function') return;

    // 监測浏览器
    if (typeof arguments.callee.browser == 'undefined') {
        var user = navigator.userAgent;
        var b = {};
        b.opera = user.indexOf("Opera") > -1 && typeof window.opera == "object";
        b.khtml = (user.indexOf("KHTML") > -1 || user.indexOf("AppleWebKit") > -1 || user.indexOf("Konqueror") > -1) && !b.opera;
        b.ie = user.indexOf("MSIE") > -1 && !b.opera;
        b.gecko = user.indexOf("Gecko") > -1 && !b.khtml;
        arguments.callee.browser = b;
    }
    if (element == window)
        element = document;
    if (arguments.callee.browser.ie)
        element.attachEvent('onmousewheel', wheelHandle);
    else
        element.addEventListener(arguments.callee.browser.gecko ?
 'DOMMouseScroll' : 'mousewheel', wheelHandle, false);
}

function wheelHandle(e) {
    var upcheck;

    if (e.wheelDelta) {
        upcheck = e.wheelDelta > 0 ? 1 : 0;
    } else {
        upcheck = e.detail < 0 ? 1 : 0;
    }
    if (upcheck) {
        myGraph.zoomIn();
    }
    else {
        myGraph.zoomOut();
    }

    if (window.event) {
        e.returnValue = false;
        window.event.cancelBubble = true;
    } else {
        e.preventDefault();
        e.stopPropagation();
    }
}

PS:myGraph是一个全局变量，mxGraph的实例