function GetWindowViewport() {
    var viewportwidth;
    var viewportheight;

    // the more standards compliant browsers (mozilla/netscape/opera/IE7) use window.innerWidth and window.innerHeight
    if (typeof window.innerWidth != 'undefined') {
        viewportwidth = window.innerWidth;
        viewportheight = window.innerHeight;
    }

    // IE6 in standards compliant mode (i.e. with a valid doctype as the first line in the document)
    else if (typeof document.documentElement != 'undefined' && typeof document.documentElement.clientWidth != 'undefined' && document.documentElement.clientWidth != 0) {
        viewportwidth = document.documentElement.clientWidth;
        viewportheight = document.documentElement.clientHeight;
    }

    // older versions of IE
    else {
        viewportwidth = document.getElementsByTagName('body')[0].clientWidth;
        viewportheight = document.getElementsByTagName('body')[0].clientHeight;
    }

    return [viewportwidth, viewportheight];
}