canvas调用scale或者drawImage图片操作后，锯齿感很明显的解决

    <script type="text/javascript">
    //解决canvas画画图片
    var mengvalue = -1;    
    var phoneWidth = parseInt(window.screen.width);
    var phoneScale = phoneWidth / 640;
    var ua = navigator.userAgent;
    if (/Android (\d+\.\d+)/.test(ua)) {
        var version = parseFloat(RegExp.$1);
        // andriod 2.3
        if (version > 2.3) {
            document.write('<meta name="viewport" content="width=640, minimum-scale = ' + phoneScale + ', maximum-scale = ' + phoneScale + ', target-densitydpi=device-dpi">');
            // andriod 2.3以上
        } else {
            document.write('<meta name="viewport" content="width=640, target-densitydpi=device-dpi">');
        }
        // 其他系统
    } else {
        document.write('<meta name="viewport" content="width=640, user-scalable=no, target-densitydpi=device-dpi">');
    }
    </script>