                        课程
                    
                        /前端开发
                        
                            /Html5
                        
                        /炫丽的倒计时效果Canvas绘图与动画基础

怎么什么都显示不出来啊？看了好几遍，都没找出错误在哪？

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<canvas id="canvas" style="border:1px solid blue;display: block">
</canvas>
<script type="text/javascript">
    var WINDOW_WIDTH=1024;
    var WINDOW_HEIGHT=768;
    var RADIUS=8;
window.onload=function(){
    var canvas = document.getElementById("canvas");
    canvas.width = WINDOW_WIDTH;
    canvas.height = WINDOW_HEIGHT;
    var context = canvas.getContext("2d");
    render(context)
}

function render(cxt){
    //定义时钟变量
        var hours=12;
        var miniutes=24;
        var seconds=48;
    renderDigit(0,0,parseInt(hours/10),cxt)
}
function renderDigit(x,y,num,cxt){
    cxt.fillStyle="rgb(0,102,153)";
    for(var i=0;i<digit[num].length;i++)
       for(var j=0;j<digit[num][i].length;j++)
         if(digit[num][i][j]==1){
             cxt.beginPath();
             cxt.arc(x+j*2*(RADIUS+1)+(RADIUS+1),y+i*2*(RADIUS+1)+(RADIUS+1),RADIUS,0,2*Math.PI);
             cxt.closePath();
             cxt.fill();
             cxt.stroke();
         }

    }
</script>
</body>
</html>