js仿黑客帝国文字数字雨效果

<!DOCTYPE html>
<html>
 <head>
  <meta charset="utf-8">
  <title>黑客帝国文字下落</title>
  <style>
  html, body {margin:0; padding:0; background-color:#000;}
   </style>
  <script src="http://apps.bdimg.com/libs/jquery/1.9.0/jquery.min.js"></script>
 </head>
 <body>
 <canvas id="matrix" height="943" width="1920"></canvas>
    <script type="text/javascript">
    //文字
    var txts = "0123456789!@#$%^&*()~_+℃☆○※";
    //转为数组
    txts = txts.split("");
    var matrix=document.getElementById("matrix");
    var context=matrix.getContext("2d");
    matrix.height=window.innerHeight;
    matrix.width=window.innerWidth;
    var drop=[];
    var font_size=16;
    var columns=matrix.width/font_size;
    for(var i=0;i<columns;i++)
        drop[i]=1;

    function drawMatrix(){

        context.fillStyle="rgba(0, 0, 0, 0.09)";
        context.fillRect(0,0,matrix.width,matrix.height);

        context.fillStyle="green";
        context.font=font_size+"px";
        for(var i=0;i<columns;i++){
            //随机取要输出的文字
            var text = txts[Math.floor(Math.random()*txts.length)];
            //输出文字，注意坐标的计算
            context.fillText(text,i*font_size,drop[i]*font_size);/*get 0 and 1*/

            if(drop[i]*font_size>(matrix.height*2/3)&&Math.random()>0.95)/*reset*/
                drop[i]=0;
            drop[i]++;
        }
    }
    setInterval(drawMatrix,33);
</script>
 </body>
</html>