【JS】代码雨特效

html代码

<canvas id="code_rain_canvas" width="1440" height="900">canvas>

js 代码

window.onload = function() {
         //获取画布对象
         var canvas = document.getElementById("code_rain_canvas");
         //获取画布的上下文
         var context = canvas.getContext("2d");
         var s = window.screen;
         var W = canvas.width = s.width;
         var H = canvas.height;
         //获取浏览器屏幕的宽度和高度
         //var W = window.innerWidth;
         //var H = window.innerHeight;
         //设置canvas的宽度和高度
         canvas.width = W;
         canvas.height = H;
         //每个文字的字体大小
         var fontSize = 12;
         //计算列
         var colunms = Math.floor(W / fontSize);
         //记录每列文字的y轴坐标
         var drops = [];
         //给每一个文字初始化一个起始点的位置
         for (var i = 0; i < colunms; i++) {
             drops.push(0);
         }
         //运动的文字
         var str = "WELCOME TO WWW.ITRHX.COM";
         //4:fillText(str,x,y);原理就是去更改y的坐标位置
         //绘画的函数
         function draw() {
             context.fillStyle = "rgba(238,238,238,.08)"; //遮盖层
             context.fillRect(0, 0, W, H);
             //给字体设置样式
             context.font = "600 " + fontSize + "px  Georgia";
             //给字体添加颜色
             context.fillStyle = ["#33B5E5", "#0099CC", "#AA66CC", "#9933CC", "#99CC00", "#669900", "#FFBB33", "#FF8800", "#FF4444", "#CC0000"][parseInt(Math.random() * 10)]; //randColor();可以rgb,hsl, 标准色，十六进制颜色
             //写入画布中
             for (var i = 0; i < colunms; i++) {
                 var index = Math.floor(Math.random() * str.length);
                 var x = i * fontSize;
                 var y = drops[i] * fontSize;
                 context.fillText(str[index], x, y);
                 //如果要改变时间，肯定就是改变每次他的起点
                 if (y >= canvas.height && Math.random() > 0.99) {
                     drops[i] = 0;
                 }
                 drops[i]++;
             }
         };

         function randColor() { //随机颜色
             var r = Math.floor(Math.random() * 256);
             var g = Math.floor(Math.random() * 256);
             var b = Math.floor(Math.random() * 256);
             return "rgb(" + r + "," + g + "," + b + ")";
         }
         draw();
         setInterval(draw, 35);
     };

展示效果：