绚丽小球

参考@叶建华 @www.IT666.com

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>绚丽小球</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        body{
            margin: 50px;
        }
        #canvas{
           /* margin: 100px auto;*/
            box-shadow: 0 0 10px #000;
        }
    </style>
</head>
<body>

<canvas id="canvas"></canvas>
<script src="lib/underscore-min.js"></script>
<script>
    let canvas = document.getElementById('canvas');
    const ctx = canvas.getContext('2d');

    canvas.width =1000;
    canvas.height = 600;
    canvas.style.backgroundColor = '#000';

    //小球类
    class Ball {
        constructor(x,y,color){
            this.x = x;
            this.y = y;
            this.color = color;
            this.r = 40;
        }
        /** 绘制小球*/
        render(){
            ctx.save();
            ctx.beginPath();
            ctx.arc(this.x, this.y,this.r,0,Math.PI*2);
            ctx.fillStyle = this.color;
            ctx.fill();
            ctx.restore();
        }
    }
    /**
     * 会移动的小球
     * */
    class MoveBall extends Ball {
        constructor(x ,y, color){
            super(x ,y, color);
            //量的变化
            this.dX = _.random(-5,5);
            this.dY = _.random(-5,5);
            this.dR = _.random(1,3);
        }
        /** */
        upDate(){
            this.x +=this.dX;
            this.y += this.dY;
            this.r -= this.dR;
            if(this.r<0){
                this.r =0;
            }

        }
    }


   /* let ball = new Ball(50,50,'red');
    ball.render();*/
   let ballArr = [];
   let colorArr = ['red','green','blue','yellow','purple','pink','orange'];

   //监听鼠标事件
    canvas.addEventListener('mousemove',function (e) {
        var a= _.random(0,colorArr.length-1);
        console.log(a);
        let ball = new MoveBall(e.offsetX, e.offsetY,colorArr[a]);
        ballArr.push(ball);
    });
    canvas.addEventListener('mouseout',function (e) {
       setTimeout(function () {
           ballArr = [];
       },2000)
    });
    //开启定时器
    setInterval(function () {
        //清屏
        ctx.clearRect(0, 0, canvas.width, canvas.height);

        /** ball 对象不能无限的增长，性能问题*/
        if(ballArr.length>1000){
            ballArr = [];
        }
        for(let i=0; i<ballArr.length; i++){
            ballArr[i].render();
            ballArr[i].upDate();
        }
    },50);

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

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