<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>particle nets</title>

    <style>

        html,body{

            margin: 0;

            padding: 0;

            height: 100%;

            overflow: hidden;}

    </style>

</head>

<body>

<canvas id="cas"></canvas>

<script>

    var canvas = document.getElementById("cas");

    var ctx = canvas.getContext("2d");

    resize();

    window.onresize = resize;

    function resize(){

        canvas.width = window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth;

        canvas.height = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;

    }

    var RAF = (function () {

        return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function (callback) {

                    window.setTimeout(callback, 1000 / 60);

                };

    })();

    // 鼠标活动时，获取鼠标坐标

    var warea = {x: null, y: null, max: 20000};

    window.onmousemove = function(e){

        e = e || window.event;

        warea.x = e.clientX;

        warea.y = e.clientY;

    };

    window.onmouseout = function(e){

        warea.x = null;

        warea.y = null;

    };

    // 添加粒子

    // x，y为粒子坐标，xa, ya为粒子xy轴加速度，max为连线的最大距离

    var dots = [];

    for(var i=0;i<300;i++){

        var x = Math.random()canvas.width;

        var y = Math.random()canvas.height;

        var xa = Math.random() 2 - 1;

        var ya = Math.random() 2 - 1;

        dots.push({

            x: x,

            y: y,

            xa: xa,

            ya: ya,

            max: 6000

        })

    }

    // 延迟100秒开始执行动画，如果立即执行有时位置计算会出错

    setTimeout(function(){

        animate();

    }, 100);

    // 每一帧循环的逻辑

    function animate(){

        ctx.clearRect(0,0,canvas.width, canvas.height);

        // 将鼠标坐标添加进去，产生一个用于比对距离的点数组

        var ndots  = [warea].concat(dots);

        dots.forEach(function(dot){

            // 粒子位移

            dot.x += dot.xa;

            dot.y += dot.ya;

            // 遇到边界将加速度反向

            dot.xa = (dot.x > canvas.width || dot.x < 0)? -1 : 1;

            dot.ya = (dot.y > canvas.height || dot.y < 0)? -1 : 1;

            // 绘制点

            ctx.fillRect(dot.x - 0.5, dot.y - 0.5, 1, 1);

            // 循环比对粒子间的距离

            for (var i = 0; i < ndots.length; i++) {

                var d2 = ndots[i];

                if (dot === d2 || d2.x === null || d2.y === null) continue;

                var xc = dot.x - d2.x;

                var yc = dot.y - d2.y;

                // 两个粒子之间的距离

                var dis = xc xc + yc yc;

                // 距离比

                var ratio;

                // 如果两个粒子之间的距离小于粒子对象的max值，则在两个粒子间画线

                if(dis < d2.max){

                    // 如果是鼠标，则让粒子向鼠标的位置移动

                    if (d2 === warea && dis > (d2.max / 2)) {

                        dot.x -= xc 0.03;

                        dot.y -= yc 0.03;

                    }

                    // 计算距离比

                    ratio = (d2.max - dis) / d2.max;

                    // 画线

                    ctx.beginPath();

                    ctx.lineWidth = ratio/2;

                    ctx.strokeStyle = 'rgba(0,0,0,' + (ratio + 0.2) + ')';

                    ctx.moveTo(dot.x , dot.y);

                    ctx.lineTo(d2.x , d2.y);

                    ctx.stroke();

                }

            }

            // 将已经计算过的粒子从数组中删除

            ndots.splice(ndots.indexOf(dot), 1);

        });

        RAF(animate);

    }

</script>

</body>

</html>