使用js实现动态背景

window.onload = function () {    //定义body的margin由默认值8px->0px    document.body.style.margin = "0";    document.body.style.background = "#30333F";    //创建canvas画布    document.body.appendChild(document.createElement('canvas'));    var canvas = document.querySelector('canvas'),        ctx = canvas.getContext('2d') //ctx返回一个在canvas上画图的api/dom    canvas.width = window.innerWidth;    canvas.height = window.innerHeight;    canvas.style.position = 'fixed';    ctx.lineWidth = .3;    ctx.strokeStyle = (new Color(150)).style;    //定义鼠标覆盖范围    var mousePosition = {        x: 30 * canvas.width / 100,        y: 30 * canvas.height / 100    };    var dots = {        nb: 1000,//Dot的总数        distance: 50,        d_radius: 100,        array: []    };    //创建颜色类，Color类返回字符串型rgba（*,*,*,.8）    function mixComponents(comp1, weight1, comp2, weight2) {        return (comp1 * weight1 + comp2 * weight2) / (weight1 + weight2);    }    function averageColorStyles(dot1, dot2) {        var color1 = dot1.color,            color2 = dot2.color;        var r = mixComponents(color1.r, dot1.radius, color2.r, dot2.radius),            g = mixComponents(color1.g, dot1.radius, color2.g, dot2.radius),            b = mixComponents(color1.b, dot1.radius, color2.b, dot2.radius);        return createColorStyle(Math.floor(r), Math.floor(g), Math.floor(b));    }    function colorValue(min) {        return Math.floor(Math.random() * 255 + min);    }    function createColorStyle(r, g, b) {        return 'rgba(' + r + ',' + g + ',' + b + ', 0.8)';    }    function Color(min) {        min = min || 0;        this.r = colorValue(min);        this.g = colorValue(min);        this.b = colorValue(min);        this.style = createColorStyle(this.r, this.g, this.b);    }    //创建Dot类以及一系列方法    function Dot() {        this.x = Math.random() * canvas.width;        this.y = Math.random() * canvas.height;        this.vx = -.5 + Math.random();        this.vy = -.5 + Math.random();        this.radius = Math.random() * 2;        this.color = new Color();    }    Dot.prototype = {        draw: function () {            ctx.beginPath();            ctx.fillStyle = this.color.style;            ctx.arc(this.x, this.y, this.radius, 0, Math.PI * 2, false);            ctx.fill();        }    };    function moveDots() {//Dot对象的移动        for (i = 0; i < dots.nb; i++) {            var dot = dots.array[i];            if (dot.y < 0 || dot.y > canvas.height) {                dot.vx = dot.vx;                dot.vy = - dot.vy;            }            else if (dot.x < 0 || dot.x > canvas.width) {                dot.vx = - dot.vx;                dot.vy = dot.vy;            }            dot.x += dot.vx;            dot.y += dot.vy;        }    }    function connectDots() {//DOt对象的连接        for (i = 0; i < dots.nb; i++) {            for (j = i; j < dots.nb; j++) {                i_dot = dots.array[i];                j_dot = dots.array[j];                if ((i_dot.x - j_dot.x) < dots.distance && (i_dot.y - j_dot.y) < dots.distance && (i_dot.x - j_dot.x) > - dots.distance && (i_dot.y - j_dot.y) > - dots.distance) {                    if ((i_dot.x - mousePosition.x) < dots.d_radius && (i_dot.y - mousePosition.y) < dots.d_radius && (i_dot.x - mousePosition.x) > - dots.d_radius && (i_dot.y - mousePosition.y) > - dots.d_radius) {                        ctx.beginPath();                        ctx.strokeStyle = averageColorStyles(i_dot, j_dot);                        ctx.moveTo(i_dot.x, i_dot.y);                        ctx.lineTo(j_dot.x, j_dot.y);                        ctx.stroke();//绘制定义的路线                        ctx.closePath();//创建从当前点回到起始点的路径                    }                }            }        }    }    function createDots() {//创建nb个Dot对象        for (i = 0; i < dots.nb; i++) {            dots.array.push(new Dot());        }    }    function drawDots() {//引用Dot原型链，使用draw方法，在canvas上画出Dot对象        for (i = 0; i < dots.nb; i++) {            var dot = dots.array[i];            dot.draw();        }    }    function animateDots() {        ctx.clearRect(0, 0, canvas.width, canvas.height);//清除画布，否则线条会连在一起        moveDots();        connectDots();        drawDots();        requestAnimationFrame(animateDots);    }    createDots();//使用创建Dot类函数    requestAnimationFrame(animateDots);//使用canvas独有的60Hz刷新屏幕画布的方法    document.querySelector('canvas').addEventListener('mousemove', function (e) {        mousePosition.x = e.pageX;        mousePosition.y = e.pageY;    })    document.querySelector('canvas').addEventListener('mouseleave', function (e) {//鼠标离开时，连接自动返回到画布中心        mousePosition.x = canvas.width / 2;        mousePosition.y = canvas.height / 2;    })}