基于 canvas 一款非常酷炫的动态气泡背景实现方法

canvas 是 HTML5 新增的标签，利用它我们可以轻松实现图形的绘制。canvas 元素本身并没有绘制能力，它只是一个图形的容器，必须使用脚本（通常是 JavaScript）配合来完成绘图任务。今天为大家分享一下基于 canvas 动态气泡背景的实现方法。

实现方式

将下面的内容保存为 .js 文件，然后在网页中引入即可。

document.writeln("<div id=\'bubble\' style=\'width:100%;height:100%;position:fixed;top:0;left:0;z-index:-1;\'></div>");

class BGBubble {
    constructor(opts) {
        this.defaultOpts = {
            id: '',                 // 容器ID
            num: 100,               // 个数
            start_probability: 0.1, // 如果数量小于num，有这些几率添加一个新的
            radius_min: 1,          // 初始半径最小值
            radius_max: 2,          // 初始半径最大值
            radius_add_min: .3,     // 半径增加最小值
            radius_add_max: .5,     // 半径增加最大值
            opacity_min: 0.3,       // 初始透明度最小值
            opacity_max: 0.5,       // 初始透明度最大值
            opacity_prev_min: .003, // 透明度递减值最小值
            opacity_prev_max: .005, // 透明度递减值最大值
            light_min: 40,          // 颜色亮度最小值
            light_max: 70,          // 颜色亮度最大值
            is_same_color: false,   // 泡泡颜色是否相同
            background: "#f1f3f4"
        }
        if (Object.prototype.toString.call(opts) == "[object Object]") {
            this.userOpts = {...this.defaultOpts, ...opts}
        } else {
            this.userOpts = {...this.defaultOpts, id: opts}
        }
        this.color = this.random(0, 360)
        this.bubbleNum = []
        this.requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame || window.webkitRequestAnimationFrame || window.msRequestAnimationFrame
        this.cancelAnimationFrame = window.cancelAnimationFrame || window.mozCancelAnimationFrame
    }

    random(a, b) {
        return Math.random() * (b - a) + a //取a-b之间的随机值
    }

    initBubble(color, isSameColor) {
        const width = window.innerWidth
        const height = window.innerHeight
        const userOpts = this.userOpts
        const light = this.random(userOpts.light_min, userOpts.light_max)
        this.bubble = {
            x: this.random(0, width),
            y: this.random(0, height),
            radius: this.random(userOpts.radius_min, userOpts.radius_max),
            radiusChange: this.random(userOpts.radius_add_min, userOpts.radius_add_max),
            opacity: this.random(userOpts.opacity_min, userOpts.opacity_max),
            opacityChange: this.random(userOpts.opacity_prev_min, userOpts.opacity_prev_max),
            light,
            color: `hsl(${isSameColor ? color : this.random(0, 360)},100%,${light}%)`,
        }
    }

    bubbling(ctx, color, isSameColor) {
        !this.bubble && this.initBubble(color, isSameColor)
        const bubble = this.bubble
        ctx.fillStyle = bubble.color;
        ctx.globalAlpha = bubble.opacity;
        ctx.beginPath();
        ctx.arc(bubble.x, bubble.y, bubble.radius, 0, 2 * Math.PI, true);
        ctx.closePath();
        ctx.fill();
        ctx.globalAlpha = 1;
        bubble.opacity -= bubble.opacityChange;
        bubble.radius += bubble.radiusChange;
        if (bubble.opacity <= 0) {
            this.initBubble(color, isSameColor)
            return
        }
    }

    createCanvas() {
        this.canvas = document.createElement('canvas')
        this.ctx = this.canvas.getContext('2d')
        this.canvas.id = "bg_canvas";
        this.canvas.style.display = 'block' //防止全屏的canvas出现滚动条
        this.canvas.width = window.innerWidth
        this.canvas.height = window.innerHeight
        this.canvas.style.position = 'fixed'
        this.canvas.style.top = '0'
        this.canvas.style.left = '0'
        this.canvas.style.zIndex = '-1'
        document.getElementById(this.userOpts.id).appendChild(this.canvas)
        window.onresize = () => {
            this.canvas.width = window.innerWidth
            this.canvas.height = window.innerHeight
        }
    }

    start() {
        const width = window.innerWidth
        const height = window.innerHeight
        this.color += 0.1
        this.ctx.fillStyle = this.defaultOpts.background; //这里修改颜色hsl(${this.color},100%,97%)//rgba(255, 255, 255, 0)
        this.ctx.fillRect(0, 0, width, height);
        if (this.bubbleNum.length < this.userOpts.num && Math.random() < this.userOpts.start_probability) {
            this.bubbleNum.push(new BGBubble())
        }
        this.bubbleNum.forEach(bubble => bubble.bubbling(this.ctx, this.color, this.userOpts.is_same_color))
        const requestAnimationFrame = this.requestAnimationFrame
        this.myReq = requestAnimationFrame(() => this.start())
    }

    destory() {
        const cancelAnimationFrame = this.cancelAnimationFrame
        cancelAnimationFrame(this.myReq)
        window.onresize = null
    }
}

const bubbleDemo = new BGBubble('bubble')
bubbleDemo.createCanvas()
bubbleDemo.start()