文章主要介绍了html5 canvas 实现光线沿不规则路径运动,本文通过实例代码给大家介绍的非常详细,需要的朋友可以参考下。

g让动画沿着不规则路径运动

查阅svg文档后发现,svg动画运动有两种实现方式,且都非常简单,但对于100%实现设计师给出的效果有很大的距离

使用offset-path偏移路径和offset-roate偏移角度让元素沿着不规则路径走

<!DOCTYPE html>
    <html>
    <head>
        <title>offset-path/offset-roate</title>
    </head>
    <style type="text/css">
        * {
            padding: 0;
            margin: 0;
            box-sizing: border-box;
        }
        body {
            background: #000;
        }
        .line {
            width: 80px;
            height: 3px;
            position: absolute;
            background: red;
            offset-path: path("M10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500");
            animation: move 10s linear infinite;
        }
        @keyframes move {
            100% {
                offset-distance: 2000px;
            }
        }
        .line1 {
            position: absolute;
            left: 100px;
            width: 20px;
            height: 20px;
            border-radius: 50%;
            background: red;
            offset-path: path("M0,0a72.5,72.5 0 1,0 145,0a72.5,72.5 0 1,0 -145,0");
            offset-rotate: 0deg;
            animation: load 1.8s cubic-bezier(0.86, 0, 0.07, 1) infinite;
            animation-delay: 0.147s;
            animation-fill-mode: forwards;
        }
        @keyframes load {
            from {
                offset-distance: 0;
            }
            to {
                offset-distance: 100%;
            }
        }
    </style>
    <body>
        <h2>路径偏移</h2>
        <div class="line"></div>
        <svg width="100%" height="600px" version="1.0" id="svg1">
            <path d="M10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500" fill="#tranparent" stroke="#FFF"></path>
        </svg>
        <h2>角度偏移</h2>
        <div class="line1">
        </div>
    </body>
    </html>

此种方式的限制是滚动元素无法随路径进行没有规律的变化

使用stroke-dasharray和stroke-dashoffset让路径边线动起来

stroke-dasharray:设置shap和text 边框虚线的实线长度与实线之间的间隔(虚线长度)
stroke-dashoffser:设置边框线条相对于默认位置的偏移(正值:向左,负值:向右)

<!DOCTYPE html>
    <html>
    <head>
        <title>stroke-dasharray/stroke-dashoffser</title>
    </head>
    <style type="text/css">
        * {
            padding: 0;
            margin: 0;
            box-sizing: border-box;
        }
        body {
            background: #000;
            color: #fff;
        }
        .move {
            animation: moving 5s infinite;
        }
        @keyframes moving {
            0% {
                stroke-dashoffset: 80px;
            }
            100% {
                stroke-dashoffset: -1600px;
            }
        }
    </style>
    <body>
    <h2>设置stroke-dasharray</h2>
    <b>storke-dasharray设置为80 ,此时实线和实线间隔一样</b>
    <svg width="100%" height="600px" version="1.0" id="svg1">
        <path d="M10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500" fill="#tranparent" stroke="#FFF" stroke-dasharray="80"></path>
    </svg>
    <b>storke-dasharray设置为80 320,此时实线和是实线间隔的1/4</b>
    <svg width="100%" height="600px" version="1.0" id="svg1">
        <path d="M10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500" fill="#tranparent" stroke="#FFF" stroke-dasharray="80 320"></path>
    </svg>
    <h2>设置stroke-dashoffset让边线相对于初始位置发生偏移</h2>
    <svg width="100%" height="600px" version="1.0" id="svg1">
        <path d="M10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500" fill="#tranparent" stroke="#FFF" stroke-dasharray="80 320" stroke-dashoffset="40"></path>
    </svg>
    <h2>通过设置stroke-dasharray 和 stroke-dashoffset让边线动起来</h2>
    <svg width="100%" height="600px" version="1.0" id="svg1">
        <path d="M10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500" fill="#tranparent" stroke="#FFF"></path>
        <path d="M10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500" fill="#tranparent" stroke="red" stroke-dasharray="80 1600" stroke-dashoffset="0" class="move"></path>
    </svg>
    </body>
    </html>

此种方式通过边框偏移的效果可以设置跟随路径的滚线条,但是无法设置线条的光线效果,即实线的阴影和实线的渐变效果(渐变区域需随着偏移路径的变化而变化)

canvas实现线条延不规则路径运动

线条实现

对于不规则路径,如果直接用画线条的方式实现光线,需要计算每一个开始点和结束点的位置,中间还可能存在转折点,计算起来非常麻烦,不可取
故这边采取canvas组合图形的模式,取线条和一个图形重叠部分(类似于灯罩)来实现光线效果
 

组合前
 


 

组合后
 

<!DOCTYPE html>
    <html>
    <head>
        <title>canvas实现不规则路径光效</title>
    </head>
    <style type="text/css">
        body {
            background: #000;
        }
        #wrap {
            position: absolute;
            width: 1200px;
            height: 600px
        }
    </style>
    <body>
        <div id="wrap">
            <canvas id="canvas" width="1200" height="600"></canvas>
        </div>
    </body>
    <script type="text/javascript">
        var path = 'M 10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500';
        var list = path.match(/([A-Z]([^A-Z]){1,})/g).map(item => {
            return {
                x: item.split(' ')[1],
                y: item.split(' ')[2],
                action: item.split(' ')[0],
            }
        });//获取每个点位置
        var canvas = document.getElementById('canvas');
        var ctx = canvas.getContext('2d');
        ctx.strokeStyle = 'rgba(255,255,255,1)';
        function drawPath() {
            ctx.lineWidth = 3;
            ctx.beginPath();
            list.forEach(item => {
                if(item.action == 'M') ctx.moveTo(item.x, item.y);
                if(item.action == 'L') ctx.lineTo(item.x, item.y);
            });
            ctx.stroke();
        }
        drawPath();
 
        function drawLine() {
            //设置图形组合方式 默认source-over
            ctx.globalCompositeOperation = "destination-in";
            ctx.lineWidth = 60;
            ctx.beginPath();
            ctx.moveTo(40, 80);
            ctx.lineTo(200, 80);
            ctx.stroke();
        }
        drawLine();
 
    </script>
    </html>

让线条动起来

当我们实现好线条剩下就需要让线条动起来,由于线条是通过灯罩的方式来实现的,让线条运动只需要让灯罩动起来就好
 

<!DOCTYPE html>
    <html>
    <head>
        <title>canvas实现不规则路径光效</title>
    </head>
    <style type="text/css">
        body {
            background: #000;
        }
        #wrap {
            position: absolute;
            width: 1200px;
            height: 600px
        }
    </style>
    <body>
        <div id="wrap">
            <canvas id="canvas" width="1200" height="600"></canvas>
        </div>
    </body>
    <script type="text/javascript">
        var path = 'M 10 80 L 77.5 60 L 145 80 L 280 100 L 500 80 L 600 120 L 800 80 L 950 120 L 950 200 L 930 250 L 950 300 L 950 500';
        var list = path.match(/([A-Z]([^A-Z]){1,})/g).map(item => {
            return {
                x: item.split(' ')[1],
                y: item.split(' ')[2],
                action: item.split(' ')[0],
            }
        });//获取每个点位置
        var step = 3;
        var x1, x2, y1, y2;//确定路径中最大最小点
        var timer;
        var canvas = document.getElementById('canvas');
        var ctx = canvas.getContext('2d');
        ctx.strokeStyle = 'rgba(255,255,255,1)';
        ctx.shadowColor = 'rgba(255,255,255,1)';
        ctx.lineCap = 'round';
        ctx.shadowBlur = 3;
        list.forEach(item => {
            x1 = !x1 || Number(item.x) < x1 ? Number(item.x) : x1;
            y1 = !y1 || Number(item.y) < y1 ? Number(item.y) : y1;
            x2 = !x2 || Number(item.x) > x2 ? Number(item.x) : x2;
            y2 = !y2 || Number(item.y) > y2 ? Number(item.y) : y2;
        });
        function drawPath() {
            ctx.lineWidth = 3;
            ctx.beginPath();
            list.forEach(item => {
                if(item.action == 'M') ctx.moveTo(item.x, item.y);
                if(item.action == 'L') ctx.lineTo(item.x, item.y);
            });
            //添加光效渐变
            var grd = ctx.createLinearGradient(arrLine[arrLine.length - 1].x, arrLine[arrLine.length - 1].y, arrLine[0].x, arrLine[0].y);
            grd.addColorStop(0, 'rgba(255, 255, 255, 0)');   //定义渐变线起点颜色
            grd.addColorStop(1, 'rgba(255, 255, 255, 1)');  //定义渐变线结束点的颜色
            ctx.strokeStyle = grd;
            ctx.stroke();
        }
        //设计合适的初始线条状态
        var arrLine = Array(10).fill(0).map((item, inx) => {
            return {
                x: x1 - 20 * inx,
                y: y1 + 30,
            }
        });
        //随时间变化图形路径
        function getArrLine() {
            var isEnd
            arrLine = arrLine.map(item => {
                var x = item.x;
                var y = item.y;
                if(x < x2 - 30) {
                    x = x + step > x2 -30 ? x2 - 30 : x + step;
                } else if(x == x2 -30 && y < y2) {
                    y = y + step > y2 ? y2 : y + step;
                } else {
                    isEnd = true;
                }
                return {
                    x,
                    y
                }
            });
            isEnd && timer && cancelAnimationFrame(timer);
        }
        //绘制图形
        function drawLine() {
            //设置图形组合方式 默认source-over
            ctx.globalCompositeOperation = "destination-in";
            ctx.lineWidth = 70;
            ctx.beginPath();
            arrLine.forEach((item, inx) => {
                if(inx == 0) {
                    ctx.moveTo(item.x, item.y);
                } else {
                    ctx.lineTo(item.x, item.y);
                }
            })
            ctx.stroke();
        }
 
        function start() {
            ctx.clearRect(0, 0, 1200, 600);
            ctx.globalCompositeOperation = 'source-over';
            drawPath();
            drawLine();
            getArrLine();
            timer = requestAnimationFrame(start);
        }
 
        timer = requestAnimationFrame(start);
 
    </script>
    </html>

这种实现方式也有一定的条件限制,那就是路径可大体抽象成为一个有一定规律的图型或者线条,比如上面demo中路径可抽象成为一个矩形的两边,或者是2条连接的直线
我们必须从没有具体规则的路径中抽象出一个大体的规则,不同路径规则不同
上面的例子就是将不规则路径抽象成了一个直角的规则路径
 

可优化点

这边找到了2个可优化的点
1.时间方向上: 为了让动画消耗较小,代码中的定时器已经用的是requestAnimationFrame, 但是由于光线的特殊性(自带模糊效果),为了性能更加,尝试了2次requestAnimationFrame调用一次绘图的方式,效果较前者未有明显区别
2.绘图方向上: 从上图可发现,灯罩每次只圈出路径的一部分,故绘图中不需要每次都绘制全部路径,只需要找出灯罩前后的路径点,将这一段路径绘制出来就好

坑点

在完成这个动动画效果之后遇到一个至今原因不明的bug,随着屏幕放置时间的变长,动画越来越慢,打开任务管理器,未见内存泄漏或者CPU使用率过高。打开performance,发现页面调帧严重,屏幕帧数越来越低,单个Frame CPU time越来越长,范围来看,script和render和paint耗时未发生线性变化,只有system时间越来越来长,越来越长,期望能被大佬告知原因
一开始
 

到后来

解决的办法较为...,光线每循环一个周期,我销毁了之前的canvas并新建了canvas,上层规避了system time不知道为什么越来越长的问题
chrome版本:80.0.3987.163(正式版本) (64 位)

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