Canvas三种动态画圆实现方法说明

前言

canvas是HTML5出来的绘图API容器，对于图形的处理非常强大，下面使用canvas配合JavaScript来做一下动态画圆效果。可以用它来做圆形进度条来使用。
这里我个人总结了3种实现方法，大家可以参考一下。

方法一：arc()实现画圆

效果：

width="100%" height="381" scrolling="no" title="动态画圆：方法一" src="//codepen.io/lecein/embed/WoMyMo/?height=381&theme-id=0&default-tab=result" allowfullscreen="true">

代码：

<!DOCTYPE html>
<html>
<head><meta charset="UTF-8"><style type="text/css">#myCanvas{margin: 0 auto;display: block;}</style>
</head>
<body><canvas id="myCanvas">当前浏览器不支持canvas组件请升级！</canvas><script type="text/javascript">//方法一：arc 动态画圆var c = document.getElementById('myCanvas');var ctx = c.getContext('2d');var mW = c.width = 300;var mH = c.height = 300;var lineWidth = 5;var r = mW / 2; //中间位置var cR = r - 4 * lineWidth; //圆半径var startAngle = -(1 / 2 * Math.PI); //开始角度var endAngle = startAngle + 2 * Math.PI; //结束角度var xAngle = 1 * (Math.PI / 180); //偏移角度量var fontSize = 35; //字号大小var tmpAngle = startAngle; //临时角度变量//渲染函数var rander = function(){if(tmpAngle >= endAngle){return;}else if(tmpAngle + xAngle > endAngle){tmpAngle = endAngle;}else{tmpAngle += xAngle;}ctx.clearRect(0, 0, mW, mH);//画圈ctx.beginPath();ctx.lineWidth = lineWidth;ctx.strokeStyle = '#1c86d1';ctx.arc(r, r, cR, startAngle, tmpAngle);ctx.stroke();ctx.closePath();//写字ctx.fillStyle = '#1d89d5';ctx.font= fontSize + 'px Microsoft Yahei';ctx.textAlign='center';ctx.fillText( Math.round((tmpAngle -  startAngle) / (endAngle - startAngle) * 100) + '%', r, r + fontSize / 2);requestAnimationFrame(rander);};rander();</script>
</body>
</html>

思路：

通过设置的开始角度和结束角度来做限定，然后通过累加临时的角度变量实现动画效果。

方法二：rotate() 动态画圆

效果：

height="371" width="100%" scrolling="no" title="动态画圆：方法二" src="//codepen.io/lecein/embed/dOdKwB/?height=371&theme-id=0&default-tab=result" allowfullscreen="true">

代码：

<!DOCTYPE html>
<html>
<head><meta charset="UTF-8"><style type="text/css">#myCanvas{margin: 0 auto;display: block;}</style>
</head>
<body><canvas id="myCanvas">当前浏览器不支持canvas组件请升级！</canvas><script type="text/javascript">//方法二：rotate() 动态画圆var c = document.getElementById('myCanvas');var ctx = c.getContext('2d');var mW = c.width = 300;var mH = c.height = 300;var lineWidth = 5;var r = mW / 2; //中间位置var cR = r - 4 * lineWidth; //圆半径var startAngle = -(1 / 2 * Math.PI); //开始角度var endAngle = startAngle + 2 * Math.PI; //结束角度var xAngle = 1 * (Math.PI / 180); //偏移角度量var fontSize = 35; //字号大小var tmpAngle = startAngle; //临时角度变量//渲染函数var rander = function(){if(tmpAngle >= endAngle){return;}else if(tmpAngle + xAngle > endAngle){tmpAngle = endAngle;}else{tmpAngle += xAngle;}ctx.clearRect(0, 0, mW, mH);//画圈ctx.save();ctx.beginPath();ctx.lineWidth = lineWidth;ctx.strokeStyle = '#1c86d1';ctx.translate(r, r); //重定义圆点ctx.rotate(-Math.PI); //最上方为起点for(var i = 0; i <= tmpAngle - startAngle; i += xAngle){ //绘图ctx.moveTo(0, cR - lineWidth);ctx.lineTo(0, cR);ctx.rotate(xAngle); //通过旋转角度和画点的方式绘制圆}ctx.stroke();ctx.closePath();ctx.restore();//写字ctx.fillStyle = '#1d89d5';ctx.font= fontSize + 'px Microsoft Yahei';ctx.textAlign='center';ctx.fillText( Math.round((tmpAngle -  startAngle) / (endAngle - startAngle) * 100) + '%', r, r + fontSize / 2);requestAnimationFrame(rander);};rander();</script>
</body>
</html>

思路：

通过重新定义圆点坐标为（0，0），然后通过在规定范围内旋转图形，进行单点绘制。

方法三：获取圆坐标方式动态画圆

效果：

height="369" width="100%" scrolling="no" title="动态画圆：方法三" src="//codepen.io/lecein/embed/RoQBbW/?height=369&theme-id=0&default-tab=result" allowfullscreen="true">

代码：

<!DOCTYPE html>
<html>
<head><meta charset="UTF-8"><style type="text/css">#myCanvas{margin: 0 auto;display: block;}</style>
</head>
<body><canvas id="myCanvas">当前浏览器不支持canvas组件请升级！</canvas><script type="text/javascript">//方法三：获取圆坐标方式 动态画圆var c = document.getElementById('myCanvas');var ctx = c.getContext('2d');var mW = c.width = 300;var mH = c.height = 300;var lineWidth = 5;var r = mW / 2; //中间位置var cR = r - 4 * lineWidth; //圆半径var startAngle = -(1 / 2 * Math.PI); //开始角度var endAngle = startAngle + 2 * Math.PI; //结束角度var xAngle = 2 * (Math.PI / 180); //偏移角度量var cArr = []; //圆坐标数组//初始化圆坐标数组for(var i = startAngle; i <= endAngle; i += xAngle){//通过sin()和cos()获取每个角度对应的坐标var x = r + cR * Math.cos(i);var y = r + cR * Math.sin(i);cArr.push([x, y]);}//移动到开始点var startPoint = cArr.shift();ctx.beginPath();ctx.moveTo(startPoint[0], startPoint[1]);//渲染函数var rander = function(){//画圈if(cArr.length){ctx.lineWidth = lineWidth;ctx.strokeStyle = '#1c86d1';    var tmpPoint = cArr.shift();ctx.lineTo(tmpPoint[0], tmpPoint[1]);ctx.stroke();      }else{cArr = null;return;}requestAnimationFrame(rander);};rander();</script>
</body>
</html>