用Canvas+js 实现简单圆形百分比统计图表

示例效果图如下：

1、先来制作简单HTML代码结构：

<div class="box">
    <ul>
        <li>
            <canvas id="one" width="200" height="200"></canvas>
        </li>
        <li>
            <canvas id="two" width="200" height="200"></canvas>
        </li>
        <li>
            <canvas id="three" width="200" height="200"></canvas>
        </li>
    </ul>
</div>

2、再是CSS样式代码：

body {
    margin: 0;
    padding: 50px 0;
    background-color: #444;
}
ul,li {
    list-style: none;
    margin: 0;
    padding: 0;
}
ul li {
    float: left;
    width: 33%;
    text-align: center;
}

3、具体JS代码实现+注释如下：

function drawCircle(_options){
    var options = _options || {};    //获取或定义options对象;
    options.angle = options.angle || 1;    //定义默认角度1为360度(角度范围 0-1);
    options.color = options.color || \'#fff\';    //定义默认颜色（包括字体和边框颜色）;
    options.lineWidth = options.lineWidth || 10;    //定义默认圆描边的宽度;
    options.lineCap = options.lineCap || \'square\';    //定义描边的样式，默认为直角边，round 为圆角

    var oBoxOne = document.getElementById(options.id);
    var sCenter = oBoxOne.width / 2;    //获取canvas元素的中心点;
    var ctx = oBoxOne.getContext(\'2d\');
    var nBegin = Math.PI / 2;    //定义起始角度;
    var nEnd = Math.PI * 2;    //定义结束角度;
    var grd = ctx.createLinearGradient(0, 0, oBoxOne.width, 0);    //grd定义为描边渐变样式;
    grd.addColorStop(0, \'red\');
    grd.addColorStop(0.5, \'yellow\');
    grd.addColorStop(1, \'green\');

    ctx.textAlign = \'center\';    //定义字体居中;
    ctx.font = \'normal normal bold 20px Arial\';    //定义字体加粗大小字体样式;
    ctx.fillStyle = options.color == \'grd\' ? grd : options.color;    //判断文字填充样式为颜色，还是渐变色;
    ctx.fillText((options.angle * 100) + \'%\', sCenter, sCenter);    //设置填充文字;
    /*ctx.strokeStyle = grd;    //设置描边样式为渐变色;
    ctx.strokeText((options.angle * 100) + \'%\', sCenter, sCenter);    //设置描边文字(即镂空文字);*/
    ctx.lineCap = options.lineCap;
    ctx.strokeStyle = options.color == \'grd\' ? grd : options.color;
    ctx.lineWidth = options.lineWidth;

    ctx.beginPath();    //设置起始路径，这段绘制360度背景;
    ctx.strokeStyle = \'#D8D8D8\';
    ctx.arc(sCenter, sCenter, (sCenter - options.lineWidth), -nBegin, nEnd, false);
    ctx.stroke();

    var imd = ctx.getImageData(0, 0, 240, 240);
    function draw(current) {    //该函数实现角度绘制;
        ctx.putImageData(imd, 0, 0);
        ctx.beginPath();
        ctx.strokeStyle = options.color == \'grd\' ? grd : options.color;
        ctx.arc(sCenter, sCenter, (sCenter - options.lineWidth), -nBegin, (nEnd * current) - nBegin, false);
        ctx.stroke();
    }

    var t = 0;
    var timer = null;
    function loadCanvas(angle) {    //该函数循环绘制指定角度，实现加载动画;
        timer = setInterval(function(){
            if (t > angle) {
                draw(options.angle);
                clearInterval(timer);
            }else{
                draw(t);
                t += 0.02;
            }
        }, 20);
    }
    loadCanvas(options.angle);    //载入百度比角度  0-1 范围;
    timer = null;

}

4、代码已封装成函数，除了ID是必填选项，其它都可不填，使用默认值，展示三种调用方法如下：

drawCircle({
    id: \'one\',
    color: \'#0000ff\',
    angle: 0.5,
    lineWidth: 5
});

drawCircle({
    id: \'two\',
    angle: 0.75,
    color: \'#ff0000\',
    lineWidth: 12
});

drawCircle({
    id: \'three\',
    angle: 1,
    lineWidth: 15,
    color: \'grd\'
});

注：还可以在此基础上加强扩展功能，如：设定宽高，多种展示样式等！