canvas实现半圆环形进度条

html部分

<canvas id="canvas" width="150" height="150">
        <p>抱歉，您的浏览器不支持canvas</p>
</canvas>

js部分

toCanvas('canvas','red',30);

    /**
     *  生成环形进度条
     */
    function toCanvas(id, color, progress) {
        //canvas进度条
        var canvas = document.getElementById(id),
            ctx = canvas.getContext("2d"),
            percent = progress, //最终百分比
            circleX = canvas.width / 2, //中心x坐标
            circleY = canvas.height / 2, //中心y坐标
            radius = 60, //圆环半径
            cradius = 75, // canvas半径
            lineWidth = 6, //圆形线条的宽度
            fontSize = 20; //字体大小
        //两端圆点
        function smallcircle1(cx, cy, r) {
            ctx.beginPath();
            //ctx.moveTo(cx + r, cy);
            ctx.lineWidth = 1;
            ctx.fillStyle = '#06a8f3';
            ctx.arc(cx, cy, r, 0, Math.PI * 2);
            ctx.fill();
        }

        function smallcircle2(cx, cy, r) {
            ctx.beginPath();
            //ctx.moveTo(cx + r, cy);
            ctx.lineWidth = 1;
            ctx.fillStyle = '#fff';
            ctx.arc(cx, cy, r, 0, Math.PI * 2);
            ctx.fill();
        }

        //画圆
        function circle(cx, cy, r) {
            ctx.beginPath();
            //ctx.moveTo(cx + r, cy);
            ctx.lineWidth = lineWidth;
            ctx.strokeStyle = '#eee';
            ctx.arc(cx, cy, r, Math.PI * 2 / 3, Math.PI * 1 / 3);
            ctx.stroke();
        }

        //画弧线
        function sector(cx, cy, r, startAngle, endAngle, anti) {
            ctx.beginPath();
            //ctx.moveTo(cx, cy + r); // 从圆形底部开始画
            ctx.lineWidth = lineWidth;

            // 渐变色 - 可自定义
            //                      var linGrad = ctx.createLinearGradient(
            //                          circleX-radius-lineWidth, circleY, circleX+radius+lineWidth, circleY
            //                      );
            //                      linGrad.addColorStop(0.0, '#06a8f3');
            //                      //linGrad.addColorStop(0.5, '#9bc4eb');
            //                      linGrad.addColorStop(1.0, '#00f8bb');
            //                      ctx.strokeStyle = linGrad;
            // 进度条颜色
            ctx.strokeStyle = color;
            //圆弧两端的样式
            ctx.lineCap = 'round';

            //圆弧
            ctx.arc(
                cx, cy, r,
                (Math.PI * 2 / 3),
                (Math.PI * 2 / 3) + endAngle / 100 * (Math.PI * 5 / 3),
                false
            );
            ctx.stroke();
        }

        //刷新
        function loading() {
            if (process >= percent) {
                clearInterval(circleLoading);
            }

            //清除canvas内容
            ctx.clearRect(0, 0, circleX * 2, circleY * 2);

            //中间的字
            ctx.font = fontSize + 'px April';
            ctx.textAlign = 'center';
            ctx.textBaseline = 'middle';
            ctx.fillStyle = '#999';
            ctx.fillText(parseFloat(process).toFixed(0) + '%', circleX, circleY);

            //圆形
            circle(circleX, circleY, radius);

            //圆弧
            sector(circleX, circleY, radius, Math.PI * 2 / 3, process);
            //两端圆点
            smallcircle1(cradius + Math.cos(2 * Math.PI / 360 * 120) * radius, cradius + Math.sin(2 * Math.PI / 360 * 120) *
                radius, 0);
            smallcircle2(cradius + Math.cos(2 * Math.PI / 360 * (120 + process * 3)) * radius, cradius + Math.sin(2 * Math.PI /
                360 * (120 + process * 3)) * radius, 2);
            //控制结束时动画的速度
            if (process / percent > 0.90) {
                process += 0.30;
            } else if (process / percent > 0.80) {
                process += 0.55;
            } else if (process / percent > 0.70) {
                process += 0.75;
            } else {
                process += 1.0;
            }
        }

        var process = 0.0; //进度
        var circleLoading = window.setInterval(function() {
            loading();
        }, 20);

    }