Canvas实现圆形进度条并显示数字百分比

<canvas id="canvas" width="500" height="500" style="background:#000;"></canvas>

var canvas = document.getElementById('canvas'),  //获取canvas元素            context = canvas.getContext('2d'),  //获取画图环境，指明为2d            centerX = canvas.width/2,   //Canvas中心点x轴坐标            centerY = canvas.height/2,  //Canvas中心点y轴坐标            rad = Math.PI*2/100, //将360度分成100份，那么每一份就是rad度            speed = 0.1; //加载的快慢就靠它了

//绘制5像素宽的运动外圈        function blueCircle(n){            context.save();            context.strokeStyle = "#fff"; //设置描边样式            context.lineWidth = 5; //设置线宽            context.beginPath(); //路径开始            context.arc(centerX, centerY, 100 , -Math.PI/2, -Math.PI/2 +n*rad, false); //用于绘制圆弧context.arc(x坐标，y坐标，半径，起始角度，终止角度，顺时针/逆时针)            context.stroke(); //绘制            context.closePath(); //路径结束            context.restore();        }

//绘制白色外圈        function whiteCircle(){            context.save();            context.beginPath();            context.lineWidth = 2; //设置线宽            context.strokeStyle = "red";            context.arc(centerX, centerY, 100 , 0, Math.PI*2, false);            context.stroke();            context.closePath();            context.restore();        }

function text(n){            context.save(); //save和restore可以保证样式属性只运用于该段canvas元素            context.strokeStyle = "#fff"; //设置描边样式            context.font = "40px Arial"; //设置字体大小和字体            //绘制字体，并且指定位置            context.strokeText(n.toFixed(0)+"%", centerX-25, centerY+10);            context.stroke(); //执行绘制            context.restore();        }

//动画循环        (function drawFrame(){            window.requestAnimationFrame(drawFrame);            context.clearRect(0, 0, canvas.width, canvas.height);            whiteCircle();            text(speed);            blueCircle(speed);            if(speed > 100) speed = 0;            speed += 0.1;        }());

HTML5 Canvas 圆形进度条并显示数字百分比*{margin:0;padding:0;}body{text-align:center;background-color:#000;}<canvas id="canvas" width="500" height="500" style="background:#000;"></canvas><script>    window.onload = function(){        var canvas = document.getElementById(&amp;#39;canvas&amp;#39;),  //获取canvas元素            context = canvas.getContext(&amp;#39;2d&amp;#39;),  //获取画图环境，指明为2d            centerX = canvas.width/2,   //Canvas中心点x轴坐标            centerY = canvas.height/2,  //Canvas中心点y轴坐标            rad = Math.PI*2/100, //将360度分成100份，那么每一份就是rad度            speed = 0.1; //加载的快慢就靠它了                     //绘制5像素宽的运动外圈        function blueCircle(n){            context.save();            context.strokeStyle = "#fff"; //设置描边样式            context.lineWidth = 5; //设置线宽            context.beginPath(); //路径开始            context.arc(centerX, centerY, 100 , -Math.PI/2, -Math.PI/2 +n*rad, false); //用于绘制圆弧context.arc(x坐标，y坐标，半径，起始角度，终止角度，顺时针/逆时针)            context.stroke(); //绘制            context.closePath(); //路径结束            context.restore();        }        //绘制白色外圈        function whiteCircle(){            context.save();            context.beginPath();            context.lineWidth = 2; //设置线宽            context.strokeStyle = &quot;red&quot;;            context.arc(centerX, centerY, 100 , 0, Math.PI*2, false);            context.stroke();            context.closePath();            context.restore();        }          //百分比文字绘制        function text(n){            context.save(); //save和restore可以保证样式属性只运用于该段canvas元素            context.strokeStyle = "#fff"; //设置描边样式            context.font = "40px Arial"; //设置字体大小和字体            //绘制字体，并且指定位置            context.strokeText(n.toFixed(0)+"%", centerX-25, centerY+10);            context.stroke(); //执行绘制            context.restore();        }         //动画循环        (function drawFrame(){            window.requestAnimationFrame(drawFrame);            context.clearRect(0, 0, canvas.width, canvas.height);            whiteCircle();            text(speed);            blueCircle(speed);            if(speed > 100) speed = 0;            speed += 0.1;        }());    }</script>