HTML5效果：Canvas 实现圆形进度条并显示数字百分比
<!DOCTYPE html>
<htmllang="en">
<head>
<metacharset="UTF-8">
<title>HTML5 Canvas 圆形进度条并显示数字百分比</title>
<style>*{margin:0;padding:0;}body{text-align:center;background-color:#000;}</style>
</head>
<body>
<canvasid="canvas"width="500"height="500"style="background:#000;"></canvas>
<script>
window.onload= function(){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
functionblueCircle(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
functionwhiteCircle(){
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();
}
//百分比文字绘制
functiontext(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
(functiondrawFrame(){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>
</body>
