<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>arc</title>
</head>
<body>
<canvas id="canvas" style="border: 1px solid #ddd;"></canvas>
<script>
//draw an arc画曲线
var canvas = document.getElementById("canvas");
canvas.width = 1024;
canvas.height = 768;
var context = canvas.getContext("2d");
context.lineWidth = 5;
context.strokeStyle = "#058";
context.arc(300,300,200,0,0.5*Math.PI,true);
//context.arc(
//conterx,contery,radius,//圆心坐标x,圆心坐标y,半径
//startingAngle,endingAngle,//起始弧度值，终止弧度值
//anticlockwise = false//false顺时针绘制，true逆时针绘制
// );
context.stroke();
</script>
</body>
</html>
绘制单个圆：
绘制多个圆：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>arc*n</title>
</head>
<body>
<canvas id="canvas" style="border: 1px solid #ddd"></canvas>
<script>
var canvas = document.getElementById("canvas");
canvas.width = 1024;
canvas.height = 768;
var context = canvas.getContext("2d");
context.lineWidth = 5;
context.strokeStyle = "#058";
for(var i=0;i<10;i++){
context.beginPath();//重新开始新的路径
context.arc(50+100*i,60,40,0,2*Math.PI*(i+1)/10);
context.closePath();//结束当前路径，自动绘制封闭未封闭的线段
context.stroke();
}
for(var i=0;i<10;i++){
context.beginPath();//重新开始新的路径
context.arc(50+100*i,180,40,0,2*Math.PI*(i+1)/10);
context.stroke();
}
for(var i=0;i<10;i++){
context.beginPath();//重新开始新的路径
context.arc(50+100*i,300,40,0,2*Math.PI*(i+1)/10,true);
context.closePath();//结束当前路径，自动绘制封闭未封闭的线段
context.stroke();
}
for(var i=0;i<10;i++){
context.beginPath();//重新开始新的路径
context.arc(50+100*i,420,40,0,2*Math.PI*(i+1)/10,true);
context.stroke();
}
//填充图形；
context.fillStyle = "#058";
for(var i=0;i<10;i++){
context.beginPath();//重新开始新的路径
context.arc(50+100*i,540,40,0,2*Math.PI*(i+1)/10);
context.fill();
}
</script>
</body>
</html>
