效果图
html结构
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title>canvas19</title>
<link rel="stylesheet" href="">
</head>
<body>
<canvas id="canvas" style ="border:1px solid #aaa;diplay:block;margin:50px auto;">
当前浏览器不支持canvas,请更换浏览器后再试
</canvas>
</body>
</html>
js脚本
<script>
window.onload = function(){
var canvas = document.getElementById("canvas");
canvas.width = 800;
canvas.height = 800;
var context = canvas.getContext("2d");
context.arc(400,400,300,0.5*Math.PI,1.5*Math.PI,true);
context.moveTo(400,100);
context.arcTo(1200,400,400,700,(400-100)*dis(400,100,1200,400)/(1200-400));
context.stroke();
}
function dis(x1,y1,x2,y2){
return Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
</script>