<!DOCTYPE?html>
<html?lang="en">
<head>
????<meta?charset="UTF-8">
????<title>Title</title>
</head>
<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>
<body>
<canvas?id="canvas"?style="margin:?50px?auto?;display:?block;?border:1px?solid?black;"></canvas>
</body>
</html>
2016-02-17
Math.sqrt()是返回數字的平方根，所以把22行的代碼改成 ?return?Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));即可。建議你去查下兩點間距離公式