<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> </head> <body> <canvas id="canvas" style="margin:0 auto;border:1px #ddd solid;"> The current browser does not support Canvas, can replace the browser a try! </canvas> <script> window.onload = function(){ var canvas = document.getElementById(‘canvas‘); canvas.width = 1024; canvas.height = 768; if(canvas.getContext(‘2d‘)){ var context = canvas.getContext(‘2d‘); context.beginPath(); context.moveTo(150,150); context.arcTo(650,150,650,650,300); context.lineWidth = 6; context.strokeStyle = "red"; context.stroke(); // baseline context.beginPath(); context.moveTo(150,150); context.lineTo(650,150); context.lineTo(650,650); context.lineWidth = 2; context.strokeStyle = "gray" context.stroke(); }else{ alert(‘当前游览器不支持Canvas，请更换游览器后再试！‘); } } function arcToTest(cxt,x0,y0,x1,y1,x2,y2,R){ cxt.beginPath(); cxt.moveTo(x0,y0); cxt.arcTo(x1,y1,x2,y2,R); cxt.lineWidth = 6; cxt.strokeStyle = "red"; cxt.stroke(); // baseline cxt.beginPath(); cxt.moveTo(x0,y0); cxt.lineTo(x1,y1); cxt.lineTo(x2,y2); cxt.lineWidth = 2; cxt.strokeStyle = "gray" cxt.stroke(); } </script> </body> <script> /*总结 context.arc(x1,y1,x2,y2,r) */ </script> </html>
原文：http://www.cnblogs.com/cynthia-wuqian/p/4981633.html