<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>扩展方法</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> var canvas = document.getElementById(‘canvas‘); // 新的API CanvasRenderingContext2D.prototype.fillStar = function(r,R,x,y,rot){ this.beginPath(); for(var i=0;i<5;i++){ this.lineTo(Math.cos( (18+i*72 -rot)/180*Math.PI )*R+x, -Math.sin( (18+i*72 -rot)/180*Math.PI )*R+y); this.lineTo(Math.cos( (54+i*72 -rot)/180*Math.PI )*r+x, -Math.sin( (54+i*72 -rot) /180*Math.PI )*r+y); } this.closePath(); this.fill(); } window.onload = function(){ canvas.width = 1024; canvas.height = 768; if(canvas.getContext(‘2d‘)){ var context = canvas.getContext(‘2d‘); // begin context.fillStyle = "#058"; // 调用新的API context.fillStar(150,300,400,400,0) }else{ alert(‘当前游览器不支持Canvas，请更换游览器后再试！‘); } } </script> </body> </html>
原文：http://www.cnblogs.com/cynthia-wuqian/p/4991199.html