<!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> var searchLight = { x : 400, y : 400, radius : 150, vx : Math.random() * 5 + 10, vy : Math.random() * 5 + 10 } var isIncrease = true; window.onload = function(){ var canvas = document.getElementById(‘canvas‘); canvas.width = 1024; canvas.height = 768; if(canvas.getContext(‘2d‘)){ var context = canvas.getContext(‘2d‘); setInterval(function(){ draw(context); update(canvas.width,canvas.height); },40); }else{ alert(‘当前游览器不支持Canvas，请更换游览器后再试！‘); } } function draw(cxt){ var canvas = cxt.canvas; cxt.clearRect(0,0,canvas.width,canvas.height); cxt.save(); cxt.beginPath(); cxt.fillStyle = "#000"; cxt.fillRect(0,0,canvas.width,canvas.height) cxt.closePath(); cxt.save(); cxt.translate(searchLight.x,searchLight.y); cxt.scale(searchLight.radius,searchLight.radius); starPath(cxt); cxt.fillStyle = "#fff"; cxt.fill(); cxt.restore(); cxt.clip(); cxt.font = "bold 150px Arial"; cxt.textAlign = "center"; cxt.textBaseline = "middle"; cxt.fillStyle = "#058"; cxt.fillText("Canvas",canvas.width/2,canvas.height/4); cxt.fillText("Canvas",canvas.width/2,canvas.height/2); cxt.fillText("Canvas",canvas.width/2,canvas.height * 3/4); cxt.restore(); } function starPath(cxt){ cxt.beginPath(); for(var i=0;i<5;i++){ cxt.lineTo(Math.cos( (18+i*72) / 180 * Math.PI ), -Math.sin( (18+i*72) / 180 * Math.PI )); cxt.lineTo(Math.cos( (54+i*72) / 180 * Math.PI )*0.5, -Math.sin( (54+i*72) / 180 * Math.PI )*0.5); } cxt.closePath(); } function update(canvasWidth,canvasHeight){ // rot += 1; // searchLight.x += searchLight.vx; // searchLight.y += searchLight.vy; // if(searchLight.x - searchLight.radius <= 0){ // searchLight.vx = -searchLight.vx; // searchLight.x = searchLight.radius; // } // if(searchLight.x + searchLight.radius >= canvasWidth){ // searchLight.vx = -searchLight.vx; // searchLight.x = canvasWidth - searchLight.radius; // } // if(searchLight.y - searchLight.radius <= 0){ // searchLight.vy = -searchLight.vy; // searchLight.y = searchLight.radius; // } // if(searchLight.y + searchLight.radius >= canvasHeight){ // searchLight.vy = -searchLight.vy; // searchLight.y = canvasHeight - searchLight.radius; // } if(searchLight.radius > 700) isIncrease = false; else if(searchLight.radius < 150) isIncrease = true; if(isIncrease) searchLight.radius += 5; else searchLight.radius -= 5; } </script> </body> </html>
原文：http://www.cnblogs.com/cynthia-wuqian/p/4988537.html