HTML5 Canvas动画效果演示
主要思想：
首先要准备一张有连续帧的图片，然后利用HTML5 Canvas的draw方法在不同的时间
间隔绘制不同的帧，这样看起来就像动画在播放。
关键技术点：
JavaScript 函数setTimeout()有两个参数，第一个是参数可以传递一个JavaScript方法，
另外一个参数代表间隔时间，单位为毫秒数。代码示例：
setTimeout( update, 1000/30);
Canvas的API-drawImage()方法，需要指定全部9个参数：
ctx.drawImage(myImage, offw, offh, width,height, x2, y2, width, height);
其中offw, offh是指源图像的起始坐标点，width, height表示源图像的宽与高，x2,y2表
示源图像在目标Canvas上的起始坐标点。
一个22帧的大雁飞行图片实现的效果：
源图像：
程序代码：
<!DOCTYPE html> <html> <head> <meta http-equiv="X-UA-Compatible" content="chrome=IE8"> <meta http-equiv="Content-type" content="text/html;charset=UTF-8"> <title>Canvas Mouse Event Demo</title> <link href="default.css" rel="stylesheet" /> <script> var ctx = null; // global variable 2d context var started = false; var mText_canvas = null; var x = 0, y =0; var frame = 0; // 22 5*5 + 2 var imageReady = false; var myImage = null; var px = 300; var py = 300; var x2 = 300; var y2 = 0; window.onload = function() { var canvas = document.getElementById("animation_canvas"); console.log(canvas.parentNode.clientWidth); canvas.width = canvas.parentNode.clientWidth; canvas.height = canvas.parentNode.clientHeight; if (!canvas.getContext) { console.log("Canvas not supported. Please install a HTML5 compatible browser."); return; } // get 2D context of canvas and draw rectangel ctx = canvas.getContext("2d"); ctx.fillStyle="black"; ctx.fillRect(0, 0, canvas.width, canvas.height); myImage = document.createElement('img'); myImage.src = "../robin.png"; myImage.onload = loaded(); } function loaded() { imageReady = true; setTimeout( update, 1000/30); } function redraw() { ctx.clearRect(0, 0, 460, 460) ctx.fillStyle="black"; ctx.fillRect(0, 0, 460, 460); // find the index of frames in image var height = myImage.naturalHeight/5; var width = myImage.naturalWidth/5; var row = Math.floor(frame / 5); var col = frame - row * 5; var offw = col * width; var offh = row * height; // first robin px = px - 5; py = py - 5; if(px < -50) { px = 300; } if(py < -50) { py = 300; } //var rate = (frame+1) /22; //var rw = Math.floor(rate * width); //var rh = Math.floor(rate * height); ctx.drawImage(myImage, offw, offh, width, height, px, py, width, height); // second robin x2 = x2 - 5; y2 = y2 + 5; if(x2 < -50) { x2 = 300; y2 = 0; } ctx.drawImage(myImage, offw, offh, width, height, x2, y2, width, height); } function update() { redraw(); frame++; if (frame >= 22) frame = 0; setTimeout( update, 1000/30); } </script> </head> <body> <h2>HTML Canvas Animations Demo - By Gloomy Fish</h2> <pre>Play Animations</pre> <div id="my_painter"> <canvas id="animation_canvas"></canvas> </div> </body> </html>发现上传透明PNG格式有点问题，所以我上传 不透明的图片。可以用其它图片替换，替换以后
请修改最大帧数从22到你的实际帧数即可运行。
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