HTML5 Canvas动画效果演示

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：

HTML5 Canvas动画效果演示

源图像：

HTML5 Canvas动画效果演示

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>
<h1>HTML Canvas Animations Demo - By Gloomy Fish</h1>
<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。

秒客网

HTML5 Canvas动画效果演示

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