JavaScript 图像动画的小demo

更新时间：2012年05月23日 22:18:31 作者：

深夜没睡着，起来翻了翻《JavaScript权威指南》这本书，看了下图形动画的demo，学习学习了

 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml" > 
<head> 
<title>图形动画</title> 
<style type="text/css"> 
.de{ font-size:30px; text-decoration:none; font-family:微软雅黑; color:#ccc;} 
.de:hover{ color:#933;} 
</style> 
<script type="text/javascript"> 
/** 
* ImageLoop.js: An ImageLoop class for performing image animations 
* 
* Constructor Arguments: 
* imageId: the id of the <img> tag which will be animated 
* fps: the number of frames to display per second 
* frameURLs: an array of URLs, one for each frame of the animation 
* 
* Public Methods: 
* start(): start the animation (but wait for all frames to load first) 
* stop(): stop the animation 
* 
* Public Properties: 
* loaded: true if all frames of the animation have loaded, 
* false otherwise 
*/ 
function ImageLoop(imageId, fps, frameURLs) { 
// Remember the image id. Don't look it up yet since this constructor 
// may be called before the document is loaded. 
this.imageId = imageId; 
// Compute the time to wait between frames of the animation 
this.frameInterval = 1000 / fps; 
// An array for holding Image objects for each frame 
this.frames = new Array(frameURLs.length); 

this.image = null; // The <img> element, looked up by id 
this.loaded = false; // Whether all frames have loaded 
this.loadedFrames = 0; // How many frames have loaded 
this.startOnLoad = false; // Start animating when done loading? 
this.frameNumber = -1; // What frame is currently displayed 
this.timer = null; // The return value of setInterval() 

// Initialize the frames[] array and preload the images 
for (var i = 0; i < frameURLs.length; i++) { 
this.frames[i] = new Image(); // Create Image object 
// Register an event handler so we know when the frame is loaded 
this.frames[i].onload = countLoadedFrames; // defined later 
this.frames[i].src = frameURLs[i]; // Preload the frame's image 
} 

// This nested function is an event handler that counts how many 
// frames have finished loading. When all are loaded, it sets a flag, 
// and starts the animation if it has been requested to do so. 
var loop = this; 
function countLoadedFrames() { 
loop.loadedFrames++; 
if (loop.loadedFrames == loop.frames.length) { 
loop.loaded = true; 
if (loop.startOnLoad) loop.start(); 
} 
} 

// Here we define a function that displays the next frame of the 
// animation. This function can't be an ordinary instance method because 
// setInterval() can only invoke functions, not methods. So we make 
// it a closure that includes a reference to the ImageLoop object 
this._displayNextFrame = function () { 
// First, increment the frame number. The modulo operator (%) means 
// that we loop from the last to the first frame 
loop.frameNumber = (loop.frameNumber + 1) % loop.frames.length; 
// Update the src property of the image to the URL of the new frame 
loop.image.src = loop.frames[loop.frameNumber].src; 
}; 
} 

/** 
* This method starts an ImageLoop animation. If the frame images have not 
* finished loading, it instead sets a flag so that the animation will 
* automatically be started when loading completes 
*/ 
ImageLoop.prototype.start = function () { 
if (this.timer != null) return; // Already started 
// If loading is not complete, set a flag to start when it is 
if (!this.loaded) this.startOnLoad = true; 
else { 
// If we haven't looked up the image by id yet, do so now 
if (!this.image) this.image = document.getElementById(this.imageId); 
// Display the first frame immediately 
this._displayNextFrame(); 
// And set a timer to display subsequent frames 
this.timer = setInterval(this._displayNextFrame, this.frameInterval); 
} 
}; 

/** Stop an ImageLoop animation */ 
ImageLoop.prototype.stop = function () { 
if (this.timer) clearInterval(this.timer); 
this.timer = null; 
}; 

</script> 
<script type="text/javascript"> 
function de() { 
var animation = new ImageLoop("loop", 1, ["img/img_01.jpg", "img/img_02.jpg",]); 
var sta = document.getElementById("sta"); 
var stp = document.getElementById("stp"); 
sta.onclick = function () { 
animation.start(); 
} 
stp.onclick = function () { 
animation.stop(); 
} 
} 
window.onload = function () { 
de(); 
} 
</script> 
</head> 
<body> 
<img src="img/img_01.jpg" id="loop" alt="" title="" /> 
<a href="#" class="de" id="sta">Start</a> 
<a href="#" class="de" id="stp">Stop</a> 
</body> 
</html> 

图像动画

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