图像动画的小demo，JavaScript
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 ="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="#" id="sta">Start</a> <a href="#" id="stp">Stop</a></body></html>TAG:
