Javascript DHTML动画
JS实现的动画效果多半是用timmer实现的某个属性不断改变的过程。以下这个写好的函数是十分强大的~摘自JSDG 5th ed。附上我的注释：/** * AnimateCSS.js: * This file defines a function named animateCSS(), which serves as a framework * for creating CSS-based animations. The arguments to this function are: * * element: The HTML element to be animated. * numFrames: The total number of frames in the animation. * timePerFrame: The number of milliseconds to display each frame. * animation: An object that defines the animation; described below. * whendone: An optional function to call when the animation finishes. * If specified, this function is passed element as its argument. * * The animateCSS() function simply defines an animation framework. It is * the properties of the animation object that specify the animation to be * done. Each property should have the same name as a CSS style property. The * value of each property must be a function that returns values for that * style property. Each function is passed the frame number and the total * amount of elapsed time, and it can use these to compute the style value it * should return for that frame. For example, to animate an image so that it * slides in from the upper left, you might invoke animateCSS as follows: * *animateCSS(image, 25, 50,// Animate image for 25 frames of 50ms each * {// Set top and left attributes for each frame as follows: * top: function(frame,time) { return frame*8 + "px"; }, * left: function(frame,time) { return frame*8 + "px"; } * }); * * animateCSS()函数是作为一个基于CSS的动画实现框架。通过传递参数对象来制定动画样式。 * element：需要创建动画的HTML元素节点 * numFrames：动画的总帧数 * timePerFrame：每一帧的毫秒数 *animation：定义动画的详细参数对象 *whendone：动画执行完毕后的回调函数 * *animation对象，每个属性的名称必须对应CSS的JS名，属性值为该CSS属性的计算函数 * **/function animateCSS(element, numFrames, timePerFrame, animation, whendone) { var frame = 0;// Store current frame number var time = 0; // Store total elapsed time // Arrange to call displayNextFrame() every timePerFrame milliseconds. // This will display each of the frames of the animation.// 很显然只是安排调用displayNextFrame(),关键就在这个函数中 var intervalId = setInterval(displayNextFrame, timePerFrame); // The call to animateCSS() returns now, but the previous line ensures that // the following nested function will be invoked once for each frame // of the animation.// 在这里我们检查是否已经完成所有帧数，如果是，就清除timmer然后执行回调函数；// 如果没有就遍历animation对象里的属性设置element的CSS属性。 function displayNextFrame() { if (frame >= numFrames) { // First, see if we're done clearInterval(intervalId); // If so, stop calling ourselves if (whendone) whendone(element);// Invoke whendone function return; // And we're finished } // Now loop through all properties defined in the animation object for(var cssprop in animation) { // For each property, call its animation function, passing the // frame number and the elapsed time. Use the return value of the // function as the new value of the corresponding style property // of the specified element. Use try/catch to ignore any // exceptions caused by bad return values.// 这里执行每个属性的计算函数，给计算函数传递的是frame当前帧数，time已执行时间 try { element.style = animation(frame, time); } catch(e) {} } frame++; // Increment the frame number time += timePerFrame;// Increment the elapsed time }}
这个函数和jQuery的$.fn.animate()有异曲同工之妙……
文中的计算函数其实就是jQuery中的esaing函数
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