在再谈js拖拽（二）仿iGoogle自定义首页模块拖拽的最后，我说了接下来要写Js动画，转瞬拖到了今天，呵呵。这篇主要讲动画的基础，就是几个最基本的特效，即：移动，渐变和尺寸变化。接下来写个梦幻西游版逍遥生角色行走的动画，然后再适时的写些动画有关的例子，争取把这个系列写好。
我们玩魔兽世界的时候可以通过ctrl+r来查看当前的帧数，当帧数很小时，会觉得很卡，帧数很高则很流畅。所谓帧数就是1秒内显示图片的数量。当这么多帧图片连起来显示，就形成了动画。
Js中实现动画都是靠setInterval或者setTimeout来实现。setInterval自身就能不断循环来执行计算从而显示新的帧，setTimeout是间隔一段时间后仅执行一次，他需要配合函数循环实现，很多人偏爱setTimeout来实现。本文采用setInterval实现。
据说，普通人眼能看到1/24秒，就是说1秒至少24帧，每次移位间隔需要小于1000/24=41.7毫秒，也就说setInterval要每隔至少40毫秒执行一次，一般地，我们采用10毫秒，当然间隔时间越短，客户端执行计算次数就越多，如果你code计算量大则可以适当调长些。
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首先贴上封装好的动画类Animation。
Animation- Animation = {<br> timer: 10,<br> SetOpacity: function(obj, n) {<br> if (document.all) {<br> obj.filters.alpha.opacity = n;<br> }<br> else {<br> obj.style.opacity = n / 100;<br> }<br> },<br> fade: function(obj, target, count, Func) {<br> obj = this.getItself(obj);<br> var currentCount = 0;<br> count = Math.abs(count) || 1;<br> target = target < 0 ? 0 : (target > 100) ? 100 : target;<br> var init = document.all ? obj.filters.alpha.opacity : window.getComputedStyle(obj, null).opacity * 100;<br> Func = Func || Tween.Linear;<br> var opr = this;<br> var flag = setInterval(function() {<br> if (currentCount > count) {<br> clearInterval(flag);<br> }<br> else {<br> currentCount++;<br> var tmp = Func(init, target, currentCount, count);<br> opr.SetOpacity(obj, tmp);<br> //清除小数点的误差<br> if (Math.abs(tmp - target) < 1) {<br> opr.SetOpacity(obj, target);<br> }<br> }<br> }<br> , this.timer);<br> },<br> resize: function(obj, targetPos, count, Func) {<br> obj = this.getItself(obj);<br> var currentCount = 0;<br> count = Math.abs(count) || 1;<br> var initPos = { x: obj.offsetWidth, y: obj.offsetHeight }<br> Func = Func || Tween.Linear;<br> targetPos = { x: targetPos.x < 0 ? 0 : targetPos.x, y: targetPos.y < 0 ? 0 : targetPos.y }<br> var flag = setInterval(function() {<br> if (currentCount > count) {<br> clearInterval(flag);<br> }<br> else {<br> currentCount++;<br> var tmpX = Func(initPos.x, targetPos.x, currentCount, count);<br> var tmpY = Func(initPos.y, targetPos.y, currentCount, count);<br> //width值不能小于0，但是算法返回值有可能出现负值<br> try {<br> obj.style.width = tmpX + "px";<br> obj.style.height = tmpY + "px";<br> }<br> catch (e) {<br> }<br> //清除小数点的误差<br> if (Math.abs(tmpX - targetPos.x) < 1) {<br> obj.style.width = targetPos.x + "px";<br> }<br> if (Math.abs(tmpY - targetPos.y) < 1) {<br> obj.style.height = targetPos.y + "px";<br> }<br> }<br> }<br> , this.timer);<br> },<br> move: function(obj, targetPos, count, Func) {<br> obj = this.getItself(obj);<br> var currentCount = 0;<br> count = Math.abs(count) || 1;<br> var elPos = this.getElementPos(obj);<br> var initPos = { x: elPos.x, y: elPos.y }<br> Func = Func || Tween.Linear;<br> var flag = setInterval(function() {<br> if (currentCount > count) {<br> clearInterval(flag);<br> }<br> else {<br> currentCount++;<br> var tmpX = Func(initPos.x, targetPos.x, currentCount, count);<br> var tmpY = Func(initPos.y, targetPos.y, currentCount, count);<br> obj.style.left = tmpX + "px";<br> obj.style.top = tmpY + "px";<br> //清除小数点的误差<br> if (Math.abs(tmpX - targetPos.x) < 1) {<br> obj.style.left = targetPos.x + "px";<br> }<br> if (Math.abs(tmpY - targetPos.y) < 1) {<br> obj.style.top = targetPos.y + "px";<br> }<br> }<br> }<br> , this.timer);<br> },<br> getElementPos: function(el) {<br> el = this.getItself(el);<br> var _x = 0, _y = 0;<br> do {<br> _x += el.offsetLeft;<br> _y += el.offsetTop;<br> } while (el = el.offsetParent);<br> return { x: _x, y: _y };<br> },<br> getItself: function(id) {<br> return "string" == typeof id ? document.getElementById(id) : id;<br> }<br> }
其中fade方法是实现渐变效果的，resize方法是改变对象尺寸大小的，move方法是实现移动效果的。首先看下move方法，其他2个方法实现其实是类似的。
move方法的调用：Animation.move('divObj',{x:500,y:500},100,Tween.Quart.easeInOut); 第一个参数是移动的对象，第二个参数是移动的目标坐标，第三个参数是一共执行多少次移位，即移动时间内一共的帧数，即执行多少次，第4个参数是可选参数，指定Tween具体算法，若不加，则默认采用Tween.Linear。
移动问题的关键就是每次移位后，应该将移动对象定位到什么位置，即其left和top是多少。来看一个简单的数学题，当我们知道了一个点的起始位置initPos和终点位置targetPos，要求在count次移动后达到终点，该点为匀速运动，求第currentCount次移动后该点位置在哪里？显然的位置在：（targetPos - initPos）*（currentCount/count）+initPos。这个就是Tween.Linear算法。当这个点不是匀速运动时，就是Tween的其他算法。Tween来自Flash的AS，你可以参考http://www.robertpenner.com/easing/easing_demo.html去查看Tween各种算法的运动效果，也可以参考cloudgamer的一篇文章JavaScript Tween算法及缓动效果。相比下，我将Tween各种算法的传入参数稍改了下，将移动的总距离的运算放到了Tween算法内部，然后最后个参数是作为总共计算次数理解的，而不是持续时间。我本来是想用持续时间运算的，但是发现还是要将持续时间除以10毫秒得到总次数，然后参与运算，总次数还可能非整数，有误差，所以我干脆直接传总次数过来，当然你也可以改成持续时间。那在应用时，究竟移动次数应该写多少，在每次间隔10毫秒进行移动下，次数越多，耗时越长。譬如采用Tween.Linear计算移动位置时，大概是耗时count*10ms的1.5倍，譬如写100，就是100*10*1.5=1.5s左右，这个多出来的0.5倍是Tween.Linear计算花费的时间。贴上改写后的Tween。
Tween- /*<br> t:currentCount 当前执行第t次<br> b:initPos 初始值<br> c:targetPos - initPos 发生偏移的距离值<br> d:count 一共执行d次<br> 效果：http://www.robertpenner.com/easing/easing_demo.html <br> JavaScript Tween算法及缓动效果 http://www.cnblogs.com/cloudgamer/archive/2009/01/06/tween.html<br> */<br> var Tween = {<br> Linear: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * t / d + b;<br> },<br> Quad: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * (t /= d) * t + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return -c * (t /= d) * (t - 2) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if ((t /= d / 2) < 1) return c / 2 * t * t + b;<br> return -c / 2 * ((--t) * (t - 2) - 1) + b;<br> }<br> },<br> Cubic: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * (t /= d) * t * t + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * ((t = t / d - 1) * t * t + 1) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;<br> return c / 2 * ((t -= 2) * t * t + 2) + b;<br> }<br> },<br> Quart: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * (t /= d) * t * t * t + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return -c * ((t = t / d - 1) * t * t * t - 1) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if ((t /= d / 2) < 1) return c / 2 * t * t * t * t + b;<br> return -c / 2 * ((t -= 2) * t * t * t - 2) + b;<br> }<br> },<br> Quint: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * (t /= d) * t * t * t * t + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * ((t = t / d - 1) * t * t * t * t + 1) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if ((t /= d / 2) < 1) return c / 2 * t * t * t * t * t + b;<br> return c / 2 * ((t -= 2) * t * t * t * t + 2) + b;<br> }<br> },<br> Sine: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return -c * Math.cos(t / d * (Math.PI / 2)) + c + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * Math.sin(t / d * (Math.PI / 2)) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;<br> }<br> },<br> Expo: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return (t == 0) ? b : c * Math.pow(2, 10 * (t / d - 1)) + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return (t == d) ? b + c : c * (-Math.pow(2, -10 * t / d) + 1) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (t == 0) return b;<br> if (t == d) return b + c;<br> if ((t /= d / 2) < 1) return c / 2 * Math.pow(2, 10 * (t - 1)) + b;<br> return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b;<br> }<br> },<br> Circ: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if ((t /= d / 2) < 1) return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b;<br> return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;<br> }<br> },<br> Elastic: {<br> easeIn: function(initPos, targetPos, currentCount, count, a, p) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (t == 0) return b; if ((t /= d) == 1) return b + c; if (!p) p = d * .3;<br> if (!a || a < Math.abs(c)) { a = c; var s = p / 4; }<br> else var s = p / (2 * Math.PI) * Math.asin(c / a);<br> return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count, a, p) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (t == 0) return b; if ((t /= d) == 1) return b + c; if (!p) p = d * .3;<br> if (!a || a < Math.abs(c)) { a = c; var s = p / 4; }<br> else var s = p / (2 * Math.PI) * Math.asin(c / a);<br> return (a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b);<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count, a, p) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (t == 0) return b; if ((t /= d / 2) == 2) return b + c; if (!p) p = d * (.3 * 1.5);<br> if (!a || a < Math.abs(c)) { a = c; var s = p / 4; }<br> else var s = p / (2 * Math.PI) * Math.asin(c / a);<br> if (t < 1) return -.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;<br> return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * .5 + c + b;<br> }<br> },<br> Back: {<br> easeIn: function(initPos, targetPos, currentCount, count, s) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (s == undefined) s = 1.70158;<br> return c * (t /= d) * t * ((s + 1) * t - s) + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count, s) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (s == undefined) s = 1.70158;<br> return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count, s) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (s == undefined) s = 1.70158;<br> if ((t /= d / 2) < 1) return c / 2 * (t * t * (((s *= (1.525)) + 1) * t - s)) + b;<br> return c / 2 * ((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2) + b;<br> }<br> },<br> Bounce: {<br> easeIn: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> return c - Tween.Bounce.easeOut(d - t, 0, c, d) + b;<br> },<br> easeOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if ((t /= d) < (1 / 2.75)) {<br> return c * (7.5625 * t * t) + b;<br> } else if (t < (2 / 2.75)) {<br> return c * (7.5625 * (t -= (1.5 / 2.75)) * t + .75) + b;<br> } else if (t < (2.5 / 2.75)) {<br> return c * (7.5625 * (t -= (2.25 / 2.75)) * t + .9375) + b;<br> } else {<br> return c * (7.5625 * (t -= (2.625 / 2.75)) * t + .984375) + b;<br> }<br> },<br> easeInOut: function(initPos, targetPos, currentCount, count) {<br> var b = initPos, c = targetPos - initPos, t = currentCount, d = count;<br> if (t < d / 2) return Tween.Bounce.easeIn(t * 2, 0, c, d) * .5 + b;<br> else return Tween.Bounce.easeOut(t * 2 - d, 0, c, d) * .5 + c * .5 + b;<br> }<br> }<br> }
相比move方法，fade方法是用Tween算法去计算透明度，而resize方法是用Tween算法去计算width和height，没有大的区别。利用这3个特效，一些简单的动画都能实现了。如果某对象要在移动过程中同时改变大小和设置透明度，只要三个方法连续写下来即可。如：
[code][/code]
（ps:若无特别声明，此博客所有例子均可在IE/FF/Chrome中运行）
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