用慣了jquery的同學,相信都很欣賞其動畫引擎。確實相對比較完善！如果，如果想像力足夠豐富的話，相信可以做出超出想像的效果。當然，跟2d庫比起來，還是相差相當一段距離。jquery壓根也不是專門為動畫而設計的。模擬真實世界方面，還是不足的。但在web世界裡還是游刃有余的。動畫其實一直是flash的專屬領地(web區哉)。只是它常常淪為黑客攻擊的漏洞所在，而且要裝插件，有時候文件實在太大，而且性耗實在是高啊。html5出現後，其實adobe自己都轉移陣地到html5了。當然，我覺得很長一段時間內,flash是不會被放棄的。
長話短說，步入正題。仿照flash的動畫原理，自己寫了一個非常簡單的js動畫引擎。
首先，用過flash的同學都知道。flash有個時間線，上面布滿了“幀”。其實每個幀都是一個鏡頭，鏡頭連貫起來就是一副動畫效果。其實，這跟電影的原理也一樣的，小時候玩過膠片的都知道，對著光可以看到一副副的鏡頭。人眼分辨兩個畫面的連貫是有時間限度的。如果想看不到兩個畫面變換時的閃爍大概30幀/秒左右，電影是24幀的。所以，如果能保證，動畫切換能保證每秒30次，基本上，就做到了動畫的流暢效果，但是這取決環境。所以具體情況，具體而定，其實關於這方面的知識我也是一知半解。就這個動畫引擎而言，了解這麼多也差不多足夠了，有興趣可以查找相關知識！
下面開始說說設計原理。
首先需要一個幀頻，也就是多少幀每秒。如果有了總用時，就可以計算出整個動畫下來有多少個“畫面”（總幀數）。這種設計，顯然有個不足的地方，不能保證時間正好是個整數幀。除非1ms一幀。這是一個網友提出來的，我感覺不好就沒有采用。所以這個引擎是有時間誤差的。有了總幀數，當動畫運行到最後一幀的時候，整個動畫也就播放完。如果需要重復播放，重新把當前幀歸0。這種動畫有一個好處，就可以直接運行到指定幀。也就是flash裡的gotoAndStop和gotoAndPlay。其實整個動畫設計原理都是照著flash實現的。包括一個很重要的方法：enterFrame。位置就是根據進入當前幀來計算的。還有其它一些方法：stop、play、next......等等因為目前來說，這個引擎是寫非常簡單和粗糙的，先不說這麼詳細了。下面先上代碼和示例吧！
animate.js 動畫核心
復制代碼 代碼如下:
var animation = function(obj) {
this.obj = obj;
this.frames = 0;
this.timmer = undefined;
this.running = false;
this.ms = [];
}
animation.prototype = {
fps: 36,
init: function(props, duration, tween) {
//console.log('初始化');
this.curframe = 0;
this.initstate = {};
this.props = props;
this.duration = duration || 1000;
this.tween = tween || function(t, b, c, d) {
return t * c / d + b;
};
this.frames = Math.ceil(this.duration * this.fps/1000);
for (var prop in this.props) {
this.initstate[prop] = {
from: parseFloat($util.dom.getStyle(this.obj, prop)),
to: parseFloat(this.props[prop])
};
}
},
start: function() {
if (!this.running && this.hasNext()) {
//console.log('可以執行...');
this.ms.shift().call(this)
}
return this;
},
//開始播放
play: function(callback) {
//console.log('開始動畫！');
var that = this;
this.running = true;
if (this.timmer) {
this.stop();
}
this.timmer = setInterval(function() {
if (that.complete()) {
that.stop();
that.running = false;
if (callback) {
callback.call(that);
}
return;
}
that.curframe++;
that.enterFrame.call(that);
},
/ this.fps);
return this;
},
// 停止動畫
stop: function() {
//console.log('結束動畫！');
if (this.timmer) {
clearInterval(this.timmer);
// 清除掉timmer id
this.timmer = undefined;
}
},
go: function(props, duration, tween) {
var that = this;
//console.log(tween)
this.ms.push(function() {
that.init.call(that, props, duration, tween);
that.play.call(that, that.start);
});
return this;
},
//向後一幀
next: function() {
this.stop();
this.curframe++;
this.curframe = this.curframe > this.frames ? this.frames: this.curframe;
this.enterFrame.call(this);
},
//向前一幀
prev: function() {
this.stop();
this.curframe--;
this.curframe = this.curframe < 0 ? 0 : this.curframe;
this.enterFrame.call(this);
},
//跳躍到指定幀並播放
gotoAndPlay: function(frame) {
this.stop();
this.curframe = frame;
this.play.call(this);
},
//跳到指定幀停止播放
gotoAndStop: function(frame) {
this.stop();
this.curframe = frame;
this.enterFrame.call(this);
},
//進入幀動作
enterFrame: function() {
//console.log('進入幀：' + this.curframe)
var ds;
for (var prop in this.initstate) {
//console.log('from: ' + this.initstate[prop]['from'])
ds = this.tween(this.curframe, this.initstate[prop]['from'], this.initstate[prop]['to'] - this.initstate[prop]['from'], this.frames).toFixed(2);
//console.log(prop + ':' + ds)
$util.dom.setStyle(this.obj, prop, ds)
}
},
//動畫結束
complete: function() {
return this.curframe >= this.frames;
},
hasNext: function() {
return this.ms.length > 0;
}
}
下面是一個簡單的工具,其中有所用到的緩動公式：
util.js
復制代碼 代碼如下:
$util = {
/**
* 類型檢測
*/
type : function(obj){
var rep = /\[object\s+(\w+)\]/i;
var str = Object.prototype.toString.call(obj).toLowerCase();
str.match(rep);
return RegExp.$1;
},
/**
* 深拷貝
*/
$unlink :function (object){
var unlinked;
switch ($type(object)){
case 'object':
unlinked = {};
for (var p in object) {
unlinked[p] = $unlink(object[p]);
}
break;
case 'array':
unlinked = [];
for (var i = 0, l = object.length; i < l; i++) {
unlinked[i] = $unlink(object[i]);
}
break;
default: return object;
}
return unlinked;
},
/**
*Dom 相關操作
*/
dom:{
$: function(id) {
return document.getElementById(id);
},
getStyle: function(obj, prop) {
var style = obj.currentStyle || window.getComputedStyle(obj, '');
if (obj.style.filter) {
return obj.style.filter.match(/\d+/g)[0];
}
return style[prop];
},
setStyle: function(obj, prop, val) {
switch (prop) {
case 'opacity':
if($util.client.browser.ie){
obj.style.filter = 'alpha(' + prop + '=' + val*100 + ')'
}else{
obj.style[prop] = val;
}
break;
default:
obj.style[prop] = val + 'px';
break;
}
},
setStyles: function(obj, props) {
for (var prop in props) {
switch (prop) {
case 'opacity':
if($util.client.browser.ie){
obj.style.filter = 'alpha(' + prop + '=' + props[prop] + ')'
}else{
obj.style[prop] = props[prop];
}
break;
default:
obj.style[prop] = props[prop] + 'px';
break;
}
}
}
},
/**
*Event 事件相關
*/
evt : {
addEvent : function(oTarget, sEventType, fnHandler) {
if (oTarget.addEventListener) {
oTarget.addEventListener(sEventType, fnHandler, false);
} else if (oTarget.attachEvent) {
oTarget.attachEvent("on" + sEventType, fnHandler);
} else {
oTarget["on" + sEventType] = fnHandler;
}
},
rmEvent : function removeEventHandler (oTarget, sEventType, fnHandler) {
if (oTarget.removeEventListener) {
oTarget.removeEventListener(sEventType, fnHandler, false);
} else if (oTarget.detachEvent) {
oTarget.detachEvent("on" + sEventType, fnHandler);
} else {
oTarget["on" + sEventType] = null;
}
}
},
/**
*Ajax 異步加載
*/
ajax : {
request:function (options) {
var xhr, res;
var url = options.url,
context = options.context,
success = options.success,
type = options.type,
datatype = options.datatype,
async = options.async,
send = options.send,
headers = options.headers;
try {
xhr = new XMLHttpRequest();
} catch(e) {
try {
xhr = new ActiveXObject('MSXML2.XMLHTTP');
} catch(e) {
xhr = new ActiveXObject('Microsoft.XMLHTTP');
}
}
xhr.onreadystatechange = function() {
if (xhr.readyState == 4 && xhr.status == 200) {
res = xhr.responseText;
success(res);
}
}
xhr.open(type, url, async);
xhr.send(send);
}
},
/**
*Array 數組相關
*/
array : {
minIndex : function(ary){
return Math.min.apply(null,ary);
},
maxitem : function(ary){
return Math.max.apply(null,ary);
}
},
/**
*Client 客戶端檢測
*/
client : function(){
// 浏覽器渲染引擎 engines
var engine = {
ie: 0,
gecko: 0,
webkit: 0,
khtml: 0,
opera: 0,
//complete version
ver: null
};
// 浏覽器
var browser = {
//browsers
ie: 0,
firefox: 0,
safari: 0,
konq: 0,
opera: 0,
chrome: 0,
//specific version
ver: null
};
// 客戶端平台platform/device/OS
var system = {
win: false,
mac: false,
x11: false,
//移動設備
iphone: false,
ipod: false,
ipad: false,
ios: false,
android: false,
nokiaN: false,
winMobile: false,
//game systems
wii: false,
ps: false
};
// 檢測浏覽器引擎
var ua = navigator.userAgent;
if (window.opera){
engine.ver = browser.ver = window.opera.version();
engine.opera = browser.opera = parseFloat(engine.ver);
} else if (/AppleWebKit\/(\S+)/.test(ua)){
engine.ver = RegExp["$1"];
engine.webkit = parseFloat(engine.ver);
//figure out if it's Chrome or Safari
if (/Chrome\/(\S+)/.test(ua)){
browser.ver = RegExp["$1"];
browser.chrome = parseFloat(browser.ver);
} else if (/Version\/(\S+)/.test(ua)){
browser.ver = RegExp["$1"];
browser.safari = parseFloat(browser.ver);
} else {
//approximate version
var safariVersion = 1;
if (engine.webkit < 100){
safariVersion = 1;
} else if (engine.webkit < 312){
safariVersion = 1.2;
} else if (engine.webkit < 412){
safariVersion = 1.3;
} else {
safariVersion = 2;
}
browser.safari = browser.ver = safariVersion;
}
} else if (/KHTML\/(\S+)/.test(ua) || /Konqueror\/([^;]+)/.test(ua)){
engine.ver = browser.ver = RegExp["$1"];
engine.khtml = browser.konq = parseFloat(engine.ver);
} else if (/rv:([^\)]+)\) Gecko\/\d{8}/.test(ua)){
engine.ver = RegExp["$1"];
engine.gecko = parseFloat(engine.ver);
//determine if it's Firefox
if (/Firefox\/(\S+)/.test(ua)){
browser.ver = RegExp["$1"];
browser.firefox = parseFloat(browser.ver);
}
} else if (/MSIE ([^;]+)/.test(ua)){
engine.ver = browser.ver = RegExp["$1"];
engine.ie = browser.ie = parseFloat(engine.ver);
}
//detect browsers
browser.ie = engine.ie;
browser.opera = engine.opera;
//detect platform
var p = navigator.platform;
system.win = p.indexOf("Win") == 0;
system.mac = p.indexOf("Mac") == 0;
system.x11 = (p == "X11") || (p.indexOf("Linux") == 0);
//detect windows operating systems
if (system.win){
if (/Win(?:dows )?([^do]{2})\s?(\d+\.\d+)?/.test(ua)){
if (RegExp["$1"] == "NT"){
switch(RegExp["$2"]){
case "5.0":
system.win = "2000";
break;
case "5.1":
system.win = "XP";
break;
case "6.0":
system.win = "Vista";
break;
case "6.1":
system.win = "7";
break;
default:
system.win = "NT";
break;
}
} else if (RegExp["$1"] == "9x"){
system.win = "ME";
} else {
system.win = RegExp["$1"];
}
}
}
//mobile devices
system.iphone = ua.indexOf("iPhone") > -1;
system.ipod = ua.indexOf("iPod") > -1;
system.ipad = ua.indexOf("iPad") > -1;
system.nokiaN = ua.indexOf("NokiaN") > -1;
//windows mobile
if (system.win == "CE"){
system.winMobile = system.win;
} else if (system.win == "Ph"){
if(/Windows Phone OS (\d+.\d+)/.test(ua)){;
system.win = "Phone";
system.winMobile = parseFloat(RegExp["$1"]);
}
}
//determine iOS version
if (system.mac && ua.indexOf("Mobile") > -1){
if (/CPU (?:iPhone )?OS (\d+_\d+)/.test(ua)){
system.ios = parseFloat(RegExp.$1.replace("_", "."));
} else {
system.ios = 2; //can't really detect - so guess
}
}
//determine Android version
if (/Android (\d+\.\d+)/.test(ua)){
system.android = parseFloat(RegExp.$1);
}
//gaming systems
system.wii = ua.indexOf("Wii") > -1;
system.ps = /playstation/i.test(ua);
//return it
return {
engine: engine,
browser: browser,
system: system
};
}(),
/**
*Tween 緩動相關
*/
tween: {
Linear: function(t, b, c, d) {
return c * t / d + b;
},
Quad: {
easeIn: function(t, b, c, d) {
return c * (t /= d) * t + b;
},
easeOut: function(t, b, c, d) {
return - c * (t /= d) * (t - 2) + b;
},
easeInOut: function(t, b, c, d) {
if ((t /= d / 2) < 1) return c / 2 * t * t + b;
return - c / 2 * ((--t) * (t - 2) - 1) + b;
}
},
Cubic: {
easeIn: function(t, b, c, d) {
return c * (t /= d) * t * t + b;
},
easeOut: function(t, b, c, d) {
return c * ((t = t / d - 1) * t * t + 1) + b;
},
easeInOut: function(t, b, c, d) {
if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;
return c / 2 * ((t -= 2) * t * t + 2) + b;
}
},
Quart: {
easeIn: function(t, b, c, d) {
return c * (t /= d) * t * t * t + b;
},
easeOut: function(t, b, c, d) {
return - c * ((t = t / d - 1) * t * t * t - 1) + b;
},
easeInOut: function(t, b, c, d) {
if ((t /= d / 2) < 1) return c / 2 * t * t * t * t + b;
return - c / 2 * ((t -= 2) * t * t * t - 2) + b;
}
},
Quint: {
easeIn: function(t, b, c, d) {
return c * (t /= d) * t * t * t * t + b;
},
easeOut: function(t, b, c, d) {
return c * ((t = t / d - 1) * t * t * t * t + 1) + b;
},
easeInOut: function(t, b, c, d) {
if ((t /= d / 2) < 1) return c / 2 * t * t * t * t * t + b;
return c / 2 * ((t -= 2) * t * t * t * t + 2) + b;
}
},
Sine: {
easeIn: function(t, b, c, d) {
return - c * Math.cos(t / d * (Math.PI / 2)) + c + b;
},
easeOut: function(t, b, c, d) {
return c * Math.sin(t / d * (Math.PI / 2)) + b;
},
easeInOut: function(t, b, c, d) {
return - c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
}
},
Expo: {
easeIn: function(t, b, c, d) {
return (t == 0) ? b: c * Math.pow(2, 10 * (t / d - 1)) + b;
},
easeOut: function(t, b, c, d) {
return (t == d) ? b + c: c * ( - Math.pow(2, -10 * t / d) + 1) + b;
},
easeInOut: function(t, b, c, d) {
if (t == 0) return b;
if (t == d) return b + c;
if ((t /= d / 2) < 1) return c / 2 * Math.pow(2, 10 * (t - 1)) + b;
return c / 2 * ( - Math.pow(2, -10 * --t) + 2) + b;
}
},
Circ: {
easeIn: function(t, b, c, d) {
return - c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
},
easeOut: function(t, b, c, d) {
return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;
},
easeInOut: function(t, b, c, d) {
if ((t /= d / 2) < 1) return - c / 2 * (Math.sqrt(1 - t * t) - 1) + b;
return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;
}
},
Elastic: {
easeIn: function(t, b, c, d, a, p) {
if (t == 0) return b;
if ((t /= d) == 1) return b + c;
if (!p) p = d * .3;
if (!a || a < Math.abs(c)) {
a = c;
var s = p / 4;
} else var s = p / (2 * Math.PI) * Math.asin(c / a);
return - (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
},
easeOut: function(t, b, c, d, a, p) {
if (t == 0) return b;
if ((t /= d) == 1) return b + c;
if (!p) p = d * .3;
if (!a || a < Math.abs(c)) {
a = c;
var s = p / 4;
} else var s = p / (2 * Math.PI) * Math.asin(c / a);
return (a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b);
},
easeInOut: function(t, b, c, d, a, p) {
if (t == 0) return b;
if ((t /= d / 2) == 2) return b + c;
if (!p) p = d * (.3 * 1.5);
if (!a || a < Math.abs(c)) {
a = c;
var s = p / 4;
} else var s = p / (2 * Math.PI) * Math.asin(c / a);
if (t < 1) return - .5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * .5 + c + b;
}
},
Back: {
easeIn: function(t, b, c, d, s) {
if (s == undefined) s = 1.70158;
return c * (t /= d) * t * ((s + 1) * t - s) + b;
},
easeOut: function(t, b, c, d, s) {
if (s == undefined) s = 1.70158;
return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
},
easeInOut: function(t, b, c, d, s) {
if (s == undefined) s = 1.70158;
if ((t /= d / 2) < 1) return c / 2 * (t * t * (((s *= (1.525)) + 1) * t - s)) + b;
return c / 2 * ((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2) + b;
}
},
Bounce: {
easeIn: function(t, b, c, d) {
return c - Tween.Bounce.easeOut(d - t, 0, c, d) + b;
},
easeOut: function(t, b, c, d) {
if ((t /= d) < (1 / 2.75)) {
return c * (7.5625 * t * t) + b;
} else if (t < (2 / 2.75)) {
return c * (7.5625 * (t -= (1.5 / 2.75)) * t + .75) + b;
} else if (t < (2.5 / 2.75)) {
return c * (7.5625 * (t -= (2.25 / 2.75)) * t + .9375) + b;
} else {
return c * (7.5625 * (t -= (2.625 / 2.75)) * t + .984375) + b;
}
},
easeInOut: function(t, b, c, d) {
if (t < d / 2) return Tween.Bounce.easeIn(t * 2, 0, c, d) * .5 + b;
else return Tween.Bounce.easeOut(t * 2 - d, 0, c, d) * .5 + c * .5 + b;
}
}
}
}
下面是個應用：
復制代碼 代碼如下:
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>無標題文檔</title>
<script src="util.js" type="text/javascript"></script>
<script src="animate.js" type="text/javascript"></script>
<style type="text/css">
body{behavior:url("csshover.htc")}
*{padding:0;margin:0}
.mianbox{width:480px;margin:50px auto;height:240px;}
.leftbtn{width:20px;background:#eee;border:1px solid #ddd;float:left;margin-right:8px;height:240px;}
.leftbtn:hover{background:#fff}
.rightbtn{width:20px;background:#eee;border:1px solid #ddd;float:right;height:240px;}
.rightbtn:hover{background:#fff}
.con{width:420px;float:left;height:240px;overflow:hidden;position:relative}
.con ul{ white-space:nowrap;font-size:0;position:absolute;left:0;top:0;}
.con li{display:inline; vertical-align:bottom;margin-right:10px}
</style>
</head>
<body>
<div class="mianbox">
<div class="leftbtn" id="leftbtn"></div>
<div class="con">
<ul>
<li><img src="http://pic25.nipic.com/20121121/2969675_091845785000_2.jpg" width="205" height="240" /></li>
<li><img src="http://pic23.nipic.com/20120818/9715349_114354586392_2.jpg" width="205" height="240" /></li>
<li><img src="http://pic20.nipic.com/20120329/9715349_154806479182_2.jpg" width="205" height="240" /></li>
<li><img src="http://pic20.nipic.com/20120329/9715349_162301568121_2.jpg" width="205" height="240" /></li>
<li><img src="http://pic23.nipic.com/20120824/9715349_160522342186_2.jpg" width="205" height="240" /></li>
<li><img src="http://pic23.nipic.com/20120824/9715349_160651385195_2.jpg" width="205" height="240" /></li>
<li><img src="http://pic20.nipic.com/20120329/9715349_163520278182_2.jpg" width="205" height="240" /></li>
<li><img src="http://pic23.nipic.com/20120827/9715349_110350505124_2.jpg" width="205" height="240" /></li>
</ul>
</div>
<div class="rightbtn" id="rightbtn"></div>
</div>
<script>
/**
* @para obj 內容對象
* @para lbtn 左按鈕
* @para rbtn 右按鈕
* @para w 每次滾動的寬
* @para duration 每次運行時間
* @para tween 緩動類型
*/
function scOnce(obj, lbtn, rbtn, w, autotime, duration,tween){
var am = new animation(_ul),
step=0,
ulen = obj.scrollWidth,
timmerm
dr = 'left',
that = this;
// 最右端?
function isr(){
return parseInt($util.dom.getStyle(obj, 'left')) >=0;
}
// 最左端?
function isl(){
return ulen - Math.abs(parseInt($util.dom.getStyle(obj, 'left')))-10 <= w;
}
if(isr()&&isl())
return;
// 左移
this.goleft = function (){
step += -1*w;
am.go({left:step+"px"},duration,tween).start();
}
// 右移
this.goright = function (){
step += w;
am.go({left:step+"px"},duration,tween).start();
}
// 注冊左按鈕事件
$util.evt.addEvent(lbtn,'click',function(){
isl()? that.goright():that.goleft();
})
// 注冊右按鈕事件
$util.evt.addEvent(rbtn,'click',function(){
isr()? that.goleft():that.goright();
})
$util.evt.addEvent(rbtn,'mouseover',function(){
clearTimeout(timmer);
})
$util.evt.addEvent(lbtn,'mouseover',function(){
clearTimeout(timmer);
})
$util.evt.addEvent(rbtn,'mouseout',function(){
timmer = setInterval(auto,autotime);
})
$util.evt.addEvent(lbtn,'mouseout',function(){
timmer = setInterval(auto,autotime);
})
function auto(){
if(isl()){
dr = "right";
}
if(isr()){
dr = "left";
}
that['go'+dr]();
}
timmer = setInterval(auto,autotime);
}
var _ul = document.getElementsByTagName('ul')[0],
lbtn = document.getElementById('leftbtn'),
rbtn = document.getElementById('rightbtn');
var startgo = new scOnce(_ul,lbtn,rbtn,430,3000,500,$util.tween.Quint.easeInOut);
</script>
</body>
</html>