欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页

Js动画(一)基础

程序员文章站 2022-06-30 19:11:54
...
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。
<!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></title>

<script type="text/javascript">
/*
t:currentCount 当前执行第t次
b:initPos 初始值
c:targetPos - initPos 发生偏移的距离值
d:count 一共执行d次
效果:http://www.robertpenner.com/easing/easing_demo.html
JavaScript Tween算法及缓动效果 http://www.cnblogs.com/cloudgamer/archive/2009/01/06/tween.html
*/
var Tween = {
Linear: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * t / d + b;
},
Quad: {
easeIn: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * (t /= d) * t + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return -c * (t /= d) * (t - 2) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
if ((t /= d / 2) < 1) return c / 2 * t * t + b;
return -c / 2 * ((--t) * (t - 2) - 1) + b;
}
},
Cubic: {
easeIn: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * (t /= d) * t * t + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * ((t = t / d - 1) * t * t + 1) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;
return c / 2 * ((t -= 2) * t * t + 2) + b;
}
},
Quart: {
easeIn: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * (t /= d) * t * t * t + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return -c * ((t = t / d - 1) * t * t * t - 1) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * (t /= d) * t * t * t * t + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * ((t = t / d - 1) * t * t * t * t + 1) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return -c * Math.cos(t / d * (Math.PI / 2)) + c + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * Math.sin(t / d * (Math.PI / 2)) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
}
},
Expo: {
easeIn: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return (t == 0) ? b : c * Math.pow(2, 10 * (t / d - 1)) + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return (t == d) ? b + c : c * (-Math.pow(2, -10 * t / d) + 1) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count, a, p) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count, a, p) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count, a, p) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count, s) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
if (s == undefined) s = 1.70158;
return c * (t /= d) * t * ((s + 1) * t - s) + b;
},
easeOut: function(initPos, targetPos, currentCount, count, s) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
if (s == undefined) s = 1.70158;
return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
},
easeInOut: function(initPos, targetPos, currentCount, count, s) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
return c - Tween.Bounce.easeOut(d - t, 0, c, d) + b;
},
easeOut: function(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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(initPos, targetPos, currentCount, count) {
var b = initPos, c = targetPos - initPos, t = currentCount, d = count;
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;
}
}
}

///------------------------------------------------------------------------------------------------------
Animation = {
timer: 10,
SetOpacity: function(obj, n) {
if (document.all) {
obj.filters.alpha.opacity = n;
}
else {
obj.style.opacity = n / 100;
}
},
fade: function(obj, target, count, Func) {
obj = this.getItself(obj);
var currentCount = 0;
count = Math.abs(count) || 1;
target = target < 0 ? 0 : (target > 100) ? 100 : target;
var init = document.all ? obj.filters.alpha.opacity : window.getComputedStyle(obj, null).opacity * 100;
Func = Func || Tween.Linear;
var opr = this;
var flag = setInterval(function() {
if (currentCount > count) {
clearInterval(flag);
}
else {
currentCount++;
var tmp = Func(init, target, currentCount, count);
opr.SetOpacity(obj, tmp);
//清除小数点的误差
if (Math.abs(tmp - target) < 1) {
opr.SetOpacity(obj, target);
}
}
}
, this.timer);
},
resize: function(obj, targetPos, count, Func) {
obj = this.getItself(obj);
var currentCount = 0;
count = Math.abs(count) || 1;
var initPos = { x: obj.offsetWidth, y: obj.offsetHeight }
Func = Func || Tween.Linear;
targetPos = { x: targetPos.x < 0 ? 0 : targetPos.x, y: targetPos.y < 0 ? 0 : targetPos.y }
var flag = setInterval(function() {
if (currentCount > count) {
clearInterval(flag);
}
else {
currentCount++;
var tmpX = Func(initPos.x, targetPos.x, currentCount, count);
var tmpY = Func(initPos.y, targetPos.y, currentCount, count);
//width值不能小于0,但是算法返回值有可能出现负值
try {
obj.style.width = tmpX + "px";
obj.style.height = tmpY + "px";
}
catch (e) {
}
//清除小数点的误差
if (Math.abs(tmpX - targetPos.x) < 1) {
obj.style.width = targetPos.x + "px";
}
if (Math.abs(tmpY - targetPos.y) < 1) {
obj.style.height = targetPos.y + "px";
}
}
}
, this.timer);
},
move: function(obj, targetPos, count, Func) {
obj = this.getItself(obj);
var currentCount = 0;
count = Math.abs(count) || 1;
var elPos = this.getElementPos(obj);
var initPos = { x: elPos.x, y: elPos.y }
Func = Func || Tween.Linear;
var flag = setInterval(function() {
if (currentCount > count) {
clearInterval(flag);
}
else {
currentCount++;
var tmpX = Func(initPos.x, targetPos.x, currentCount, count);
var tmpY = Func(initPos.y, targetPos.y, currentCount, count);
obj.style.left = tmpX + "px";
obj.style.top = tmpY + "px";
//清除小数点的误差
if (Math.abs(tmpX - targetPos.x) < 1) {
obj.style.left = targetPos.x + "px";
}
if (Math.abs(tmpY - targetPos.y) < 1) {
obj.style.top = targetPos.y + "px";
}
}
}
, this.timer);
},
getElementPos: function(el) {
el = this.getItself(el);
var _x = 0, _y = 0;
do {
_x += el.offsetLeft;
_y += el.offsetTop;
} while (el = el.offsetParent);
return { x: _x, y: _y };
},
getItself: function(id) {
return "string" == typeof id ? document.getElementById(id) : id;
}
}
</script>

<style type="text/css">
.div
{
position: absolute;
border: solid 1px #849BCA;
left: 50px;
top: 100px;
width: 160px;
height: 130px;
background-color: #DBE4ED;
white-space: nowrap;
overflow: hidden;
opacity: 1;
filter: alpha(opacity=100);
}
</style>
</head>
<body>
<input type="button" value="Move" onclick="Animation.move('divObj',{x:500,y:500},100,Tween.Quart.easeInOut);" />
<input type="button" value="Resize" onclick="Animation.resize('divObj',{x:50,y:50},100,Tween.Cubic.easeIn);" />
<input type="button" value="SetOpacity" onclick="Animation.fade('divObj',50,100);" />
<input type="button" value="Move&Resize" onclick="Animation.resize('divObj',{x:300,y:200},100);Animation.move('divObj',{x:300,y:300},100);" />
<input type="button" value="Move&Resize&SetOpacity" onclick="Animation.fade('divObj',50,100);Animation.resize('divObj',{x:300,y:200},100);Animation.move('divObj',{x:100,y:100},100);" />
<input type="button" value="Reset" onclick="javascript:window.location.reload();" />
<div id="divObj" class="div" style="">
<div style="border: solid 1px green; width: 70px;">
~_~ ----></div>
<input type="text" value="input" style="width: 50px;" /><br />
<input type="button" value="button" /><br />
<img src="http://images.cnblogs.com/logo_small.gif" alt="" />
</div>
</body>
</html>


首先贴上封装好的动画类Animation.
+Animation:

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:

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:

<input type="button" value="Move&Resize&SetOpacity" onclick="Animation.fade('divObj',50,100);Animation.resize('divObj',{x:300,y:200},100);Animation.move('divObj',{x:100,y:100},100);" />