CSS3 动画_html/css_WEB-ITnose
概览
通过 CSS3，我们能够创建动画，这可以在许多网页中取代动画图片、Flash 动画以及 JavaScript。
由于是CSS3 嘛，所以部分旧版本浏览器当然无法完美呈现，节哀。
小试牛刀学习任何东西都需要有一定的成就感才会有继续学习的动力，先别管那么多，先让我们的动画动起来。
<!DOCTYPE html><html><head><style> @keyframes myfirst { from {background:red;} to {background:yellow;} } /* Firefox */ @-moz-keyframes myfirst { from {background:red;} to {background:yellow;} } /* Safari and Chrome */ @-webkit-keyframes myfirst { from {background:red;} to {background:yellow;} } /* Opera */ @-o-keyframes myfirst { from {background:red;} to {background:yellow;} } div { width:100px; height:100px; margin: 50px auto; background:red; animation:myfirst 5s; -moz-animation:myfirst 5s; /* Firefox */ -webkit-animation:myfirst 5s; /* Safari and Chrome */ -o-animation:myfirst 5s; /* Opera */ }</style></head><body><div></div></body></html>是不是很简单，很炫酷呀？
实现CSS3 动画需要至少以下几个条件：
使用 @keyframes 创建动画并命名
使用 animation简写属性 或 其他具体属性 调用动画并设置动画时长
将 animation 绑定到某个选择器上
下面具体介绍各相关属性吧。
创建动画 @keyframes通过 @keyframes 规则，您能够创建动画。
创建动画的原理是将一套 CSS 样式逐渐变化为另一套样式。
在动画过程中，您能够多次改变这套 CSS 样式。
以百分比来规定改变发生的时间，或者通过关键词 from 和 to来规定改变发生的时间。
0% 是动画的开始时间，100% 动画的结束时间。
为了获得最佳的浏览器支持，您应该始终定义 0% 和 100% 选择器。
@keyframes myfirst { 0% {background: red; left:0px; top:0px;} 25% {background: yellow; left:200px; top:0px;} 50% {background: blue; left:200px; top:200px;} 75% {background: green; left:0px; top:200px;} 100% {background: red; left:0px; top:0px;}}/* Firefox */@-moz-keyframes myfirst { 0% {background: red; left:0px; top:0px;} 25% {background: yellow; left:200px; top:0px;} 50% {background: blue; left:200px; top:200px;} 75% {background: green; left:0px; top:200px;} 100% {background: red; left:0px; top:0px;}}/* Safari 和 Chrome */@-webkit-keyframes myfirst { 0% {background: red; left:0px; top:0px;} 25% {background: yellow; left:200px; top:0px;} 50% {background: blue; left:200px; top:200px;} 75% {background: green; left:0px; top:200px;} 100% {background: red; left:0px; top:0px;}}/* Opera */@-o-keyframes myfirst { 0% {background: red; left:0px; top:0px;} 25% {background: yellow; left:200px; top:0px;} 50% {background: blue; left:200px; top:200px;} 75% {background: green; left:0px; top:200px;} 100% {background: red; left:0px; top:0px;}}上面我们使用 @keyframes 创建了动画，接下来我们来调用动画。
上面也说了，调用动画最基本的是动画名称和动画花费的时间，下面将具体介绍动画调用的相关属性。
animation-name
指定要调用的动画。
animation-name: keyframename | none;
none 规定无动画效果（可用于覆盖来自级联的动画）。
keyframename 命名遵循如下规则：
名字可以是字母，数字，_ 或 -,区分大小写，只能以字母或单-开头，不能使用none,unset,initial,inherit关键字。
animation-duration
animation-duration 属性定义动画完成一个周期所需要的时间，以秒或毫秒计。
animation-duration: 2s; /*等价于 2000ms*/
animation-timing-function
animation-timing-function 规定动画的速度曲线。
animation-timing-function: value;
此属性值使用名为三次贝塞尔（Cubic Bezier）函数的数学函数来生成速度曲线。
有如下值可选：
| 值 | 描述 |
|---|---|
| linear | 动画从头到尾的速度是相同的。 |
| ease | 默认。动画以低速开始，然后加快，在结束前变慢。 |
| ease-in | 动画以低速开始。 |
| ease-out | 动画以低速结束。 |
| ease-in-out | 动画以低速开始和结束。 |
| cubic-bezier(n, n, n, n) | 在 cubic-bezier 函数中自己的值。可能的值是从 0 到 1 的数值。 |
5 个预定义关键字对应的贝塞尔函数为：
linear: cubic-bezier(0.0, 0.0, 1.0, 1.0)ease: cubic-bezier(0.25, 0.1, 0.25, 1.0)ease-in: cubic-bezier(0.42, 0, 1.0, 1.0)ease-out: cubic-bezier(0, 0, 0.58, 1.0)ease-in-out: cubic-bezier(0.42, 0, 0.58, 1.0)
简单体会一下 5 种速度曲线的效果：
想亲自去体验各种值对速度的影响，请移步这里：贝塞尔速度曲线
animation-delay
animation-delay 属性定义动画何时开始。
animation-delay: time;
值以秒或毫秒计。允许负值，-2s 使动画马上开始，但跳过 2 秒进入动画。
animation-iteration-count
animation-iteration-count 属性定义动画的播放次数。
animation-iteration-count: n | infinite;
n 表示具体的次数，默认为1，infinite 规定无限次播放。
animation-direction
animation-direction 属性定义是否应该轮流反向播放动画。
animation-direction: normal | reverse | alternate | alternate-reverse;
两个关键字可选，normal 表示动画正常播放，默认值，从 0% -> 100% 再从 0% -> 100%. reverse 与 normal 相反，从 100% -> 0% 再从 100% -> 0%. alternate 表示轮流反向播放，从 0% -> 100% 再从 100% -> 0% 再从 0% -> 100%. alternate-reverse 与 alternate 相反。
animation-play-state
animation-play-state 属性规定动画正在运行还是暂停。
animation-play-state: paused | running;
paused 表示动画正在暂停，动画不会动。running 表示动画正在动，默认。
animation
此属性为上述七个具体属性的简写属性。
animation: name duration timing-function delay iteration-count direction play-state;
对CSS3 动画先简单了解这么多，后续可能有新内容再补充。
参考资料CSS3 动画
cubic-bezier贝塞尔曲线CSS3动画工具
Cubic-Bezier
Mozilla animation
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