div中img依据不同分辨率居中显示，超出部分隐藏

在做banner居中时 碰到的问题，知道可以用背景图实现居中显示，但是内心是想深究下的，故找到几种办法收集一下，后面两种真的是奇技淫巧

来着下面两处

https://www.zhihu.com/question/39742237

https://www.v2ex.com/t/187544

1. flex
2. position:absolute + negative margin
3. background-image + background-size + background-position

4.父元素position:relative，子元素

{ transform: translate(-50%,-50%);
position: absolute;
top: 50%;
left: 50%; }

父子元素都可以不定宽度。translate百分比根据自身高度宽度。只在UC浏览器及overflow：hidden叠加时会有问题

5.p元素 和隐藏的img扩充父元素的宽高

http://nec.netease.com/library/141122

<div class="m-demo">
    <p>
        <img src="http://nec.netease.com/img/s/1.jpg" class="hidden"/>
        <img src="http://nec.netease.com/img/s/1.jpg" alt=""/>
    </p>
</div>
<div class="m-demo">
    <p>
        <img src="http://nec.netease.com/img/m/1.jpg" class="hidden"/>
        <img src="http://nec.netease.com/img/m/1.jpg" alt=""/>
    </p>
</div>
<div class="m-demo">
    <p>
        <img src="http://nec.netease.com/img/l/1.jpg" class="hidden"/>
        <img src="http://nec.netease.com/img/l/1.jpg" alt=""/>
    </p>
</div>

/* 图片居中溢出隐藏  */
.m-demo{position:relative;width:300px;height:300px;overflow:hidden;border:1px solid #ddd;}
.m-demo p{position:absolute;top:50%;left:50%;margin:;padding:;}
.m-demo img{position:absolute;top:-50%;left:-50%;display:block;}
.m-demo img.hidden{visibility:hidden;position:static;}

6.将a设置top: -100%; bottom: -100%; left: -100%; right: -100%;扩充至原来的3倍，然后text-align: center;居中

http://dabblet.com/gist/e191e05066016cb040d4

<div class="banner">
    <a href="#"><img src="//placehold.it/500x300" alt=""/></a>
</div>

<div class="banner">
    <a href="#"><img src="//placehold.it/100x100" alt=""/></a>
</div>

.banner { width: 300px; height: 200px; overflow: hidden; position: relative; }
.banner > a { position: absolute; top: -100%; bottom: -100%; left: -100%; right: -100%; text-align: center; }
.banner > a:before { content: ""; display: inline-block; vertical-align: middle; height: 100%; }
.banner > a > img { vertical-align: middle; }