理解 clip

参考

http://developer.51cto.com/art/201009/223326.htm

http://vsfor.blog.51cto.com/4165449/1179853

http://www.zhangxinxu.com/wordpress/2011/04/css-cliprect%E7%9F%A9%E5%BD%A2%E5%89%AA%E8%A3%81%E5%8A%9F%E8%83%BD%E5%8F%8A%E4%B8%80%E4%BA%9B%E5%BA%94%E7%94%A8%E4%BB%8B%E7%BB%8D/

http://vsfor.blog.51cto.com/4165449/1179853

http://tympanus.net/codrops/2013/01/16/understanding-the-css-clip-property/

http://tympanus.net/codrops/2013/01/17/putting-css-clip-to-work-expanding-overlay-effect/

今晚回来整理