Viewport的理解
http://www.cnblogs.com/2050/p/3877280.html
http://www.cnblogs.com/koukouyifan/p/4066567.html
缩放比例和DPI
http://www.qianduan.net/mobile-webapp-develop-essential-knowledge/
http://imququ.com/post/devicepixelratio-and-border-width.html
原文：http://www.cnblogs.com/as3lib/p/4720439.html