Android 半透明手势指引遮罩

http://blog.csdn.net/sunmanzth/article/details/6902458 

http://blog.csdn.net/huanghai381/article/details/42222315?ref=myread

http://www.jcodecraeer.com/a/opensource/2014/1119/2009.html

Android用户首次打开APP的使用教学蒙板效果实现:

http://blog.csdn.net/jdsjlzx/article/details/42387769