窗口透明效果

http://www.vckbase.com/document/viewdoc/?id=333

http://blog.youkuaiyun.com/s91/archive/2006/02/03/591328.aspx

http://www.utblog.com/plog/1/article/1192 

http://topic.youkuaiyun.com/t/20050607/17/4066236.html

http://topic.youkuaiyun.com/t/20020222/17/537759.html

http://www.codeproject.com/gdi/pxalphablend.asp