Fog Of War Advice

Can anyone give me good techniques for implementing fog of war. I did read this link here and it did give me a idea of one method of doing it with a transparent, full and semi transparent tiles set

Another cool set of algorithms ill be experimenting with here seem really awesome. Suppose efficiency is whats im curious about and what can phones handle, along with tablets

I want a top down unit to only see where he looks. When he turns away it all becomes hidden again. So units only see what they should see. If there looking at a building, they cant see behind it. Like having a flash light in a pitch black room

Needs to be a good method for android, win32 and IOS. Would need be as efficient as possible not to be eating resources

Much thanks for any links, sources or ideas

I cannot help more but this link may help you to start

Ok ill read this thread and see what the crack is !! Thanks