Small update. I’ve added a first version of fog of war, difficult terrain (that can provide a cover bonus).
Also, a tile type can now indicate if a unit should go “crouched” when they enter it. This gives a sense of immersion, as the unit actively appears to be hiding among the shrubbery 
It also decreases the walk speed of the unit, so it makes for some very cool sneaking movement when traversing multiple tiles of forest!
http://oi63.tinypic.com/2my11rd.jpg
The fog of war implementation is working well enough. But I’m getting small frame drops when I’m setting the fog-of-war vision range to higher values (say, >3 tiles).
So I’ll need to think up something to make that more efficient.