What I have been doing as a temporary workaround while we wait for a "fog of war" is while yes, they can just pan and see the rooms etc. Keep the enemies in the rooms as separate encounters and deactivate them. Pause when they enter the room, possibly add a vignette for RP descriptions etc activate the room encounter and unpause. They players have almost no advantage from what I would consider cheating which is the point of a fog of war.
