fog of war and limited visibility

[daydreamer]

"fog of war" as in old starcraft/warcraft and limited visibility to see enemies in a circle around your Player character
wouldnt it be easiest to render entirely in a huge backbuffer+offscreen surfaces and blit only the visible part of terrain to screen
1:sort out enemies outside visibility circle
2:limited visibility of enemies is to use ARGB,alpha channel from offscreen surfaces to control partial visibility

its good for a game to be more fun to explore new areas and make it more challenging to not knowing whats behind the corner, dead ends and/or enemy ambushes,also could be fun to find terrain that is good for an ambush before enemy