Fog of War
Strategic information hiding
Fog of war hides what the player has not scouted. Computer wargames argued about it from 1982, Empire painted the unexplored world black, and Warcraft II split the black shroud from the fog that returns when your units leave.
What you can’t see can kill you. Fog of war is the rule that a player sees only what their own units can see. It came into computer games through the wargame, where reviewers were using the phrase by 1982 and arguing about it by 1985, and it reached most players through Empire and then the real-time strategy games of the 1990s, which turned the unexplored map into a black sheet that scouting peels back.
Fast facts
- The phrase: a wargamers’ term for “those factors in warfare which force command decisions to be made without full knowledge” (Computer Gaming World, 1985).
- Early computer use: Galaxy (1982) hid each player’s typed orders so “no one can tell what you are doing”.
- The black map: Empire (Walter Bright, 1977; Interstel, 1987) starts with the world “a tapestry of black” and nine known squares out of 5,684.
- The RTS split: Warcraft had a black shroud that exploration removed; Warcraft II (1995) added a fog that returns when your units leave.
A wargamers’ argument
The earliest use in the library is not about hidden maps. Computer Gaming World’s January 1982 review of Galaxy, a multiplayer space-conquest game, praised it because “the orders which you key into the computer are invisible, so no one can tell what you are doing. This simulation of ‘the fog of war’ makes it possible to launch surprise attacks on your opponents.” Antic explained the term to Atari owners in 1984: “A computer is also an ideal tool for introducing the ‘fog of war’ into a war game. This term refers to the element of uncertainty and randomness that is a constant aspect of real combat.”
By 1985 it was, in Jay Selover’s words in Computer Gaming World, one of “the most popular catch-phrases of computer wargaming”. His article sorted the games on sale into three treatments. The first ignored intelligence altogether — “a game in which all units of both sides are open to free inspection, and corresponds closely to most board wargames. Since this approach wastes one of the greatest assets of the computer, it is not surprising that only a few games fall in this category anymore.” The other extreme used “battlefield intelligence as a focal design point” — he named SSI’s Carrier Force, Simulations Canada’s Grey Seas, Grey Skies and Fall Gelb, and SSG’s Carriers at War. The same magazine had reviewed a Persian Gulf wargame that January in which enemy unit types were shown “only when a friendly unit is ‘adjacent’. This simulates the ‘fog of war’ and prevents you from knowing what the enemy units are until you have recon’ed them.” Ahoy!’s wargame column described the board-game equivalent, hidden movement, “which keeps enemy units off the board until they move or engage in fighting”.
It was contested. Computer Gaming World ran a designers’ round-robin in 1988 prompted by the suggestion that “extreme limited intelligence” made games frustrating. Dave Arneson answered for the other side: “Creating an effective Fog of War is one of the biggest ‘plus’ factors in computer simulations today. Not knowing what is going on is certainly the most common factor found in wars throughout history.” His proposed fix for the frustration was the after-action report, so that players could “see what happened that he couldn’t see during the game”. Your Sinclair’s reviewer took the same view of a computer-moderated board game that showed everything: “The computer should be used to simulate the ‘fog of war.’”
Empire: the black map
Empire is where the fog became a map. Walter Bright wrote it in 1977 — “while he attended Caltech”, Amazing Computing said, before rewriting it for the PDP-11 — and Interstel published the “authorized edition”, co-written with Mark Baldwin, for the Atari ST, Amiga and PC in 1987. Todd Heimarck’s review in COMPUTE!’s Atari ST describes the opening turn: “At the beginning of a game, most of the world is terra incognita, a tapestry of black. Your first priority is to send out scouting parties to discover some of the 50-100 cities. In turn one, you own a city. The map tells you the status of your city and its neighbors — only 9 of the 5,684 squares.” A world-map window showed “the entire known world (with unexplored territory in black)”, and “the role of the maverick explorer” was “the key to the early rounds”. Computer Play thought “the ‘fog of war’ and the mechanics of meshing the disparate units into a cohesive force of conquest” were what made it worth the time.
Real-time strategy
Westwood’s Dune II (1992) carried the black map into real time. Amiga Power used it as the reference point two years later: “you can only see areas of the map you’ve explored, so like Dune 2; the screen’s black until you explore everything.” Command & Conquer (1995) kept it, and Computer Gaming World’s reviewer was not pleased: “One annoying holdout from Dune II is the Fog of War; you’ll die several times in each scenario just trying to unveil the terrain.” A year later the same magazine called them “ludicrous fog of war rules: despite satellite technology, you couldn’t see a tree a hundred yards away until you sent a scout to recon.” Nintendo Power described the Nintendo 64 port’s version as “a black cloud” that lifts as troops move in.
Blizzard’s Warcraft II (1995) is where the two states separated. The first Warcraft had “a black shroud that was eliminated through exploration”; the sequel, as a 2001 retrospective put it, “went a step further. The fog of war meant that you could only see enemy units that were within the line of sight of your own units. Now you had to rely on scouting patrols and observation posts to bring you detailed intelligence.” It was an option. A German magazine explained it in 1997: switch on the Fog of War and even in explored territory you see the enemy only around your own units; the rest of the map and its enemies vanish into fog as soon as your people move away, though buildings stay on the minimap. Blizzard’s StarCraft preview in 1997 promised the fog “will be blended, to make for a more realistic darkness effect”.
How it works
The Warcraft II model gives every map cell one of three states. Unexplored cells are black: nothing has ever been seen there. Explored cells show terrain and buildings as they were last seen, but no units. Visible cells lie within the sight radius of a friendly unit and show everything. Each frame, the game clears the visible set, walks its own units and marks the cells within each one’s sight radius as visible (and, permanently, as explored), then draws the map through that mask. Enemy units are drawn only in visible cells; the minimap uses the same mask.
Two design choices follow from the sources above. Whether the computer opponent obeys the same fog is invisible to the player and, as Selover noted of the earliest wargames, ignoring it “wastes one of the greatest assets of the computer”. And whether the fog is on at all was, for Warcraft II, a checkbox — the argument Computer Gaming World’s designers had in 1988 became a setting the player chose.