Fog of War
Strategic information hiding
Fog of war obscures unexplored areas and enemy movements in strategy games, forcing players to scout and making information as valuable as military might.
Overview
What you can’t see can kill you. Fog of war transformed strategy games from perfect-information puzzles into tense contests of scouting and deduction. The term is borrowed from Carl von Clausewitz’s On War (1832), describing the uncertainty inherent to combat. Computer wargames adopted it in the late 1970s; Empire (Walter Bright, 1977 mainframe / 1984 home) was an early implementation. Dune II (Westwood, 1992) brought it to real-time strategy and made it the genre’s defining mechanic.
Far from being deprecated, fog of war remains absolutely central to modern RTS and 4X games — StarCraft II (2010), Total War: Warhammer III (2022), Age of Empires IV (2021), Civilization VI (2016) all depend on it.
Fast facts
- Origin: Board game wargaming (manually hidden pieces, double-blind play).
- Computer wargame pioneer: Empire (1977 mainframe, 1984 home).
- RTS pioneer: Dune II (Westwood, 1992).
- Purpose: Information uncertainty and asymmetry.
- Impact: Scouting becomes a core gameplay loop.
Implementation types
Modern fog of war typically uses three states per map cell:
| State | Visibility |
|---|---|
| Unexplored / black | Never seen — total darkness |
| Shrouded / explored | Seen at some point; terrain visible, units no longer shown |
| Visible / actively observed | Currently in line-of-sight of a friendly unit; full information |
The “shrouded” state is the genre’s key innovation — you remember the layout but can’t see what’s there now. Warcraft II (Blizzard, 1995) popularised this three-state model.
Strategic impact
| Effect | Consequence |
|---|---|
| Hidden movements | Surprise attacks possible; ambushes a viable strategy |
| Scouting value | Information gathering becomes a primary objective |
| Defensive advantage | Attacker doesn’t know what’s behind walls |
| Map control | Vision becomes a resource to fight over |
| Bluffing | Threatening from off-screen creates real psychological pressure |
Scouting methods
| Unit type | Scouting role |
|---|---|
| Fast units | Quick exploration (Wolves, Knights, Speedsters) |
| Air units | Overview capability — see over terrain (Bombers, Drones) |
| Static buildings | Perimeter vision (Watch Towers, Outposts) |
| Reveal abilities | Magical / tech reveal spells (StarCraft Scanner Sweep) |
| Detector units | Counter-stealth — see invisible / cloaked units |
| Civilians / scouts | Cheap, expendable units sent to die for information |
RTS implementation
| Game | Year | Fog system |
|---|---|---|
| Dune II | 1992 | Two-state: unexplored vs visible (no separate shroud) |
| Warcraft II | 1995 | Three-state shroud system; revealed terrain stays visible but units don’t |
| Command & Conquer | 1995 | Two-state initially; shroud added in later titles |
| Total Annihilation | 1997 | Radar gives partial information without full vision |
| StarCraft | 1998 | Refined three-state; cloaked / detected mechanics layered on top |
| Age of Empires | 1997+ | Line-of-sight with terrain blocking |
| Civilization | 1991+ | Per-tile fog; whole-map satellite reveal at late game |
Implementation strategies
The technical approach to fog of war:
| Approach | Use |
|---|---|
| Per-tile/cell fog grid | Standard for tile-based RTS (Dune II, Warcraft, AoE) |
| Per-pixel mask | Smoother visuals; StarCraft II and modern engines |
| Vision radii sum | Each unit contributes a circular radius; cells inside any radius are visible |
| Line-of-sight ray casting | Terrain blocks vision; units behind hills don’t see over them |
| Mip-mapped fog texture | Modern: store fog as a texture, blur for soft edges |
Minimap importance
The minimap becomes critical when fog of war is active:
| Feature | Function |
|---|---|
| Territory | Shows explored areas (often dimmer for shrouded) |
| Friendly units | Always visible — your own positions |
| Enemy units | Only when in current vision |
| Alerts | Flash on attack notifications |
| Strategy | Bird’s-eye planning view |
Late-game RTS players spend nearly as much time looking at the minimap as the main view; the minimap is where macro-strategy happens.
Design considerations
| Factor | Balance |
|---|---|
| Vision range | Differentiates units (scouts have far vision, melee units short) |
| Reveal speed | Pace of information gathering |
| Permanent reveal | Terrain memory; do you remember the layout forever? |
| Detection | Counter-stealth — scanners, detectors, sensor towers |
| Cheating AI | Computer opponents often see through fog (a balancing fudge) |
| Replay visibility | Replays usually disable fog so spectators see the whole game |
Modern relevance
Fog of war is a defining feature of:
- RTS: StarCraft II, Total War series, Age of Empires IV, They Are Billions
- 4X / grand strategy: Civilization series, Stellaris, Crusader Kings, Total War campaign maps
- MOBAs: League of Legends, Dota 2 — vision wards are a core economic / strategic resource
- Tactical: XCOM 2 — fog of war on the squad-level battlefield
- Survival / horror: Don’t Starve — sanity-based fog
- Roguelikes: Caves of Qud, Dwarf Fortress — fog as core navigation challenge
- Modern board games: Twilight Imperium, Scythe — physical fog-of-war via hidden chits