Skip to content

Warcraft III Fog And Cinematic Visibility

This document covers gameplay fog of war (exploration/current sight). Atmospheric distance mist from SetTerrainFogEx is a separate renderer/environment system; see Environmental Terrain Fog.

Contract

Camera position, fog state, and entity visibility are independent systems. Camera natives move the gameplay camera without changing fog, while fog natives can reveal or mask remote terrain without moving the camera.

OpenRealm represents Warcraft's three fog states with the existing per-player explored and visible planes:

JASS state explored visible Meaning
FOG_OF_WAR_MASKED 0 0 unexplored
FOG_OF_WAR_FOGGED 1 0 explored without current sight
FOG_OF_WAR_VISIBLE 1 1 explored with current sight

G_FowClearVisible() clears current visibility without clearing exploration. A temporary visible reveal therefore naturally becomes fogged after the modifier stops when no normal sight source still covers the area.

Direct Trigger Reveals

SetFogStateRect, SetFogStateRadius, and SetFogStateRadiusLoc write directly into the authoritative player fog grid through G_FowSetStateRect() and G_FowSetStateRadius().

  • MASKED clears visible and explored.
  • FOGGED clears visible and sets explored.
  • VISIBLE sets both planes.

The operations reuse the existing server fog-grid resolution and dirty-row network path. They do not maintain a second cinematic exploration map. With useSharedVision, the same state is also applied to viewers receiving the source player's shared vision.

Per-Unit Shared Vision

UnitShareVision(unit, player, true) adds that player to the unit's persistent shared_vision recipient mask. During G_FowUpdate(), the unit's ordinary day/night sight is rasterized for the union of its normal owner/alliance viewers and its explicit per-unit recipients. Passing false removes only that explicit relationship. This is deliberately separate from ALLIANCE_SHARED_VISION: sharing one unit does not expose the owner's other units or change alliance state.

The relationship is saved with the unit, follows the unit as it moves, and is idempotent because it is represented as a player bit rather than a reference count. Removing the unit naturally removes the sight source. UnitShareVision does not create a fog modifier, force camera movement, or grant true sight/detection; entity invisibility continues through the existing per-viewer visibility policy. The NightElf06 UnitShareVisionBJ(true, gg_unit_Utic_0055, udg_Player) campaign reveal therefore works through the generic sight pipeline rather than a Tichondrius-specific exception.

Fog Modifiers

CreateFogModifierRect, CreateFogModifierRadius, and CreateFogModifierRadiusLoc create disabled modifier handles. FogModifierStart applies the modifier once immediately and then makes it participate in G_FowUpdate(); FogModifierStop removes it. The synchronous first application is required for map scripts that start and stop/destroy a VISIBLE modifier in the same trigger turn to permanently explore an area without holding current sight open.

Started modifiers apply the same three-state cell writer after normal unit sight:

  • VISIBLE keeps terrain explored and currently visible;
  • FOGGED keeps terrain explored while suppressing current sight in the modifier area;
  • MASKED keeps the modifier area unexplored while active.

Stopping a VISIBLE modifier stops forcing current vision but does not erase the exploration it already created, so the normal VISIBLE -> FOGGED transition is preserved.

Camera And Consumers

Camera movement does not call the fog API, and fog state changes do not call camera APIs. Maps that want a cinematic pan and reveal must request both actions explicitly.

The server's existing G_FowPlayerCanSeeEntity() remains the foreign-entity visibility gate. Known gameplay invisibility is evaluated there per viewer: owners/shared-vision allies keep access to their invisible units, while hostile viewers need a detector covering the target. Permanent Invisibility (Apiv) and Shadow Meld (Ashm/Ahid) have dedicated saved state; Sorceress Invisibility/Wind Walk and hidden wards retain RF_HIDDEN, but only those recognized invisibility states participate in this visibility policy. Snapshot customization clears RF_HIDDEN only for a viewer who is allowed to see that invisible entity, leaving the authoritative entity flag untouched. This deliberately avoids treating cargo, mine workers, revival/training placeholders, and other non-invisibility uses of RF_HIDDEN as revealable. The same viewer-specific predicate gates selection, automatic hostile acquisition, attack continuation, and unit-target spell validation. Far Sight's saved timed thinker and passive detector abilities contribute true sight through the shared query.

The client receives current and explored fog as separate planes, so world fog and minimap fog consume the same authoritative state while the minimap camera box continues to derive from camera state independently.

The WC3 model renderer applies gameplay fog after the shaded/unshaded material branch. This is required for unshaded doodad and model layers: their lighting bypass must not bypass fog of war. A zero fog texture sample discards the fragment, hiding it in unexplored terrain; nonzero samples attenuate its RGB according to the fog texture. Entities authored with RF_NO_FOGOFWAR use the renderer's white fog texture and remain unaffected by this mask. The fog sampler is declared third in the model shader, so the shader loader assigns it texture unit 2, where the world frame binds the fog texture; no explicit sampler assignment is needed.

Day/night sight-radius selection consumes the server-owned clock documented in time-of-day.md; fog must not derive a second clock from level.time.

Known Gaps

This change intentionally does not alter unrelated compatibility areas that need broader evidence:

  • FogEnable / FogMaskEnable retain their existing global behavior.
  • Ghost/Ghost Visible are not yet normalized into the player-aware invisibility path. Shadow Meld now uses dedicated unit state with the same owner/shared-vision/detector visibility query as Permanent Invisibility, Sorceress Invisibility, Wind Walk, and explicitly hidden ward mechanics.
  • FOW_CELL_SIZE is unchanged.
  • Camera Z-offset native parity is separate from fog-state handling.

Verification

The WC3 API tests cover:

  • all three direct fog states through rect/radius/radius-location natives;
  • useSharedVision propagation;
  • per-unit UnitShareVision recipient isolation, revocation, idempotence, and save persistence;
  • a same-turn VISIBLE start/stop still recording exploration;
  • a temporary VISIBLE modifier falling back to FOGGED;
  • active FOGGED and MASKED modifiers;
  • Far Sight true sight and player-local Permanent Invisibility visibility are covered by the spell/ward regression suite.

Runtime campaign validation should additionally check that a camera-only pan into unexplored terrain remains masked and that a cinematic reveal can show a remote area without coupling camera movement to fog mutation.

The headless renderer model suite also checks that the generated fragment shader applies fog after the unshaded lighting branch, discards zero fog samples, and that the fog sampler resolves to texture unit 2 for both regular and instanced model programs.