fog_volume

Fog in Counter-Strike: Global Offensive

Class hierarchy
CFogVolume ↳CServerOnlyEntity ↳CBaseEntity
`fogvolume.cpp`

fog_volume is a brush entity available in all Source games since Left 4 Dead. It's also in Black Mesa and Mapbase. It controls fog and other visual cinematic elements within its volume. It is necessary to have at least one fog_volume in order for (a master) color_correction to take effect in the Left 4 Dead series.

Warning:This entity applies its effect based on its AABB instead of its brush model.

Tip:

There is a Fog Panel in Left 4 Dead 2 that allows in-game manipulation of fog parameters. It is loaded via console command fogui. This command exists in Portal 2, but will not work unless resource/foguipanel.res is copied from another game.
Use tools/toolsfog texture for your fog volumes to distinguish them from triggers during level creation.

Note:

Alien Swarm does not use the origin of a player to decide which fog volume they are in, but rather the camera position. Due to this, you must make sure that your fog volume is taller (height) than the highest point a marine's camera can reach, i.e: The distance from the camera in height from the marine.
Mods using Source 2007 or Source 2013 can create client-side fog-changing functionality in a multiplayer game using instead trigger_multiple. Place at least 2 env_fog_controller with different fog settings and one checked with Master flag. Use OnStartTouch > !activator > SetFogController > [name of env_fog_controller entity]. The input will appear as red, but it still works. Use OnEndTouch() to change the fog back.
In (and perhaps other games), binding multiple brushes to fog_volume will produce the fog effect for the bounding box of the group of brushes i.e. if you have 2 blocks for fog_volume in an L-shaped hallway, standing in a room in the inside corner of that hallway will trigger the fog as well

Keyvalues

Name (targetname) <string>: The name that other entities refer to this entity by, via Inputs/Outputs or other keyvalues (e.g. parentname or target).
Also displayed in Hammer's 2D views and Entity Report. See also: Generic Keyvalues, Inputs and Outputs available to all entities

Fog Name (FogName) <targetname>: The name of the fog entity associated with this volume.
Postprocess Name (PostProcessName) <targetname> (not in ): The name of the postprocess_controller entity associated with this volume.}
ColorCorrection Name (ColorCorrectionName) <targetname>: The name of the color_correction entity associated with this volume.

Start Disabled (StartDisabled) <boolean>: Stay dormant until activated (with theEnableinput).

EnableDisable:

Enable / Disable: Enable/disable this entity from performing its task. It might also disappear from view.