Source: Fog

[Afr]

How to add fog to your map:

Place a "env_fog_controller" anywhere on your map.

Set "fog enabled" to "yes".

To change the colour of the fog change the value of "primare/secondary fog colour".

To determine how thick or thin the fog is change the value of "fog start/end".
The higher value in fog start the thinner the fog will be.


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How to add a single area of fog.

Draw a brush where you want your fog to be, then give it the NoDraw texture.
Assign the brush to the entity "func_smokevolume".
Open up "properties" set "materials" to "particle/particle_noisesphere" (you can try other particles).

[Aeris]

Does the fog go inside buildings and stuff aswell? Or is like the rain and snow, being that it wont go inside areas that are closed off?

[Afr]

Updated for thoose who dont want their entire map foggy :P