there are many ways to create fog, but only one gives you the stock base fog that you see in airfield, makin, zombie maps, and so on
some use expfog , volfog, which forces your fog on the map ,
the stock way allows you to make a floor, mid ,and ceiling, settings,
 as well as, set depth ,thickness of each

first make your self a vision file ,and name it mp_mapname.vision, and place it in raw/vision
put in your csv     rawfile,vision/mp_mapname.vision
here is a common vision file

r_glow                    "1"
r_glowRadius0             "5"
r_glowRadius1             "0"
r_glowBloomCutoff         "0.260564"
r_glowBloomDesaturation   "0"
r_glowBloomIntensity0     "0.65"
r_glowBloomIntensity1     "0"
r_glowSkyBleedIntensity0  "0"
r_glowSkyBleedIntensity1  "0"
 
r_filmEnable              "1"
r_filmContrast            "1.6"
r_filmBrightness          "0.34"
r_filmDesaturation        "0.175"
r_filmInvert              "0"
r_filmLightTint           "0.930 0.8676 0.754"
r_filmDarkTint            "0.315 0.299 0.275"

r_reviveFX_enable       "0"
r_reviveFX_contrastEdge    "0"
r_reviveFX_brightnessEdge   "0"
r_reviveFX_desaturationEdge  "0"
r_reviveFX_darkTintEdge    "1 1 1"
r_reviveFX_lightTintEdge   "1 1 1"
r_reviveFX_blurRadiusEdge   "0"
r_reviveFX_motionblurWeight  "0"
r_reviveFX_contrastCenter   "0"
r_reviveFX_brightnessCenter  "0"
r_reviveFX_desaturationCenter "0"
r_reviveFX_darkTintCenter   "1 1 1"
r_reviveFX_lightTintCenter  "1 1 1"

second we want to make a art.gsc
name it  mp_mapname_art.gsc
and put it in
raw/maps/mp/createart
add this to your csv
rawfile,maps/mp/createart/mp_mapname_art.gsc

in here are all the settings for fog , you can ajust any thing to you own

//_createart generated.  modify at your own risk. Changing values should be fine.
main()
{

 level.tweakfile = true;
 
 //* Fog section *

 setdvar("scr_fog_exp_halfplane", "808.57");
 setdvar("scr_fog_exp_halfheight", "100");
 setdvar("scr_fog_nearplane", "200");
 setdvar("scr_fog_red", "0.52");
 setdvar("scr_fog_green", "0.49");
 setdvar("scr_fog_blue", "0.384");
 setdvar("scr_fog_baseheight", "50");

 setdvar("visionstore_glowTweakEnable", "0");
 setdvar("visionstore_glowTweakRadius0", "5");
 setdvar("visionstore_glowTweakRadius1", "");
 setdvar("visionstore_glowTweakBloomCutoff", "0.5");
 setdvar("visionstore_glowTweakBloomDesaturation", "0");
 setdvar("visionstore_glowTweakBloomIntensity0", "1");
 setdvar("visionstore_glowTweakBloomIntensity1", "");
 setdvar("visionstore_glowTweakSkyBleedIntensity0", "");
 setdvar("visionstore_glowTweakSkyBleedIntensity1", "");

 setVolFog(400, 1600.57, 100, 50, 0.50, 0.49, 0.421, 0);

}

// setVolFog(, , , , , , , )

set the dvar setting to your own "you can check the stock files to see different settings you will find them in
raw/maps/mp/createart folder

now add this line to  your map gsc and compile

mapsmpcreateartmp_mapname_art::main():

be sure to change mapname to yours

 by COL.MAC and the modsonline team