Fog

Fog is a feature introduced by Hexen.

In Hexen, some levels are marked as having fog. In these, instead of using the normal COLORMAP lump, an alternate colormap, defined by MAPINFO (and named FOGMAP in the original levels) is used. When a fadetable other than COLORMAP is defined in MAPINFO, Hexen assumes that it is fog and fullbright sprites, such as most light sources and projectiles, will fade with distance like non-fullbright sprites. In essence, the FOGMAP colormap included in HEXEN.WAD behaves as fullbright (there is no light diminution): colors are unchanged in the first 14 levels, desaturate to grayness in the next 9 levels, and are all the same shade of gray (color index 23: #939393) in the last 9 levels.

// Load colormap and set the fullbright flag i = P_GetMapFadeTable(gamemap); W_ReadLump(i, colormaps); if(i == W_GetNumForName("COLORMAP")) { 		LevelUseFullBright = true; } 	else { // Probably fog ... don't use fullbright sprites LevelUseFullBright = false; }

Levels with fogs include, in Hexen itself, Darkmere, Orchard of Lamentations and Sacred Grove, and in the expansion, Sump and Deathfog.

Source ports
Some source ports may provide alternate implementation of fog effects, using methods do not replace light levels. Source ports with such features (which might complement support for Hexen-type fog) include:
 * Doom Legacy
 * GZDoom
 * ZDoom