D2X-XL has been able to fill parts of a level with fog, water or lava haze for a while; for 2.0 I have rebuilt this.

There are four media: water, lava, light fog and dense fog. Connected segments holding the same medium form a volume, and everything in and behind such a volume is tinted depending on how much of it you are looking through.

The medium is not uniform anymore: wisps of it drift through the volume, each medium with a flow of its own.

Fog is also lit now. It picks up the light of the lamps around it and of lights that change, so a shot lights up the fog it flies through.

Level authors tag the segments in DLE and set color and view range for each medium there. In the game, fog can be switched off in the effect options.