Atmospheric Fog User Guide

Atmospheric Fog Actors provide a realistic sense of atmosphere, air density, and light scattering through atmospheric media.

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Atmospheric Fog gives an approximation of light scattering through a planetary atmosphere. This can give your outdoor levels a much more realistic look. This total effect includes the following:

  • The dominant directional light in your level will receive a sun disc effect in the sky. This will be placed infinitely far away, opposite the light's direction.

  • A sky color that will vary depending on the altitude of the sun (or put another way, how close the dominant directional light's vector gets to being parallel with the ground).

  • Control over scattering and decay settings, allowing for full control of your atmospheric density.


Best of all, the settings for this Actor are easy to use and quick to set up.

Adding Atmospheric Fog to a Level

Adding Atmospheric Fog to your level is as easy as adding its Actor from the Place Actors panel under the Visual Effects section:

This may be done via drag-and-drop:


Atmospheric Fog Properties

The Atmospheric Fog Actor contains the following properties:




Sun Multiplier

This is an overall multiplier for the directional light brightness. It brightens both the sky and fog color.

Fog Multiplier

This multiplier only affects the fog color, not the directional light.

Density Multiplier

This control factor only affects the fog density, not the directional light.

Density Offset

This offset value controls fog opacity; its effective range is from -1 to 1.

Distance Scale

Controls a distance factor. The default value of 1 assumes a 1:1 scale of Unreal Units to centimeters. This makes for a very small world. As your world size increases, you will want to increase this value accordingly. Larger values cause changes in the fog attenuation to occur more quickly.

Altitude Scale

Controls the scale along the z axis only. The default value is 1.

Ground Color Additive

Currently, the irradiance color is based on the scene color. This can cause blackening in shadowed areas. To combat this effect, this parameter allows you to add a small boost (i.e. ~0.05) to make the irradiance color more visible in dark areas.

Z Offset

This is an offset for sea level, calculated in km from the location of the Atmospheric Fog Actor. The system does not work for regions below 0 (sea level), so make sure that all terrain remains above this value. This can be used to adjust the height at which scattering and fog color changes take place.

Start Distance

This is the distance from the camera that the fog will start.

Default Brightness

This is the default light brightness, used when there is no sunlight placed in the level. This property is expressed in lumens.

Default Light Color

Used when there is no sunlight placed in the level.

Disable Sun Disk

If checked, disables Sun Disk rendering.

Disable Ground Scattering

If checked, disables color scattering from the ground.

Precompute Params

The properties included in this group require re-computation of pre-computed texture data. They include:



Density Height

This value controls fog density decay height. Lower values cause the fog to be denser, while higher values thin the fog, causing less scatter. Values range from [0..1]

Max Scattering Num

This sets a limit on the number of scattering calculations, from 1 (single scattering) to 4 (quadruple scattering).

Inscatter Altitude Sample

Number of different altitudes at which to sample inscatter color (Size of 3d texture dimension; 1-32).


Shows or hides the fog effect.

Hidden in Game

If checked, the effect will not be visible in-game.

Example Settings with Images



Density Decay Height of 0.5 (8 km)

Density Decay Height of 0.35 (2.744 km)



Density Decay Height of 1.0 (64 km) and Max Scattering of 4

Density Decay Height of 1.0 (64 km) and Max Scattering of 1

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