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Fog color – Defines the color of the fog when it is illuminate by light sources. You can also use a texture map to drive the fog color. For more information, see The Fog Color example below.

Fog distance – Controls the fog density. Larger values make the fog more transparent, while smaller values make it more dense. You can also control the density with a texture map. For more information, see see The Fog Distance example below.

Fog transparency –  Controls the color of the volumetric shadows and the tint for the objects seen through the fog. Brighter colors make the fog more transparent, while darker colors make it more dense at a distance given by the Fog distance parameter. For more information, see The Fog Transparency example below.

Fog emission – Controls the fog emission (self-illumination). You can use this parameter to substitute the ambient illumination inside the fog, instead of using GI. For more information, see The Fog Emission example below below.

Scatter GI – When on, the fog also scatters global illumination. Note that this can be quite slow. In many cases, global illumination within the fog can be substituted with a simple emission term. When this option is on, the currently selected global illumination algorithm in the V-Ray settings is used to accelerate GI inside the volume (e.g. the the irradiance map, light cache or brute-force ). 

Scatter bounces – When Scatter GI is enabled, this controls the number of GI bounces that are calculated inside the fog. For more information, see see The Scatter GI and Scatter Bounces example and the Importance of GI example below.

Fog height – If no atmospheric gizmos are specified, the fog is assumed to start from a certain Z-level height and continue downward indefinitely. This parameter determines the starting point along the Z-axis. If there are atmospheric gizmos listed in the Nodes section, this parameter is ignored. For more information, see see The Fog Height example below below.

Sampling parameters

VRayEnvironmentFog can use either of two algorithms to calculate volumetric lighting. The first algorithm is a simple exponential sampling scheme, which is used when there are no texture maps specified. In this mode, VRayEnvironmentFog takes a number of random points inside the volume and calculates the volumetric lighting at those points. The second algorithm is a raymarching scheme, which is used when any of the volume properties are mapped with a texture. In that case, VRayEnvironmentFog traverses the fog volume in small steps, calculates the volume properties at each step and computes the volume lighting accordingly.

Exponential sampler – This sampler is used when there are no texture maps specified, in which case the volume properties are the same everywhere.

Raymarching sampler

This sampler is used when any of the fog properties (color, density, or emission) is mapped with a 3D texture. The sampler steps through the volume, evaluating volumetric textures and lighting, until it leaves the volume (if there are atmospheric gizmos specified), or until the accumulated volume transparency falls below a certain cut-off threshold, or until a specified number of maximum steps is reached. For more information, see The Sampling Parameters (raymarcher with textures) example below below.

Step size – Determines the size of one step through the volume. Smaller steps produce more accurate results but are slower to render. In general, dense volumes require smaller step sizes than more transparent volumes. In practice, step sizes that are two to three times smaller than the Fog distance parameter work well.

Texture samples – Determines the number of texture samples for each step through the volume. This allows to sample textures more accurately than the volumetric lighting. It is useful in cases where the textures vary much faster than the lighting itself (e.g. for detailed fractal textures).

Cutoff threshold – Controls when the raymarcher stops traversing the volume. If the accumulated volume transparency falls below this threshold, the volume is considered opaque and tracing is aborted. Higher values make the rendering faster but may introduce artifacts. 

Max steps – Specifies the maximum number of steps through the volume.

Gizmo falloff radius – When the fog effect is contained within a gizmo this option allows you to specify a falloff radius for it. This way the fog effect does not have sharp edges at the edges of the gizmo.

Gizmo falloff mode – Allows you to chose between two different falloff modes: Multiply by density and Add density to falloff. For further information, see see The Gizmo nodes example below.

Gizmo merge mode – Specifies how overlapping gizmos are rendered.

Deep Output – Specifies whether to include VRayEnvironmentFog in deep images.

Affect alpha – Enables or disables the tracing of Alpha rays through the volumetric.

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This section allows the user to map various properties of the fog – its color, density and emission. Note that whenever a texture is used, VRayEnvironmentFog uses the ray marching sampler to calculate the fog.

You can use any 3ds Max 3D texture map to define the volume properties.

Fog color texture – Controls the Fog color when it is illuminated by light sources.

Fog density texture – Allows you to modify the texture density. Black values in the texture correspond to perfectly transparent fog; white areas correspond to the density specified by the Fog distance parameter.

Fog emission texture – Controls the fog light emission (self-illumination).

Fog transparency texture – Controls the transparency of the fog density. A 100% white transparency (when fog distance is 0) makes the fog completely transparent. This is also valid per color channel.Fog emission texture – Controls the fog light emission (self-illumination).

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This section allows you to specify gizmos that confine the fog atmospheric effect, and also to specify which scene lights contribute to the illumination of the volume.

Gizmos – A list of atmospheric gizmos and arbitrary meshes within which the fog is calculated. Note that when using a mesh acting as a Gizmo you should either hide it or make it not renderable in order to be able to see the atmospheric effect inside the mesh. For more information, see The Gizmo nodes example below.

Use all lights – When enabled, all scene lights contribute to the illumination of the volume, and the Lights list is ignored.

Lights – A list of lights that affect the volume when Use all lights is off.

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