V- Ray Volume Scatter Fog
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The VRayVolumeScatterFog is a simple volumetric effect that allows us to trace light scattering inside a volume.
Color - defines the color of the fog when it is illuminated by light sources. You can also use a texture map to drive the fog color.
Multiplier - a multiplier for the Color parameter
IOR - index of refraction for the volume. If simulating a fog inside an enclosed volume light rays entering or leaving the volume will be refracted based on this parameter
Bias - this parameter allows to change the way the Color is applied; by adjusting it you can make thin parts of the volume to appear more transparent than normal, or less transparent than normal.
Thickness - this limits the rays that will be traced within the volume. This is useful if you do not want or don't need to trace the whole volume.
Scatter coeff - the amount of scattering inside the volume. 0.0 means rays will be scattered in all directions; 1.0 means a ray cannot change its direction inside the volume.
Fwd/bck coeff - controls the direction of scattering for a ray. 0.0 means a ray can only go forward (inside the volume); 0.5 means that a ray has an equal chance of going forward or backward; 1.0 means a ray will be scattered backward (towards the outside of the volume).
Light multiplier - a multiplier for the scattered light
Scatter levels - specifies the maximum number of scattering bounces
Subdivs - this parameter determines the number of points inside the fog at which volumetric lighting is evaluated. Smaller values for this parameter render faster, but may produce noise in the image. Higher values render longer, but with less noise. It is only used when there are no texture maps specified, in which case the volume properties are the same everywhere.
Environment fog - when enabled the VRayVolumeScatterFog node is used for environment fog for the whole scene. This option should be disabled when the node is connected to a specific volume