This page provides information about the Environment fog in V-Ray for Cinema 4D.
Overview
V-Ray Environment Fog is an atmospheric effect that allows the simulation of participating media like fog, atmospheric dust, and so forth. Volumetric properties can be determined by 3D texture maps. The atmospheric effect can also be confined to geometry objects.
Environment Fog 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, Environment Fog 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, Environment Fog traverses the fog volume in small steps, calculates the volume properties at each step, and computes the volume lighting accordingly.
How to Set Up
Fog Container
Lights
Options
Enabled – Enables or disables the Environment Fog.
Material Tag – Specifies a custom UV mapping for the displacement taken from the material currently attached in the field. If the field is empty, V-Ray uses the default or the UV mapping from the currently applied material to the object.
Fog 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.
Fog Distance – Controls the fog density. Larger values make the fog more transparent, while smaller values make it denser.
Height – If the fog is not contained within a volume, it is assumed to start from a certain Y-level height and continue downward indefinitely. This parameter determines the starting point along the Y-axis. Note the units are centimeters.
Fog Density – A multiplier for the Fog distance parameter that allows a texture to be used for the density of the fog.
Emission Color – Controls the fog emission (self-illumination). You can use this parameter to substitute the ambient illumination inside the fog, instead of using GI.
Emission Multiplier – Multiplies the Emission parameter.
Fog Transparency – Controls the transparency of the fog volume at a thickness given by the Fog distance parameter. Brighter colors make the fog more transparent.
IOR – Index of Refraction for the volume, which describes the way light bends when crossing the material surface. A value of 1.0 means the light does not change direction.
Deep Output – Toggles writing deep data to the file. Note that enabling this option forces ray marching even for simple volumetrics which can cause slower rendering.
Global Illumination
Scatter GI – When enabled, 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 enabled, the currently selected global illumination algorithm in the V-Ray settings are used to accelerate GI inside the volume (e.g. the 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.
Ray Filter
Affect Reflections – Enables or disables the tracing of reflection rays through the volumetric.
Affect Refractions – Enables or disables the tracing of refraction rays through the volumetric.
Affect Shadows – Enables or disables the tracing of shadow rays through the volumetric.
Affect GI – Enables or disables the tracing of GI rays through the volumetric.
Affect Camera – Enables or disables the tracing of Camera rays through the volumetric.
Raymarching
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 the fog is contained within a volume), or until the accumulated volume transparency falls below a certain cut-off threshold, or until a specified number of maximum steps is reached.
Simplify Texture for GI – When this option is enabled, V-Ray uses a simplified method for calculating the GI when rendering parts of the fog that are textured or are being faded out.
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.
Max Steps – Specifies the maximum number of steps through the volume.
Texture Samples – Determines the number of texture samples for each step through the volume. This samples 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. This parameter is not available when the render engine is set to GPU.
Fade Out
Fade out Mode – Allows you to choose between two different modes of fade out: Multiply by density or Add density to fallout.
Fade out Radius – Allows you to set a radius for the fade out of the fog.
Per Object Fade out Radius – When enabled, the fade out effect is applied to each fog volume independently..
