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VRay.com - Your source for all things VRay  ::  VRay for 3ds Max  ::  Manual  ::  VRayEnvironmentFog parameters

VRay for 3ds Max Manual

VRay for 3ds Max Manual

VRayEnvironmentFog parameters

[VRayEnvironmentFog example]

General
Parameters
 
General parameters
 
Sampling parameters
 
  Exponential sampler
 
  Raymarching sampler
 
Texture maps
 
VRayEnvironmentFog nodes
Notes

Search keywords: volume scattering, volume caustics, participating media, volume light, volume fog

General


VRayEnvironmentFog is an atmospheric effect that allows the simulation of participating media like fog, atmospheric dust and so. Volumetric properties can be determined by 3d texture maps. The atmospheric effect can also be confined with atmospheric gizmo helper objects.

Parameters


General parameters

[General parameters]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.

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.

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.

Scatter GI - when on, the fog will also scatter 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 will be used to accelerate GI inside the volume (e.g. the irradiance map, light cache, photon map or brute-force).

Scatter bounces - when Scatter GI is enabled, this controls the number of GI bounces that will be calculated inside the fog.

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.

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.

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.

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.

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 - this parameter controls when the raymarcher will stop traversing the volume. If the accumulated volume transparency falls below this threshold, the volume will be considered opaque and tracing will be aborted. Higher values make the rendering faster but may introduce artifacts.

Max steps - specifies the maximum number of steps through the volume.

Texture maps

This section allows you to map various properties of the fog - its color, density and emission. Note that whenever a texture is used, VRayEnvironmentFog will use the raymarching sampler to calculate the fog.

You can use any 3ds Max 3d texture map to define the volume properties. Note that you should use World XYZ mapping for the textures.

Color texture - this texture controls the fog color when it is illuminated by light sources.

Density texture - this 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.

Emission texture - this texture controls the fog light emission (self-illumination).

VRayEnvironmentFog nodes

[Nodes]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 within which the fog will be calculated.

Use all lights - when on, 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.

Notes


  • When using VRayEnvironmentFog with standard 3ds Max lights (Omni, Spot etc), you need to turn on the Atmosphere shadows option in order to get proper self-shadowing for the volume.
     
  • When using VRayEnvironmentFog, it is recommended to turn on the Optimized atmospherics evaluation option in the System rollout of the V-Ray settings.
     
  • In contrast to the native 3ds Max Volume Light atmospheric effect, VRayEnvironmentFog covers the entire volume specified by the Fog height parameter or the listed Gizmos - it's effect is not limited to the cone or area of influence of the particular lights that affect the fog.
     
  • When using VRayEnvironmentFog with weak VRayLights, it may be necessary to turn down the Cut-off threshold parameter of the lights. The default value for this parameter works fine for surfaces, but for volumes, where a lot of weak light contributions are added together, it may produce a visible sharp boundary where the light calculations stop.
     
  • You can use the various 3ds Max procedural textures to modify volume properties, including Gradient maps and Falloff maps in Distance blend or Object mode.
     
  • V-Ray does not have separate global illumination maps for volumetric rendering. Instead, all GI engines (the irradiance map, light cache, global/caustics photon maps) have been modified to support volumetric data.



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