V-Ray Environment Fog parameters
Search keywords: volume scattering, volume caustics, participating media, volume light, volume fog
VRay_Environment_Fog 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 geometry objects.
VRay_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, VRay_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, VRayEnvironmentFog traverses the fog volume in small steps, calculates the volume properties at each step and computes the volume lighting accordingly.
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.
Emission - 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 - a multiplier for the Emission parameter
Fog distance - controls the fog density. Larger values make the fog more transparent, while smaller values make it more dense.
Fog density - a multiplier for the Fog distance parameter that allows a texture to be used for the density of the fog
Fog height - if the fog is not contained within a volume, it is assumed to start from a certain Z-level height and continue downward indefinitely. This parameter determines the starting point along the Z-axis.
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.
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.
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 textures for GI - When this option is checked V-Ray will use 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 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).
Cut off 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.
Fade out mode - allows you to choose between two different modes of fade out
Fade out radius - allows you to set a radius for the fade out of the fog
Per Object Fade Out Radius - when this option is selected the fade out effect will be applied to each fog volume independently
Affect background - enables or disables the tracing of background rays through the volumetric
Affect reflection rays - enables or disables the tracing of reflection rays through the volumetric
Affect refraction rays - enables or disables the tracing of refraction rays through the volumetric
Affect shadow rays - enables or disables the tracing of shadow rays through the volumetric
Affect GI rays - enables or disables the tracing of GI rays through the volumetric
Affect camera rays - enables or disables the tracing of Camera rays through the volumetric.
All objects in the scene - a list of all scene objects that can be used as gizmos. A gizmo is a geometry object that will not be rendered directly, but instead will be used to "confine" within its volume the fog effect.
Gizmos - specifies which gizmo objects will be used for the environment fog effect. If this list is empty, the fog will be applied to the entire volume of the scene.
Fade out radius
Fade out radius - allows you to set a radius for the fade out of the selected environment fog gizmos
Set Fade out radius - applies the specified value of Fade out radius to all selected objects from the Gizmos list. Otherwise, each gizmo has its individual radius.
The radius of a certain gizmo object will be displayed in the Fade out radius field when you select it from the Gizmos list.
Light Mode - this option allows you to specify which lights will be considered when rendering the environment fog.
No lights - the lights in the scene will not affect the environment fog
Use all lights - all scene lights will have effect when rendering the environment fog
Use lights from list - all lights specified in the lights list affect the environment fog
lights - a list of lights that can be picked to take part in the final rendering of the environment fog.