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Scattering
Determines how much of the light bouncing around in the volume ends up scattering the light out of
the fog. If the light scatters more, or more accurately, then there’s a higher probability of the light being
scattered out of the volume, hence less light is left to continue through the fog. This option can make
the fog seem denser.
Asymmetry
Determines in what direction the light is scattered. A value of 0 produces uniform, or isotropic,
scattering, meaning all directions have equal probability. A value greater than 0 causes “forward
scattering,” meaning the light is scattered more into the direction of the light rays. This is similar to
what happens with water droplets in clouds. A value smaller than 0 produces “back scattering,” where
the light is more scattered back toward the original light source.
Transmission
Defines the color that is transmitted through the fog. The light that doesn’t get scattered out will tend
toward this color. It is a multiplier, though, so if you have a red light, but blue transmission, you won’t
see any blue.
Reflection
Changes the intensity of the light that is scattered out. Reflection can be used to modify the overall
color before Emission is added. This will be combined with the color channels of the volume texture
and then used to scale the values. The color options and the color channels of the volume texture are
multiplied together, so if the volume texture were red, setting the Reflection color options to blue
would not make the result blue. In such a case, they will multiply together to produce black.
Emission
This adds a bit of “glowing” to the fog, adding energy/light back into the calculation. If there are no
lights in the scene, and the fog emission is set to be 1.0, the results are similar to no lighting, like
turning off the Do Lighting option. Glowing can also be done while producing a different kind of look,
by having a Transmission greater than 1. This, however, would never happen in the real world.
Common Controls
Settings Tab
The Settings tab in the Inspector is also duplicated in other Position nodes. These common controls
are described in detail at the end of this chapter in “The Common Controls” section.
Examples
In these examples, we are looking at a volume from the outside. On the left, you see how the
Volume Fog looks with straight accumulation. That means the Do Lighting option is turned off.
On the right, you see the same volume with lighting/scattering turned on, and a single
point light.
Chapter 113Position Nodes 2247
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