User Manual

Density
This is similar to scattering in that it makes the fog appear thicker. With a high amount of
scattering, though, the light will be scattered out of the volume before it has had much chance
to travel through the fog, meaning it won’t pick up a lot of the transmission color. With a high
density instead, the fog still appears thicker, but the light gets a chance to be transmitted, thus
picking up the transmission color before it gets scattered out. Scattering is affected by the light
direction when Asymmetry is not 0.0. Density is not affected by light direction at all.
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.
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