9.5.2

884 • CHAPTER 18
THE SHADERS • 885
Initial Offset
Use this setting to dene the distance between the original surface point to be sampled ((P) in above
illustrations) and the rst sample point. This rst sample point is a point in space along the surface
normal.
Sample Radius
Use this setting to dene the size of the area sample, in the illustrations above labeled (R). A larger
radius generally means that you need more samples to get a smooth (read: low-noise) appearance.
Sample Type
Use this setting to select the sample type. It can be set to either “Along Normal” or to “Area”. If set to
“Along Normal”, samples will be taken along the surface normal. This can be either a set of regularly
spaced samples (if stochastic is turned off) or random samples anywhere along the normal, resulting
in a more noisiy appearance. If “Sample Type” is set to “Area”, ChanLum will need to take random
samples within the area, so the stochastic option will be grayed out.
Stochastic
If this setting is turned on, ChanLum will take randomly-placed samples for you. If it is turned off
(only possible if “Along Normal” was selected), it will take samples at regular intervals, leading to a
smoother result with fewer samples.
Gaussian
This is an extra option when in “Stochastic” mode. If it is turned off, the random samples can be
anywhere in the dened area. If it is turned on, the chance of getting samples closer to the offset rst
sample point is much greater than getting samples further away. This will generally lead to a more
pleasant appearance. If you turn “Gaussian” off, you may want to decrease the sample area in order
to get about the same effect as if it were turned on
Shadows
Turn this setting off to omit shadows from the calculation. It is not advisable to do this in the instances
described above, because they rely on shadows for the entire appearance. But there may be some
instances where you may want to use ChanLum’s fog sample method without requiring shadows to
be taken into account (such as with particle sprites), that’s what this setting was designed to do.
Seed
Use this setting to dene the initial amount of random variation for “Stochastic” interpolation.