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110 Chapter 17: Rendering
Like photon maps and shadow maps, the fast
lookup computation can be saved in a file and then
reused in subsequent renderings.
Prev iew (No Precalculations )—When on, final
gathering skips the precalculation phase. This
results in a rendering with artifacts, but begins
rendering more quick ly, so it c an u seful when you
want to do a series of trial renderings. Default=off.
Final Gather Map group
These controls tell mental ray how to calculate the
final gather map for indirect illumination. The
map is an
FGM fi le (page 3–1031)
.
Rebuild (Do Not Re-Use Cache)—If Rebuild is turned
on, t he renderer saves the recalculated final gather
map to the file specified by the Browse button.
Default=on.
•
Use File—When on, the mental ray renderer
either saves the final gather map to an .
fgm
file,
or loads an existing file. The state of Rebuild
determines whether the .
fgm
file is saved or
loaded.
This option is unavailable unless you click
Browse (“...”) to provide a name for the .
fgm
file.
•
Browse (“ ...” )—Click to display a file selector
dialog , which lets you specify a name for the
final gather map (.
fgm)
file, and the folder
where it is saved.
•
File name—When you have used the Save
button to specify a final gather map file, the
name field displays its name and path.
•
Delete File—Click to delete the current
.
fgm
file.
Trace Depth group
The Trace Depth controls are similar to those for
calculating reflections and refractions, but they
refer to the light rays used by final gathering,
rather than to rays used in diffuse reflection and
refraction.
Max. Depth—Limits the combination of reflection
and refraction. Reflection and refraction of a
photon stop when the total number of both equals
the Maximum Depth setting. For example, if
Maximum Depth equals 3 and the tr ace depths
each equal 2, a photon can be reflected twice
and refracted once, or vice versa, but it can’t be
reflected and refracted four times. Default=5.
Max Bounces—Sets the number of times
diffuse light bounces are calculated for a single
diffuseray,whichtherenderercastsforthis
purpose. Default=0.
Like Maximum Reflections and Maximum
Refractions, this value is subject to the restriction
of Max Depth. If Max Bounces is set higher than
Max Depth, the latter setting is automatically
raised to the Max Bounces value in the
.mi
file, but
not in the 3ds Max interface.
Max. R eflections—Sets the number of times a
photon can be reflected. At 0, no reflection occurs.
A t 1, the photon can be reflected once only. At
2, the photon can be reflected twice, and so on.
Default=5.
Max. R ef ractions—Sets the number of t imes a
photon can be refracted. At 0, no refraction
occurs. At 1, the photon can b e refracted once
only. At 2, the photon can be refracted twice, and
so on. Default=5.
Use Falloff (Limits R ay Distance)—When on, uses
the Start and Stop values to limit the lengt h of light
rays used for regathering. This can help improve
regathering time, especially for scenes that are not
fully enclosed by geometr y. Default=off.
•
Start—Specifies the distance, in 3ds Max units,
at which rays begin. You can use this value to
exclude geometry that is too close to the light
source. Default=0.0.