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80 Chapter 17: Rendering
To mak e t he menta l r ay Render er the defa ult
render er for new scenes:
• After you make the mental ray renderer the
active production renderer, click Save As
Defaults on the Assign Renderer rollout.
Getting Good R esults with mental
ray Rendering
Although the mental ray renderer is relat ively
easytouseonceyou’vesetitupcorrectly,there
are several "gotchas" that you mig ht encounter
immediately, especially if you’re primarily
accustomed to the 3ds Max scanline renderer and
its workflow. For example, see
3ds Max Materials
in mental ray Renderings (page 3–82)
.Beloware
some basic r ules of thumb for using mental ray 3.4
in 3ds Max.
Using L ights with t he mental r ay
Renderer
When you set up a scene for rendering with the
mental ray renderer, keep the following tips in
mind:
• The O vershoot parameter for lights doesn’t
work w hen you use mental ray to render
shadow-mapped shadows. To use Overshoot,
use ray-traced shadows.
• Excluding an object from shadow casting
doesn’t work w hen you use mental ray to render
shadow-mapped shadows. To exclude objects
from shadow casting , use r ay-traced shadows.
(TheExcludebuttonisonalight’sGeneral
Parameters rollout.)
• When you assign a map to object shadows in the
light’ s Shadow Parameters rollout, the mental
ray renderer does not recognize the toggle for
themap(totheleftoftheMapbutton),and
renders the map whether the toggle is on or off.
To stop using the map, you must click the Map
button and in the Material/Map Browser, assign
NONE as the map type.
• Using the default s canli ne renderer, you can set
alighttohaveavalueofzero,withashadow
color of white, and a shadow density of
1.
With these settings, the li ght casts shadows but
does not illuminate the scene. To get the same
effect using the mental ray renderer, the light
value must not be zero. Instead, set it to a value
close to zero (for example, 0.001 or -0.001).
• The mental ray renderer disregards the bias
parameters in the Shadow Map Params rollout
and the Ray Tr aced Shadow Params rollout.
• The mental ray renderer assumes that all
directional lights come from infinity, so objects
thatarebehindthedirectlightobjectinthe
3dsMaxscenewillalsobeilluminated.
Ray Tracing
The mental ray raytracer is fast and provides
excellent quality images, but you have to use it
correctly within 3ds Max.
The mental ray renderer does not fully support
cubic maps for
Reflect/Refract maps (page
2–1509)
. It uses them if they have already been
generated by the default scanline renderer, but it
does not generate them. If Source > From File is
active and the mental r ay renderer can find the six
cubic maps, it uses them. If Source > Automatic
is act ive, or if t he cubic maps cannot be found,
the mental ray renderer generates ray-traced
reflections or refractions instead.
Ray Tracing Setup
On the rendering menu, Ray Tracer Settin gs and
Raytrace Global Include/Exclude are disabled
while the mental ray renderer is active. These
controls adjust ray-trace settings for the scanline
renderer only. The settings of these controls
have no impact on the mental ray renderer. T he
ray-tracing con trols for mental ray appear on the