9

Getting Good Results with mental ray Rendering 81
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 3–83) .Beloware
some basic rules of thumb for using mental ray 3.5
in 3ds Max.
Using L ights wi th the menta l r ay
Renderer
When you set up a scene for rendering with the
mental ray renderer, keep the following tips in
mind:
• The Overshoot parameter for lights doesn’t
work when 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 when 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 whet her 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 scanline renderer, you can set
alighttohaveavalueofzero,withashadow
color of white, and a shadow density of
1.
With these settings, the light c asts 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 va lue
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 rayt racer 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/Ref ract maps (page 2–1699).
It uses them if they have already been generated
by the default sca nline renderer, but it do es not
generate them. If Source > From File is active
and the mental ray renderer c an find the s ix cubic
maps, it uses them. If Source > Automa tic is active,
or if the cubic maps cannot be found, the mental
ray renderer generates ray-traced reflec tions or
refractions instead.
Ray Tracing Setup
On the rendering m enu, Ray Tracer Settings 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. The
ray-tracing controls for mental ra y appear on the
Renderer panel > Rendering Algorithms rollout
(page 3–116).
Tip: While the mental ray renderer ignores the
global inclusion or exclusion settings for the ray
tracer, you can enable or disable ray-tracing at the
local level of a Raytrace material or map.
Ray Tracing Rules of Thumb
Let’s say you’re rendering a (lathed) wineglass,
w ith an inner and outer surface and a piece
of geometry representing the wine. The wine
geometr y is just slig htly smaller than the inner
surfaces of the wineglass, and capped with a