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3dsMaxMaterialsinmentalrayRenderings 83
• Be careful of the total number of photons
you’re emitting: A very hig h number (100,000
and above) can dramatically increase your
rendering time. Then again, for some simple
scenes, you might actually be able to set these
to 1,000,000 and still render in an acceptable
amount of time.
Wa rning: The number of photons specified for
each light indicates the number of photons that
need to be stored for each light, not the number
of photons to be shot. This is a pretty important
distinction. If a light is pointed in a direc tion where
thereisnosurface,thementalrayrenderermight
shoot photons forever. In the Messages Window
(page 3 –87), the mental ray renderer will display
warnings that no photons are being stored. To avoid
the slowdowns related to this issue, make sure that
every light points in the direction of a surface (this
is sometimes impossible to do with omni lights).
Another way to avoid this problem is to add a big
sphere around your entire model.
Coincident Faces
When it encounters coincident faces, the mental
ray renderer can produce artifacts, because it can’t
decide which face is nearer the camera (neither is).
To fix this, move or scale one of the objects so faces
are no longer coincident.
B ack fa ce Culling
mental ray rendering correctly performs backface
culling, and renders one-sided faces much as the
scanline renderer does.
3ds Max Materials in mental ray
Renderings
For the most part, the mental ray renderer treats
3ds Max maps and materials the same way the
default scanline renderer does. The exceptions are
listed below. In general, if the mental ray renderer
does not recognize a m ap or material, it renders
it as opaque black.
Wa rn in g : The mental ray renderer does not necessarily
suppor t maps or materials provided as plug-ins from
third-party vendors. It supports third-par ty maps and
materials only if the vendor has explicitly used the
mental ray SDK to add support for the mental ray format.
Unless the third-party vendor clearly specifies mental
ray sup port, you should assume the map or material is
unsupported, and will render as black.
See also
mental ray Renderer (page 3–78)
Getting Good Results with mental ray Rendering
(page 3–80)
Is sues for R efl ections an d R ef r actions
The maps used to create reflections or refractions,
Flat Mir ror, Ray trace, Reflect/Refract, and Thin
Wall Refraction, are supported by the mental ray
renderer. However, the mental ray renderer simply
usesthesemapsasindicationstouseitsown
ray-tracing metho d, leading to s ome restrictions
on which parameters are suppor ted, as described
in the sections “Materials” and “Maps,” below.
Map Blurring
When reflections and refractions are ray traced,
applying Blur (or Distortion, in Flat Mirror)
does not apply to reflections or refract ions
of environment maps. In general, Blur and
Distortion render differently than they do with
the default scanli ne renderer, and you mig ht have
to experiment with parameter values to get a
comparable rendering result.
Tip: If Blur effects are not rendering well with the
mental ray renderer, try increasing the Maximum
number of samples in the Renderer panel >
Sampling Quality Rollout (page 3–98).