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Arch & Design Material (mental ray) 1559
When Caus tics a re ena bled, tr ans par ent
obj ects : —
When not rendering caustics, the Arch
& Design m aterial u ses a shadow shader to create
transparentshadows.Forobjectssuchaswindow
panesthisisperfectlyadequate,andactually
creates a better result than using caustics, because
thedirectlightisallowedtopassmoreorless
undisturbed through the glass into a space such
as a room.
Traditionally, enabling caustics i n mental ray
causes a l l materials to stop casting transparent
shadows and instead start to generate refractive
caustics. In most architectural scenes this is
undesirable; you might want a glass decorat ion on
a table to generate c austic effect, but still want the
windows to the room to let in normal direct ligh t.
This switch makes this possible at the material
level.
•
Refract light and generate Caustic effects—The
material refracts light and generates caustics.
•
Use Transparent Shadows—No caustics are
produced; the material and object simply
transmit the light, with greater shadowing in
thicke r areas.
In the following il lustration, t he left side shows the
result with Use Transparent Shadows chosen, and
the right side shows the result with Refract Light
And Generate Caustic Effects chosen. You can
freely mix the two modes in the same rendering.
Photons are automatically treated accordingly
bythebuilt-inphotonshader,shootingstraight
through as direct light in the former c ase, and
being refracted as caustics in the latter.
Left: Using transparent shadows; R ight: Using refractive
caustics.
Ba ck Face Culling—When on, enables a special
modethatmakessurfacesinvisibletothecamera
when seen from the reverse side. You can use t his
to create “magic walls ” in a room. If all walls are
planes with the normals facing inward s, the Back
Face Culling switch allows the room to be rendered
from “outside.” The c amera can see into the room,
butthewallswillstillexistandcastshadows,
bounce photons, etc. while b eing inv isible when
the camera goes outside.
Left: Back Face Culling=off ; Right: Back Face Culling=on
Transparency propagates Alpha channel—Defines
how transparent objects treats any alpha channel
informationinthebackground. Whenon,
refraction and other transparency effects
propagate the alpha of t he background “through”
the transparent object. When off, transparent
objectshaveanopaquealpha.
Indirect Illumination Options
FG/GI multiplier—Allows tweaking of how strongly
the material responds to indirect light.
FG Quality—Alocalmultiplierforthenumberof
final gather rays shot by the material.
Fast Glossy Interpolation rollout
Glossy reflections and refraction can be
interpolated, which causes them to render faster
and look smoother. Interpolation works by
precalculating glossy reflection in a grid across the
image. The number of samples (rays) taken at each
point is govern by the Reflection > Glossy Samples
or Refraction > Glossy Samples parameters, as in
the non-interpolated case.