9

Arch & Design Material (mental ray) 1553
The leftmost cup looks completely unrealistic and
is almost invisible. Because an IOR of 1.0, which
equals that of air, is impossible in solid matter, we
get no change in reflectivity across the material
and hence perceive no edges or changes of any
kind. On the other hand, the center and rightmost
cups have realistic changes in reflectivity guided
by the IOR.
Instead of basing the reflectivity on the IOR, you
can instead use the BRDF mode to set it manually:
Different types of transparency
As in the previous illustration, the leftmost cup
acquires its curve from the index of refraction. The
center cup has a manually defined curve, which
has been set to a 9 0 degree reflect iv ity of 1.0 and
a 0 degree reflectivity of 0.2; this looks a bit more
like metallized glass. The rig htmost cup uses the
same BRDF curve, but instead is set to thin-walled
transparency (page 2–1558). Clearly, this method
is be tter for making non-refractive objects than
simply setting IOR to 1.0, as we tr ied above.
Translucency group
Translucency is handled as a special case of
transparency; in order to use translu cency there
must first exist s ome level of transparency. The
implementation of translucency in the Arch &
Design material is a simplification concerned
solely with the transport of light from the back
ofanobjecttoitsfrontfacesandisnottrueSSS
(subsur face scattering) effect. You can create
an SSS-like effect by using glossy transparency
coupled with transl ucency, but this is neither as
fastnoraspowerfulasthededicatedSSS shaders
(page 2–1583).
Tra nsl ucency—When on, the remaining
Translucency become available and take effect
when rendering.
Weigh t—Determines how much of the existing
transparency is used as translucency. For example,
if Weight=0.0, all of the transparency is used as
transparency. If Weight=0.3, 30 percent of the
transparency is used as translucency.
All: Transparency=0.75. Left: Weight=0.0; Center: Weight=0.5;
Right: Weight=1.0
Translucency is intended for use pr imarily in
thin-walled mode,asintheexampleabove)to
model things like curtains, rice paper, and similar
effects. In thin-wa l led mode it simply allows the
shading of the reverse side of the object to bleed
through. The shader also operate s i n solid mode,
but, as explained above, the SSS shaders are better
suited for such purposes.
Solid translucency with: Left: Weight=0.0; Center: Weight=0.5;
Right: Weight=1.0
Co lor—The translucency color.