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Arch & Design Material (mental ray) – Overview 1567
Transparency features
Thematerialsupportsfullglossyanisotropic
transparency and includes a translucent
component, described in detail here (page 2–1553).
Translucency
Solid vs. Thin-Walled
The transparency/translucency property can treat
objects as either solid or thin-walled.
If all objects were treated as solids at all times, every
window pane in an architectural model would
have to be modeled a s two faces: an entry sur face
that refracts the lig ht slightly in one direction, and
immedia tely following it an exit surface, where
light is refracted back into the original direction.
Notonlydoesthisentailadditionalmodeling
work, it is a waste of rendering power to simulate
refraction that has ver y little net effect on the
image. Hence the material allows modeling the
entire window pane as a single flat plane, foregoing
any actual refraction of light.
Solid vs. thin-walled transparency and translucency
In the preceding illustration the helicopter canopy,
the window pane, the translucent cur tain, and the
right-hand sphere all use thin-walled tr a nsparency
or tr anslucency, whereas the glass goblet, the
plastic horse, and the left-hand sphere a l l use solid
transparency or translucency.
Cutout opacity
Beyond the “physical” transparency, which models
an ac tual property of the material, the material
provides a completely separate, non-physical
“cutout opacity” channel to allow “billboard”
objects such as t rees, or to cut out objects such as a
chainlink fence with an opacity mask.
Special Effects
Built-in Ambient Occlusion
AmbientOcclusion(AO)isamethodspearheaded
by the film industry for emulating the look of
true global illumination by using shaders that
calculate the extent to which an area is occluded,
or prevented from receiving incoming light.
Used a lone, an AO shader, such as the separate
mental ray Ambient/Reflective Occlusion shader,
creates a grayscale output t hat is dark in areas light
cannot reach and bright in areas wher e it can:
Thefollowingimageillustratesthemainresultsof
AO: dark crevices and areas where light is blocked