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1552 Chapter 16: Material Editor, Materials, and Maps
Refraction group
Tra nspare ncy—Defines the level of refraction.
Range=0.0 to 1.0. Default=0.0.
Due to the material’s energy-conserving nature,
the value set in the Tr ansparency parameter is the
maximum value; the actual value depends on the
reflectivity as well as the BRDF curve.
Co lor—Defines the color of refract ion. While
this color can be used to create “colored glass,”
aslightlymoreaccuratemethodtodothisis
described in the Colored Glass section (page
2–1570) of the Tips & Tricks topic.
Glossiness—Definesthesharpnessofthe
refraction/transparency, ranging from 1.0
(completely clear t ransparency) to 0.0 (extremely
diffuse or blurry t ransparency). D efault=1.0.
Left: Refraction Glossiness=1.0; Center: 0.5; Right: 0.25
Glossy refraction needs to trace multiple rays
to yield a smooth result, which can affect
perf ormance. For this reason, the ma terial
includes the following special feature designed to
enhance performance:
Fast (interpolate)—When on, a smoothing
algorithmallowsraystobereusedandsmoothed.
The result is faster and smoother glossy refraction
at the expense of accuracy. Interpolation is
explained in greater detail in the section on the
Fa st Glossy Interpolation rollout (page 2–1559).
Note: This method works best on flat surfaces.
Glossy S amples—Defines t he maximum number
of samples (rays) that mental ray shoots to crea te
glossy refrac tion. Higher values cause slow
rendering but create a smoother result. Lower
values render faster but create a grainier result,
like frosted glass. Generally 32 is enough for most
cases.
Av ailable only when Glossiness does not equal 1.0.
Because a Glossiness v alue of 1.0 creates a perfectly
clear (non-blurry) transparency, it is meaningless
to shoot multiple ra ys for this case, hence only one
refraction ray is shot.
Note: If you set Glossy Samples to 0, the refraction
takes the form of a “perfect lens” and only one ray
is shot, regardless of the actual value of Glossiness.
Youcanusethistoboostperformancefordraft
renderings.
IOR—The Index of Refraction, which is a
measurement of how much a ray of light bends
when entering a material.
The direction in w hich lig ht bends depends on
whether it is entering or exiting the object. The
Arch & Design material use the direction of the
surface normal as the primary cue for figuring out
whetheritisenteringorexiting. Itistherefore
important to model transparent, refractive objects
with the surface normals pointing in the proper
direction.
TheIORcanalsobeusedtodefinetheBRDF
curve, which is what happens in the class of
transparent materials k nown as “dielectric”
materials, and is illustrated here:
Left: IOR=1.0; Center: 1 .2; Rig h t: 1.5