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1554 Chapter 16: Material Editor, Materials, and Maps
Anisotropy group
Anisotropy —Controls the anisotropy, or shape, of
thehighlight.At1.0,thehighlightisround;thatis,
no anisotropy. At 0.01, the highlig ht is elongated.
One axis of the highlight graph changes to show
changesinthisparameter.Default=1.0.
Left: Anisotropy=1.0; Center: Anisotropy=4.0; Right:
Anisotropy=8.0
Rotation—Changes the orientation of the highlight.
The sample slot shows changes in orientation.
This value can range from 0.0 to 1.0, w ith 1.0=360
degrees. So, for example, 0.25=90 deg rees and
0.5=180 degrees. Default=0.0.
Left: Anisotropy Rotation=0.0; Center: Anisotropy
Rotation=0.25; Right: An isotropy Rotation=[texture map]
Tip: When using texture-mapped Anisotropy
Rotation,makesurethetextureisnotantialiased
(filtered). You can a chieve this by setting the map’s
Blur parameter to 0.0. Otherwise the antialiased
pixels cause local vortices in the anisotropy that
appear as seam artifacts.
Automatic/M ap Channel—Lets you optionally apply
anisotropy to a specific m ap channel.
If the Map Channel setting is Automatic, the
base rotation follows the object’s local coordinate
system. If it is any ot her value (in other words, a
specific map channel), the space that defines the
stretch directions of the highlights is derived from
that channel’s texture space.
Wa rn in g : Deriving the anisotropy from the texture
space creates only one space per triangle and can cause
visible seams between triangles.
Also see Brushed Metal (page 2–1575).
BRDF rollout
BRDF stands for bidirectional reflectance
distribution function.Asexplainedinthe
introduction (page 2–1566),thispropertyletsthe
material’s reflectivity be ultimately guided by the
angle from which the object surface is viewed.
0 degree (green) and 90 degree (red) view angles
[B R DF meth od]—LetsyouchoosehowtheBRDF
curve is defined:
•
B y IOR (fr esnel ref lections )—How the reflectivity
depends on the angle is guided solely by the