Graphics Reference
In-Depth Information
b
x
0
0
2
A Gaussian function
e
−
(
cx
)
Figure 8.8
; the parameter
c
controls the width of the curve.
the microfacet normal, the reflected radiance from a microfacet is given by
L
i
F
(
θ
i
)
i
.
π
cos
θ
The formula for the Fresnel reflectance
F
is rather complicated. The original
Torrance-Sparrow model uses the proper formula, but a simple approximation
suffices, such as the approximation given by Christophe Schlick [Schlick 93]:
5
F
(
θ
)
≈
F
0
+(
1
−
F
0
)(
1
−
cos
θ
)
.
Here
F
0
is the Fresnel reflection at normal incidence (
0). (See
Figure 8.9.
)
Fresnel reflection results in polarized light. Schlick's approximation does not in-
clude the effects of polarization, but polarized light is seldom considered in com-
puter graphics. (Actually, the error incurred by ignoring polarization is greater
than the error of Schlick's approximation.) The Fresnel term is wavelength depen-
θ
=
E
s
= F
(
θ
)
E
i
E
i
θ
θ
Figure 8.9
Fresnel reflection in the microgeometry.
