Graphics Reference
In-Depth Information
r
r
i
i
Ref lective
Transmissive
(a)
(b)
r
i
r
i
Mirror and Refractive
Glossy
(c)
(d)
r
r
i
i
Lambertian
Retrorelective
(e)
(f)
Figure 27.9: BSDF (black outer curves) and probability density plots (blue inner curves) for
several classes of reflections; for impulse scattering, like mirror reflection, we've indicated
the impulse direction with a green arrow as in the two right-pointing arrows in (c). For
the others, the peaks in probability density and BSDF are offset from one another because
of the cosine weighting. (a) A generic reflective material. (b) A purely transmissive mate-
rial, which is physically unrealistic. (c) A material with mirror and refractive impulses;
this is the kind of scattering we expect at an air-to-water interface. (d) Glossy scattering.
(e) Lambertian scattering. (f) Retroreflective scattering.
spectral distribution as the incoming light, while for conductors, certain frequen-
cies of light are preferentially reflected. This is why a polished piece of plastic has
white highlights, while a polished piece of gold has gold-colored highlights. We'll
return to this in Section 27.8.3.
The simplest summary representation of the spectral dependence of the
reflected light is to just give RGB values, representing the overall reflectance of
the material in response to long-, middle-, and short-wave incoming radiation.
Thus, the summary computational model becomes
Figure 27.10: A mirrored plane,
reflecting a light source above
the plane (black solid line), pro-
duces the same outgoing radi-
ance field (pink) as a “virtual”
source below the plane placed
at the proper location behind the
mirror would produce (dashed
green) in the absence of the mir-
ror.
)=
ρ
(
λ
)
L
(
P
,
−
v
i
,
λ
)
if
v
o
=
v
i
−
2
(
v
i
·
n
)
n
and
v
i
·
n
>
0,
L
(
P
,
v
o
,
λ
0
otherwise,
(27.3)
where
λ
represents the wavelength of the light as usual.
