Graphics Reference
In-Depth Information
p'
dA
n'
n
r
p
Figure 1.4.
Solid angle of quadrilateral as visible from point
p
.
1.3.2 Material and Lighting Models
After deriving the principal integral (equation (1.4)) for light rendering, we as-
sume that the light area is well defined and therefore possible to integrate. For
simplification we restrict our reasoning to simple shapes—a sphere, a disk, and a
rectangle—which are relatively easy to integrate and compute.
Our light is defined by the following parameters:
•
position,
•
orientation,
•
outgoing light radiance in lumens,
•
shape type (sphere, disk, rectangle),
•
dimensions.
With those parameters we can instantly calculate
L
in lumens. We need to find
a way to solve or approximate the integral from equation (1.4). To simplify the
problem, let us look at the generalized physically based BRDF combining diffuse
and specular reflectance models:
f
r
(
p,ω
o
,ω
i
)=
k
d
+
k
s
,
(1.5)
where
k
d
is the diffuse light model and
k
s
is the specular model.
