GPU Pro 5

72 II Lighting and Shading

n

n'

p'

dA

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