Game Development Reference
In-Depth Information
Figure 10.19. Texture mapping works on stuff that's not just a single quad
10.6
The Standard Local Lighting Model
In the rendering equation, the BRDF describes the scattering distribution
for light of a given frequency and direction of incidence. The differences in
distributions between different surfaces is precisely what causes those sur-
faces (or even different surface points on the same object) to look different
from one another. Most BRDFs are expressed in a computer by some sort
of formula, where certain numbers in the formula are adjusted to match
the desired material properties. The formula itself is often called a lighting
model, and the particular values going into the formula come from the ma-
terial assigned to the surface. It is common for a game engine to use only
a handful of lighting models, even though the materials in the scene may
be quite diverse and there may be thousands of different BRDFs. Indeed,
just a few years ago, almost all real-time rendering was done with a single
lighting model. In fact, the practice is not uncommon today.
This lighting model was so ubiquitous that it was hardwired into the
very rendering APIs of OpenGL and DirectX. Although these older parts
of the API have effectively become legacy features on hardware with pro-
grammable shaders, the standard model is still commonly used in the more
 
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