Game Engine Architecture

472 10. The Rendering Engine

lights will have at each texel. This kind of texture is called a specular power map.

An example of a gloss map is shown in Figure 10.50.

10.3.1.4. Environment Mapping

An environment map looks like a panoramic photograph of the environment

taken from the point of view of an object in the scene, covering a full 360

degrees horizontally and either 180 degrees or 360 degrees vertically. An envi-

ronment map acts like a description of the general lighting environment sur-

rounding an object. It is generally used to inexpensively render refl ections.

The two most common formats are spherical environment maps and cubic

environment maps. A spherical map looks like a photograph taken through a

fi sheye lens, and it is treated as though it were mapped onto the inside of a

sphere whose radius is infi nite, centered about the object being rendered. The

problem with sphere maps is that they are addressed using spherical coordi-

nates. Around the equator, there is plenty of resolution both horizontally and

vertically. However, as the vertical (azimuthal) angle approaches vertical, the

resolution of the texture along the horizontal (zenith) axis decreases to a single

texel. Cube maps were devised to avoid this problem.

A cube map looks like a composite photograph pieced together from pho-

tos taken in the six primary directions (up, down, left , right, front, and back).

During rendering, a cube map is treated as though it were mapped onto the

six inner surfaces of a box at infi nity, centered on the object being rendered.

To read the environment map texel corresponding to a point P on the

surface of an object, we take the ray from the camera to the point P and refl ect

Figure 10.50. This screen shot from EA’s Fight Night Round 3 shows how a gloss map can

be used to control the degree of specular refl ection that should be applied to each texel of

a surface.