GPU Pro 5

198 II Lighting and Shading

Figure 5.3. An image, found in and courtesy of [Scheuermann 04], which shows the

dual specular highlights in hair that the resulting practical real-time hair lighting model

attempts to produce.

Marschner’s paper [Marschner et al. 03] describes a primary and secondary high-

light. The primary highlight is shifted toward the hair tip, and is primarily

influenced by the light color. The secondary highlight is shifted toward the hair

root, and is influenced by the light color and hair color. To combine the two spec-

ular highlights, the reflection vector for the primary highlight is shifted in toward

the direction of the hair ta ...