GPU Pro 5

258 IV Mobile Devices

Figure 1.2. UI controls for multilayered skin and two specular lobes.

We use all four channels of pre-computed lookup texture separately to store

different information:

• the first two channels contain N · H and N · V response for both specular

lobes;

• the third channel contains a pre-computed Fresnel term for N · V ;

• the last channel contains an energy conservation term for the diffuse com-

ponent, the integral of light reflected before it enters subsurface layers.

Because of the use of pre-computed lookup texture, overhead for the second

specular lobe is negligible. Moreover, we achieve the energy conservation virtually

for free. ...