9.5.2

894 • CHAPTER 18
THE SHADERS • 895
Attenuation
Scales the amount of detail of the scratches based upon the sample’s angle to the camera and the
distance from the camera. The larger the values, the greater the attenuation, causing less scratching
(better for animation). The smaller the value, the greater the detail (better for still images). The
appropriate range is 0% - 10,000%.
Specular 1, Specular 2, Specular 3
These check boxes specify which specular channels will be affected by the anisotropic scratches.
Normal Direction (previously ‘Buffy’)
This shader colors an object based on the direction of its surface normals. Surfaces whose normals
point towards the rendering ray take Color 1, the other surfaces take Color 2.
In the example above, the surface normals for the middle ring were reversed so that they point to the
rear. The Normal Direction shader was loaded into the alpha channel, with Color 2 dened as black.
The middle ring will therefore be masked out of the outer and inner rings.
Note that it’s the other way round for the reection, where only the middle ring is seen! This is because
for reections, rendering rays are sent out from the mirror into the scene. The middle ring’s surface
normals point towards these reection rays, hence the middle ring is reected, whereas the normals
for the inner and outer rings face away from the reection rays and their surfaces are not reected.