stone - Simulate a granular stone
Surface "stone" "Ka" n "Ks" n "Kd" n "roughness" n "specularcolor" c "scale" n "nshades" n "exponent" n "graincolor" c
float Ka=0.2, Ks=0.9, Kd=0.8, roughness=0.3 float scale=0.02, nshades=4 exponent=2 color specularcolor=[1 1 1] color graincolor=[0 0 0]
This shader makes objects look like they are carved out of granular stone, like granite, by making crystals of varying intensity and color. The parameter scale controls the size of the crystals, or grains: larger values make larger grains. This is the only parameter most people will want to change.
The parameter nshades is the number of unique intensity levels found in the grains. Higher values of this will produce less simplistic looking stone. Setting nshades equal to 3 will produce stone that looks remarkably like the spattered-paint fake stone Zolatone you have probably seen. The exponent parameter controls the distribution of intensity levels: higher values push the intensities toward the darker end (actually more toward graincolor, as described below).
The intensity levels are actually levels of mixing between two colors, the surface color and the graincolor parameter. Since graincolor is black by default, the different colors normally are in fact different intensities of the surface color. However, if you want red-and-green speckly stone for some reason, you could do this by setting the surface color and graincolor appropriately, but you should probably set nshades to something pretty low to avoid getting lots of weird colors between red and green.
The parameters Ka,Ks and Kd have the usual meanings of ambient, specular and diffuse reflective intensities, respectively. roughness and specularcolor control the sharpness and color of the specular highlight.
This shader can have problems with aliasing.
Pixar Animation Studios