rand
float rand([float min, float max] [,float seed])
Generates a random number. With no parameters, the number generated is between
0 and 1. Optionally, two parameters can be passed in to give a range for the
random number. In either case a seed value can be given that will ensure that
the number returned is random, but predictable (always "x" when passed "y").
$u
The u parameters of the underlying face.
$v
The v parameters of the underlying face.
$cWidth
The final, computed width of the current primitive
$faceId
The current face id.
$P
The surface point at which the primitive is being evaluated.
$N
The surface normal at which the primitive is being evaluated.
$U
The surface U at which the primitive is being evaluated.
$V
The surface V at which the primitive is being evaluated.
PI
The ratio of the circumference of a circle to its diameter (3.14159265358979323846).
E
The base of natural logarithms (2.7182818284590452354).