Cellular
Description
A cellular noise function.
The noise value is computed using the distances of the given point to the four nearest feature points by combining them according to the specified coefficients:
result := (a0 * f0 + b0) * f0
        + (a1 * f1 + b1) * f1
        + (a2 * f2 + b2) * f2
        + (a3 * f3 + b3) * f3 + c
f0      := distance to 1st nearest feature point
f1      := distance to 2nd nearest feature point
f2      := distance to 3rd nearest feature point
f3      := distance to 4th nearest feature point