sturb expression function

Generates spatially coherent 3D noise based on sparse convolution.

See also: turb, noise, snoise

Spatially coherent noise gives random numbers which are close to each other when the X, Y, Z inputs are close to each other.

depth is the amount of fractalization of the noise.

This is very similar to turb, except instead of finding noise values on a fixed lattice and interpolating, this function finds noise values on points scattered in space and interpolated according to the Voronoi decomposition.