Practical Algorithms for 3D Computer Graphics, 2nd Edition

4.7. Perlin nois e 147

To ch oose a random vector for integer co or d in ate ix we simply look up the table

k=Ntab[ ix mod (N−1)] and use vector k from the list. (As there are only 16

vectors in the table the actual vector used is k&15.)

To choose one of the vectors based on three lattice corner coordin ates , we

can still use a single table by repetition of the look-up three times in succession,

as in:

i d = Ntab [ Ntab [ Ntab [ i x ] + iy ] + i z ] ;

This hash function is chosen because it return s results that are more irregular

than id=Ntab[ix+iy+iz];, for ex amp le.

Note that Ntab has 256 entries whose values lie in the range 0 to 255, so the

sum ...