CODEWITHSUNDEEP
javapermutationnoiseperlin-noisesimplex-noise
Kelan
Kelan

Reputation: 371

Why do noise algorithms use 256 permutation values?

I have seen many noise implementations for things like perlin and simplex noise to achieve procedural terrain generation, and they all seem to use 256 permutation values. Why is this? and what would be the effect of using more than 256?

Upvotes: 0

Views: 335

Answers (1)

bakkaa
bakkaa

Reputation: 683

You could use any number of permutation values. The reason powers of two are preferred is, because it is cheaper to compute the modulus of N^2.

The reason for that is:

value % (N^2)

is equivalent to

value & (N^2 - 1)

And it is much cheaper to compute a bitwise & instead of a %.

For example in your code you could write this:

int v = perm[(x + perm[y % 256]) % 256];

Or

int v = perm[(x + perm[y & 255]) & 255];

Both give you the same result but the second method is faster.

Of course any power of two can be used for this. I think the reason for choosing 256 is that it is a good balance between variety of pseudo random numbers and low memory consumption.

Upvotes: 2

Related Questions