Noise - Graphics Shaders - page 223

Component Term Term Range Term Limits

0 nv.r 0.5 ± .5000

0.0000 → 1.0000

1 nv.g 0.5 ± .2500

0.2500 → 0.7500

2 nv.b 0.5 ± .1250

0.3750 → 0.6250

3 nv.a 0.5 ± .0625

0.4375 → 0.5625

sum 2.0 ± ~ 1.0

~1.0 → 3.0

sum - 1 1.0 ± ~ 1.0

~0.0 → 2.0

(sum - 1) / 2 0.5 ± ~ 0.5

~0.0 → 1.0

(sum - 2) 0.0 ± ~ 1.0

~1.0 → 1.0

Table 10.1. The range of the four octaves of noise and some useful combinations.

So, if you would like to have a four-octave noise function that ranges
from 0. to 1, then do this:

float sum = nv.r + nv.g + nv.b + nv.a;
// range is 1. -> 3.
sum = ( sum - 1. ) / 2.;
// range is now 0. -> 1.

If you would like to have a four-octave noise function that ranges from -1
to 1, then do this instead:
float sum = nv.r + nv.g + nv.b + nv.a;
// range is 1. -> 3.
sum = ( sum - 2. );
// range is now -1. -> 1.

By default, the glman 3D noise texture has dimensions 64 × 64 × 64. You
can change this by puting a command in your GLIB ile of the form
Noise3D 128

to get dimension 128 × 128 × 128, or choose whatever resolution you want (up
to around 400 × 400 × 400). Remember that for the most general use, the resolu-
tion should be a power of two. The first time glman creates a 3D noise texture
for you, it will take a few seconds. But glman then writes it to a local file, and
the next time this 3D texture is needed it is read from the file, which is a lot
faster.
A 2D noise texture works the same way, except you get at it with

uniform sampler2D Noise2;
...
vec2 st = ...
vec4 nv = texture( Noise2, st );