noise - generate values with a pseudo-random noise function

       Copyright © 2011-2014 Khronos Group

[FIXME: source]                                    11/18/2024                                          NOISE(3G)

floatnoise1(genTypex);vec2noise2(genTypex);vec3noise3(genTypex);vec4noise4(genTypex);

noise1, noise2, noise3 and noise4 return noise values (vector or scalar) based on the input value x. The
       noise function is a stochastic function that can be used to increase visual complexity. Values returned
       by the noise functions give the appearance of randomness, but are not truly random. They are defined to
       have the following characteristics:

       •   The return value(s) are always in the range [-1.0,1.0], and cover at least the range [-0.6, 0.6],
           with a Gaussian-like distribution.

       •   The return value(s) have an overall average of 0.0.

       •   They are repeatable, in that a particular input value will always produce the same return value.

       •   They are statistically invariant under rotation (i.e., no matter how the domain is rotated, it has
           the same statistical character).

       •   They have a statistical invariance under translation (i.e., no matter how the domain is translated,
           it has the same statistical character).

       •   They typically give different results under translation.

       •   The spatial frequency is narrowly concentrated, centered somewhere between 0.5 to 1.0.

       •   They are C1 continuous everywhere (i.e., the first derivative is continuous).

       noise - generate values with a pseudo-random noise function

x
           Specifies the value to be used to seed the noise function.

       ┌──────────┬───────────────────────────────────────────────────────────────────────────────────┐
       │          │        OpenGLShadingLanguageVersion                                            │
       ├──────────┼──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┤
       │ Function │ 1.10 │ 1.20 │ 1.30 │ 1.40 │ 1.50 │ 3.30 │ 4.00 │ 4.10 │ 4.20 │ 4.30 │ 4.40 │ 4.50 │
       │ Name     │      │      │      │      │      │      │      │      │      │      │      │      │
       ├──────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │ noise1   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       ├──────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │ noise2   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       ├──────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │ noise3   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       ├──────────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┼──────┤
       │ noise4   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │  ✔   │
       └──────────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘