What's the origin of this GLSL rand() one-liner?

Question

I\'ve seen this pseudo-random number generator for use in shaders referred to here and there around the web:

float rand(vec2 co){
  return fract(sin(dot(co.x         


        

Answer 1

Maybe it's some non-recurrent chaotic mapping, then it could explain many things, but also can be just some arbitrary manipulation with large numbers.

EDIT: Basically, the function fract(sin(x) * 43758.5453) is a simple hash-like function, the sin(x) provides smooth sin interpolation between -1 to 1, so sin(x) * 43758.5453 will be interpolation from -43758.5453 to 43758.5453. This is a quite huge range, so even small step in x will provide large step in result and really large variation in fractional part. The "fract" is needed to get values in range -0.99... to 0.999... . Now, when we have something like hash function we should create function for production hash from the vector. The simplest way is call "hash" separetly for x any y component of the input vector. But then, we will have some symmetrical values. So, we should get some value from the vector, the approach is find some random vector and find "dot" product to that vector, here we go: fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453); Also, according to the selected vector, its lenght should be long engough to have several peroids of the "sin" function after "dot" product will be computed.