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

the constant values are arbitrary, especially that they are very large, and a couple of decimals away from prime numbers.

a modulus over 1 of a hi amplitude sinus multiplied by 4000 is a periodic function. it's like a window blind or a corrugated metal made very small because it's multiplied by 4000, and turned at an angle by the dot product.

as the function is 2-D, the dot product has the effect of turning the periodic function at an oblique relative to X and Y axis. By 13/79 ratio approximately. It is inefficient, you can actually achieve the same by doing sinus of (13x + 79y) this will also achieve the same thing I think with less maths..

If you find the period of the function in both X and Y, you can sample it so that it will look like a simple sine wave again.

Here is a picture of it zoomed in graph

I don't know the origin but it is similar to many others, if you used it in graphics at regular intervals it would tend to produce moire patterns and you could see it's eventually goes around again.