const float PHI = 1.61803398874989484820459;  // Φ = Golden Ratio
const float INV_PI = 0.31830988618379067153776752674503;
const float INV_SQRT_OF_2PI = 0.39894228040143267793994605993439;
const float PI = 3.141592653589793;

float seed = 0.0;
vec2 xy = vec2(0.0);

// based on https://www.shadertoy.com/view/ltB3zD
//
// Gold Noise ©2015 dcerisano@standard3d.com
// - based on the Golden Ratio
// - uniform normalized distribution
// - fastest static noise generator function (also runs at low precision)
// - use with indicated fractional seeding method.
float gold_noise(){
    seed += 0.1;
    return fract(tan(distance(xy * PHI, xy) * seed)*xy.x);
}

void init_random_state(in vec2 st, in float s)
{
    xy = st;
    seed = s * 0.01;
}

float luminance(in vec3 col)
{
    return dot(col, vec3(0.2126, 0.7152, 0.0722));
}