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precision mediump float;

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in vec2 pos;

out vec4 colour;

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uniform float millis; 

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const float TIME_SCALE = 0.0001;

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const vec4 low = vec4(0.165,0.345,0.31, 1.);

const vec4 high = vec4(0.988,1.,0.753, 1.);

​

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float rand(vec2 p) {

  return fract(sin(dot(p, vec2(12.9898,78.233)))*43758.5453123);

  return fract(sin(dot(p, vec2(14.234523, 120.9812879)))*23.234234);

}

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float noise(vec2 p) {

  vec2 i = floor(p); // integer part

  vec2 f = fract(p); // fractional part

  // get noise values for the four corners of a square

  float a = rand(i);

  float b = rand(i + vec2(1.0, 0.0));

  float c = rand(i + vec2(0.0, 1.0));

  float d = rand(i + vec2(1.0, 1.0));

  // add smoothing to the position

  f = smoothstep(0., 1., f);

  // interpolate between the corner values

  return mix(mix(a, b, f.x), mix(c, d, f.x), f.y);

}

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// Simple rotation matrix

const mat2 rot = mat2(1.);//mat2(0.8, 0.6, -0.6, 0.8);

const int numOctaves = 6;

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float fbm(vec2 p) {  

  float f = 0.;

  vec2 shift = vec2(100.);

  float amp = 1.;

  float totalAmp = 0.;

  for(int i = 0; i < numOctaves; i ++) {

    float spice = 0.;

    if(i == numOctaves/2 || i == numOctaves - 1) {

      spice = millis/1000.;

    }

    f += amp * noise(p + spice);

    totalAmp += amp;

    float scale = 2. + rand(vec2(float(i)))/5.;

    amp /= scale;

    p = p * rot * scale + shift;

  }

  f /= totalAmp;

  return f;

}

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float pattern(vec2 p) {

  return fbm(p + fbm(p + fbm(p)));

}

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void main() {

  float v = 1.;

  // 1. Random numbers

  v = rand(floor((pos) * 10. + 0.5));// * millis/100.);

  // 2. Smooth noise

  v = noise(pos * 10.);

  //3. Fractal brownian motion

  v = fbm(pos * 10.);

  //4. Domain warping

  // v = pattern(pos * 10.);

  float n = 4.;

  // v = round(pattern(pos * 10.) * n)/n;

  colour = mix(low, high, v);

}

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