uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

float random (in vec2 st) {
    return fract(sin(dot(st.xy,
                         vec2(12.9898,78.233)))*
        43758.5453123);
}

float noise(in vec2 st) {
  vec2 i = floor(st);
  vec2 f = fract(st);

  float a = random(i);
  float b = random(i + vec2(1.0, 0.0));
  float c = random(i + vec2(0.0, 1.0));
  float d = random(i + vec2(1.0, 1.0));

  vec2 u = f * f * (3.0 - 2.0 * f);

  return mix(a, b, u.x) +
    (c - a) * u.y * (1.0 - u.x) +
    (d - b) * u.x * u.y;
}

float fbm(in vec2 st, int octaves) {
  float value = 0.0;
  float amplitude = 0.5;
  float frequency = 0.0;

  for(int i = 0; i < octaves; i++) {
    value += amplitude * noise(st);
    st *= 2.0;
    amplitude *= 0.5;
  }

  return value;
}

void main() {
  vec2 st = gl_FragCoord.xy/u_resolution.xy;
  st.x *= u_resolution.x/u_resolution.y;

  vec3 color = vec3(0.0);
  vec2 p = st * sqrt(u_mouse.x);
  int oct = sqrt(u_mouse.y);

  color += fbm(p, oct);

  gl_FragColor = vec4(color, 1.0);
}