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;
}

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

  vec2 pos = vec2(st * 5.0);

  float n = noise(pos);

  gl_FragColor = vec4(vec3(n), 1.0);
}