#define PI 3.141592
#define BALLS 20.

mat2 rotate2d(float a) {
  return mat2(cos(a), -sin(a), sin(a), cos(a));
}

void mainImage(out vec4 fragColor, in vec2 fragCoord) {
  vec2 uv = fragCoord / iResolution.xy;
  uv.x -= .5;
  uv.y -= .5;
  uv.x *= iResolution.x / iResolution.y;

  uv *= 100.;
  float dist = length((uv));
  uv *= rotate2d(iTime / 7.);
  for (float i = 0.; i < BALLS; i++) {
    uv.y += .5 * (i / 20.) * cos(uv.y / 1000. + iTime / 4.) + sin(uv.x / 50. - iTime / 2.);
    uv.x += .5 * (i) * sin(uv.x / 300. + iTime / 6.) * sin(uv.y / 50. + iTime / 5.);
    float t = .01 * dist * (i) * PI / BALLS * (5. + 1.);
    vec2 p = 8. * vec2(-1. * cos(t), 1. * sin(t / 6.));
    p /= sin(PI * sin(uv.x / 10.) * cos(uv.y / 11.));
    vec3 col = cos(vec3(0, 1, -1) * PI * 2. / 3. + PI * (iTime / 5. + float(i) / 5.)) * 0.5 + 0.5;
    fragColor += vec4(float(i) * .2 / length(uv - p * 0.9) * col, 1.);
  }
  fragColor.xyz = pow(fragColor.xyz, vec3(2.));
  fragColor.w = 1.0;
}