Rainbow Circles

float circle(vec2 st, vec2 center, float radius) {
  float d = distance(st, center);
  return smoothstep(radius, radius - 0.01, d);
}

void main() {
  vec2 st = vUv;
  st.x *= u_resolution.x / u_resolution.y;
  st = st * 2.0 - 1.0;
  vec3 color = vec3(0.1, 0.1, 0.15);
  for (float i = 0.0; i < 6.0; i++) {
    float angle = u_time * 0.5 + i * PI / 3.0;
    float radius = 0.3 + 0.1 * sin(u_time + i);
    float offset = 0.5 + 0.1 * sin(u_time * 0.7 + i);
    
    vec2 pos = vec2(
      offset * cos(angle),
      offset * sin(angle)
    );

    vec3 circleColor = 0.5 + 0.5 * cos(u_time + i + vec3(0, 2, 4));

    float c = circle(st, pos, radius);
    color = mix(color, circleColor, c);
  }
  
  gl_FragColor = vec4(color, 1.0);
}