2021_09_21.glsl

$HEADER$

float pi = 3.1415926535;

uniform vec2 resolution;
uniform float time;

vec2 rotate(vec2 pos, float angle, vec2 origin) {
  pos -= origin;
  pos *= mat2(cos(angle), sin(-angle), sin(angle), cos(angle));
  pos += origin;
  return pos;
}

float circle(vec2 point, vec2 center, float radius, float thickness) {
  float d = distance(point, center);
  return sin(
      max(0., min(pi, radius - d * pi / thickness))
    );
}

void main() {
  vec2 center = resolution / 2.;
  vec2 pos = gl_FragCoord.xy;
  pos = rotate(pos, sin(time / 2.) * log(distance(pos, center) / 50.), center);
  pos *= .45 + .45 * sin(time) * sin(distance(pos, center) / 200.);
  pos *= .75 + .5 * sin(-time);
  float v = circle(
      mod(pos, abs(.5 * sin(time / 2.) + .75) * (.7 + .4 * sin(time / 3.)) * 50.) + center - vec2(25., 25.),
      center,
      50.,
      2.
  );
  vec3 c = vec3(
      .5 + .5 * atan(pos.y, pos.x) / pi,
      .5 + .5 * atan(pos.x, pos.y) / pi,
      .5 + .5 * sin(time)
  );
  gl_FragColor = vec4(c * v, 1.);
}