precision mediump float;

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

varying vec2 vUv;

const float PI = 3.1415926;
const float TAU = 6.2831853;

float rectSDF(vec2 p, vec2 c, vec2 d) {
  p = abs(p - c);
  return length(max(p - d, vec2(0.0))) + min(max(p.x - d.x, p.y - d.y), 0.0);
}

float circleSDF(vec2 p, vec2 c, float r) {
  return length(p - c) - r;
}

vec3 contour(float v, float interval) {
  return abs(v) < 0.01 ? vec3(0.0) :
    mod(v, interval) < 0.01 ? vec3(1.0) :
    mix(vec3(0.0, 0.0, 1.0), vec3(1.0, 0.0, 0.0), atan(v) / PI + 0.5);
}

void main() {
  vec2 pos = (2.0 * gl_FragCoord.xy - u_resolution.xy) / min(u_resolution.x, u_resolution.y);

  pos *= 1.5;

  float v1 = circleSDF(pos, vec2(0.2), 0.4);
  float v2 = rectSDF(pos, vec2(-0.2), vec2(0.4));
  float v = int(u_time) % 3 == 0 ? max(v1, v2) :
    int(u_time) % 3 == 1 ? min(v1, v2) :
    max(v1, -v2);

  vec3 col = vec3(contour(v, 0.1));

  gl_FragColor.rgb = col;
  gl_FragColor.a = 1.0;
}