Whirling

@grid: 1 / 100vw 100vh; 
@content: @shaders1000(
  void main() {
    vec2 uv = (gl_FragCoord.xy / u_resolution - .5) * 2.;
    float a = atan(uv.y, uv.x);
    float r = length(uv);
    vec3 c = vec3(1., 2., 3.);
    c = .4 + .6 * cos(c + a*2. + r*6. - u_time);
    gl_FragColor = vec4(c, 1.0);
  }
);