precision mediump float;

#endif

​

uniform vec2 u_resolution;

uniform float u_time;

​

void main() {

  vec2 coord = gl_FragCoord.xy / u_resolution;

  vec3 color = vec3(0.0);

  float angle = atan(-coord.y + 0.25, coord.x - 0.5) * 0.1;

  float len = length(coord * 4.0 -vec2(0.5, 0.25));

  color.r += (len * 40.0 + angle * 40.0 + u_time);

  color.g += cos(len * 30.0 + angle * 60.0 - u_time * 5.);

  color.b += cos(len * 50.0 + angle * 50.0 + 3.0);

  gl_FragColor = vec4(color, 1.0);

}