Source

void main() { vec2 uv = gl_FragCoord.xy / resolution.xy; float o = sin(abs(sin(time*.025))*50.*tan(length(uv)*uv.y))*.1; float c = step(length(uv - vec2(.5) + o), .1); c -= step(length(uv - vec2(.5) + o), .095); gl_FragColor = vec4(vec3(c), 1.); }