#ifdef GL_ES
precision mediump float;
#endif

uniform vec2 u_resolution;
uniform float u_time;

float random(in float x) {
    return fract(sin(x)*1e6);
}

float randcol(float x, float f, float t) {
    return step(0.75,random(floor(x*f)-floor(t)));
}

void main() {
    vec2 st = gl_FragCoord.xy/u_resolution.xy;
    st.x *= u_resolution.x/u_resolution.y;

    float cols = 8.;
    float freq = random(floor(u_time))+abs(atan(u_time)*0.1);
    float t = 40.*u_time*(1.0-freq);

    if (fract(st.y*cols*.5) < .5) t *= -1.0;

    freq += random(floor(st.y*20.));

    float offset = .025;
    vec3 color = vec3(randcol(st.x, freq*100.+random(freq), t+offset),
                      randcol(st.x, freq*100., t),
                      randcol(st.x, freq*100.+random(freq), t-offset));

    gl_FragColor = vec4(1.-color,1.);
}