thebookofshaders/10/ikeda-00.frag

// Author @patriciogv - 2015
// Title: Ikeda Test patterns

#ifdef GL_ES
precision mediump float;
#endif

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

float random (in float x) {
    return fract(sin(x)*1e4);
}

float random (in vec2 st) {
    return fract(sin(dot(st.xy, vec2(12.9898,78.233)))* 43758.5453123);
}

float randomSerie(float x, float freq, float t) {
    return step(.8,random( floor(x*freq)-floor(t) ));
}

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

    vec3 color = vec3(0.0);

    float cols = 2.;
    float freq = random(floor(u_time))+abs(atan(u_time)*0.1);
    float t = 60.+u_time*(1.0-freq)*30.;

    if (fract(st.y*cols* 0.5) < 0.5){
        t *= -1.0;
    }

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

    float offset = 0.025;
    color = vec3(randomSerie(st.x, freq*100., t+offset),
                 randomSerie(st.x, freq*100., t),
                 randomSerie(st.x, freq*100., t-offset));

    gl_FragColor = vec4(1.0-color,1.0);
}