// Author @patriciogv - 2015
// Title: Zigzag

#ifdef GL_ES
precision mediump float;
#endif

// Copyright (c) Patricio Gonzalez Vivo, 2015 - http://patriciogonzalezvivo.com/
// I am the sole copyright owner of this Work.
//
// You cannot host, display, distribute or share this Work in any form,
// including physical and digital. You cannot use this Work in any
// commercial or non-commercial product, website or project. You cannot
// sell this Work and you cannot mint an NFTs of it.
// I share this Work for educational purposes, and you can link to it,
// through an URL, proper attribution and unmodified screenshot, as part
// of your educational material. If these conditions are too restrictive
// please contact me and we'll definitely work it out.

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


vec2 mirrorTile(vec2 _st, float _zoom){
    _st *= _zoom;
    if (fract(_st.y * 0.5) > 0.5){
        _st.x = _st.x+0.5;
        _st.y = 1.0-_st.y;
    }
    return fract(_st);
}

float fillY(vec2 _st, float _pct,float _antia){
  return  smoothstep( _pct-_antia, _pct, _st.y);
}

void main(){
  vec2 st = gl_FragCoord.xy/u_resolution.xy;
  vec3 color = vec3(0.0);

  st = mirrorTile(st*vec2(1.,2.),5.);
  float x = st.x*2.;
  float a = floor(1.+sin(x*3.14));
  float b = floor(1.+sin((x+1.)*3.14));
  float f = fract(x);

  color = vec3( fillY(st,mix(a,b,f),0.01) );

  gl_FragColor = vec4( color, 1.0 );
}