// Author @patriciogv ( patriciogonzalezvivo.com ) - 2015

#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 tile(vec2 _st, float _zoom){
  _st *= _zoom;
  return fract(_st);
}

float box(in vec2 _st, in vec2 _size){
    _size = vec2(0.5) - _size*0.5;
    vec2 uv = smoothstep(_size,
                        _size+vec2(0.001),
                        _st);
    uv *= smoothstep(_size,
                    _size+vec2(0.001),
                    vec2(1.0)-_st);
    return uv.x*uv.y;
}

float cross(in vec2 _st, float _size){
    return  box(_st, vec2(_size*0.5,_size*0.125)) +
            box(_st, vec2(_size*0.125,_size*0.5));
}

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

  st = tile(st,3.0);
  vec3 color = vec3( clamp(cross(fract(st),0.3),0.0,1.0) );

  gl_FragColor = vec4(color,1.0);
}