// Author @patriciogv - 2015
// http://patriciogonzalezvivo.com
#ifdef GL_ES
precision mediump float;
#endif

#define PI 3.14159265358979323846

uniform vec2 u_resolution;
uniform float u_time;

vec2 rotate2D(vec2 _st, float _angle){
  _st -= 0.5;
  _st =  mat2(cos(_angle),-sin(_angle),
              sin(_angle),cos(_angle)) * _st;
  _st += 0.5;
  return _st;
}

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

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

vec2 offset(vec2 _st, vec2 _offset){
  vec2 uv;
  if(_st.x>0.5){
    uv.x = _st.x - 0.5;
  } else {
    uv.x = _st.x + 0.5;
  } 
  if(_st.y>0.5){
    uv.y = _st.y - 0.5;
  }else {
    uv.y = _st.y + 0.5;
  } 
  return uv;
}

void main(void){
  vec2 st = gl_FragCoord.xy/u_resolution.xy;
  st = tile(st,5.);

  vec2 offsetSt = offset(st,vec2(0.5));

  st = rotate2D(st,PI*0.25);

  vec3 color = vec3( box(offsetSt,vec2(0.95),0.01) - box(st,vec2(0.3),0.01) + 2.*box(st,vec2(0.2),0.01) );

  gl_FragColor = vec4(color,1.0);    
}