precision highp float;

uniform vec2 resolution;

uniform float time;

#define rot(a) mat2(cos(a),sin(a),-sin(a),cos(a))

#define TAU atan(1.)*8.

vec2 pmod(vec2 p, float n)

{

  float a=mod(atan(p.y, p.x),TAU/n)-.5 *TAU/n;

  return length(p)*vec2(sin(a),cos(a));

}

float map(vec3 p)

{

    p.z-=-time*2.;

    p.z=mod(p.z,4.)-2.0;

    for(int i=0;i<6;i++)

    {

        p.xy=pmod(p.xy,8.);

        p.y-=1.935;

    }

    return dot(abs(p),normalize(vec3(1,0,1)))-0.2;

}

void main(){

    vec4 fragColor = vec4(0.0);

    vec2 uv=(gl_FragCoord.xy-.5*resolution)/resolution.y;

    vec3 rd=normalize(vec3(uv,1));

    vec3 p=vec3(0,0,-70);

    float d=1.,ix;

    for(int i=0;i<99;i++){

      p+=rd*(d=map(p));

      ix++;

      if (d<.001){break;}

    }

    if(d<.001) {

      fragColor += 4.6/ix;

      fragColor += normalize(vec4(100,35,00,0))*9./ix;

    }

    gl_FragColor = fragColor;

    gl_FragColor.w = 1.0;