uniform vec2 resolution;

uniform float time;

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

#define PI 3.1416

#define changeSpeed 1.0

float cube(vec3 p,float r){vec3 q=abs(p)-r;return length(max(q,0.))+min(max(q.x,max(q.y,q.z)),0.);}

float octa(vec3 p,float r){return dot(abs(p),normalize(vec3(r)))-r;}

float tetra(vec3 p,float r){

  vec3 p1=p,p2=p,p3=p,p4=p;

  p1.xyz+=vec3(r,r,r);

  p2.xyz+=vec3(-r,r,-r);  

  p3.xyz+=vec3(r,-r,-r);

  p4.xyz+=vec3(-r,-r,r);

  return max(-octa(p4,r*1.155),max(-octa(p3,r*1.155),max(-octa(p2,r*1.155),max(-octa(p1,r*1.155),cube(p,r)))));

}

float map(vec3 p){

  p.xy*=rot(4.*PI/4.);

  p.yz*=rot(PI/2.-PI/4.-PI/16.);

  p.xz*=rot(PI/4.);

  vec3 p2 = p;

  p2.yz*=-rot(PI/2.);

  float obj1 = min(tetra(p, 5.), tetra(p2, 5.));

  float obj2 = octa(p, 2.5);

  return  mix(obj1, obj2, (cos(time*changeSpeed)+1.)/2.);

}

void main(){

  vec4 display = vec4(0.0);

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

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

  vec3 p=vec3(0,0,-20);

  float d=1.,ix;

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

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

    ix++;

    if (d<.001){break;}

  }

  if(d<.001) {

    display += 2./ix;