NEORT | Digital Art Platform

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precision highp float;
uniform vec2 resolution;
uniform float time;
float map(vec3 p){    
  if (mod(time * 2., 14.) <= 7.) {
    return length(p)-(0.009)*pow(mod(time * 2., 7.), 4.);         
  } else {   
    return length(p)-(0.009)*pow(mod(-time * 2., 7.), 4.);
  }
}
vec3 getNormal(vec3 p){
  float d = 0.0001;
  return normalize(vec3(map(p+vec3(d,0.,0.))-map(p+vec3(-d,0.,0.)),map(p+vec3(0.,d,0.))-map(p+vec3(0.,-d,0.)),map(p+vec3(0.,0.,d))-map(p+vec3(0.,0.,-d))));
}
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,-18);
    float d=1.,i;
    for(int i=0;i<99;i++){
      p+=rd*(d=map(p));
    }
    if(d<.001) {
      vec3 normal = getNormal(p);
      vec3 lightDir = vec3(0,0,-1.0);
      float diff = clamp(dot(lightDir, normal), 0.2, 1.0);
      float light = 1.0;
      if (mod(time * 2., 14.) <= 7.) {
        if ((0.009)*pow(mod(time * 2., 7.), 4.) > 15.) {
          light = 1. - (0.009)*pow(mod(time * 2., 7.), 4.) + 15.;
        }
      } else {   
        if ((0.009)*pow(mod(-time * 2., 7.), 4.) > 15.) {
          light = 1. - (0.009)*pow(mod(-time * 2., 7.), 4.) + 15.;
        }
      }          
      display = vec4(vec3(diff * light) , 1.0);
    }