float pi = 3.14159265358979323846;

// Raytrace renderer.
static vec4f trace_raytrace(const rtr::scene* scene, const ray3f& ray,
    int bounce, rng_state& rng, const trace_params& params) {

  // intersect next point
  auto inter = intersect_scene_bvh(scene, ray);
  if(!inter.hit) {return {eval_environment(scene, ray), 1};}
  // evaluate geometry
  auto& el = inter.element;
  auto& forma = scene -> objects[inter.object];
  auto new_position = transform_point(forma -> frame, eval_position(forma -> shape, el, inter.uv));
  // normal corrections
  auto normal = transform_direction(forma -> frame, eval_normal(forma -> shape, el, inter.uv));

  // evaluate material
  auto material = forma -> material;
  auto temp_coord = eval_texcoord(scene -> objects[inter.object] -> shape, el, inter.uv);
  vec2f coord = vec2f{fmod(temp_coord.x, 1), fmod(temp_coord.y, 1)};
  auto color = forma -> material -> color * eval_texture(material -> color_tex, coord);
  auto radiance = forma -> material -> emission;
  auto outgoing = -ray.d;


  // handle opacity

  // accumulate emission

  // exit if enough bounces are done
  if (bounce >= params.bounces) {return {radiance, 1};}

  // compute indirect illumination
  auto ambient = sample_hemisphere(normal, rand2f(rng));

  // transmission -> polished dielectric
  if (material -> transmission) {
    if (rand1f(rng) < mean(fresnel_schlick(vec3f(0.04f), normal, outgoing))) {
      auto incoming = reflect(outgoing, normal);
      radiance += xyz(trace_raytrace(scene, ray3f{new_position, incoming}, ++bounce, rng, params));}
    else {
      auto incoming = -outgoing;
      radiance += color * xyz(trace_raytrace(scene, ray3f{new_position, incoming}, ++bounce, rng, params));
    }
  }