static vec4f trace_naive(const ptr::scene* scene, const ray3f& ray_,
    rng_state& rng, const trace_params& params) {
  // YOUR CODE GOES HERE ------------------------------------------------------
  // initialize
  auto radiance = zero3f;
  auto weight   = vec3f{1, 1, 1};
  auto ray      = ray_;
  auto hit      = false;

  // trace  path
  for (auto bounce : range(params.bounces)) {
    // intersect next point
    auto intersection = intersect_scene_bvh(scene, ray);
    if (!intersection.hit) {
      radiance += weight * eval_environment(scene, ray);
      break;
    }

    // prepare shading point
    auto outgoing = -ray.d;
    auto object   = scene->objects[intersection.object];
    auto element  = intersection.element;
    auto uv       = intersection.uv;
    auto position = eval_position(object, element, uv);
    auto normal   = eval_shading_normal(object, element, uv, outgoing);
    auto emission = eval_emission(object, element, uv, normal, outgoing);
    auto brdf     = eval_brdf(object, element, uv, normal, outgoing);

    // handle opacity
    if (brdf.opacity < 1 && rand1f(rng) >= brdf.opacity) {
      ray = {position + ray.d * 1e-2f, ray.d};
      bounce -= 1;
      continue;
    }
    hit = true;

    // accumulate emission
    radiance += weight * eval_emission(emission, normal, outgoing);

    vec3f incoming = zero3f; //initialize incoming
    // next direction
    if (!is_delta(brdf)) {  // sample smooth brdfs (fold cos into f)
      incoming = sample_brdfcos(brdf, normal, outgoing, rand1f(rng), rand2f(rng));  // incoming
      weight *= eval_brdfcos(brdf, normal, incoming, outgoing) /
                sample_brdfcos_pdf(brdf, normal, incoming, outgoing);
    } else {                                        // sample sharp brdfs
      incoming = sample_delta(brdf, normal, outgoing, rand1f(rng));  // incoming
      weight *= eval_delta(brdf, normal, incoming, outgoing) /
                sample_delta_pdf(brdf, normal, incoming, outgoing);
    }

    // check weight
    if (weight == zero3f || !isfinite(weight)) break;

    // russian roulette
    if (max(weight) < 1 && bounce > 3) {
      auto rr_prob = max((float)0.05, 1 - max(weight));
      if (rand1f(rng) > rr_prob) break;
      weight *= 1 / rr_prob;
    }

    // setup next iteration
    ray = {position, incoming};
  }

  return {radiance, hit ? 1.0f : 0.0f};
}