message: Only "roulette out" after at least two bounces
diff: @@ -176,6 +176,8 @@ struct kernel
  throughput *= src * (dot(n, refl_dir) / brdf_pdf);
  throughput = select(zero_pdf, C(0.0), throughput);
  + if (bounce >= 2)
  + {
  // Russian roulette
  auto prob = max_element(throughput.samples());
  auto terminate = gen.next() > prob;
  @@ -186,6 +188,7 @@ struct kernel
  {
  break;
  }
  + }
  ray.ori = hit_rec.isect_pos + refl_dir * S(params.epsilon);
  ray.dir = refl_dir;
  