message: Base visibility decisions on geomtric normal dir
diff: @@ -36,11 +36,7 @@ inline spectrum<U> glass<T>::sample(
  {
  auto f = specular_bsdf_.sample_f(sr.normal, sr.view_dir, refl_dir, pdf, inter, gen);
  // If ray originates in 2nd medium, flip normal
  - auto n = select(
  - U(dot(sr.normal, sr.view_dir)) > U(0.0),
  - vector<3, U>(sr.normal),
  - vector<3, U>(-sr.normal)
  - );
  + auto n = faceforward(sr.normal, sr.view_dir, sr.geometric_normal);
  return f * (dot(n, refl_dir) / pdf);
  }
  