message: Set isect_pos before normal calculation
  Calculating sphere normals requires isect pos to be set
diff: @@ -74,6 +74,8 @@ struct kernel
  V refl_dir;
  V view_dir = -ray.dir;
  + hit_rec.isect_pos = ray.ori + ray.dir * hit_rec.t;
  +
  auto surf = get_surface(hit_rec, params);
  auto n = surf.shading_normal;
  @@ -105,8 +107,6 @@ struct kernel
  break;
  }
  - hit_rec.isect_pos = ray.ori + ray.dir * hit_rec.t;
  -
  ray.ori = hit_rec.isect_pos + refl_dir * S(params.epsilon);
  ray.dir = refl_dir;
  }
  