message: Build up procedural volume textures in parallel
diff: @@ -240,6 +240,9 @@ struct renderer : viewer_type
  return cos(2 * constants::pi<float>() * fM * cos(constants::pi<float>() * r / 2));
  };
  +#ifdef _OPENMP
  + #pragma omp parallel for
  +#endif
  for (int z = 0; z < d; ++z)
  {
  for (int y = 0; y < h; ++y)
  @@ -264,6 +267,9 @@ struct renderer : viewer_type
  {
  heart.resize(w * h * d);
  +#ifdef _OPENMP
  + #pragma omp parallel for
  +#endif
  for (int z = 0; z < d; ++z)
  {
  for (int y = 0; y < h; ++y)
  @@ -289,6 +295,9 @@ struct renderer : viewer_type
  float n = 8;
  +#ifdef _OPENMP
  + #pragma omp parallel for
  +#endif
  for (int z = 0; z < d; ++z)
  {
  for (int y = 0; y < h; ++y)
  