openMP---第一篇

//////////////////////////////////////////////////////////////////////////////////////////////
template <typename PointInT, typename PointOutT> void
pcl::MovingLeastSquares<PointInT, PointOutT>::performProcessing (PointCloudOut &output)
{
  // Compute the number of coefficients
  nr_coeff_ = (order_ + 1) * (order_ + 2) / 2;

  size_t mls_result_index = 0;

#ifdef _OPENMP
  // (Maximum) number of threads
  const unsigned int threads = threads_ == 0 ? 1 : threads_;
  // Create temporaries for each thread in order to avoid synchronization
  typename PointCloudOut::CloudVectorType projected_points (threads);
  typename NormalCloud::CloudVectorType projected_points_normals (threads);
  std::vector<PointIndices> corresponding_input_indices (threads);
#endif

  // For all points
#ifdef _OPENMP
#pragma omp parallel for schedule (dynamic,1000) num_threads (threads)
#endif
  for (int cp = 0; cp < static_cast<int> (indices_->size ()); ++cp)
  {
    // Allocate enough space to hold the results of nearest neighbor searches
    // \note resize is irrelevant for a radiusSearch ().
    std::vector<int> nn_indices;
    std::vector<float> nn_sqr_dists;

    // Get the initial estimates of point positions and their neighborhoods
    if (searchForNeighbors ((*indices_)[cp], nn_indices, nn_sqr_dists))
    {
      // Check the number of nearest neighbors for normal estimation (and later for polynomial fit as well)
      if (nn_indices.size () >= 3)
      {
        // This thread‘s ID (range 0 to threads-1)
#ifdef _OPENMP
        const int tn = omp_get_thread_num ();
        // Size of projected points before computeMLSPointNormal () adds points
        size_t pp_size = projected_points[tn].size ();
#else
        PointCloudOut projected_points;
        NormalCloud projected_points_normals;
#endif

        // Get a plane approximating the local surface‘s tangent and project point onto it
        const int index = (*indices_)[cp];

        if (cache_mls_results_)
          mls_result_index = index; // otherwise we give it a dummy location.

#ifdef _OPENMP
        computeMLSPointNormal (index, nn_indices, projected_points[tn], projected_points_normals[tn], corresponding_input_indices[tn], mls_results_[mls_result_index]);

        // Copy all information from the input cloud to the output points (not doing any interpolation)
        for (size_t pp = pp_size; pp < projected_points[tn].size (); ++pp)
          copyMissingFields (input_->points[(*indices_)[cp]], projected_points[tn][pp]);
#else
        computeMLSPointNormal (index, nn_indices, projected_points, projected_points_normals, *corresponding_input_indices_, mls_results_[mls_result_index]);

        // Append projected points to output
        output.insert (output.end (), projected_points.begin (), projected_points.end ());
        if (compute_normals_)
          normals_->insert (normals_->end (), projected_points_normals.begin (), projected_points_normals.end ());
#endif
      }
    }
  }

#ifdef _OPENMP
  // Combine all threads‘ results into the output vectors
  for (unsigned int tn = 0; tn < threads; ++tn)
  {
    output.insert (output.end (), projected_points[tn].begin (), projected_points[tn].end ());
    corresponding_input_indices_->indices.insert (corresponding_input_indices_->indices.end (),
                                                  corresponding_input_indices[tn].indices.begin (), corresponding_input_indices[tn].indices.end ());
    if (compute_normals_)
      normals_->insert (normals_->end (), projected_points_normals[tn].begin (), projected_points_normals[tn].end ());
  }
#endif

  // Perform the distinct-cloud or voxel-grid upsampling
  performUpsampling (output);
}