BlockToMeshConverterGenerator.C

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//* This file is part of the MOOSE framework
//* https://mooseframework.inl.gov
//*
//* All rights reserved, see COPYRIGHT for full restrictions
//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
//*
//* Licensed under LGPL 2.1, please see LICENSE for details
//* https://www.gnu.org/licenses/lgpl-2.1.html

#include "BlockToMeshConverterGenerator.h"
#include "CastUniquePointer.h"
#include "libmesh/elem.h"
#include "MooseMeshUtils.h"

registerMooseObject("MooseApp", BlockToMeshConverterGenerator);

InputParameters
BlockToMeshConverterGenerator::validParams()
{
  InputParameters params = MeshGenerator::validParams();

  params.addClassDescription(
      "Converts one or more blocks (subdomains) from a mesh into a stand-alone mesh with a "
      "single block in it.");

  params.addRequiredParam<MeshGeneratorName>("input", "The mesh we want to modify");
  params.addRequiredParam<std::vector<SubdomainName>>(
      "target_blocks",
      "The (list of) blocks (or 'subdomains') we wish to have moved to a new mesh (by name, not "
      "ID)");

  return params;
}

BlockToMeshConverterGenerator::BlockToMeshConverterGenerator(const InputParameters & parameters)
  : MeshGenerator(parameters),
    _input(getMesh("input")),
    _target_blocks(getParam<std::vector<SubdomainName>>("target_blocks"))
{
}

std::unique_ptr<MeshBase>
BlockToMeshConverterGenerator::generate()
{
  std::unique_ptr<MeshBase> mesh = std::move(_input);

  if (!mesh->is_replicated())
    mooseError("This generator does not support distributed meshes.");

  auto new_mesh = buildMeshBaseObject();

  const auto target_block_ids = MooseMeshUtils::getSubdomainIDs((*mesh), _target_blocks);

  // Check that the block ids/names exist in the mesh
  std::set<SubdomainID> mesh_blocks;
  mesh->subdomain_ids(mesh_blocks);

  for (const auto i : index_range(target_block_ids))
    if (target_block_ids[i] == Moose::INVALID_BLOCK_ID || !mesh_blocks.count(target_block_ids[i]))
    {
      paramError("target_blocks",
                 "The target_block '",
                 _target_blocks[i],
                 "' was not found within the mesh.");
    }

  // know which nodes have already been inserted, by tracking the old mesh's node's ids'
  std::unordered_map<dof_id_type, dof_id_type> old_new_node_map;

  for (const auto target_block_id : target_block_ids)
  {

    for (auto elem : mesh->active_subdomain_elements_ptr_range(target_block_id))
    {
      if (elem->level() != 0)
        mooseError("Refined blocks are not supported by this generator. "
                   "Can you re-organize mesh generators to refine after converting the block?");

      // make a deep copy so that mutiple meshes' destructors don't segfault at program termination
      auto copy = elem->build(elem->type());

      // index of node in the copy element must be managed manually as there is no intelligent
      // insert method
      dof_id_type copy_n_index = 0;

      // correctly assign new copies of nodes, loop over nodes
      for (dof_id_type i : elem->node_index_range())
      {
        auto & n = elem->node_ref(i);

        if (old_new_node_map.count(n.id()))
        {
          // case where we have already inserted this particular point before
          // then we need to find the already-inserted one and hook it up right
          // to it's respective element
          copy->set_node(copy_n_index++, new_mesh->node_ptr(old_new_node_map[n.id()]));
        }
        else
        {
          // case where we've NEVER inserted this particular point before
          // add them both to the element and the mesh

          // Nodes' IDs are their indexes in the nodes' respective mesh
          // If we set them as invalid they are automatically assigned
          // Add to mesh, auto-assigning a new id.
          Node * node = new_mesh->add_point(elem->point(i));

          // Add to element copy (manually)
          copy->set_node(copy_n_index++, node);

          // remember the (old) ID
          old_new_node_map[n.id()] = node->id();
        }
      }

      // it is ok to release the copy element into the mesh because derived meshes class
      // (ReplicatedMesh, DistributedMesh) manage their own elements, will delete them
      new_mesh->add_elem(copy.release());
    }
  }

  return dynamic_pointer_cast<MeshBase>(new_mesh);
}