getfem_deformable_mesh.h

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/* -*- c++ -*- (enables emacs c++ mode) */
/*===========================================================================
 
 Copyright (C) 2012-2026 Andriy Andreykiv
 
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/** @file getfem_deformable_mesh.h
@author "Andriy Andreykiv" <andriy.andreykiv@gmail.com>
@date August 7, 2012.
@brief A class adaptor to deform a mesh.
*/
 
#pragma once
#ifndef GETFEM_DEFORMABLE_MESH_H__
#define GETFEM_DEFORMABLE_MESH_H__
 
#include <getfem/getfem_mesh.h>
#include <getfem/getfem_mesh_fem.h>
#include <getfem/getfem_models.h>
 
namespace getfem {
 
  /** An object function that first deforms and then remembers 
  to restore a mesh if it has to be restored 
  for other bricks. By default the mesh is deformed on 
  construct and undeformed in the destructor (by RAII principle)
  but it's also possible to specify deform_on_construct = false 
  and then call explicitely deform() and undeform() methods.
  Optional to_be_restored flag will control whether the mesh will be restored
  when the deformator destructs.
  */
  template<class VECTOR = model_real_plain_vector> 
  class temporary_mesh_deformator
  {
  public:
    temporary_mesh_deformator(const mesh_fem &mf, const VECTOR &dU,
      bool deform_on_construct = true, bool to_be_restored = true)
       : dU_(mf.nb_basic_dof()),
         mf_(mf), 
         deform_on_construct_(deform_on_construct),
         is_deformed_(false),
         to_be_restored_(to_be_restored){
      mf.extend_vector(dU, dU_);
      if (deform_on_construct_) deform();
    }
 
    void deform(){
      if (is_deformed_) return;
      initial_nodes_ = mf_.linked_mesh().points();
      deforming_mesh_(dU_);
      is_deformed_ = true;
    }
 
    void undeform(){
      if (!is_deformed_) return;
      restore_();
      is_deformed_ = false;
    }
 
    ~temporary_mesh_deformator(){
      if (to_be_restored_ && deform_on_construct_){
        undeform();
      }
    }
 
  private:
    void deforming_mesh_(VECTOR &dU){
      auto &m_ = const_cast<getfem::mesh &>(mf_.linked_mesh());
      auto &ppts = m_.points();
      auto init_nb_points = ppts.card();
 
      dal::bit_vector conv_indices = mf_.convex_index();
      //this vector will track if a point can be deformed
      std::vector<bool> deform_pt_flag(ppts.size(), true);
      size_type cv;
      for (cv << conv_indices; cv != bgeot::size_type(-1); cv << conv_indices)
      {
        getfem::mesh::ind_set pt_index = m_.ind_points_of_convex(cv);
        getfem::mesh_fem::ind_dof_ct dof = mf_.ind_basic_dof_of_element(cv);
        bgeot::size_type num_points = m_.structure_of_convex(cv)->nb_points();
 
        GMM_ASSERT2(dof.size() % num_points == 0,
          "mesh_fem should be isoparametric to the mesh, "
          "with nb_points() of convex == size of ind_basic_dof_of_element / qdim()");
 
        size_type ddim = dof.size() / num_points;
        GMM_ASSERT2(ddim <= 3, "dimension of dof is greater than 3");
 
        for (size_type pt = 0; pt < num_points; ++pt)
        {
          /** iterate through each components of point [pt]and deform the component*/
          if (deform_pt_flag[pt_index[pt]])
          for (size_type comp = 0; comp < ddim; ++comp)
            //move pts by dU;
            ppts[pt_index[pt]][comp] += dU[dof[pt*ddim + comp]];
 
          //flag current [pt] to deformed
          deform_pt_flag[pt_index[pt]] = false;
        }
        ppts.resort();
      }
      GMM_ASSERT1(ppts.card() == init_nb_points, 
                  "Error, after deforming the mesh, number of nodes are different.");
    }
 
    void restore_()
    {
      auto &pts = const_cast<getfem::mesh &>(mf_.linked_mesh()).points();
      GMM_ASSERT1(pts.size() == initial_nodes_.size(), "Internal error, incorrect number of points.");
      for (size_type i = 0; i < pts.size(); ++i) gmm::copy(initial_nodes_[i], pts[i]);
    }
 
    VECTOR dU_;
    const mesh_fem &mf_;
    getfem::mesh::PT_TAB initial_nodes_;
    bool deform_on_construct_;
    bool is_deformed_;
    bool to_be_restored_;
  };
 
}//end of getfem namespace
 
#endif //GETFEM_DEFORMABLE_MESH_H__