text: /*=========================================================================
  
    Program:   ParaView
    Module:    vtkDataObjectToConduit.h
  
    Copyright (c) Kitware, Inc.
    All rights reserved.
    See Copyright.txt or http://www.paraview.org/HTML/Copyright.html for details.
  
       This software is distributed WITHOUT ANY WARRANTY; without even
       the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
       PURPOSE.  See the above copyright notice for more information.
  
  =========================================================================*/
  
  #include "FEDataStructures.h"
  
  #include <iostream>
  #include <iterator>
  #include <mpi.h>
  
  Grid::Grid() = default;
  
  void Grid::Initialize(const unsigned int numPoints[3], const double spacing[3])
  {
    if (numPoints[0] == 0 || numPoints[1] == 0 || numPoints[2] == 0)
    {
      std::cerr << "Must have a non-zero amount of points in each dimension.\n";
    }
    // in parallel, we do a simple partitioning in the x-direction.
    int mpiSize = 1;
    int mpiRank = 0;
    MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
    MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
  
    unsigned int startXPoint = mpiRank * numPoints[0] / mpiSize;
    unsigned int endXPoint = (mpiRank + 1) * numPoints[0] / mpiSize;
    if (mpiSize != mpiRank + 1)
    {
      endXPoint++;
    }
  
    // create the points -- slowest in the x and fastest in the z directions
    double coord[3] = { 0, 0, 0 };
    for (unsigned int x = startXPoint; x < endXPoint; x++)
    {
      coord[0] = x * spacing[0];
      for (unsigned int y = 0; y < numPoints[1]; y++)
      {
        coord[1] = y * spacing[1];
        for (unsigned int z = 0; z < numPoints[2]; z++)
        {
          coord[2] = z * spacing[2];
          // add the coordinate to the end of the vector
          std::copy(coord, coord + 3, std::back_inserter(this->Points));
        }
      }
    }
    // create the hex cells
    unsigned int numXPoints = endXPoint - startXPoint;
    for (unsigned int i = 0; i < numXPoints - 1; i++)
    {
      for (unsigned int j = 0; j < numPoints[1] - 1; j++)
      {
        for (unsigned int k = 0; k < numPoints[2] - 1; k++)
        {
          unsigned int cellPoints[8] = { i * numPoints[1] * numPoints[2] + j * numPoints[2] + k,
            (i + 1) * numPoints[1] * numPoints[2] + j * numPoints[2] + k,
            (i + 1) * numPoints[1] * numPoints[2] + (j + 1) * numPoints[2] + k,
            i * numPoints[1] * numPoints[2] + (j + 1) * numPoints[2] + k,
            i * numPoints[1] * numPoints[2] + j * numPoints[2] + k + 1,
            (i + 1) * numPoints[1] * numPoints[2] + j * numPoints[2] + k + 1,
            (i + 1) * numPoints[1] * numPoints[2] + (j + 1) * numPoints[2] + k + 1,
            i * numPoints[1] * numPoints[2] + (j + 1) * numPoints[2] + k + 1 };
          std::copy(cellPoints, cellPoints + 8, std::back_inserter(this->Cells));
        }
      }
    }
  }
  
  size_t Grid::GetNumberOfPoints()
  {
    return this->Points.size() / 3;
  }
  
  size_t Grid::GetNumberOfCells()
  {
    return this->Cells.size() / 8;
  }
  
  double* Grid::GetPointsArray()
  {
    if (this->Points.empty())
    {
      return nullptr;
    }
    return this->Points.data();
  }
  
  double* Grid::GetPoint(size_t pointId)
  {
    if (pointId >= this->GetNumberOfPoints())
    {
      return nullptr;
    }
    return this->Points.data() + pointId * 3;
  }
  
  unsigned int* Grid::GetCellPoints(size_t cellId)
  {
    if (cellId >= this->GetNumberOfCells())
    {
      return nullptr;
    }
    return this->Cells.data() + cellId * 8;
  }
  
  Attributes::Attributes()
  {
    this->GridPtr = nullptr;
  }
  
  void Attributes::Initialize(Grid* grid)
  {
    this->GridPtr = grid;
  }
  
  void Attributes::UpdateFields(double time)
  {
    size_t numPoints = this->GridPtr->GetNumberOfPoints();
    this->Velocity.resize(numPoints * 3);
    for (size_t pt = 0; pt < numPoints; pt++)
    {
      double* coord = this->GridPtr->GetPoint(pt);
      this->Velocity[pt] = coord[1] * time;
    }
    std::fill(this->Velocity.begin() + numPoints, this->Velocity.end(), 0.);
    size_t numCells = this->GridPtr->GetNumberOfCells();
    this->Pressure.resize(numCells);
    std::fill(this->Pressure.begin(), this->Pressure.end(), 1.f);
  }
  
  double* Attributes::GetVelocityArray()
  {
    if (this->Velocity.empty())
    {
      return nullptr;
    }
    return this->Velocity.data();
  }
  
  float* Attributes::GetPressureArray()
  {
    if (this->Pressure.empty())
    {
      return nullptr;
    }
    return this->Pressure.data();
  }
  