/*=========================================================================

  Program:   Visualization Toolkit
  Module:    vtkHyperTreeGridPlaneCutter.cxx

  Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
  All rights reserved.
  See Copyright.txt or http://www.kitware.com/Copyright.htm 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 "vtkHyperTreeGridPlaneCutter.h"

#include "vtkBitArray.h"
#include "vtkCellArray.h"
#include "vtkCellData.h"
#include "vtkCleanPolyData.h"
#include "vtkCutter.h"
#include "vtkDataObject.h"
#include "vtkHyperTreeGrid.h"
#include "vtkHyperTreeGridNonOrientedGeometryCursor.h"
#include "vtkHyperTreeGridNonOrientedMooreSuperCursor.h"
#include "vtkIdList.h"
#include "vtkInformation.h"
#include "vtkMath.h"
#include "vtkObjectFactory.h"
#include "vtkPlane.h"
#include "vtkPointData.h"
#include "vtkPoints.h"
#include "vtkPolyData.h"
#include "vtkUnstructuredGrid.h"

#include <cassert>
#include <cmath>

namespace
{
vtkIdType First8Integers[] = { 0, 1, 2, 3, 4, 5, 6, 7 };

constexpr unsigned int MooreCursors3D[26] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16,
  17, 18, 19, 20, 21, 22, 23, 24, 25, 26 };
}

vtkStandardNewMacro(vtkHyperTreeGridPlaneCutter);

//------------------------------------------------------------------------------
vtkHyperTreeGridPlaneCutter::vtkHyperTreeGridPlaneCutter()
{
  this->Points = nullptr;
  this->Cells = nullptr;

  // Initialize plane parameters
  std::fill(this->Plane, this->Plane + 4, 0.);

  // By default a non-conforming output mesh is produced for better rendering
  this->Dual = 0;

  // By default member variables for dual-based computation are not used
  this->SelectedCells = nullptr;
  this->Centers = nullptr;
  this->Cutter = nullptr;
  this->Leaves = nullptr;
}

//------------------------------------------------------------------------------
vtkHyperTreeGridPlaneCutter::~vtkHyperTreeGridPlaneCutter()
{
  if (this->Points)
  {
    this->Points->Delete();
    this->Points = nullptr;
  }

  if (this->Cells)
  {
    this->Cells->Delete();
    this->Cells = nullptr;
  }

  if (this->Leaves)
  {
    this->Leaves->Delete();
    this->Leaves = nullptr;
  }

  if (this->Centers)
  {
    this->Centers->Delete();
    this->Centers = nullptr;
  }

  if (this->Cutter)
  {
    this->Cutter->Delete();
    this->Cutter = nullptr;
  }

  if (this->SelectedCells)
  {
    this->SelectedCells->Delete();
    this->SelectedCells = nullptr;
  }
}

//------------------------------------------------------------------------------
void vtkHyperTreeGridPlaneCutter::PrintSelf(ostream& os, vtkIndent indent)
{
  this->Superclass::PrintSelf(os, indent);

  os << indent << "Plane: ( " << this->Plane[0] << " ) * X + ( " << this->Plane[1] << " ) * Y + ( "
     << this->Plane[2] << " ) * Z = " << this->Plane[3] << "\n";

  if (this->Dual)
  {
    os << indent << "Dual: Yes\n";
  }
  else
  {
    os << indent << "Dual: No\n";
  }

  if (this->Points)
  {
    os << indent << "Points:\n";
    this->Points->PrintSelf(os, indent.GetNextIndent());
  }
  else
  {
    os << indent << "Points: ( none )\n";
  }

  if (this->Cells)
  {
    os << indent << "Cells:\n";
    this->Cells->PrintSelf(os, indent.GetNextIndent());
  }
  else
  {
    os << indent << "Cells: ( none )\n";
  }

  if (this->Leaves)
  {
    os << indent << "Leaves:\n";
    this->Leaves->PrintSelf(os, indent.GetNextIndent());
  }
  else
  {
    os << indent << "Leaves: ( none )\n";
  }

  if (this->Centers)
  {
    os << indent << "Centers:\n";
    this->Centers->PrintSelf(os, indent.GetNextIndent());
  }
  else
  {
    os << indent << "Centers: ( none )\n";
  }

  if (this->Cutter)
  {
    os << indent << "Cutter:\n";
    this->Cutter->PrintSelf(os, indent.GetNextIndent());
  }
  else
  {
    os << indent << "Cutter: ( none )\n";
  }
}

//------------------------------------------------------------------------------
int vtkHyperTreeGridPlaneCutter::FillOutputPortInformation(int, vtkInformation* info)
{
  info->Set(vtkDataObject::DATA_TYPE_NAME(), "vtkPolyData");
  return 1;
}

//------------------------------------------------------------------------------
void vtkHyperTreeGridPlaneCutter::Reset()
{
  // Points and Cells are created in the constructor
  if (this->Points)
  {
    this->Points->Delete();
  }
  this->Points = vtkPoints::New();
  if (this->Cells)
  {
    this->Cells->Delete();
  }
  this->Cells = vtkCellArray::New();
  if (this->Centers)
  {
    this->Centers->Initialize();
  }
  if (this->Leaves)
  {
    this->Leaves->Initialize();
  }
  if (this->Cutter)
  {
    this->Cutter->SetNumberOfContours(0);
  }
  if (this->SelectedCells)
  {
    this->SelectedCells->Initialize();
  }
}

//------------------------------------------------------------------------------
int vtkHyperTreeGridPlaneCutter::ProcessTrees(vtkHyperTreeGrid* input, vtkDataObject* outputDO)
{
  vtkPolyData* output = vtkPolyData::SafeDownCast(outputDO);
  if (!output)
  {
    vtkErrorMacro("Incorrect type of output: " << outputDO->GetClassName());
    return 0;
  }

  // This filter works only with 3D grids
  if (input->GetDimension() != 3)
  {
    vtkErrorMacro(<< "Bad input dimension:" << input->GetDimension());
    return 0;
  }

  // Reset Data
  this->Reset();
  output->Initialize();

  // Retrieve input point data
  this->InData = input->GetCellData();

  // Retrieve material mask
  this->InMask = input->HasMask() ? input->GetMask() : nullptr;

  // Compute cut on dual or primal input depending on specification
  if (this->Dual)
  {
    // Initialize output point data
    this->OutData = output->GetPointData();
    this->OutData->CopyAllocate(this->InData);

    // Storage for leaf indices
    if (this->Leaves == nullptr)
    {
      this->Leaves = vtkIdList::New();
    }
    this->Leaves->SetNumberOfIds(8);

    // Initialize storage for dual geometry
    if (this->Centers == nullptr)
    {
      this->Centers = vtkPoints::New();
    }
    this->Centers->SetNumberOfPoints(8);

    // Convert plane parameters into normal/origin specification
    unsigned int maxId = 0;
    if (fabs(this->Plane[1]) > fabs(this->Plane[0]))
    {
      maxId = 1;
    }
    if (fabs(this->Plane[2]) > fabs(this->Plane[maxId]))
    {
      maxId = 2;
    }
    double origin[] = { 0., 0., 0. };
    origin[maxId] = this->Plane[3] / this->Plane[maxId];
    vtkPlane* plane = vtkPlane::New();
    plane->SetOrigin(origin);
    plane->SetNormal(this->Plane[0], this->Plane[1], this->Plane[2]);

    // Initialize plane cutter
    if (this->Cutter == nullptr)
    {
      this->Cutter = vtkCutter::New();
    }
    this->Cutter->GenerateTrianglesOff();
    this->Cutter->SetCutFunction(plane);

    // Clean up
    plane->Delete();

    // Create storage to keep track of selected cells
    if (this->SelectedCells == nullptr)
    {
      this->SelectedCells = vtkBitArray::New();
    }
    vtkIdType numCells = input->GetNumberOfCells();
    this->SelectedCells->SetNumberOfTuples(numCells);
    for (vtkIdType i = 0; i < numCells; ++i)
    {
      // Initialization is needed because not all cells are pre-processed
      this->SelectedCells->SetValue(i, 0);
    }

    // First pass across tree roots to evince cells intersected by contours
    vtkIdType index;
    vtkHyperTreeGrid::vtkHyperTreeGridIterator it;
    input->InitializeTreeIterator(it);
    vtkNew<vtkHyperTreeGridNonOrientedGeometryCursor> cursor;
    while (it.GetNextTree(index))
    {
      // Initialize new geometric cursor at root of current input tree
      input->InitializeNonOrientedGeometryCursor(cursor, index);
      // Pre-process tree recursively
      this->RecursivelyPreProcessTree(cursor);
    } // it

    // Second pass across tree roots: now compute isocontours recursively
    input->InitializeTreeIterator(it);
    vtkNew<vtkHyperTreeGridNonOrientedMooreSuperCursor> supercursor;
    while (it.GetNextTree(index))
    {
      // Initialize new Moore cursor at root of current tree
      input->InitializeNonOrientedMooreSuperCursor(supercursor, index);
      // Generate leaf cell centers recursively
      this->RecursivelyProcessTreeDual(supercursor);
    } // it

    // Clean up
    this->SelectedCells->Delete();
    this->SelectedCells = nullptr;
  } // if ( this->Dual )
  else
  {
    // Initialize output cell data
    this->OutData = output->GetCellData();
    this->OutData->CopyAllocate(this->InData);

    // Iterate over all hyper trees
    vtkIdType index;
    vtkHyperTreeGrid::vtkHyperTreeGridIterator it;
    input->InitializeTreeIterator(it);
    vtkNew<vtkHyperTreeGridNonOrientedGeometryCursor> cursor;
    while (it.GetNextTree(index))
    {
      // Initialize new geometric cursor at root of current tree
      input->InitializeNonOrientedGeometryCursor(cursor, index);
      // Generate leaf cell centers recursively
      this->RecursivelyProcessTreePrimal(cursor);
    } // it
  }   // else

  // Set output geometry and topology
  output->SetPoints(this->Points);
  this->Points->FastDelete();
  this->Points = nullptr;
  output->SetPolys(this->Cells);
  this->Cells->FastDelete();
  this->Cells = nullptr;

  // Clean and squeeze output
  vtkCleanPolyData* cleaner = vtkCleanPolyData::New();
  cleaner->ConvertPolysToLinesOff();
  cleaner->SetInputData(output);
  cleaner->Update();
  output->ShallowCopy(cleaner->GetOutput());
  output->Squeeze();
  cleaner->Delete();
  return 1;
}

//------------------------------------------------------------------------------
void vtkHyperTreeGridPlaneCutter::RecursivelyProcessTreePrimal(
  vtkHyperTreeGridNonOrientedGeometryCursor* cursor)
{
  // If cursor is at a masked cell stop recursion
  vtkIdType inId = cursor->GetGlobalNodeIndex();
  if (this->InMask && this->InMask->GetValue(inId))
  {
    return;
  }

  // Retrieve cursor geometry
  double* origin = cursor->GetOrigin();
  double* size = cursor->GetSize();

  // Initialize cell coordinates
  double cellCoords[8][3];
  for (int i = 0; i < 8; ++i)
  {
    cellCoords[i][0] = (i & 1) ? origin[0] + size[0] : origin[0];
    // Checking if the plane is equal to the boundary of a cell.
    // If it is, we need to shift it a tiny bit.
    // Check is done on all axis.
    // NOTE: we set cellCoords to std::sqrt(VTK_DBL_MIN) if the plane passes by the origin
    // because distance computation, needed later, requires squaring those values.
    // Since VTK_DBL_MIN is the smallest normal double value, VTK_DBL_MIN*VTK_DBL_MIN == 0,
    // and sqrt(VTK_DBL_MIN)*std::sqrt(VTK_DBL_MIN) == VTK_DBL_MIN, which is what we want
    if (this->IsPlaneOrthogonalToXAxis())
    {
      if (cellCoords[i][0] == this->Plane[3])
      {
        cellCoords[i][0] += std::abs(cellCoords[i][0]) > std::sqrt(VTK_DBL_MIN)
          ? VTK_DBL_EPSILON * std::abs(cellCoords[i][0])
          : std::sqrt(VTK_DBL_MIN);
      }
    }
    cellCoords[i][1] = (i & 2) ? origin[1] + size[1] : origin[1];
    if (this->IsPlaneOrthogonalToYAxis())
    {
      if (cellCoords[i][1] == this->Plane[3])
      {
        cellCoords[i][1] += std::abs(cellCoords[i][1]) > std::sqrt(VTK_DBL_MIN)
          ? VTK_DBL_EPSILON * std::abs(cellCoords[i][1])
          : std::sqrt(VTK_DBL_MIN);
      }
    }
    cellCoords[i][2] = (i & 4) ? origin[2] + size[2] : origin[2];
    if (this->IsPlaneOrthogonalToZAxis())
    {
      if (cellCoords[i][2] == this->Plane[3])
      {
        cellCoords[i][2] += std::abs(cellCoords[i][2]) > std::sqrt(VTK_DBL_MIN)
          ? VTK_DBL_EPSILON * std::abs(cellCoords[i][2])
          : std::sqrt(VTK_DBL_MIN);
      }
    }
  }

  const double SQRT_DBL_EPSILON = std::sqrt(VTK_DBL_EPSILON);

  // Check cell-plane intersection
  double functEval[8];
  if (this->CheckIntersection(cellCoords, functEval))
  {
    // Create plane cut if cursor is at leaf
    if (cursor->IsLeaf())
    {
      // Keep track of the number of intersection points
      int n = 0;

      // Storage for intersection points
      double points[8][3];

      // Iterate over cell vertices
      for (int i = 0; i < 8; ++i)
      {
        // Check all cell edges
        if (std::abs(functEval[i]) < SQRT_DBL_EPSILON)
        {
          // If current vertex is intersected then save it
          memcpy(points[n], cellCoords[i], 3 * sizeof(double));
          ++n;
        }
        else
        {
          // Check every edge of the current vertex.
          if (!(i & 1) && functEval[i] * functEval[i + 1] < 0)
          {
            // Edge in X
            this->PlaneCut(i, i + 1, cellCoords, n, points);
          }
          if (!(i & 2) && functEval[i] * functEval[i + 2] < 0)
          {
            // Edge in Y
            this->PlaneCut(i, i + 2, cellCoords, n, points);
          }
          if (!(i & 4) && functEval[i] * functEval[i + 4] < 0)
          {
            // Edge in Z
            this->PlaneCut(i, i + 4, cellCoords, n, points);
          }
        } // else
      }   // i

      // Now reorder points if necessary
      this->ReorderCutPoints(n, points);

      // Storage for face vertex IDs
      vtkIdType ids[8];
      for (int i = 0; i < n; ++i)
      {
        // Save points and get their IDs
        ids[i] = this->Points->InsertNextPoint(points[i]);
      }

      // Insert next face
      vtkIdType outId = this->Cells->InsertNextCell(n, ids);

      // Copy face data from that of the cell from which it comes
      this->OutData->CopyData(this->InData, inId, outId);
    } // if ( cursor->IsLeaf() )
    else
    {
      // Cursor is not at leaf, recurse to all children
      int numChildren = cursor->GetNumberOfChildren();
      for (int ichild = 0; ichild < numChildren; ++ichild)
      {
        cursor->ToChild(ichild);
        // Recurse
        this->RecursivelyProcessTreePrimal(cursor);
        cursor->ToParent();
      } // ichild
    }   // else
  }     // CheckIntersection
}

//------------------------------------------------------------------------------
bool vtkHyperTreeGridPlaneCutter::RecursivelyPreProcessTree(
  vtkHyperTreeGridNonOrientedGeometryCursor* cursor)
{
  // If cursor is at a masked cell stop recursion
  vtkIdType id = cursor->GetGlobalNodeIndex();
  if (this->InMask && this->InMask->GetValue(id))
  {
    return false;
  }

  // A node is not selected until proven otherwise
  bool selected = false;

  // Retrieve cursor geometry
  double* origin = cursor->GetOrigin();
  double* size = cursor->GetSize();

  // Initialize cell coordinates
  double cellCoords[8][3];
  for (int i = 0; i < 8; ++i)
  {
    cellCoords[i][0] = (i & 1) ? origin[0] + size[0] : origin[0];
    cellCoords[i][1] = (i & 2) ? origin[1] + size[1] : origin[1];
    cellCoords[i][2] = (i & 4) ? origin[2] + size[2] : origin[2];
  }

  // Check cell-plane intersection
  if (this->CheckIntersection(cellCoords))
  {
    // Selected this node
    if (cursor->IsLeaf())
    {
      selected = true;
    } // if ( cursor->IsLeaf() )
    else
    {
      // Cursor is not at leaf, recurse to all children
      int numChildren = cursor->GetNumberOfChildren();
      for (int ichild = 0; ichild < numChildren; ++ichild)
      {
        cursor->ToChild(ichild);
        // Recurse and keep track of whether this branch is selected
        selected |= this->RecursivelyPreProcessTree(cursor);
        cursor->ToParent();
      } // ichild
    }   // else
  }     // if ( this->CheckIntersection )

  // Update list of selected cells
  this->SelectedCells->SetTuple1(id, selected);

  // Return whether current node was selected
  return selected;
}

//------------------------------------------------------------------------------
void vtkHyperTreeGridPlaneCutter::RecursivelyProcessTreeDual(
  vtkHyperTreeGridNonOrientedMooreSuperCursor* cursor)
{
  // If cursor is at a masked cell stop recursion
  vtkIdType id = cursor->GetGlobalNodeIndex();
  if (this->InMask && this->InMask->GetValue(id))
  {
    return;
  }

  // Descend further into input trees only if cursor is not a leaf
  if (!cursor->IsLeaf())
  {
    // Check if cursor is at selected cell
    if (!this->SelectedCells->GetTuple1(id))
    {
      // Cell is not selected until proven otherwise
      bool selected = false;

      // Iterate over all cursors of Von Neumann neighborhood around center
      for (unsigned int neighbor = 0; neighbor < 26 && !selected; ++neighbor)
      {
        // Retrieve global index of neighbor
        unsigned int indN = MooreCursors3D[neighbor];
        if (cursor->HasTree(indN))
        {
          vtkIdType idN = cursor->GetGlobalNodeIndex(indN);

          // Decide whether neighbor was selected
          selected = (this->SelectedCells->GetTuple1(idN) != 0.0);
        }
        else
        {
          selected = false;
        }
      } // neighbor

      // No dual cell with a corner at cursor center will be intersected
      if (!selected)
      {
        return;
      }
    } // if ( this->SelectedCells->GetTuple1( id ) )

    // Recurse to all children
    int numChildren = cursor->GetNumberOfChildren();
    for (int ichild = 0; ichild < numChildren; ++ichild)
    {
      cursor->ToChild(ichild);
      // Recurse
      this->RecursivelyProcessTreeDual(cursor);
      cursor->ToParent();
    } // ichild
  }   // if ( ! cursor->IsLeaf() )
  else
  {
    // Cursor is at leaf, iterate over its corners
    for (unsigned int cornerIdx = 0; cornerIdx < 8; ++cornerIdx)
    {
      // Cell is not selected until proven otherwise
      bool owner = true;

      // Iterate over every leaf touching the corner and check ownership
      for (unsigned int leafIdx = 0; leafIdx < 8 && owner; ++leafIdx)
      {
        owner = cursor->GetCornerCursors(cornerIdx, leafIdx, this->Leaves);
      } // leafIdx

      // If cell owns dual cell, compute intersection thereof
      if (owner)
      {
        // Create dual cell to be intersected as unstructured grid
        vtkUnstructuredGrid* dual = vtkUnstructuredGrid::New();
        dual->Allocate(1, 1);
        dual->InsertNextCell(VTK_VOXEL, 8, First8Integers);
        dual->GetPointData()->CopyAllocate(this->InData);

        // Iterate over cell corners
        double x[3];
        for (int _cornerIdx = 0; _cornerIdx < 8; ++_cornerIdx)
        {
          // Get cursor corresponding to this corner
          vtkIdType cursorId = this->Leaves->GetId(_cornerIdx);

          // Retrieve neighbor coordinates and store them
          cursor->GetPoint(cursorId, x);
          this->Centers->SetPoint(_cornerIdx, x);

          // Retrieve neighbor index and corresponding input scalar value
          vtkIdType idN = cursor->GetGlobalNodeIndex(cursorId);

          // Assign scalar value attached to this cell corner
          dual->GetPointData()->CopyData(this->InData, idN, _cornerIdx);
        } // _cornerIdx

        // Assign geometry of dual cell
        dual->SetPoints(this->Centers);

        // Compute intersection with plane
        this->Cutter->SetInputData(dual);
        this->Cutter->Update();

        // Append computed polygons if some are present in cutter output
        vtkPolyData* pd = this->Cutter->GetOutput();
        vtkIdType nPoints = pd->GetNumberOfPoints();
        if (nPoints)
        {
          // Keep handle to cut point data
          vtkPointData* pdata = pd->GetPointData();

          // Append new points to existing cut points
          vtkIdType offset = this->Points->GetNumberOfPoints();
          double pt[3];
          for (vtkIdType i = 0; i < nPoints; ++i)
          {
            // Retrieve cut point coordinates and insert them into output points
            pd->GetPoint(i, pt);
            this->Points->InsertNextPoint(pt);

            // Copy cut point data to that of corresponding output point
            this->OutData->CopyData(pdata, i, i + offset);
          } // i

          // Append new elements to existing cut element
          vtkIdType ids[8];
          vtkIdType nCells = pd->GetNumberOfCells();
          for (int i = 0; i < nCells; ++i)
          {
            // Retrieve element vertex ids
            vtkIdList* vertices = pd->GetCell(i)->GetPointIds();

            // Appropriately offset vertex ids
            vtkIdType n = vertices->GetNumberOfIds();
            for (int j = 0; j < n; ++j)
            {
              ids[j] = vertices->GetId(j) + offset;
            } // j

            // Insert next cell with offset ids
            this->Cells->InsertNextCell(n, ids);
          } // i
        }   // if ( nPoints )

        // Clean up
        dual->Delete();
      } // if ( owner )
    }   // cornerIdx
  }     // else
}

//------------------------------------------------------------------------------
bool vtkHyperTreeGridPlaneCutter::CheckIntersection(double cellCoords[8][3], double functEval[8])
{
  // Iterate over cell vertices
  int i;
  for (i = 0; i < 8; ++i)
  {
    // Evaluate the plane in every coordinate
    functEval[i] = cellCoords[i][0] * this->Plane[0] + cellCoords[i][1] * this->Plane[1] +
      cellCoords[i][2] * this->Plane[2] - this->Plane[3];
  } // i

  // Evaluate plane equation at first corner
  double firstVal = functEval[0];

  // Check if there is any sign change
  i = 7;
  while (i && functEval[i] * firstVal > 0.)
  {
    --i;
  }

  // Intersection if while statement broke early
  return (i != 0);
}

//------------------------------------------------------------------------------
bool vtkHyperTreeGridPlaneCutter::CheckIntersection(double cellCoords[8][3])
{
  // Evaluate plane equation at first corner
  double firstVal = cellCoords[0][0] * this->Plane[0] + cellCoords[0][1] * this->Plane[1] +
    cellCoords[0][2] * this->Plane[2] - this->Plane[3];

  // Check if there is any sign change
  int i = 1;
  bool sameSign = true;
  while (i < 8 && sameSign)
  {
    double functEval = cellCoords[i][0] * this->Plane[0] + cellCoords[i][1] * this->Plane[1] +
      cellCoords[i][2] * this->Plane[2] - this->Plane[3];
    sameSign = (firstVal * functEval > 0);
    ++i;
  }

  return !sameSign;
}

//------------------------------------------------------------------------------
void vtkHyperTreeGridPlaneCutter::SetPlane(double a, double b, double c, double d)
{
  assert(!(a == 0 && b == 0 && c == 0) && "Plane's normal equals zero");
  this->Plane[0] = a;
  this->Plane[1] = b;
  this->Plane[2] = c;
  this->Plane[3] = d;
  if (a == 0.0 && b == 0.0)
  {
    this->AxisAlignment = 2;
  }
  else if (b == 0.0 && c == 0.0)
  {
    this->AxisAlignment = 0;
  }
  else if (a == 0.0 && c == 0.0)
  {
    this->AxisAlignment = 1;
  }
  else
  {
    this->AxisAlignment = -1;
  }
  this->Modified();
}

//------------------------------------------------------------------------------
void vtkHyperTreeGridPlaneCutter::PlaneCut(
  int i, int j, double cellCoords[8][3], int& n, double point[][3])
{
  // The distance between vertex indices gives us the axis direction
  if (j - i == 1)
  {
    // X direction
    point[n][0] =
      (this->Plane[3] - this->Plane[1] * cellCoords[i][1] - this->Plane[2] * cellCoords[i][2]) /
      this->Plane[0];
    point[n][1] = cellCoords[i][1];
    point[n][2] = cellCoords[i][2];
  } // if ( j - i == 1 )
  else if (j - i == 2)
  {
    // Y direction
    point[n][0] = cellCoords[i][0];
    point[n][1] =
      (this->Plane[3] - this->Plane[0] * cellCoords[i][0] - this->Plane[2] * cellCoords[i][2]) /
      this->Plane[1];
    point[n][2] = cellCoords[i][2];
  }    // else if ( j - i == 2 )
  else // if ( j - i == 4 )
  {
    // Z direction
    point[n][0] = cellCoords[i][0];
    point[n][1] = cellCoords[i][1];
    point[n][2] =
      (this->Plane[3] - this->Plane[0] * cellCoords[i][0] - this->Plane[1] * cellCoords[i][1]) /
      this->Plane[2];
  } // else if ( j - i == 4 )

  // Move to next point
  ++n;
}

//------------------------------------------------------------------------------
void vtkHyperTreeGridPlaneCutter::ReorderCutPoints(int n, double points[][3])
{
  // Iterate over all polygonal vertices but the last one
  for (int i = 0; i < n - 2; ++i)
  {
    // Search the closest point to i in the sense of sharing the most coordinates
    int index = i + 1; // in practice a don't care, set to satisfy -Wuninitialized
    int minDistance = 4;
    for (int j = i + 1; j < n; ++j)
    {
      // Compute the distance: number of different coordinates
      int distance = 0;
      if (points[j][0] != points[i][0])
      {
        ++distance;
      }
      if (points[j][1] != points[i][1])
      {
        ++distance;
      }
      if (points[j][2] != points[i][2])
      {
        ++distance;
      }
      if (distance < minDistance)
      {
        // Store the index of current point and update minDistance
        index = j;
        minDistance = distance;
      }
    }
    if (index != i + 1)
    {
      // If the closest point is not i + 1, then swap point positions
      double swap[3];
      memcpy(swap, points[index], 3 * sizeof(double));
      memcpy(points[index], points[i + 1], 3 * sizeof(double));
      memcpy(points[i + 1], swap, 3 * sizeof(double));
    }
  }
}
