CellPointNeighbors

#include <vtkActor.h>
#include <vtkCell.h>
#include <vtkDataSetMapper.h>
#include <vtkExtractSelection.h>
#include <vtkIdList.h>
#include <vtkIdTypeArray.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPolyData.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSelection.h>
#include <vtkSelectionNode.h>
#include <vtkSphereSource.h>
#include <vtkTriangleFilter.h>

#include <list>

int main(int, char*[])
{
  // Create a sphere
  vtkNew<vtkSphereSource> sphereSource;
  sphereSource->Update();

  vtkNew<vtkTriangleFilter> triangleFilter;
  triangleFilter->SetInputConnection(sphereSource->GetOutputPort());
  triangleFilter->Update();

  // Find all cells connected to point 0
  vtkIdType cellId = 0;

  vtkNew<vtkIdList> cellPointIds;
  triangleFilter->GetOutput()->GetCellPoints(cellId, cellPointIds);

  // neighbor cells may be listed multiple times
  // use std::set instead of std::list if you want a unique list of neighbors
  std::list<vtkIdType> neighbors;

  /* For each vertex of the cell, we calculate which cells use that point.
   So if we do this for each vertex, we have all the neighbors.
   In the case of using "cellPointIds" as a parameter of "GetCellNeighbors",
   we will obtain an empty set. This is because the only cell that is using that
   set of points is the current one. That is why we have to make each vertice at
   time.*/

  for (vtkIdType i = 0; i < cellPointIds->GetNumberOfIds(); i++)
  {
    vtkNew<vtkIdList> idList;
    idList->InsertNextId(cellPointIds->GetId(i));

    // get the neighbors of the cell
    vtkNew<vtkIdList> neighborCellIds;

    triangleFilter->GetOutput()->GetCellNeighbors(cellId, idList,
                                                  neighborCellIds);

    for (vtkIdType j = 0; j < neighborCellIds->GetNumberOfIds(); j++)
    {
      neighbors.push_back(neighborCellIds->GetId(j));
    }
  }

  std::cout << "Point neighbor ids are: " << std::endl;

  for (auto it1 = neighbors.begin(); it1 != neighbors.end(); ++it1)
  {
    std::cout << " " << *it1;
  }
  std::cout << std::endl;

  vtkNew<vtkNamedColors> colors;

  vtkNew<vtkDataSetMapper> sphereMapper;
  sphereMapper->SetInputConnection(sphereSource->GetOutputPort());
  sphereMapper->SetResolveCoincidentTopologyToPolygonOffset();

  vtkNew<vtkActor> sphereActor;
  sphereActor->SetMapper(sphereMapper);
  sphereActor->GetProperty()->SetEdgeColor(
      colors->GetColor3d("Lamp_Black").GetData());
  sphereActor->GetProperty()->EdgeVisibilityOn();
  sphereActor->GetProperty()->SetLineWidth(3);

  vtkNew<vtkDataSetMapper> mainCellMapper;

  vtkNew<vtkDataSetMapper> neighborCellsMapper;

  // Create a dataset with the cell of interest
  {
    vtkNew<vtkIdTypeArray> ids;
    ids->SetNumberOfComponents(1);
    ids->InsertNextValue(cellId);

    vtkNew<vtkSelectionNode> selectionNode;
    selectionNode->SetFieldType(vtkSelectionNode::CELL);
    selectionNode->SetContentType(vtkSelectionNode::INDICES);
    selectionNode->SetSelectionList(ids);

    vtkNew<vtkSelection> selection;
    selection->AddNode(selectionNode);

    vtkNew<vtkExtractSelection> extractSelection;
    extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    extractSelection->SetInputData(1, selection);
    extractSelection->Update();

    mainCellMapper->SetInputConnection(extractSelection->GetOutputPort());
  }

  vtkNew<vtkActor> mainCellActor;
  mainCellActor->SetMapper(mainCellMapper);
  mainCellActor->GetProperty()->SetColor(
      colors->GetColor3d("Tomato").GetData());

  // Create a dataset with the neighbor cells
  {
    vtkNew<vtkIdTypeArray> ids;
    ids->SetNumberOfComponents(1);
    for (auto it1 = neighbors.begin(); it1 != neighbors.end(); ++it1)
    {
      ids->InsertNextValue(*it1);
    }

    vtkNew<vtkSelectionNode> selectionNode;
    selectionNode->SetFieldType(vtkSelectionNode::CELL);
    selectionNode->SetContentType(vtkSelectionNode::INDICES);
    selectionNode->SetSelectionList(ids);

    vtkNew<vtkSelection> selection;
    selection->AddNode(selectionNode);

    vtkNew<vtkExtractSelection> extractSelection;
    extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    extractSelection->SetInputData(1, selection);
    extractSelection->Update();

    neighborCellsMapper->SetInputConnection(extractSelection->GetOutputPort());
  }

  vtkNew<vtkActor> neighborCellsActor;
  neighborCellsActor->SetMapper(neighborCellsMapper);
  neighborCellsActor->GetProperty()->SetColor(
      colors->GetColor3d("Mint").GetData());

  // Create a renderer, render window, and interactor
  vtkNew<vtkRenderer> renderer;
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(renderer);
  renderWindow->SetWindowName("CellPointNeighbors");

  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  renderWindowInteractor->SetRenderWindow(renderWindow);

  // Add the actors to the scene
  renderer->AddActor(sphereActor);
  renderer->AddActor(mainCellActor);
  renderer->AddActor(neighborCellsActor);
  renderer->SetBackground(colors->GetColor3d("SlateGray").GetData());

  // Render and interact
  renderWindow->SetSize(640, 480);
  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(CellPointNeighbors)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonCore
  vtkCommonDataModel
  vtkFiltersCore
  vtkFiltersExtraction
  vtkFiltersSources
  vtkInteractionStyle
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  vtkRenderingOpenGL2
  QUIET
)

if (NOT VTK_FOUND)
  message("Skipping CellPointNeighbors: ${VTK_NOT_FOUND_MESSAGE}")
  return()
endif()
message (STATUS "VTK_VERSION: ${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
  # old system
  include(${VTK_USE_FILE})
  add_executable(CellPointNeighbors MACOSX_BUNDLE CellPointNeighbors.cxx )
  target_link_libraries(CellPointNeighbors PRIVATE ${VTK_LIBRARIES})
else()
  # Prevent a "command line is too long" failure in Windows.
  set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
  add_executable(CellPointNeighbors MACOSX_BUNDLE CellPointNeighbors.cxx )
  target_link_libraries(CellPointNeighbors PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS CellPointNeighbors
    MODULES ${VTK_LIBRARIES}
    )
endif()

cd CellPointNeighbors/build

cmake ..

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

make

./CellPointNeighbors