CellPointNeighbors

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

#include <list>

int main(int, char*[])
{
  // Create a sphere
  auto sphereSource = vtkSmartPointer<vtkSphereSource>::New();
  sphereSource->Update();

  auto triangleFilter = vtkSmartPointer<vtkTriangleFilter>::New();
  triangleFilter->SetInputConnection(sphereSource->GetOutputPort());
  triangleFilter->Update();

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

  auto cellPointIds = vtkSmartPointer<vtkIdList>::New();
  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++)
  {
    auto idList = vtkSmartPointer<vtkIdList>::New();
    idList->InsertNextId(cellPointIds->GetId(i));

    // get the neighbors of the cell
    auto neighborCellIds = vtkSmartPointer<vtkIdList>::New();

    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;

  auto colors = vtkSmartPointer<vtkNamedColors>::New();

  auto sphereMapper = vtkSmartPointer<vtkDataSetMapper>::New();
  sphereMapper->SetInputConnection(sphereSource->GetOutputPort());
  sphereMapper->SetResolveCoincidentTopologyToPolygonOffset();

  auto sphereActor = vtkSmartPointer<vtkActor>::New();
  sphereActor->SetMapper(sphereMapper);
  sphereActor->GetProperty()->SetEdgeColor(
      colors->GetColor3d("Lamp_Black").GetData());
  sphereActor->GetProperty()->EdgeVisibilityOn();
  sphereActor->GetProperty()->SetLineWidth(3);

  auto mainCellMapper = vtkSmartPointer<vtkDataSetMapper>::New();

  auto neighborCellsMapper = vtkSmartPointer<vtkDataSetMapper>::New();

  // Create a dataset with the cell of interest
  {
    auto ids = vtkSmartPointer<vtkIdTypeArray>::New();
    ids->SetNumberOfComponents(1);
    ids->InsertNextValue(cellId);

    auto selectionNode = vtkSmartPointer<vtkSelectionNode>::New();
    selectionNode->SetFieldType(vtkSelectionNode::CELL);
    selectionNode->SetContentType(vtkSelectionNode::INDICES);
    selectionNode->SetSelectionList(ids);

    auto selection = vtkSmartPointer<vtkSelection>::New();
    selection->AddNode(selectionNode);

    auto extractSelection = vtkSmartPointer<vtkExtractSelection>::New();
    extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    extractSelection->SetInputData(1, selection);
    extractSelection->Update();

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

  auto mainCellActor = vtkSmartPointer<vtkActor>::New();
  mainCellActor->SetMapper(mainCellMapper);
  mainCellActor->GetProperty()->SetColor(
      colors->GetColor3d("Tomato").GetData());

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

    auto selectionNode = vtkSmartPointer<vtkSelectionNode>::New();
    selectionNode->SetFieldType(vtkSelectionNode::CELL);
    selectionNode->SetContentType(vtkSelectionNode::INDICES);
    selectionNode->SetSelectionList(ids);

    auto selection = vtkSmartPointer<vtkSelection>::New();
    selection->AddNode(selectionNode);

    auto extractSelection = vtkSmartPointer<vtkExtractSelection>::New();
    extractSelection->SetInputConnection(0, sphereSource->GetOutputPort());
    extractSelection->SetInputData(1, selection);
    extractSelection->Update();

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

  auto neighborCellsActor = vtkSmartPointer<vtkActor>::New();
  neighborCellsActor->SetMapper(neighborCellsMapper);
  neighborCellsActor->GetProperty()->SetColor(
      colors->GetColor3d("Mint").GetData());

  // Create a renderer, render window, and interactor
  auto renderer = vtkSmartPointer<vtkRenderer>::New();
  auto renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);
  auto renderWindowInteractor =
      vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);

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

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

  return EXIT_SUCCESS;
}

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(CellPointNeighbors)

find_package(VTK COMPONENTS 
  vtkvtkCommonColor
  vtkvtkCommonCore
  vtkvtkCommonDataModel
  vtkvtkFiltersCore
  vtkvtkFiltersExtraction
  vtkvtkFiltersSources
  vtkvtkInteractionStyle
  vtkvtkRenderingContextOpenGL2
  vtkvtkRenderingCore
  vtkvtkRenderingFreeType
  vtkvtkRenderingGL2PSOpenGL2
  vtkvtkRenderingOpenGL2 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 ()
  # include all components
  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