CellPicking

Description¶

This example demonstrates how to get the coordinates of the point on an actor that is clicked with the left mouse button. It also indicates which cell the selected point belongs to by highlighting the edges of that cell.

Question

If you have a question about this example, please use the VTK Discourse Forum

Code¶

CellPicking.cxx

#include <vtkActor.h>
#include <vtkCellArray.h>
#include <vtkCellPicker.h>
#include <vtkCommand.h>
#include <vtkDataSetMapper.h>
#include <vtkExtractSelection.h>
#include <vtkIdTypeArray.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkObjectFactory.h>
#include <vtkPlaneSource.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkRendererCollection.h>
#include <vtkSelection.h>
#include <vtkSelectionNode.h>
#include <vtkSmartPointer.h>
#include <vtkTriangleFilter.h>
#include <vtkUnstructuredGrid.h>

namespace {

// Catch mouse events
class MouseInteractorStyle : public vtkInteractorStyleTrackballCamera
{
public:
  static MouseInteractorStyle* New();

  MouseInteractorStyle()
  {
    selectedMapper = vtkSmartPointer<vtkDataSetMapper>::New();
    selectedActor = vtkSmartPointer<vtkActor>::New();
  }

  virtual void OnLeftButtonDown() override
  {
    vtkNew<vtkNamedColors> colors;

    // Get the location of the click (in window coordinates)
    int* pos = this->GetInteractor()->GetEventPosition();

    vtkNew<vtkCellPicker> picker;
    picker->SetTolerance(0.0005);

    // Pick from this location.
    picker->Pick(pos[0], pos[1], 0, this->GetDefaultRenderer());

    double* worldPosition = picker->GetPickPosition();
    std::cout << "Cell id is: " << picker->GetCellId() << std::endl;

    if (picker->GetCellId() != -1)
    {

      std::cout << "Pick position is: " << worldPosition[0] << " "
                << worldPosition[1] << " " << worldPosition[2] << endl;

      vtkNew<vtkIdTypeArray> ids;
      ids->SetNumberOfComponents(1);
      ids->InsertNextValue(picker->GetCellId());

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

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

      vtkNew<vtkExtractSelection> extractSelection;
      extractSelection->SetInputData(0, this->Data);
      extractSelection->SetInputData(1, selection);
      extractSelection->Update();

      // In selection
      vtkNew<vtkUnstructuredGrid> selected;
      selected->ShallowCopy(extractSelection->GetOutput());

      std::cout << "There are " << selected->GetNumberOfPoints()
                << " points in the selection." << std::endl;
      std::cout << "There are " << selected->GetNumberOfCells()
                << " cells in the selection." << std::endl;
      selectedMapper->SetInputData(selected);
      selectedActor->SetMapper(selectedMapper);
      selectedActor->GetProperty()->EdgeVisibilityOn();
      selectedActor->GetProperty()->SetColor(
          colors->GetColor3d("Red").GetData());

      selectedActor->GetProperty()->SetLineWidth(3);

      this->Interactor->GetRenderWindow()
          ->GetRenderers()
          ->GetFirstRenderer()
          ->AddActor(selectedActor);
    }
    // Forward events
    vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
  }

  vtkSmartPointer<vtkPolyData> Data;
  vtkSmartPointer<vtkDataSetMapper> selectedMapper;
  vtkSmartPointer<vtkActor> selectedActor;
};

vtkStandardNewMacro(MouseInteractorStyle);

} // namespace

int main(int, char*[])
{
  vtkNew<vtkNamedColors> colors;

  vtkNew<vtkPlaneSource> planeSource;
  planeSource->Update();

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

  vtkNew<vtkPolyDataMapper> mapper;
  mapper->SetInputConnection(triangleFilter->GetOutputPort());

  vtkNew<vtkActor> actor;
  actor->GetProperty()->SetColor(colors->GetColor3d("Green").GetData());
  actor->SetMapper(mapper);

  vtkNew<vtkRenderer> renderer;
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(renderer);
  renderWindow->SetWindowName("CellPicking");

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

  // Set the custom stype to use for interaction.
  vtkNew<MouseInteractorStyle> style;
  style->SetDefaultRenderer(renderer);
  style->Data = triangleFilter->GetOutput();

  renderWindowInteractor->SetInteractorStyle(style);

  renderer->AddActor(actor);
  renderer->ResetCamera();

  renderer->SetBackground(colors->GetColor3d("Blue").GetData());

  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(CellPicking)

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

if (NOT VTK_FOUND)
  message("Skipping CellPicking: ${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(CellPicking MACOSX_BUNDLE CellPicking.cxx )
  target_link_libraries(CellPicking PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(CellPicking MACOSX_BUNDLE CellPicking.cxx )
  target_link_libraries(CellPicking PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS CellPicking
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build CellPicking¶

Click here to download CellPicking and its CMakeLists.txt file. Once the tarball CellPicking.tar has been downloaded and extracted,

cd CellPicking/build

If VTK is installed:

cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

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

Build the project:

make

and run it:

./CellPicking

WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.