Picking

#include <vtkSmartPointer.h>
#include <vtkActor.h>
#include <vtkSphereSource.h>
#include <vtkRendererCollection.h>
#include <vtkCellArray.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkObjectFactory.h>
#include <vtkPlaneSource.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkPropPicker.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

// Handle mouse events
class MouseInteractorStyle2 : public vtkInteractorStyleTrackballCamera
{
public:
  static MouseInteractorStyle2* New();
  vtkTypeMacro(MouseInteractorStyle2, vtkInteractorStyleTrackballCamera);

  virtual void OnLeftButtonDown() override
  {
    int* clickPos = this->GetInteractor()->GetEventPosition();

    // Pick from this location.
    vtkSmartPointer<vtkPropPicker>  picker =
      vtkSmartPointer<vtkPropPicker>::New();
    picker->Pick(clickPos[0], clickPos[1], 0, this->GetDefaultRenderer());

    double* pos = picker->GetPickPosition();
    std::cout << "Pick position (world coordinates) is: "
              << pos[0] << " " << pos[1]
              << " " << pos[2] << std::endl;

    std::cout << "Picked actor: " << picker->GetActor() << std::endl;
    //Create a sphere
    vtkSmartPointer<vtkSphereSource> sphereSource =
      vtkSmartPointer<vtkSphereSource>::New();
    sphereSource->SetCenter(pos[0], pos[1], pos[2]);
    sphereSource->SetRadius(0.1);

    //Create a mapper and actor
    vtkSmartPointer<vtkPolyDataMapper> mapper =
      vtkSmartPointer<vtkPolyDataMapper>::New();
    mapper->SetInputConnection(sphereSource->GetOutputPort());

    vtkSmartPointer<vtkActor> actor =
      vtkSmartPointer<vtkActor>::New();
    actor->SetMapper(mapper);

    this->GetDefaultRenderer()->AddActor(actor);
    // Forward events
    vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
  }

private:

};

vtkStandardNewMacro(MouseInteractorStyle2);

// Execute application.
int main(int, char *[])
{
  vtkSmartPointer<vtkPlaneSource> planeSource =
    vtkSmartPointer<vtkPlaneSource>::New();
  planeSource->Update();

  // Create a polydata object
  vtkPolyData* polydata = planeSource->GetOutput();

  // Create a mapper
  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputData ( polydata );

  // Create an actor
  vtkSmartPointer<vtkActor> actor =
    vtkSmartPointer<vtkActor>::New();
  actor->SetMapper ( mapper );

  std::cout << "Actor address: " << actor << std::endl;

  // A renderer and render window
  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  vtkSmartPointer<vtkRenderWindow> renderWindow =
    vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer ( renderer );

  // An interactor
  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow ( renderWindow );

  // Set the custom stype to use for interaction.
  vtkSmartPointer<MouseInteractorStyle2> style =
    vtkSmartPointer<MouseInteractorStyle2>::New();
  style->SetDefaultRenderer(renderer);

  renderWindowInteractor->SetInteractorStyle( style );

  // Add the actors to the scene
  renderer->AddActor ( actor );
  renderer->SetBackground ( 0,0,1 );

  // Render and interact
  renderWindow->Render();
  renderWindowInteractor->Initialize();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(Picking)

find_package(VTK COMPONENTS 
  vtkvtkCommonCore
  vtkvtkCommonDataModel
  vtkvtkFiltersSources
  vtkvtkInteractionStyle
  vtkvtkRenderingContextOpenGL2
  vtkvtkRenderingCore
  vtkvtkRenderingFreeType
  vtkvtkRenderingGL2PSOpenGL2
  vtkvtkRenderingOpenGL2 QUIET)
if (NOT VTK_FOUND)
  message("Skipping Picking: ${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(Picking MACOSX_BUNDLE Picking.cxx )
  target_link_libraries(Picking PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(Picking MACOSX_BUNDLE Picking.cxx )
  target_link_libraries(Picking PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS Picking
    MODULES ${VTK_LIBRARIES}
    )
endif ()

cd Picking/build

cmake ..

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

make

./Picking