ClientData

#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkSmartPointer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkPolyData.h>
#include <vtkSphereSource.h>
#include <vtkCallbackCommand.h>
#include <vtkCommand.h>

static void KeypressCallbackFunction ( vtkObject* caller, long unsigned int eventId,
          void* clientData, void* callData );

int main(int, char *[])
{
  // Create a sphere
  vtkSmartPointer<vtkSphereSource> sphereSource =
      vtkSmartPointer<vtkSphereSource>::New();
  sphereSource->SetCenter(0.0, 0.0, 0.0);
  sphereSource->SetRadius(5.0);
  sphereSource->Update();

  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputConnection(sphereSource->GetOutputPort());

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

  // 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);

  vtkSmartPointer<vtkCallbackCommand> keypressCallback =
    vtkSmartPointer<vtkCallbackCommand>::New();

  // Allow the observer to access the sphereSource
  keypressCallback->SetClientData(sphereSource);
  keypressCallback->SetCallback(KeypressCallbackFunction );
  renderWindowInteractor->AddObserver(vtkCommand::KeyPressEvent, keypressCallback);

  renderer->AddActor(actor);
  renderer->SetBackground(1,1,1); // Background color white
  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

void KeypressCallbackFunction(vtkObject*, long unsigned int vtkNotUsed(eventId), void* clientData, void* vtkNotUsed(callData) )
{
  // Prove that we can access the sphere source
  vtkSphereSource* sphereSource =
    static_cast<vtkSphereSource*>(clientData);
  std::cout << "Radius is " << sphereSource->GetRadius() << std::endl;
}

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ClientData)

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

cd ClientData/build

cmake ..

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

make

./ClientData