# WorldPointPicker

VTKExamples/Cxx/Interaction/WorldPointPicker

### Description

This example demonstrates how to get the position of the point in 3D that is exactly behind the mouse click. This point is not likely a point that exists in the data set - i.e. it can be a point on the interior of a cell.

### Code

WorldPointPicker.cxx

    #include <vtkSmartPointer.h>
    #include <vtkRendererCollection.h>
    #include <vtkWorldPointPicker.h>
    #include <vtkSphereSource.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkActor.h>
    #include <vtkInteractorStyleTrackballCamera.h>
    #include <vtkObjectFactory.h>

    // Define interaction style
    class MouseInteractorStyle : public vtkInteractorStyleTrackballCamera
    {
      public:
        static MouseInteractorStyle* New();
        vtkTypeMacro(MouseInteractorStyle, vtkInteractorStyleTrackballCamera);

        virtual void OnLeftButtonDown()
        {

          std::cout << "Picking pixel: " << this->Interactor->GetEventPosition()[0] << " " << this->Interactor->GetEventPosition()[1] << std::endl;
          this->Interactor->GetPicker()->Pick(this->Interactor->GetEventPosition()[0],
                             this->Interactor->GetEventPosition()[1],
                             0,  // always zero.
                             this->Interactor->GetRenderWindow()->GetRenderers()->GetFirstRenderer());
          double picked[3];
          this->Interactor->GetPicker()->GetPickPosition(picked);
          std::cout << "Picked value: " << picked[0] << " " << picked[1] << " " << picked[2] << std::endl;
          // Forward events
          vtkInteractorStyleTrackballCamera::OnLeftButtonDown();
        }

    };
    vtkStandardNewMacro(MouseInteractorStyle);

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

      vtkSmartPointer<vtkWorldPointPicker> worldPointPicker =
        vtkSmartPointer<vtkWorldPointPicker>::New();

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

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

      vtkSmartPointer<MouseInteractorStyle> style =
        vtkSmartPointer<MouseInteractorStyle>::New();
      renderWindowInteractor->SetInteractorStyle( style );

      // Add the actor to the scene
      renderer->AddActor(actor);
      renderer->SetBackground(1,1,1); // Background color white

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

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(WorldPointPicker)

    find_package(VTK REQUIRED)
    include(${VTK_USE_FILE})

    add_executable(WorldPointPicker MACOSX_BUNDLE WorldPointPicker.cxx )

    target_link_libraries(WorldPointPicker ${VTK_LIBRARIES})

### Download and Build WorldPointPicker

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

    cd WorldPointPicker/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:

    ./WorldPointPicker

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