# SelectedVerticesAndEdgesObserver

VTKExamples/Cxx/Graphs/SelectedVerticesAndEdgesObserver

### Description

- Thanks to Eric Monson

### Code

SelectedVerticesAndEdgesObserver.cxx

    #include <vtkSmartPointer.h>
    #include <vtkCallbackCommand.h>
    #include <vtkAnnotationLink.h>
    #include <vtkRenderedGraphRepresentation.h>
    #include <vtkRenderer.h>
    #include <vtkDoubleArray.h>
    #include <vtkSelectionNode.h>
    #include <vtkIdTypeArray.h>
    #include <vtkSelection.h>
    #include <vtkRenderWindow.h>
    #include <vtkUnsignedCharArray.h>
    #include <vtkObjectFactory.h>
    #include <vtkGraphLayoutStrategy.h>
    #include <vtkGraphLayoutView.h>
    #include <vtkGraphWriter.h>
    #include <vtkMutableUndirectedGraph.h>
    #include <vtkRenderWindowInteractor.h>

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

    int main(int, char *[])
    {
      vtkSmartPointer<vtkMutableUndirectedGraph> g =
        vtkSmartPointer<vtkMutableUndirectedGraph>::New();

      vtkIdType v1 = g->AddVertex();
      vtkIdType v2 = g->AddVertex();

      g->AddEdge(v1, v2);
      g->AddEdge(v1, v2);

      vtkSmartPointer<vtkCallbackCommand> selectionCallback =
        vtkSmartPointer<vtkCallbackCommand>::New();
      selectionCallback->SetCallback (SelectionCallbackFunction);

      vtkSmartPointer<vtkGraphLayoutView> view =
        vtkSmartPointer<vtkGraphLayoutView>::New();
      view->AddRepresentationFromInput(g);
      view->SetLayoutStrategy("Simple 2D");
      view->GetRepresentation()->GetAnnotationLink()->AddObserver("AnnotationChangedEvent", selectionCallback);

      view->ResetCamera();
      view->Render();

      view->GetInteractor()->Start();

      return EXIT_SUCCESS;
    }

    void SelectionCallbackFunction(vtkObject* caller, long unsigned int eventId, void* clientData, void* callData)
    {

      vtkAnnotationLink* annotationLink =
        static_cast<vtkAnnotationLink*>(caller);

      vtkSelection* selection = annotationLink->GetCurrentSelection();
      vtkSelectionNode* vertices;
      vtkSelectionNode* edges;
      if(selection->GetNode(0)->GetFieldType() == vtkSelectionNode::VERTEX)
      {
        vertices = selection->GetNode(0);
      }
      else if(selection->GetNode(0)->GetFieldType() == vtkSelectionNode::EDGE)
      {
        edges = selection->GetNode(0);
      }

      if(selection->GetNode(1)->GetFieldType() == vtkSelectionNode::VERTEX)
      {
        vertices = selection->GetNode(1);
      }
      else if(selection->GetNode(1)->GetFieldType() == vtkSelectionNode::EDGE)
      {
        edges = selection->GetNode(1);
      }

      vtkIdTypeArray* vertexList = vtkIdTypeArray::SafeDownCast(vertices->GetSelectionList());
      std::cout << "There are " << vertexList->GetNumberOfTuples() << " vertices selected." << std::endl;

      if(vertexList->GetNumberOfTuples() > 0)
      {
        std::cout << "Vertex Ids: ";
      }
      for(vtkIdType i = 0; i < vertexList->GetNumberOfTuples(); i++)
      {
        std::cout << vertexList->GetValue(i) << " ";
      }

      std::cout << std::endl;
      vtkIdTypeArray* edgeList = vtkIdTypeArray::SafeDownCast(edges->GetSelectionList());
      std::cout << "There are " << edgeList->GetNumberOfTuples() << " edges selected." << std::endl;
      if(edgeList->GetNumberOfTuples() > 0)
      {
        std::cout << "Edge Ids: ";
      }

      for(vtkIdType i = 0; i < edgeList->GetNumberOfTuples(); i++)
      {
        std::cout << edgeList->GetValue(i) << " ";
      }
      std::cout << std::endl;

    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(SelectedVerticesAndEdgesObserver)

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

    add_executable(SelectedVerticesAndEdgesObserver MACOSX_BUNDLE SelectedVerticesAndEdgesObserver.cxx )

    target_link_libraries(SelectedVerticesAndEdgesObserver ${VTK_LIBRARIES})

### Download and Build SelectedVerticesAndEdgesObserver

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

    cd SelectedVerticesAndEdgesObserver/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:

    ./SelectedVerticesAndEdgesObserver

WINDOWS USERS

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