# VisualizeDirectedGraph

VTKExamples/Cxx/Graphs/VisualizeDirectedGraph

### Code

VisualizeDirectedGraph.cxx

    #include <vtkSmartPointer.h>

    #include <vtkActor.h>
    #include <vtkGlyph3D.h>
    #include <vtkGlyphSource2D.h>
    #include <vtkGraphLayout.h>
    #include <vtkGraphLayoutView.h>
    #include <vtkGraphToPolyData.h>
    #include <vtkMutableDirectedGraph.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkSimple2DLayoutStrategy.h>

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

      vtkIdType v1 = g->AddVertex();
      vtkIdType v2 = g->AddVertex();
      vtkIdType v3 = g->AddVertex();

      g->AddEdge ( v1, v2 );
      g->AddEdge ( v2, v3 );
      g->AddEdge ( v3, v1 );

      // Do layout manually before handing graph to the view.
      // This allows us to know the positions of edge arrows.
      vtkSmartPointer<vtkGraphLayoutView> graphLayoutView =
        vtkSmartPointer<vtkGraphLayoutView>::New();

      vtkSmartPointer<vtkGraphLayout> layout =
        vtkSmartPointer<vtkGraphLayout>::New();
      vtkSmartPointer<vtkSimple2DLayoutStrategy> strategy =
        vtkSmartPointer<vtkSimple2DLayoutStrategy>::New();
      layout->SetInput(g);
      layout->SetLayoutStrategy(strategy);

      // Tell the view to use the vertex layout we provide
      graphLayoutView->SetLayoutStrategyToPassThrough();
      // The arrows will be positioned on a straight line between two
      // vertices so tell the view not to draw arcs for parallel edges
      graphLayoutView->SetEdgeLayoutStrategyToPassThrough();

      // Add the graph to the view. This will render vertices and edges,
      // but not edge arrows.
      graphLayoutView->AddRepresentationFromInputConnection(
        layout->GetOutputPort());

      // Manually create an actor containing the glyphed arrows.
      vtkSmartPointer<vtkGraphToPolyData> graphToPoly =
        vtkSmartPointer<vtkGraphToPolyData>::New();
      graphToPoly->SetInputConnection(layout->GetOutputPort());
      graphToPoly->EdgeGlyphOutputOn();

      // Set the position (0: edge start, 1: edge end) where
      // the edge arrows should go.
      graphToPoly->SetEdgeGlyphPosition(0.98);

      // Make a simple edge arrow for glyphing.
      vtkSmartPointer<vtkGlyphSource2D> arrowSource =
        vtkSmartPointer<vtkGlyphSource2D>::New();
      arrowSource->SetGlyphTypeToEdgeArrow();
      arrowSource->SetScale(0.1);
      arrowSource->Update();

      // Use Glyph3D to repeat the glyph on all edges.
      vtkSmartPointer<vtkGlyph3D> arrowGlyph =
        vtkSmartPointer<vtkGlyph3D>::New();
      arrowGlyph->SetInputConnection(0, graphToPoly->GetOutputPort(1));
      arrowGlyph->SetInputConnection(1, arrowSource->GetOutputPort());

      // Add the edge arrow actor to the view.
      vtkSmartPointer<vtkPolyDataMapper> arrowMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      arrowMapper->SetInputConnection(arrowGlyph->GetOutputPort());
      vtkSmartPointer<vtkActor> arrowActor =
        vtkSmartPointer<vtkActor>::New();
      arrowActor->SetMapper(arrowMapper);
      graphLayoutView->GetRenderer()->AddActor(arrowActor);

      graphLayoutView->ResetCamera();
      graphLayoutView->Render();
      graphLayoutView->GetInteractor()->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(VisualizeDirectedGraph)

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

    add_executable(VisualizeDirectedGraph MACOSX_BUNDLE VisualizeDirectedGraph.cxx)

    target_link_libraries(VisualizeDirectedGraph ${VTK_LIBRARIES})

### Download and Build VisualizeDirectedGraph

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

    cd VisualizeDirectedGraph/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:

    ./VisualizeDirectedGraph

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.