# GraphAlgorithmFilter

VTKExamples/Cxx/Developers/GraphAlgorithmFilter

### Description

This example demonstrates how to create a filter that takes a vtkGraph as input and produces a vtkGraph as output.

### Code

GraphAlgorithmFilter.cxx

    #include <vtkVersion.h>
    #include <vtkSmartPointer.h>
    #include <vtkGraph.h>
    #include <vtkMutableUndirectedGraph.h>
    #include <vtkMutableDirectedGraph.h>

    #include "vtkTestGraphAlgorithmFilter.h"

    void TestDirected();
    void TestUndirected();

    int main(int, char *[])
    {
      TestDirected();
      TestUndirected();

      return EXIT_SUCCESS;
    }

    void TestDirected()
    {

      vtkSmartPointer<vtkMutableDirectedGraph> g =
        vtkSmartPointer<vtkMutableDirectedGraph>::New();
      vtkIdType v1 = g->AddVertex();
      vtkIdType v2 = g->AddVertex();

      g->AddEdge(v1, v2);
      std::cout << "Input type: " << g->GetClassName() << std::endl;

      vtkSmartPointer<vtkTestGraphAlgorithmFilter> filter =
        vtkSmartPointer<vtkTestGraphAlgorithmFilter>::New();
    #if VTK_MAJOR_VERSION <= 5
      filter->SetInput(g);
    #else
      filter->SetInputData(g);
    #endif
      filter->Update();

      std::cout << "Output type: " << filter->GetOutput()->GetClassName() << std::endl;
      std::cout << "Output has " << filter->GetOutput()->GetNumberOfVertices() << " vertices." << std::endl;
      std::cout << std::endl;
    }

    void TestUndirected()
    {
      std::cout << "TestUndirected" << std::endl;
      vtkSmartPointer<vtkMutableUndirectedGraph> g =
        vtkSmartPointer<vtkMutableUndirectedGraph>::New();
      vtkIdType v1 = g->AddVertex();
      vtkIdType v2 = g->AddVertex();

      g->AddEdge(v1, v2);
      std::cout << "Input type: " << g->GetClassName() << std::endl;

      vtkSmartPointer<vtkTestGraphAlgorithmFilter> filter =
        vtkSmartPointer<vtkTestGraphAlgorithmFilter>::New();
    #if VTK_MAJOR_VERSION <= 5
      filter->SetInput(g);
    #else
      filter->SetInputData(g);
    #endif
      filter->Update();

      std::cout << "Output type: " << filter->GetOutput()->GetClassName() << std::endl;
      std::cout << "Output has " << filter->GetOutput()->GetNumberOfVertices() << " vertices." << std::endl;
    }

vtkTestGraphAlgorithmFilter.h

    #ifndef __vtkTestGraphAlgorithmFilter_h
    #define __vtkTestGraphAlgorithmFilter_h

    #include "vtkGraphAlgorithm.h"

    class vtkTestGraphAlgorithmFilter : public vtkGraphAlgorithm
    {
    public:
      vtkTypeMacro(vtkTestGraphAlgorithmFilter,vtkGraphAlgorithm);

      static vtkTestGraphAlgorithmFilter *New();

    protected:
      vtkTestGraphAlgorithmFilter(){}
      ~vtkTestGraphAlgorithmFilter(){}

      int RequestData(vtkInformation *, vtkInformationVector **, vtkInformationVector *);

    private:
      vtkTestGraphAlgorithmFilter(const vtkTestGraphAlgorithmFilter&);  // Not implemented.
      void operator=(const vtkTestGraphAlgorithmFilter&);  // Not implemented.

    };

    #endif

vtkTestGraphAlgorithmFilter.cxx

    #include "vtkTestGraphAlgorithmFilter.h"

    #include "vtkObjectFactory.h"
    #include "vtkStreamingDemandDrivenPipeline.h"
    #include "vtkInformationVector.h"
    #include "vtkInformation.h"
    #include "vtkDataObject.h"
    #include "vtkSmartPointer.h"
    #include "vtkMutableUndirectedGraph.h"
    #include "vtkMutableDirectedGraph.h"
    #include "vtkMutableGraphHelper.h"

    vtkStandardNewMacro(vtkTestGraphAlgorithmFilter);

    int vtkTestGraphAlgorithmFilter::RequestData(vtkInformation *vtkNotUsed(request),
                                                 vtkInformationVector **inputVector,
                                                 vtkInformationVector *outputVector)
    {

      // get the info objects
      vtkInformation *inInfo = inputVector[0]->GetInformationObject(0);
      vtkInformation *outInfo = outputVector->GetInformationObject(0);

      // get the input and ouptut
      vtkGraph *input = vtkGraph::SafeDownCast(
          inInfo->Get(vtkDataObject::DATA_OBJECT()));

      vtkGraph *output = vtkGraph::SafeDownCast(
                                        outInfo->Get(vtkDataObject::DATA_OBJECT()));

      vtkSmartPointer<vtkMutableDirectedGraph> mdg =
        vtkSmartPointer<vtkMutableDirectedGraph>::New();

      vtkSmartPointer<vtkMutableUndirectedGraph> mug =
        vtkSmartPointer<vtkMutableUndirectedGraph>::New();

      if(input->IsA("vtkMutableUndirectedGraph"))
      {
        vtkSmartPointer<vtkMutableUndirectedGraph> ug =
          vtkSmartPointer<vtkMutableUndirectedGraph>::New();
        ug->AddVertex();
        output->ShallowCopy(ug);
      }
      else if(input->IsA("vtkMutableDirectedGraph"))
      {
        vtkSmartPointer<vtkMutableDirectedGraph> dg =
          vtkSmartPointer<vtkMutableDirectedGraph>::New();
        dg->AddVertex();
        output->ShallowCopy(dg);
      }

      std::cout << "Output is type: " << output->GetClassName() << std::endl;

      return 1;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(GraphAlgorithmFilter)

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

    add_executable(GraphAlgorithmFilter MACOSX_BUNDLE GraphAlgorithmFilter.cxx  vtkTestGraphAlgorithmFilter.cxx)

    target_link_libraries(GraphAlgorithmFilter ${VTK_LIBRARIES})

### Download and Build GraphAlgorithmFilter

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

    cd GraphAlgorithmFilter/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:

    ./GraphAlgorithmFilter

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.