# 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 <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();
      filter->SetInputData(g);
      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();
      filter->SetInputData(g);
      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 *) override;

    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 = dynamic_cast<vtkGraph*>(
          inInfo->Get(vtkDataObject::DATA_OBJECT()));

      vtkGraph *output = dynamic_cast<vtkGraph*>(
                                        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 3.3 FATAL_ERROR)

    project(GraphAlgorithmFilter)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel QUIET)
    if (NOT VTK_FOUND)
      message("Skipping GraphAlgorithmFilter: ${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(GraphAlgorithmFilter MACOSX_BUNDLE GraphAlgorithmFilter.cxx )
      target_link_libraries(GraphAlgorithmFilter PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(GraphAlgorithmFilter MACOSX_BUNDLE GraphAlgorithmFilter.cxx )
      target_link_libraries(GraphAlgorithmFilter PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS GraphAlgorithmFilter
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### 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

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