# ReverseAccess

VTKExamples/Cxx/Visualization/ReverseAccess

### Code

ReverseAccess.cxx

    //
    // This example demonstrates how to access the source object
    // (e.g. vtkSphereSource) from the actor reversely.
    //
    // some standard vtk headers
    #include <vtkSphereSource.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkRenderWindow.h>
    #include <vtkCamera.h>
    #include <vtkActor.h>
    #include <vtkRenderer.h>
    #include <vtkSmartPointer.h>
    #include <vtkMath.h>

    // additionally needed vtk header for this example
    #include <vtkAlgorithmOutput.h>

    int main(int, char *[])
    {
      // source
      vtkSmartPointer<vtkSphereSource> sphere =
        vtkSmartPointer<vtkSphereSource>::New();
      sphere->SetRadius( 0.5 );
      // mapper
      vtkSmartPointer<vtkPolyDataMapper> sphereMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      sphereMapper->SetInputConnection( sphere->GetOutputPort() );
      // actor
      vtkSmartPointer<vtkActor> sphereActor =
        vtkSmartPointer<vtkActor>::New();
      sphereActor->SetMapper( sphereMapper );
      //renderer
      vtkSmartPointer<vtkRenderer> ren1 =
        vtkSmartPointer<vtkRenderer>::New();
      ren1->SetBackground( 0.1, 0.2, 0.4 );
      vtkSmartPointer<vtkRenderWindow> renWin =
        vtkSmartPointer<vtkRenderWindow>::New();
      renWin->AddRenderer( ren1 );
      renWin->SetSize( 300, 300 );
      // add actor to the renderer
      ren1->AddActor( sphereActor );

      //
      // Now we retrieve the source object from vtkActor reversely,
      // meaning we don't use the spheresource object we instantiated
      // above directly,
      // instead we retrieve a reference to the spheresource through the
      // actor.
      // An advantage of this concept might be that we don't need to
      // maintain the source object anymore
      // in a more complex application.
      // To demonstrate that we can modify properties of the spheresource
      // through this reference
      // beside changing some properties of the actor (in this example we
      // change actor's x-position),
      // we change the radius of the spheresource as well.
      //
      // next two lines are the core lines for reverse access
      //
      vtkSmartPointer<vtkAlgorithm> algorithm =
        sphereActor->GetMapper()->GetInputConnection(0, 0)->GetProducer();
      vtkSmartPointer<vtkSphereSource> srcReference =
        vtkSphereSource::SafeDownCast(algorithm);

      float origRadius = srcReference->GetRadius();
      for (int i = 0; i < 360; ++i)
      {
        // change radius of the spheresource
        srcReference->SetRadius(origRadius * (1 + sin((float)i/180.0 * vtkMath::Pi())));
        // change x-position of the actor
        sphereActor->SetPosition(sin((float)i/45.0 * vtkMath::Pi())*0.5, 0, 0);
        renWin->Render();
      }

      //
      // Thanks to the usage of vtkSmartPointer there is no explicit need
      // to free any objects at this point.
      //
      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(ReverseAccess)

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

    add_executable(ReverseAccess MACOSX_BUNDLE ReverseAccess.cxx)

    target_link_libraries(ReverseAccess ${VTK_LIBRARIES})

### Download and Build ReverseAccess

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

    cd ReverseAccess/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:

    ./ReverseAccess

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.