# Circle

VTKExamples/Cxx/GeometricObjects/Circle

### Description

A circle is simply the limiting case of a regular polygon. We use vtkRegularPolygonSource with a large number of Sides to approximate a circle.

### Code

Circle.cxx

    // Classes specific to this example
    #include <vtkRegularPolygonSource.h>
    #include <vtkPolyData.h>
    #include <vtkPolyDataMapper.h>
    // Generic VTK pipeline elements
    #include <vtkActor.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    // Auxiliary class
    #include <vtkSmartPointer.h>

    int main(int, char *[])
    {
      // Create a circle
      vtkSmartPointer<vtkRegularPolygonSource> polygonSource =
        vtkSmartPointer<vtkRegularPolygonSource>::New();

      //polygonSource->GeneratePolygonOff(); // Uncomment this line to generate only the outline of the circle
      polygonSource->SetNumberOfSides(50);
      polygonSource->SetRadius(5);
      polygonSource->SetCenter(0, 0, 0);

      // Visualize
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(polygonSource->GetOutputPort());;

      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);

      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderer->AddActor(actor);
      renderer->SetBackground(.3,.3,.5); // Background color purple

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);

      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(Circle)

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

    add_executable(Circle MACOSX_BUNDLE Circle.cxx )

    target_link_libraries(Circle ${VTK_LIBRARIES})

### Download and Build Circle

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

    cd Circle/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:

    ./Circle

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.