# Subdivision

VTKExamples/Cxx/Meshes/Subdivision

### Description

In this example a mesh is read from a file and then subdivided using linear subdivision. The SetNumberOfSubdivisions(n) function controls how many times the mesh is subdivided. For each n, the number of triangles will increase by approximately a factor of 4. For example, if n=2, the number of triangles in the resulting mesh will be 16x the number of triangles in the original mesh.

Different types of subdivisions can be obtained by replacing vtkLinearSubdivisionFilter with either vtkLoopSubdivisionFilter or vtkButterflySubdivisionFilter.

### Code

Subdivision.cxx

    #include <vtkVersion.h>
    #include <vtkSmartPointer.h>
    #include <vtkCellData.h>
    #include <vtkCellArray.h>
    #include <vtkDoubleArray.h>
    #include <vtkPoints.h>
    #include <vtkTriangle.h>
    #include <vtkPolyData.h>
    #include <vtkPointData.h>
    #include <vtkSphereSource.h>
    #include <vtkXMLPolyDataReader.h>
    #include <vtkTriangleFilter.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>

    #include <string>

    #include <vtkButterflySubdivisionFilter.h>
    #include <vtkLoopSubdivisionFilter.h>
    #include <vtkLinearSubdivisionFilter.h>

    int main(int argc, char *argv[])
    {
      vtkSmartPointer<vtkPolyData> originalMesh;

      if(argc > 1) //If a file name is specified, open and use the file.
      {
        vtkSmartPointer<vtkXMLPolyDataReader> reader =
          vtkSmartPointer<vtkXMLPolyDataReader>::New();
        reader->SetFileName(argv[1]);

        // Subdivision filters only work on triangles
        vtkSmartPointer<vtkTriangleFilter> triangles =
          vtkSmartPointer<vtkTriangleFilter>::New();
        triangles->SetInputConnection(reader->GetOutputPort());
        triangles->Update();
        originalMesh = triangles->GetOutput();
      }
      else //If a file name is not specified, create a sphere
      {
        vtkSmartPointer<vtkSphereSource> sphereSource =
          vtkSmartPointer<vtkSphereSource>::New();
        sphereSource->Update();
        originalMesh = sphereSource->GetOutput();
      }

      std::cout << "Before subdivision" << std::endl;
      std::cout << "    There are " << originalMesh->GetNumberOfPoints()
                << " points." << std::endl;
      std::cout << "    There are " << originalMesh->GetNumberOfPolys()
                << " triangles." << std::endl;

      double numberOfViewports = 3.;

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(200* numberOfViewports,200); //(width, height)

      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
          vtkSmartPointer<vtkRenderWindowInteractor>::New();

      renderWindowInteractor->SetRenderWindow(renderWindow);

      int numberOfSubdivisions = 2;
      for(unsigned i = 0; i < numberOfViewports; i++)
      {
        // Note: Here we create a superclass pointer (vtkPolyDataAlgorithm) so that we can easily instantiate different
        // types of subdivision filters. Typically you would not want to do this, but rather create the pointer to be the type
        // filter you will actually use, e.g.
        // vtkSmartPointer<vtkLinearSubdivisionFilter>  subdivisionFilter = vtkSmartPointer<vtkLinearSubdivisionFilter>::New();
        vtkSmartPointer<vtkPolyDataAlgorithm> subdivisionFilter;
        switch(i)
        {
          case 0:
            subdivisionFilter = vtkSmartPointer<vtkLinearSubdivisionFilter>::New();
            dynamic_cast<vtkLinearSubdivisionFilter *> (subdivisionFilter.GetPointer())->SetNumberOfSubdivisions(numberOfSubdivisions);
            break;
          case 1:
            subdivisionFilter =  vtkSmartPointer<vtkLoopSubdivisionFilter>::New();
            dynamic_cast<vtkLoopSubdivisionFilter *> (subdivisionFilter.GetPointer())->SetNumberOfSubdivisions(numberOfSubdivisions);
            break;
          case 2:
            subdivisionFilter = vtkSmartPointer<vtkButterflySubdivisionFilter>::New();
            dynamic_cast<vtkButterflySubdivisionFilter *> (subdivisionFilter.GetPointer())->SetNumberOfSubdivisions(numberOfSubdivisions);
            break;
          default:
            break;
        }
    #if VTK_MAJOR_VERSION <= 5
        subdivisionFilter->SetInputConnection(originalMesh->GetProducerPort());
    #else
        subdivisionFilter->SetInputData(originalMesh);
    #endif
        subdivisionFilter->Update();

        vtkSmartPointer<vtkRenderer> renderer =
          vtkSmartPointer<vtkRenderer>::New();

        renderWindow->AddRenderer(renderer);
        renderer->SetViewport(static_cast<double>(i)/numberOfViewports,0,static_cast<double>(i+1)/numberOfViewports,1);

        //Create a mapper and actor
        vtkSmartPointer<vtkPolyDataMapper> mapper =
            vtkSmartPointer<vtkPolyDataMapper>::New();
        mapper->SetInputConnection(subdivisionFilter->GetOutputPort());
        vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
        actor->SetMapper(mapper);
        renderer->AddActor(actor);
        renderer->ResetCamera();

        renderWindow->Render();
        renderWindow->SetWindowName("Multiple ViewPorts");

      }

      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(Subdivision)

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

    add_executable(Subdivision MACOSX_BUNDLE Subdivision.cxx )

    target_link_libraries(Subdivision ${VTK_LIBRARIES})

### Download and Build Subdivision

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

    cd Subdivision/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:

    ./Subdivision

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.