# FlatVersusGouraud

VTKExamples/Cxx/Rendering/FlatVersusGouraud

### Description

Flat and Gouraud shading. Different shading methods can dramatically improve the look of an object represented with polygons. On the top, flat shading uses a constant surface normal across each polygon. On the bottom, Gouraud shading interpolates normals from polygon vertices to give a smoother look.

In this example, the flat and gouraud images for each pair have linked cameras. Rotate and zoom a pair to get a better look at the differences.

Info

See Figure 3-7 in Chapter 3 the VTK Textbook.

Other Languages

See (Python)

### Code

FlatVersusGouraud.cxx

    #include <vtkActor.h>
    #include <vtkCamera.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>

    #include <vtkContourFilter.h>
    #include <vtkCylinderSource.h>
    #include <vtkOBJReader.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkProperty.h>
    #include <vtkQuadric.h>
    #include <vtkSampleFunction.h>
    #include <vtkSphereSource.h>

    #include <vtkNamedColors.h>

    namespace
    {
    void CreateSphere(vtkSmartPointer<vtkRenderer>&, bool);
    void CreateCylinder(vtkSmartPointer<vtkRenderer>&, bool);
    void CreateIsoSurface(vtkSmartPointer<vtkRenderer>&, bool);
    void CreateModel(vtkSmartPointer<vtkRenderer>&, bool, char*);
    }

    int main(int argc, char* argv[])
    {

      if (argc < 2)
      {
        std::cout << "Usage: " << argv[0] << " filename" << std::endl;
        std::cout << "where: filename is the file cow.obj" << std::endl;
        return EXIT_FAILURE;
      }

      std::vector<vtkSmartPointer<vtkRenderer>> renderers;

      // Create the 8 renderers
      vtkSmartPointer<vtkRenderer> flatSphereRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(flatSphereRenderer);
      vtkSmartPointer<vtkRenderer> flatCylinderRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(flatCylinderRenderer);
      vtkSmartPointer<vtkRenderer> flatIsoSurfaceRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(flatIsoSurfaceRenderer);
      vtkSmartPointer<vtkRenderer> flatModelRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(flatModelRenderer);
      vtkSmartPointer<vtkRenderer> smoothSphereRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(smoothSphereRenderer);
      vtkSmartPointer<vtkRenderer> smoothCylinderRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(smoothCylinderRenderer);
      vtkSmartPointer<vtkRenderer> smoothIsoSurfaceRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(smoothIsoSurfaceRenderer);
      vtkSmartPointer<vtkRenderer> smoothModelRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderers.push_back(smoothModelRenderer);

      // Add the actors
      CreateSphere(flatSphereRenderer, true);
      CreateCylinder(flatCylinderRenderer, true);
      CreateIsoSurface(flatIsoSurfaceRenderer, true);
      CreateModel(flatModelRenderer, true, argv[1]);

      CreateSphere(smoothSphereRenderer, false);
      CreateCylinder(smoothCylinderRenderer, false);
      CreateIsoSurface(smoothIsoSurfaceRenderer, false);
      CreateModel(smoothModelRenderer, false, argv[1]);

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();

      // Setup viewports for the renderers
      int rendererSize = 256;
      unsigned int xGridDimensions = 4;
      unsigned int yGridDimensions = 2;
      renderWindow->SetSize(rendererSize * xGridDimensions,
                            rendererSize * yGridDimensions);
      for (int row = 0; row < static_cast<int>(yGridDimensions); row++)
      {
        for (int col = 0; col < static_cast<int>(xGridDimensions); col++)
        {
          int index = row * xGridDimensions + col;
          // (xmin, ymin, xmax, ymax)
          double viewport[4] = {
            static_cast<double>(col) / xGridDimensions,
            static_cast<double>(yGridDimensions - (row + 1)) / yGridDimensions,
            static_cast<double>(col + 1) / xGridDimensions,
            static_cast<double>(yGridDimensions - row) / yGridDimensions};
          renderers[index]->SetViewport(viewport);
        }
      }

      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();
      for (size_t r = 0; r < renderers.size(); ++r)
      {
        renderers[r]->SetBackground(colors->GetColor3d("SlateGray").GetData());
        renderers[r]->GetActiveCamera()->Azimuth(20);
        renderers[r]->GetActiveCamera()->Elevation(30);
        renderers[r]->ResetCamera();
        if (r > 3)
        {
          renderers[r]->SetActiveCamera(renderers[r - 4]->GetActiveCamera());
        }
        renderWindow->AddRenderer(renderers[r]);
      }
      vtkSmartPointer<vtkRenderWindowInteractor> interactor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      interactor->SetRenderWindow(renderWindow);

      renderWindow->Render();
      interactor->Start();

      return EXIT_SUCCESS;
    }

    namespace
    {
    void CreateSphere(vtkSmartPointer<vtkRenderer>& renderer, bool flat)
    {
      vtkSmartPointer<vtkSphereSource> sphere =
        vtkSmartPointer<vtkSphereSource>::New();
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(sphere->GetOutputPort());

      vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);
      if (flat)
      {
        actor->GetProperty()->SetInterpolationToFlat();
      }
      else
      {
        actor->GetProperty()->SetInterpolationToGouraud();
      }
      renderer->AddActor(actor);
    }

    void CreateCylinder(vtkSmartPointer<vtkRenderer>& renderer, bool flat)
    {
      vtkSmartPointer<vtkCylinderSource> cylinder =
        vtkSmartPointer<vtkCylinderSource>::New();
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(cylinder->GetOutputPort());

      vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);
      if (flat)
      {
        actor->GetProperty()->SetInterpolationToFlat();
      }
      else
      {
        actor->GetProperty()->SetInterpolationToGouraud();
      }
      renderer->AddActor(actor);
    }

    void CreateIsoSurface(vtkSmartPointer<vtkRenderer>& renderer, bool flat)
    {
      double range[2];
      // Sample quadric function
      vtkSmartPointer<vtkQuadric> quadric = vtkSmartPointer<vtkQuadric>::New();
      quadric->SetCoefficients(1, 2, 3, 0, 1, 0, 0, 0, 0, 0);

      vtkSmartPointer<vtkSampleFunction> sample =
        vtkSmartPointer<vtkSampleFunction>::New();
      sample->SetSampleDimensions(25, 25, 25);
      sample->SetImplicitFunction(quadric);

      // Generate implicit surface
      vtkSmartPointer<vtkContourFilter> contour =
        vtkSmartPointer<vtkContourFilter>::New();
      contour->SetInputConnection(sample->GetOutputPort());
      range[0] = 1.0;
      range[1] = 6.0;
      contour->GenerateValues(5, range);

      // Map contour
      vtkSmartPointer<vtkPolyDataMapper> contourMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      contourMapper->SetInputConnection(contour->GetOutputPort());
      contourMapper->SetScalarRange(0, 7);

      vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(contourMapper);
      if (flat)
      {
        actor->GetProperty()->SetInterpolationToFlat();
      }
      else
      {
        actor->GetProperty()->SetInterpolationToGouraud();
      }
      renderer->AddActor(actor);
      return;
    }

    void CreateModel(vtkSmartPointer<vtkRenderer>& renderer, bool flat,
                     char* fileName)
    {
      vtkSmartPointer<vtkOBJReader> reader = vtkSmartPointer<vtkOBJReader>::New();
      reader->SetFileName(fileName);

      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(reader->GetOutputPort());

      vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);
      if (flat)
      {
        actor->GetProperty()->SetInterpolationToFlat();
      }
      else
      {
        actor->GetProperty()->SetInterpolationToGouraud();
      }
      renderer->AddActor(actor);
    }
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(FlatVersusGouraud)

    find_package(VTK COMPONENTS
      vtkCommonColor
      vtkCommonDataModel
      vtkFiltersCore
      vtkFiltersSources
      vtkIOGeometry
      vtkImagingHybrid
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping FlatVersusGouraud: ${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(FlatVersusGouraud MACOSX_BUNDLE FlatVersusGouraud.cxx )
      target_link_libraries(FlatVersusGouraud PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(FlatVersusGouraud MACOSX_BUNDLE FlatVersusGouraud.cxx )
      target_link_libraries(FlatVersusGouraud PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS FlatVersusGouraud
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build FlatVersusGouraud

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

    cd FlatVersusGouraud/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:

    ./FlatVersusGouraud

WINDOWS USERS

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