# Triangle

VTKExamples/Cxx/GeometricObjects/Triangle

### Description

The triangle is a primary two-dimensional cell. The triangle is defined by a counterclockwise ordered list of three points. The order of the points specifies the direction of the surface normal using the right-hand rule.

Other Languages

See (Python), (Java), (CSharp)

### Code

Triangle.cxx

    #include <vtkActor.h>
    #include <vtkCellArray.h>
    #include <vtkNamedColors.h>
    #include <vtkPolyData.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkProperty.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkSmartPointer.h>
    #include <vtkTriangle.h>

    int main(int , char *[])
    {
      vtkSmartPointer<vtkNamedColors> colors =
        vtkSmartPointer<vtkNamedColors>::New();

      // Create a triangle
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();
      points->InsertNextPoint ( 1.0, 0.0, 0.0 );
      points->InsertNextPoint ( 0.0, 0.0, 0.0 );
      points->InsertNextPoint ( 0.0, 1.0, 0.0 );

      vtkSmartPointer<vtkTriangle> triangle =
        vtkSmartPointer<vtkTriangle>::New();
      triangle->GetPointIds()->SetId ( 0, 0 );
      triangle->GetPointIds()->SetId ( 1, 1 );
      triangle->GetPointIds()->SetId ( 2, 2 );

      vtkSmartPointer<vtkCellArray> triangles =
        vtkSmartPointer<vtkCellArray>::New();
      triangles->InsertNextCell ( triangle );

      // Create a polydata object
      vtkSmartPointer<vtkPolyData> trianglePolyData =
        vtkSmartPointer<vtkPolyData>::New();

      // Add the geometry and topology to the polydata
      trianglePolyData->SetPoints ( points );
      trianglePolyData->SetPolys ( triangles );

      // Create mapper and actor
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputData(trianglePolyData);

      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->GetProperty()->SetColor(colors->GetColor3d("Cyan").GetData());
      actor->SetMapper(mapper);

      // Create a renderer, render window, and an interactor
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetWindowName("Triangle");
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      // Add the actors to the scene
      renderer->AddActor(actor);
      renderer->SetBackground(colors->GetColor3d("DarkGreen").GetData());

      // Render and interact
      renderWindow->Render();
      renderWindowInteractor->Start();
      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(Triangle)

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

### Download and Build Triangle

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

    cd Triangle/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:

    ./Triangle

WINDOWS USERS

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