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# ContourWidget

VTKEx/Cxx/Widgets/ContourWidget

### Description

This example generates a set of points which lie on a circle, and the contour through these points. This contour can be interactively warped/modified by dragging the control points.

Other languages

See (Python)

Question

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### Code

ContourWidget.cxx

    #include <vtkSmartPointer.h>
    // To setup the ContourWidget and its representation:
    #include <vtkContourWidget.h>
    #include <vtkProperty.h>
    #include <vtkOrientedGlyphContourRepresentation.h>
    // To create the geometry:
    #include <vtkPolyData.h>
    #include <vtkCellArray.h>
    #include <vtkPoints.h>
    #include <vtkMath.h>
    // Usual VTK pipeline elements:
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkInteractorStyleTrackballCamera.h>

    int main( int /* argc */, char * /* argv */ [] )
    {
        // Create the contour widget
        vtkSmartPointer<vtkContourWidget> contourWidget =
            vtkSmartPointer<vtkContourWidget>::New();

        // Override the default representation for the contour widget to customize its look
        vtkSmartPointer<vtkOrientedGlyphContourRepresentation> contourRepresentation =
            vtkSmartPointer<vtkOrientedGlyphContourRepresentation>::New();
        contourRepresentation->GetLinesProperty()->SetColor(1, 0, 0); // Set color to red
        contourWidget->SetRepresentation(contourRepresentation);

        // Generate a set of points arranged in a circle
        int numPts = 10;
        vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
        for (int i = 0; i < numPts; i++)
        {
            // Create numPts points evenly spread around a circumference of radius 0.1
            const double angle = 2.0*vtkMath::Pi()*i/numPts;
            points->InsertPoint(static_cast<vtkIdType>(i), 0.1*cos(angle), 0.1*sin(angle), 0.0 );
        }

        // Create a cell array to connect the points into meaningful geometry
        vtkIdType* vertexIndices = new vtkIdType[numPts+1];
        for (int i = 0; i < numPts; i++) { vertexIndices[i] = static_cast<vtkIdType>(i); }
        // Set the last vertex to 0; this means the last line segment will join the 19th point (vertices[19])
        // with the first one (vertices[0]), thus closing the circle.
        vertexIndices[numPts] = 0;
        vtkSmartPointer<vtkCellArray> lines = vtkSmartPointer<vtkCellArray>::New();
        lines->InsertNextCell(numPts+1, vertexIndices);

        // Create polydata to hold the geometry just created, and populate it
        vtkSmartPointer<vtkPolyData> polydata = vtkSmartPointer<vtkPolyData>::New();
        polydata->SetPoints(points);
        polydata->SetLines(lines);

        // Create the renderer to visualize the scene
        vtkSmartPointer<vtkRenderer> renderer =
            vtkSmartPointer<vtkRenderer>::New();
        renderer->SetBackground(0.1, 0.2, 0.4); // Set a dark blue background (default is black)

        // Create the GUI window to hold the rendered scene
        vtkSmartPointer<vtkRenderWindow> renderWindow =
            vtkSmartPointer<vtkRenderWindow>::New();
        renderWindow->AddRenderer(renderer);

        // Create the events manager for the renderer window
        vtkSmartPointer<vtkRenderWindowInteractor> interactor =
            vtkSmartPointer<vtkRenderWindowInteractor>::New();
        interactor->SetRenderWindow(renderWindow);

        // Use the "trackball camera" interactor style, rather than the default "joystick camera"
        vtkSmartPointer<vtkInteractorStyleTrackballCamera> style =
          vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();
        interactor->SetInteractorStyle(style);

        // Set up the contour widget within the visualization pipeline just assembled
        contourWidget->SetInteractor(interactor);
        contourWidget->On(); // Turn on the interactor observer
        contourWidget->Initialize(polydata);
        renderer->ResetCamera(); // Reposition camera to fit the scene elements

        // Start the interaction
        renderWindow->Render();
        interactor->Start();

        return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(ContourWidget)

    find_package(VTK COMPONENTS
      vtkvtkCommonCore
      vtkvtkCommonDataModel
      vtkvtkInteractionStyle
      vtkvtkInteractionWidgets
      vtkvtkRenderingContextOpenGL2
      vtkvtkRenderingCore
      vtkvtkRenderingFreeType
      vtkvtkRenderingGL2PSOpenGL2
      vtkvtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping ContourWidget: ${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(ContourWidget MACOSX_BUNDLE ContourWidget.cxx )
      target_link_libraries(ContourWidget PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(ContourWidget MACOSX_BUNDLE ContourWidget.cxx )
      target_link_libraries(ContourWidget PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS ContourWidget
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build ContourWidget

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

    cd ContourWidget/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:

    ./ContourWidget

WINDOWS USERS

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