# Opacity

VTKExamples/Cxx/Visualization/Opacity

### Code

Opacity.cxx

    #include <vtkSmartPointer.h>
    #include <vtkCubeSource.h>
    #include <vtkSphereSource.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkProperty.h>
    #include <vtkActor.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>

    int main(int, char *[])
    {
      // Cube
      vtkSmartPointer<vtkCubeSource> cubeSource =
        vtkSmartPointer<vtkCubeSource>::New();
      vtkSmartPointer<vtkPolyDataMapper> cubeMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      cubeMapper->SetInputConnection(cubeSource->GetOutputPort());

      vtkSmartPointer<vtkActor> cubeActor =
        vtkSmartPointer<vtkActor>::New();
      cubeActor->GetProperty()->SetOpacity(0.5);
      cubeActor->SetMapper(cubeMapper);

      // Sphere
      vtkSmartPointer<vtkSphereSource> sphereSource =
        vtkSmartPointer<vtkSphereSource>::New();
      vtkSmartPointer<vtkPolyDataMapper> sphereMapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      sphereMapper->SetInputConnection(sphereSource->GetOutputPort());

      vtkSmartPointer<vtkActor> sphereActor =
        vtkSmartPointer<vtkActor>::New();
      sphereActor->GetProperty()->SetColor(0.5,1,0.5);
      sphereActor->GetProperty()->SetOpacity(0.5);
      sphereActor->SetMapper(sphereMapper);

      // Create renderers and add actors of plane and cube
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      renderer->AddActor(cubeActor);
      renderer->AddActor(sphereActor);

      // Add renderer to renderwindow and render
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);

      vtkSmartPointer<vtkRenderWindowInteractor> interactor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      interactor->SetRenderWindow(renderWindow);
      renderer->SetBackground(0,0,0);
      renderWindow->Render();

      interactor->Start();
      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(Opacity)

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

### Download and Build Opacity

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

    cd Opacity/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:

    ./Opacity

WINDOWS USERS

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