# OffScreenRendering

VTKExamples/Cxx/Utilities/OffScreenRendering

### Description

This example renders a scene directly to a file without displaying a window. You must turn on VTK_OPENGL_HAS_OSMESA in the VTK advanced build configuration.

### Code

OffScreenRendering.cxx

    #include <vtkVersion.h>
    #if VTK_MAJOR_VERSION >= 6
    int main(int, char *argv[])
    {
      std::cout << argv[0] << " requires VTK 5.10 or earlier. This VTK version is " << vtkVersion::GetVTKVersion() << std::endl;
      return EXIT_SUCCESS;
    }
    #else
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkPolyData.h>
    #include <vtkSmartPointer.h>
    #include <vtkSphereSource.h>
    #include <vtkWindowToImageFilter.h>
    #include <vtkPNGWriter.h>
    #include <vtkGraphicsFactory.h>
    #include <vtkImagingFactory.h>

    int main(int, char *[])
    {
      // Setup offscreen rendering
      vtkSmartPointer<vtkGraphicsFactory> graphics_factory =
        vtkSmartPointer<vtkGraphicsFactory>::New();
      graphics_factory->SetOffScreenOnlyMode( 1);
      graphics_factory->SetUseMesaClasses( 1 );

      vtkSmartPointer<vtkImagingFactory> imaging_factory =
        vtkSmartPointer<vtkImagingFactory>::New();
      imaging_factory->SetUseMesaClasses( 1 );

      // Create a sphere
      vtkSmartPointer<vtkSphereSource> sphereSource =
        vtkSmartPointer<vtkSphereSource>::New();

      // Create a mapper and actor
      vtkSmartPointer<vtkPolyDataMapper> mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(sphereSource->GetOutputPort());

      vtkSmartPointer<vtkActor> actor =
        vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);

      // A renderer and render window
      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetOffScreenRendering( 1 );
      renderWindow->AddRenderer(renderer);

      // Add the actors to the scene
      renderer->AddActor(actor);
      renderer->SetBackground(1,1,1); // Background color white

      renderWindow->Render();

      vtkSmartPointer<vtkWindowToImageFilter> windowToImageFilter =
        vtkSmartPointer<vtkWindowToImageFilter>::New();
      windowToImageFilter->SetInput(renderWindow);
      windowToImageFilter->Update();

      vtkSmartPointer<vtkPNGWriter> writer =
        vtkSmartPointer<vtkPNGWriter>::New();
      writer->SetFileName("screenshot.png");
      writer->SetInputConnection(windowToImageFilter->GetOutputPort());
      writer->Write();

      return EXIT_SUCCESS;
    }
    #endif

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(OffScreenRendering)

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

### Download and Build OffScreenRendering

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

    cd OffScreenRendering/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:

    ./OffScreenRendering

WINDOWS USERS

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