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# CubeMap

VTKEx/Cxx/Shaders/CubeMap

Question

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### Code

CubeMap.cxx

    // Inspired by the VTK test Rendering/OpenGL2/Testing/Cxx/TesCubeMap.cxx

    #include <vtkActor.h>
    #include <vtkCamera.h>
    #include <vtkImageFlip.h>
    #include <vtkInteractorStyleTrackballCamera.h>
    #include <vtkJPEGReader.h>
    #include <vtkNamedColors.h>
    #include <vtkOpenGLPolyDataMapper.h>
    #include <vtkOpenGLRenderWindow.h>
    #include <vtkPLYReader.h>
    #include <vtkPolyDataNormals.h>
    #include <vtkProperty.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkRenderer.h>
    #include <vtkShaderProgram.h>
    #include <vtkSmartPointer.h>
    #include <vtkTexture.h>
    #include <vtkVersion.h>

    #if VTK_VERSION_NUMBER >= 89000000000ULL
    #define USE_SHADER_PROPERTIES 1
    #include <vtkShaderProperty.h>
    #endif

    namespace {
    /**
     * Read the cube map.
     *
     * @param folderPath: The folder where the cube maps are stored.
     * @param fileRoot: The root of the individual cube map file names.
     * @param ext: The extension of the cube map files.
     * @param key: The key to data used to build the full file name.
     *
     * @return The cubemap texture.
     */
    vtkSmartPointer<vtkTexture> ReadCubeMap(std::string const& folderPath,
                                            std::string const& fileRoot,
                                            std::string const& ext, int const& key);

    } // namespace

    //----------------------------------------------------------------------------
    int main(int argc, char* argv[])
    {
      if (argc < 3)
      {
        std::cout << "Usage: " << argv[0]
                  << " horse.ply path_to_cubemap_files"
                  << std::endl;
        return EXIT_FAILURE;
      }
      auto colors = vtkSmartPointer<vtkNamedColors>::New();
      auto renderer = vtkSmartPointer<vtkRenderer>::New();
      renderer->SetBackground(colors->GetColor3d("SlateGray").GetData());
      auto renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->SetSize(640, 480);
      renderWindow->AddRenderer(renderer);
      auto interactor = vtkSmartPointer<vtkRenderWindowInteractor>::New();
      interactor->SetRenderWindow(renderWindow);
      auto reader = vtkSmartPointer<vtkPLYReader>::New();
      reader->SetFileName(argv[1]);

      auto norms = vtkSmartPointer<vtkPolyDataNormals>::New();
      norms->SetInputConnection(reader->GetOutputPort());

      auto texture = ReadCubeMap(argv[2], "/skybox", ".jpg", 2);

      auto mapper = vtkSmartPointer<vtkOpenGLPolyDataMapper>::New();
      mapper->SetInputConnection(norms->GetOutputPort());

      auto actor = vtkSmartPointer<vtkActor>::New();
      renderer->AddActor(actor);
      actor->SetTexture(texture);
      actor->SetMapper(mapper);

      // Add new code in default VTK vertex shader
    #if USE_SHADER_PROPERTIES
      vtkShaderProperty* sp = actor->GetShaderProperty();
      sp->AddVertexShaderReplacement(
    #else
      mapper->AddShaderReplacement(
          vtkShader::Vertex,
    #endif
          "//VTK::PositionVC::Dec",  // replace the normal block
          true,                      // before the standard replacements
          "//VTK::PositionVC::Dec\n" // we still want the default
          "out vec3 TexCoords;\n",
          false // only do it once
      );
    #if USE_SHADER_PROPERTIES
      sp->AddVertexShaderReplacement(
    #else
      mapper->AddShaderReplacement(
          vtkShader::Vertex,
    #endif
          "//VTK::PositionVC::Impl",  // replace the normal block
          true,                       // before the standard replacements
          "//VTK::PositionVC::Impl\n" // we still want the default
          "vec3 camPos = -MCVCMatrix[3].xyz * mat3(MCVCMatrix);\n"
          "TexCoords.xyz = reflect(vertexMC.xyz - camPos, normalize(normalMC));\n",
          false // only do it once
      );

      // Replace VTK fragment shader
    #if USE_SHADER_PROPERTIES
      sp->SetFragmentShaderCode(
    #else
      mapper->SetFragmentShaderCode(
    #endif
          "//VTK::System::Dec\n" // always start with this line
          "//VTK::Output::Dec\n" // always have this line in your FS
          "in vec3 TexCoords;\n"
          "uniform samplerCube texture_0;\n"
          "void main () {\n"
          "  gl_FragData[0] = texture(texture_0, TexCoords);\n"
          "}\n");

      renderer->GetActiveCamera()->SetFocalPoint(0, 0, 0);
      renderer->GetActiveCamera()->SetPosition(-.4, .2, .15);
      renderer->GetActiveCamera()->SetViewUp(.3, -.1, .9);
      renderer->ResetCamera();
      renderer->GetActiveCamera()->Zoom(1.4);
      renderWindow->Render();
      renderWindow->SetWindowName("CubeMap");
      renderWindow->Render();

      auto style = vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();
      renderWindow->GetInteractor()->SetInteractorStyle(style);

      interactor->Start();

      return EXIT_SUCCESS;
    }

    namespace {

    vtkSmartPointer<vtkTexture> ReadCubeMap(std::string const& folderPath,
                                            std::string const& fileRoot,
                                            std::string const& ext, int const& key)
    {
      // A map of cube map naming conventions and the corresponding file name
      // components.
      std::map<int, std::vector<std::string>> fileNames{
          {0, {"right", "left", "top", "bottom", "front", "back"}},
          {1, {"posx", "negx", "posy", "negy", "posz", "negz"}},
          {2, {"-px", "-nx", "-py", "-ny", "-pz", "-nz"}},
          {3, {"0", "1", "2", "3", "4", "5"}}};
      std::vector<std::string> fns;
      if (fileNames.count(key))
      {
        fns = fileNames.at(key);
      }
      else
      {
        std::cerr << "ReadCubeMap(): invalid key, unable to continue." << std::endl;
        std::exit(EXIT_FAILURE);
      }
      auto texture = vtkSmartPointer<vtkTexture>::New();
      texture->CubeMapOn();
      // Build the file names.
      std::for_each(fns.begin(), fns.end(),
                    [&folderPath, &fileRoot, &ext](std::string& f) {
                      f = folderPath + fileRoot + f + ext;
                    });
      auto i = 0;
      for (auto const& fn : fns)
      {
        auto imgReader = vtkSmartPointer<vtkJPEGReader>::New();
        imgReader->SetFileName(fn.c_str());

        auto flip = vtkSmartPointer<vtkImageFlip>::New();
        flip->SetInputConnection(imgReader->GetOutputPort());
        flip->SetFilteredAxis(1); // flip y axis
        texture->SetInputConnection(i, flip->GetOutputPort(0));
        ++i;
      }
      return texture;
    }

    } // namespace

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(CubeMap)

    find_package(VTK COMPONENTS
      vtkCommonColor
      vtkCommonCore
      vtkFiltersCore
      vtkIOImage
      vtkIOPLY
      vtkImagingCore
      vtkInteractionStyle
      vtkRenderingContextOpenGL2
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingGL2PSOpenGL2
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping CubeMap: ${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(CubeMap MACOSX_BUNDLE CubeMap.cxx )
      target_link_libraries(CubeMap PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(CubeMap MACOSX_BUNDLE CubeMap.cxx )
      target_link_libraries(CubeMap PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS CubeMap
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build CubeMap

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

    cd CubeMap/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:

    ./CubeMap

WINDOWS USERS

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