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PBR Skybox

vtk-examples/Cxx/Rendering/PBR_Skybox

Description

Demonstrates physically based rendering using image based lighting and a skybox.

Physically based rendering sets color, metallicity and roughness of the object, sliders are provided for:

  • metallicity
  • roughness

Image based lighting uses a cubemap texture to specify the environment. A Skybox is used to create the illusion of distant three-dimensional surroundings. Textures for the image based lighting and the skymap are supplied from a cubemap. You can select different cubemaps and different surfaces to visualise.

Additionally HDR or JPEG equirectangular Environment maps can be used to generate the cubemaps. A good source for Skybox HDRSs and Textures is Poly Haven. Start with the 4K HDR versions of Skyboxes.

Here are the parameters used to make the example image using the six individual cubemap files:

<DATA>/Skyboxes/spiaggia_di_mondello_4k.hdr Boy

We can also use the six individual cubemap files by specifying the folder where the cubemap files are:

<DATA>/Skyboxes/skybox2/ Boy

We also provide an equirectangular file (useful when using ParaView): <DATA>/Skyboxes/skybox2/skybox.jpg.

Where <DATA> is the path to vtk-examples/src/Testing/Data.

Note that three cubemap skyboxes are available in <DATA>/Skyboxes/ namely skybox0, skybox1 and skybox2.

Further Reading

Note

  • Support was added for HDR images in VTK 9.0, Thus for better performance, the skybox texture should set MipmapOn as well as InterpolateOn to exploit hardware capabilities when using HDR images.
  • We are using a cubemap texture (and not a traditional texture), so one should set UseSphericalHarmonicsOff on the texture as well. This means that we need to use vtkOpenGLRenderer instead of vtkRenderer as the renderer.
  • Physically Based Rendering (PBR) is only available in VTK 9.0+
  • The cubemap/skybox files are found in vtk-examples/src/Testing/Data/skyboxes/.

Other languages

See (Python)

Question

If you have a question about this example, please use the VTK Discourse Forum

Code

PBR_Skybox.cxx

#include <vtkActor.h>
#include <vtkAxesActor.h>
#include <vtkCameraPass.h>
#include <vtkCubeSource.h>
#include <vtkEquirectangularToCubeMapTexture.h>
#include <vtkFloatArray.h>
#include <vtkHDRReader.h>
#include <vtkImageFlip.h>
#include <vtkImageReader2.h>
#include <vtkImageReader2Factory.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkLightsPass.h>
#include <vtkLinearSubdivisionFilter.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkOpaquePass.h>
#include <vtkOpenGLRenderer.h>
#include <vtkOpenGLTexture.h>
#include <vtkOrientationMarkerWidget.h>
#include <vtkOverlayPass.h>
#include <vtkParametricBoy.h>
#include <vtkParametricFunctionSource.h>
#include <vtkParametricMobius.h>
#include <vtkParametricRandomHills.h>
#include <vtkParametricTorus.h>
#include <vtkPointData.h>
#include <vtkPolyDataMapper.h>
#include <vtkPolyDataNormals.h>
#include <vtkPolyDataTangents.h>
#include <vtkProperty.h>
#include <vtkProperty2D.h>
#include <vtkRenderPassCollection.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkSequencePass.h>
#include <vtkSkybox.h>
#include <vtkSliderRepresentation2D.h>
#include <vtkSliderWidget.h>
#include <vtkSmartPointer.h>
#include <vtkTextProperty.h>
#include <vtkTexture.h>
#include <vtkTexturedSphereSource.h>
#include <vtkToneMappingPass.h>
#include <vtkTransform.h>
#include <vtkTransformPolyDataFilter.h>
#include <vtkTriangleFilter.h>
#include <vtkVersion.h>

#include <array>
#include <cstdlib>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <regex>
#include <sstream>
#include <string>
#include <vector>

#if VTK_VERSION_NUMBER >= 90020210809ULL
#define VTK_HAS_COW 1
#endif

#if VTK_HAS_COW
#include <vtkCameraOrientationWidget.h>
#endif

namespace {
/**
 * Show the command lime parameters.
 *
 * @param fn: The program name.
 *
 * @return A string describing the usage.
 */
std::string ShowUsage(std::string fn);

/**
 * Check the VTK version.
 *
 * @param major: Major version.
 * @param major: Minor version.
 * @param major: Build version.
 *
 * @return True if the requested VTK version is greater or equal to the actual
 * VTK version.
 */
bool VTKVersionOk(unsigned long long const& major,
                  unsigned long long const& minor,
                  unsigned long long const& build);

// Some sample surfaces to try.
vtkSmartPointer<vtkPolyData> GetBoy();
vtkSmartPointer<vtkPolyData> GetMobius();
vtkSmartPointer<vtkPolyData> GetRandomHills();
vtkSmartPointer<vtkPolyData> GetTorus();
vtkSmartPointer<vtkPolyData> GetSphere();
vtkSmartPointer<vtkPolyData> GetCube();

/**
 * Read six images forming a cubemap.
 *
 * @param folderRoot: The folder where the cube maps are stored.
 * @param fileNames: The names of the cubemap files.
 *
 * @return The cubemap texture.
 */
vtkSmartPointer<vtkTexture>
ReadCubeMap(std::string const& folderRoot,
            std::vector<std::string> const& fileNames);

/**
 * Read an equirectangular environment file and convert it to a cube map.
 *
 * @param fileName: The equirectangular file.
 *
 * @return The cubemap texture.
 */
vtkSmartPointer<vtkTexture> ReadEnvironmentMap(std::string const& fileName);

/**
 * Generate u, v texture coordinates on a parametric surface.
 *
 * @param uResolution: u resolution
 * @param vResolution: v resolution
 * @param pd: The polydata representing the surface.
 *
 * @return The polydata with the texture coordinates added.
 */
vtkSmartPointer<vtkPolyData> UVTcoords(const float& uResolution,
                                       const float& vResolution,
                                       vtkSmartPointer<vtkPolyData> pd);

class SliderCallbackExposure : public vtkCommand
{
public:
  static SliderCallbackExposure* New()
  {
    return new SliderCallbackExposure;
  }
  virtual void Execute(vtkObject* caller, unsigned long, void*)
  {
    vtkSliderWidget* sliderWidget = reinterpret_cast<vtkSliderWidget*>(caller);
    double value = static_cast<vtkSliderRepresentation2D*>(
                       sliderWidget->GetRepresentation())
                       ->GetValue();
    this->property->SetExposure(value);
  }
  SliderCallbackExposure() : property(nullptr)
  {
  }
  vtkToneMappingPass* property;
};

class SliderCallbackMetallic : public vtkCommand
{
public:
  static SliderCallbackMetallic* New()
  {
    return new SliderCallbackMetallic;
  }
  virtual void Execute(vtkObject* caller, unsigned long, void*)
  {
    vtkSliderWidget* sliderWidget = reinterpret_cast<vtkSliderWidget*>(caller);
    double value = static_cast<vtkSliderRepresentation2D*>(
                       sliderWidget->GetRepresentation())
                       ->GetValue();
    this->property->SetMetallic(value);
  }
  SliderCallbackMetallic() : property(nullptr)
  {
  }
  vtkProperty* property;
};

class SliderCallbackRoughness : public vtkCommand
{
public:
  static SliderCallbackRoughness* New()
  {
    return new SliderCallbackRoughness;
  }
  virtual void Execute(vtkObject* caller, unsigned long, void*)
  {
    vtkSliderWidget* sliderWidget = reinterpret_cast<vtkSliderWidget*>(caller);
    double value = static_cast<vtkSliderRepresentation2D*>(
                       sliderWidget->GetRepresentation())
                       ->GetValue();
    this->property->SetRoughness(value);
  }
  SliderCallbackRoughness() : property(nullptr)
  {
  }
  vtkProperty* property;
};

struct SliderProperties
{
  // Set up the sliders
  double tubeWidth{0.008};
  double sliderLength{0.008};
  double titleHeight{0.025};
  double labelHeight{0.025};

  double minimumValue{0.0};
  double maximumValue{1.0};
  double initialValue{0.0};

  std::array<double, 2> p1{0.2, 0.1};
  std::array<double, 2> p2{0.8, 0.1};

  std::string title{""};

  std::string titleColor{"MistyRose"};
  std::string valueColor{"Cyan"};
  std::string sliderColor{"Coral"};
  std::string selectedColor{"Lime"};
  std::string barColor{"PeachPuff"};
  std::string barEndsColor{"Thistle"};
};

vtkSmartPointer<vtkSliderWidget>
MakeSliderWidget(SliderProperties const& properties);

} // namespace

int main(int argc, char* argv[])
{
  if (!VTKVersionOk(9, 0, 0))
  {
    std::cerr << "You need VTK version 9.0 or greater to run this program."
              << std::endl;
    return EXIT_FAILURE;
  }
  if (argc < 2)
  {
    std::cout << ShowUsage(argv[0]) << std::endl;
    return EXIT_FAILURE;
  }

  // Split  path into its components.
  auto splitPath = [](std::string path) {
    std::replace(path.begin(), path.end(), '\\', '/');

    std::regex regex("/");

    std::vector<std::string> elements(
        std::sregex_token_iterator(path.begin(), path.end(), regex, -1),
        std::sregex_token_iterator());
    return elements;
  };

  // Build a string from a vector of strings using a separator.
  auto join = [](std::vector<std::string> strings, std::string separator) {
    std::string res =
        std::accumulate(std::begin(strings), std::end(strings), std::string(),
                        [&](std::string& ss, std::string& s) {
                          return ss.empty() ? s : ss + separator + s;
                        });
    return res;
  };

  // A map of the skybox folder name and the skybox files in it.
  std::map<std::string, std::vector<std::string>> skyboxFiles{
      {"skybox0",
       {"right.jpg", "left.jpg", "top.jpg", "bottom.jpg", "front.jpg",
        "back.jpg"}},
      {"skybox1",
       {"skybox-px.jpg", "skybox-nx.jpg", "skybox-py.jpg", "skybox-ny.jpg",
        "skybox-pz.jpg", "skybox-nz.jpg"}},
      {"skybox2",
       {"posx.jpg", "negx.jpg", "posy.jpg", "negy.jpg", "posz.jpg",
        "negz.jpg"}}};

  std::vector<std::string> path = splitPath(std::string(argv[1]));
  // std::string root = join(path, "/");

  vtkSmartPointer<vtkTexture> skybox;
  // Load the skybox or cube map.
  if (path.back().find(".", 0) != std::string::npos)
  {
    skybox = ReadEnvironmentMap(argv[1]);
  }
  else
  {
    skybox = ReadCubeMap(argv[1], skyboxFiles[path.back()]);
  }

  // Get the surface
  std::string desiredSurface = "boy";
  if (argc > 2)
  {
    desiredSurface = argv[2];
  }
  std::cout << desiredSurface << std::endl;
  std::transform(desiredSurface.begin(), desiredSurface.end(),
                 desiredSurface.begin(),
                 [](char c) { return std::tolower(c); });
  std::map<std::string, int> availableSurfaces = {
      {"boy", 0},   {"mobius", 1}, {"randomhills", 2},
      {"torus", 3}, {"sphere", 4}, {"cube", 5}};
  if (availableSurfaces.find(desiredSurface) == availableSurfaces.end())
  {
    desiredSurface = "boy";
  }
  vtkSmartPointer<vtkPolyData> source;
  switch (availableSurfaces[desiredSurface])
  {
  case 1:
    source = GetMobius();
    break;
  case 2:
    source = GetRandomHills();
    break;
  case 3:
    source = GetTorus();
    break;
  case 4:
    source = GetSphere();
    break;
  case 5:
    source = GetCube();
    break;
  case 0:
  default:
    source = GetBoy();
  };

  vtkNew<vtkNamedColors> colors;

  // Set the background color.
  std::array<unsigned char, 4> bkg{{26, 51, 102, 255}};
  colors->SetColor("BkgColor", bkg.data());

  vtkNew<vtkOpenGLRenderer> renderer;
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(renderer);
  vtkNew<vtkRenderWindowInteractor> interactor;
  interactor->SetRenderWindow(renderWindow);

  // Turn off the default lighting and use image based lighting.
  renderer->AutomaticLightCreationOff();
  renderer->UseImageBasedLightingOn();
  renderer->SetEnvironmentTexture(skybox);
  renderer->UseSphericalHarmonicsOff();
  renderer->SetBackground(colors->GetColor3d("BkgColor").GetData());

  // Set up tone mapping so we can vary the exposure.
  //
  // Custom Passes.
  vtkNew<vtkCameraPass> cameraP;
  vtkNew<vtkSequencePass> seq;
  vtkNew<vtkOpaquePass> opaque;
  vtkNew<vtkLightsPass> lights;
  vtkNew<vtkOverlayPass> overlay;

  vtkNew<vtkRenderPassCollection> passes;
  passes->AddItem(lights);
  passes->AddItem(opaque);
  passes->AddItem(overlay);
  seq->SetPasses(passes);
  cameraP->SetDelegatePass(seq);

  vtkNew<vtkToneMappingPass> toneMappingP;
  toneMappingP->SetToneMappingType(vtkToneMappingPass::GenericFilmic);
  toneMappingP->SetGenericFilmicUncharted2Presets();
  toneMappingP->SetExposure(1.0);
  toneMappingP->SetDelegatePass(cameraP);

  vtkOpenGLRenderer::SafeDownCast(renderer)->SetPass(toneMappingP);

  auto slwP = SliderProperties();
  slwP.initialValue = 1.0;
  slwP.maximumValue = 5.0;
  slwP.title = "Exposure";

  auto sliderWidgetExposure = MakeSliderWidget(slwP);
  sliderWidgetExposure->SetInteractor(interactor);
  sliderWidgetExposure->SetAnimationModeToAnimate();
  sliderWidgetExposure->EnabledOn();

  // Lets use a smooth metallic surface.
  auto diffuseCoefficient = 1.0;
  auto roughnessCoefficient = 0.05;
  auto metallicCoefficient = 1.0;

  slwP.initialValue = metallicCoefficient;
  slwP.title = "Metallicity";
  slwP.maximumValue = 1.0;
  slwP.p1[0] = 0.1;
  slwP.p1[1] = 0.2;
  slwP.p2[0] = 0.1;
  slwP.p2[1] = 0.8;

  auto sliderWidgetMetallic = MakeSliderWidget(slwP);
  sliderWidgetMetallic->SetInteractor(interactor);
  sliderWidgetMetallic->SetAnimationModeToAnimate();
  sliderWidgetMetallic->EnabledOn();

  slwP.initialValue = roughnessCoefficient;
  slwP.title = "Roughness";
  slwP.p1[0] = 0.85;
  slwP.p1[1] = 0.2;
  slwP.p2[0] = 0.85;
  slwP.p2[1] = 0.8;

  auto sliderWidgetRoughness = MakeSliderWidget(slwP);
  sliderWidgetRoughness->SetInteractor(interactor);
  sliderWidgetRoughness->SetAnimationModeToAnimate();
  sliderWidgetRoughness->EnabledOn();

  // Build the pipeline
  vtkNew<vtkPolyDataMapper> mapper;
  mapper->SetInputData(source);

  vtkNew<vtkActor> actor;
  actor->SetMapper(mapper);
  // Enable PBR on the model.
  actor->GetProperty()->SetInterpolationToPBR();
  // Configure the basic properties.
  actor->GetProperty()->SetColor(colors->GetColor4d("White").GetData());
  actor->GetProperty()->SetDiffuse(diffuseCoefficient);
  actor->GetProperty()->SetRoughness(roughnessCoefficient);
  actor->GetProperty()->SetMetallic(metallicCoefficient);

  // Create the slider callback to manipulate exposure.
  vtkNew<SliderCallbackExposure> callbackExposure;
  callbackExposure->property =
      dynamic_cast<vtkToneMappingPass*>(renderer->GetPass());
  sliderWidgetExposure->AddObserver(vtkCommand::InteractionEvent,
                                    callbackExposure);
  // Create the slider callbacks to manipulate metallicity and roughness
  vtkNew<SliderCallbackMetallic> callbackMetallic;
  callbackMetallic->property = actor->GetProperty();
  sliderWidgetMetallic->AddObserver(vtkCommand::InteractionEvent,
                                    callbackMetallic);
  vtkNew<SliderCallbackRoughness> callbackRoughness;
  callbackRoughness->property = actor->GetProperty();
  sliderWidgetRoughness->AddObserver(vtkCommand::InteractionEvent,
                                     callbackRoughness);

  vtkNew<vtkSkybox> skyboxActor;
  skyboxActor->SetTexture(skybox);
  skyboxActor->GammaCorrectOn();

  renderer->AddActor(actor);
  // Comment out if you don't want a skybox.
  renderer->AddActor(skyboxActor);

  renderWindow->SetSize(800, 500);
  renderWindow->Render();
  renderWindow->SetWindowName("PBR_Skybox");

  vtkNew<vtkAxesActor> axes;

  vtkNew<vtkOrientationMarkerWidget> widget;
  double rgba[4]{0.0, 0.0, 0.0, 0.0};
  colors->GetColor("Carrot", rgba);
  widget->SetOutlineColor(rgba[0], rgba[1], rgba[2]);
  widget->SetOrientationMarker(axes);
  widget->SetInteractor(interactor);
  widget->SetViewport(0.0, 0.0, 0.2, 0.2);
  widget->EnabledOn();
  widget->InteractiveOn();

  interactor->SetRenderWindow(renderWindow);
#if VTK_HAS_COW
  vtkNew<vtkCameraOrientationWidget> camOrientManipulator;
  camOrientManipulator->SetParentRenderer(renderer);
  // Enable the widget.
  camOrientManipulator->On();
#endif

  interactor->Start();
  return EXIT_SUCCESS;
}

namespace {
std::string ShowUsage(std::string fn)
{
  // Remove the folder (if present) then remove the extension in this order
  // since the folder name may contain periods.
  auto last_slash_idx = fn.find_last_of("\\/");
  if (std::string::npos != last_slash_idx)
  {
    fn.erase(0, last_slash_idx + 1);
  }
  auto period_idx = fn.rfind('.');
  if (std::string::npos != period_idx)
  {
    fn.erase(period_idx);
  }
  std::ostringstream os;
  os << "\nusage: " << fn << " path [surface]\n\n"
     << "Demonstrates physically based rendering, image based lighting and a "
        "skybox.\n\n"
     << "positional arguments:\n"
     << "  path        The path to the cubemap files e.g. Skyboxes/skybox2/\n"
     << "               or to a .hdr, .png, or .jpg equirectangular file.\n"
     << "  surface     The surface to use. Boy's surface is the default.\n\n"
     << "Physically based rendering sets color, metallicity and roughness of "
        "the object.\n"
     << "Image based lighting uses a cubemap texture to specify the "
        "environment.\n"
     << "A Skybox is used to create the illusion of distant three-dimensional "
        "surroundings.\n"
     << "\n"
     << std::endl;
  return os.str();
}

bool VTKVersionOk(unsigned long long const& major,
                  unsigned long long const& minor,
                  unsigned long long const& build)
{
  unsigned long long neededVersion =
      10000000000ULL * major + 100000000ULL * minor + build;
#ifndef VTK_VERSION_NUMBER
  vtkNew<vtkVersion>();
  ver;
  unsigned long long vtk_version_number =
      10000000000ULL * ver->GetVTKMajorVersion() +
      100000000ULL * ver->GetVTKMinorVersion() + ver->GetVTKBuildVersion();
  if (vtk_version_number >= neededVersion)
  {
    return true;
  }
  return false;
#else
  if (VTK_VERSION_NUMBER >= neededVersion)
  {
    return true;
  }
  return false;
#endif
}

vtkSmartPointer<vtkTexture>
ReadCubeMap(std::string const& folderRoot,
            std::vector<std::string> const& fileNames)
{
  auto root = folderRoot;
  if (folderRoot.back() != '/')
  {
    root += '/';
  }

  vtkNew<vtkTexture> texture;
  texture->CubeMapOn();
  // Build the file names.
  std::vector<std::string> paths;
  for (auto f : fileNames)
  {
    paths.push_back(root + f);
  }
  auto i = 0;
  for (auto const& fn : paths)
  {
    // Read the images
    vtkNew<vtkImageReader2Factory> readerFactory;
    vtkSmartPointer<vtkImageReader2> imgReader;
    imgReader.TakeReference(readerFactory->CreateImageReader2(fn.c_str()));
    imgReader->SetFileName(fn.c_str());

    vtkNew<vtkImageFlip> flip;
    flip->SetInputConnection(imgReader->GetOutputPort());
    flip->SetFilteredAxis(1); // flip y axis
    texture->SetInputConnection(i, flip->GetOutputPort(0));
    ++i;
  }
  texture->MipmapOn();
  texture->InterpolateOn();

  return texture;
}

vtkSmartPointer<vtkTexture> ReadEnvironmentMap(std::string const& fileName)
{
  // Split  path into its components.
  auto splitPath = [](std::string path) {
    std::replace(path.begin(), path.end(), '\\', '/');

    std::regex regex("/");

    std::vector<std::string> elements(
        std::sregex_token_iterator(path.begin(), path.end(), regex, -1),
        std::sregex_token_iterator());
    return elements;
  };

  // Build a string from a vector of strings using a separator.
  auto join = [](std::vector<std::string> strings, std::string separator) {
    std::string res =
        std::accumulate(std::begin(strings), std::end(strings), std::string(),
                        [&](std::string& ss, std::string& s) {
                          return ss.empty() ? s : ss + separator + s;
                        });
    return res;
  };

  // Get the file name extension.
  auto getSuffix = [](const std::string& fn) -> std::string {
    auto position = fn.find_last_of('.');
    if (position == std::string::npos)
      return "";
    else
    {
      std::string ext(fn.substr(position + 1));
      if (std::regex_search(ext, std::regex("[^A-Za-z0-9]")))
        return "";
      else
        return "." + ext;
    }
  };

  std::vector<std::string> path = splitPath(std::string(fileName));
  auto suffix = getSuffix(path.back());

  vtkNew<vtkTexture> texture;

  if (std::string(".jpg .png").find(suffix, 0) != std::string::npos)
  {
    vtkNew<vtkImageReader2Factory> readerFactory;
    vtkSmartPointer<vtkImageReader2> imgReader;
    imgReader.TakeReference(
        readerFactory->CreateImageReader2(fileName.c_str()));
    imgReader->SetFileName(fileName.c_str());

    texture->SetInputConnection(imgReader->GetOutputPort());
  }
  else
  {
    vtkNew<vtkHDRReader> reader;
    auto extensions = reader->GetFileExtensions();
    if (std::string(extensions).find(suffix, 0) != std::string::npos)
    {
      if (reader->CanReadFile(fileName.c_str()))
      {
        reader->SetFileName(fileName.c_str());

        texture->SetColorModeToDirectScalars();
        texture->SetInputConnection(reader->GetOutputPort());
      }
      else
      {
        std::cerr << "Unable to read the file: " << fileName << std::endl;
        return texture;
      }
    }
  }

  // Convert to a cube map.
  vtkNew<vtkEquirectangularToCubeMapTexture> tcm;
  tcm->SetInputTexture(vtkOpenGLTexture::SafeDownCast(texture));
  // Enable mipmapping to handle HDR image.
  tcm->MipmapOn();
  tcm->InterpolateOn();

  return tcm;
}

vtkSmartPointer<vtkPolyData> GetBoy()
{
  auto uResolution = 51;
  auto vResolution = 51;
  vtkNew<vtkParametricBoy> surface;

  vtkNew<vtkParametricFunctionSource> source;
  source->SetUResolution(uResolution);
  source->SetVResolution(vResolution);
  source->GenerateTextureCoordinatesOn();
  source->SetParametricFunction(surface);
  source->Update();

  // Build the tangents
  vtkNew<vtkPolyDataTangents> tangents;
  tangents->SetInputConnection(source->GetOutputPort());
  tangents->Update();

  return tangents->GetOutput();
}

vtkSmartPointer<vtkPolyData> GetMobius()
{
  auto uResolution = 51;
  auto vResolution = 51;
  vtkNew<vtkParametricMobius> surface;
  surface->SetMinimumV(-0.25);
  surface->SetMaximumV(0.25);

  vtkNew<vtkParametricFunctionSource> source;
  source->SetUResolution(uResolution);
  source->SetVResolution(vResolution);
  source->GenerateTextureCoordinatesOn();
  source->SetParametricFunction(surface);
  source->Update();

  // Build the tangents
  vtkNew<vtkPolyDataTangents> tangents;
  tangents->SetInputConnection(source->GetOutputPort());
  tangents->Update();

  vtkNew<vtkTransform> transform;
  transform->RotateX(-90.0);
  vtkNew<vtkTransformPolyDataFilter> transformFilter;
  transformFilter->SetInputConnection(tangents->GetOutputPort());
  transformFilter->SetTransform(transform);
  transformFilter->Update();

  return transformFilter->GetOutput();
}

vtkSmartPointer<vtkPolyData> GetRandomHills()
{
  auto uResolution = 51;
  auto vResolution = 51;
  vtkNew<vtkParametricRandomHills> surface;
  surface->SetRandomSeed(1);
  surface->SetNumberOfHills(30);
  // If you want a plane
  // surface->SetHillAmplitude(0);

  vtkNew<vtkParametricFunctionSource> source;
  source->SetUResolution(uResolution);
  source->SetVResolution(vResolution);
  source->GenerateTextureCoordinatesOn();
  source->SetParametricFunction(surface);
  source->Update();

  // Build the tangents
  vtkNew<vtkPolyDataTangents> tangents;
  tangents->SetInputConnection(source->GetOutputPort());
  tangents->Update();

  vtkNew<vtkTransform> transform;
  transform->Translate(0.0, 5.0, 15.0);
  transform->RotateX(-90.0);
  vtkNew<vtkTransformPolyDataFilter> transformFilter;
  transformFilter->SetInputConnection(tangents->GetOutputPort());
  transformFilter->SetTransform(transform);
  transformFilter->Update();

  return transformFilter->GetOutput();
}

vtkSmartPointer<vtkPolyData> GetTorus()
{
  auto uResolution = 51;
  auto vResolution = 51;
  vtkNew<vtkParametricTorus> surface;

  vtkNew<vtkParametricFunctionSource> source;
  source->SetUResolution(uResolution);
  source->SetVResolution(vResolution);
  source->GenerateTextureCoordinatesOn();
  source->SetParametricFunction(surface);
  source->Update();

  // Build the tangents
  vtkNew<vtkPolyDataTangents> tangents;
  tangents->SetInputConnection(source->GetOutputPort());
  tangents->Update();

  vtkNew<vtkTransform> transform;
  transform->RotateX(-90.0);
  vtkNew<vtkTransformPolyDataFilter> transformFilter;
  transformFilter->SetInputConnection(tangents->GetOutputPort());
  transformFilter->SetTransform(transform);
  transformFilter->Update();

  return transformFilter->GetOutput();
}

vtkSmartPointer<vtkPolyData> GetSphere()
{
  auto thetaResolution = 32;
  auto phiResolution = 32;
  vtkNew<vtkTexturedSphereSource> surface;
  surface->SetThetaResolution(thetaResolution);
  surface->SetPhiResolution(phiResolution);

  // Now the tangents
  vtkNew<vtkPolyDataTangents> tangents;
  tangents->SetInputConnection(surface->GetOutputPort());
  tangents->Update();
  return tangents->GetOutput();
}

vtkSmartPointer<vtkPolyData> GetCube()
{
  vtkNew<vtkCubeSource> surface;

  // Triangulate
  vtkNew<vtkTriangleFilter> triangulation;
  triangulation->SetInputConnection(surface->GetOutputPort());
  // Subdivide the triangles
  vtkNew<vtkLinearSubdivisionFilter> subdivide;
  subdivide->SetInputConnection(triangulation->GetOutputPort());
  subdivide->SetNumberOfSubdivisions(3);
  // Now the tangents
  vtkNew<vtkPolyDataTangents> tangents;
  tangents->SetInputConnection(subdivide->GetOutputPort());
  tangents->Update();
  return tangents->GetOutput();
}

vtkSmartPointer<vtkPolyData> UVTcoords(const float& uResolution,
                                       const float& vResolution,
                                       vtkSmartPointer<vtkPolyData> pd)
{
  float u0 = 1.0;
  float v0 = 0.0;
  float du = 1.0 / (uResolution - 1.0);
  float dv = 1.0 / (vResolution - 1.0);
  vtkIdType numPts = pd->GetNumberOfPoints();
  vtkNew<vtkFloatArray> tCoords;
  tCoords->SetNumberOfComponents(2);
  tCoords->SetNumberOfTuples(numPts);
  tCoords->SetName("Texture Coordinates");
  vtkIdType ptId = 0;
  float u = u0;
  for (auto i = 0; i < uResolution; ++i)
  {
    float v = v0;
    for (auto j = 0; j < vResolution; ++j)
    {
      float tc[2]{u, v};
      tCoords->SetTuple(ptId, tc);
      v += dv;
      ptId++;
    }
    u -= du;
  }
  pd->GetPointData()->SetTCoords(tCoords);
  return pd;
}

vtkSmartPointer<vtkSliderWidget>
MakeSliderWidget(SliderProperties const& properties)
{
  vtkNew<vtkNamedColors> colors;
  vtkNew<vtkSliderRepresentation2D> slider;

  slider->SetMinimumValue(properties.minimumValue);
  slider->SetMaximumValue(properties.maximumValue);
  slider->SetValue(properties.initialValue);
  slider->SetTitleText(properties.title.c_str());

  slider->GetPoint1Coordinate()->SetCoordinateSystemToNormalizedDisplay();
  slider->GetPoint1Coordinate()->SetValue(properties.p1[0], properties.p1[1]);
  slider->GetPoint2Coordinate()->SetCoordinateSystemToNormalizedDisplay();
  slider->GetPoint2Coordinate()->SetValue(properties.p2[0], properties.p2[1]);

  slider->SetTubeWidth(properties.tubeWidth);
  slider->SetSliderLength(properties.sliderLength);
  slider->SetTitleHeight(properties.titleHeight);
  slider->SetLabelHeight(properties.labelHeight);

  // Set the color properties
  // Change the color of the bar.
  slider->GetTubeProperty()->SetColor(
      colors->GetColor3d(properties.barColor).GetData());
  // Change the color of the ends of the bar.
  slider->GetCapProperty()->SetColor(
      colors->GetColor3d(properties.barEndsColor).GetData());
  // Change the color of the knob that slides.
  slider->GetSliderProperty()->SetColor(
      colors->GetColor3d(properties.sliderColor).GetData());
  // Change the color of the knob when the mouse is held on it.
  slider->GetSelectedProperty()->SetColor(
      colors->GetColor3d(properties.selectedColor).GetData());
  // Change the color of the text displaying the value.
  slider->GetLabelProperty()->SetColor(
      colors->GetColor3d(properties.valueColor).GetData());

  vtkNew<vtkSliderWidget> sliderWidget;
  sliderWidget->SetRepresentation(slider);

  return sliderWidget;
}

} // namespace

CMakeLists.txt

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(PBR_Skybox)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonComputationalGeometry
  vtkCommonCore
  vtkCommonDataModel
  vtkCommonTransforms
  vtkFiltersCore
  vtkFiltersGeneral
  vtkFiltersModeling
  vtkFiltersSources
  vtkIOImage
  vtkImagingCore
  vtkInteractionStyle
  vtkInteractionWidgets
  vtkRenderingAnnotation
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  vtkRenderingOpenGL2
  QUIET
)

if (NOT VTK_FOUND)
  message("Skipping PBR_Skybox: ${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(PBR_Skybox MACOSX_BUNDLE PBR_Skybox.cxx )
  target_link_libraries(PBR_Skybox PRIVATE ${VTK_LIBRARIES})
else()
  # Prevent a "command line is too long" failure in Windows.
  set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
  add_executable(PBR_Skybox MACOSX_BUNDLE PBR_Skybox.cxx )
  target_link_libraries(PBR_Skybox PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS PBR_Skybox
    MODULES ${VTK_LIBRARIES}
    )
endif()

Download and Build PBR_Skybox

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

cd PBR_Skybox/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:

./PBR_Skybox

WINDOWS USERS

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