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NormalsDemo

vtk-examples/Cxx/Visualization/NormalsDemo

Description

This example demonstrates the generation of normals. The left image shows the orignal faceted model. The center image shows the model with generated normals, but no consideration for sharp features. The third image shows the model with a 30 degree feature angle and splitting on.

Theis example uses the src/Testing/Data/42400-IDGH.stl dataset.

Info

See Figure 9-24 in Chapter 9 The VTK Textbook.

Other languages

See (Python)

Question

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

Code

NormalsDemo.cxx

#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkCleanPolyData.h>
#include <vtkColor.h>
#include <vtkImplicitBoolean.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkProperty.h>

#include <vtkBYUReader.h>
#include <vtkOBJReader.h>
#include <vtkPLYReader.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkPolyDataNormals.h>
#include <vtkPolyDataReader.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSTLReader.h>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkXMLPolyDataReader.h>
#include <vtksys/SystemTools.hxx>

namespace {
vtkSmartPointer<vtkPolyData> ReadPolyData(const char* fileName);
}

int main(int argc, char* argv[])
{
  vtkSmartPointer<vtkPolyData> polyData = ReadPolyData(argc > 1 ? argv[1] : "");

  vtkNew<vtkNamedColors> colors;

  // A renderer and render window
  vtkNew<vtkRenderer> renderer;
  renderer->SetBackground(colors->GetColor3d("White").GetData());

  // Create background colors for each viewport
  std::vector<vtkColor3d> backgroundColors;
  backgroundColors.push_back(colors->GetColor3d("Cornsilk"));
  backgroundColors.push_back(colors->GetColor3d("NavajoWhite"));
  backgroundColors.push_back(colors->GetColor3d("Tan"));

  // Create a renderer for each view port
  std::vector<vtkSmartPointer<vtkRenderer>> ren;
  ren.push_back(vtkSmartPointer<vtkRenderer>::New());
  ren.push_back(vtkSmartPointer<vtkRenderer>::New());
  ren.push_back(vtkSmartPointer<vtkRenderer>::New());
  ren[0]->SetViewport(0, 0, 1.0 / 3.0, 1);         // Input
  ren[1]->SetViewport(1.0 / 3.0, 0, 2.0 / 3.0, 1); // Normals (no split)
  ren[2]->SetViewport(2.0 / 3.0, 0, 1, 1);         // Normals (split)

  // Shared camera
  vtkNew<vtkCamera> camera;

  vtkNew<vtkPolyDataNormals> normals;
  normals->SetInputData(polyData);
  normals->SetFeatureAngle(30.0);
  for (int i = 0; i < 3; ++i)
  {
    if (i == 0)
    {
      normals->ComputePointNormalsOff();
    }
    else if (i == 1)
    {
      normals->ComputePointNormalsOn();
      normals->SplittingOff();
    }
    else
    {
      normals->ComputePointNormalsOn();
      normals->SplittingOn();
    }

    normals->Update();

    vtkNew<vtkPolyData> normalsPolyData;
    normalsPolyData->DeepCopy(normals->GetOutput());

    // mapper
    vtkNew<vtkPolyDataMapper> mapper;
    mapper->SetInputData(normalsPolyData);
    mapper->ScalarVisibilityOff();

    vtkNew<vtkActor> actor;
    actor->SetMapper(mapper);
    actor->GetProperty()->SetDiffuseColor(
        colors->GetColor3d("Peacock").GetData());
    actor->GetProperty()->SetDiffuse(.7);
    actor->GetProperty()->SetSpecularPower(20);
    actor->GetProperty()->SetSpecular(.5);

    // add the actor
    ren[i]->SetBackground(backgroundColors[i].GetData());
    ren[i]->SetActiveCamera(camera);
    ren[i]->AddActor(actor);
  }

  // render window
  vtkNew<vtkRenderWindow> renwin;
  renwin->AddRenderer(ren[0]);
  renwin->AddRenderer(ren[1]);
  renwin->AddRenderer(ren[2]);
  renwin->SetWindowName("NormalsDemo");

  // An interactor
  vtkNew<vtkRenderWindowInteractor> interactor;
  interactor->SetRenderWindow(renwin);

  renwin->SetSize(900, 300);
  ren[0]->GetActiveCamera()->SetFocalPoint(0, 0, 0);
  ren[0]->GetActiveCamera()->SetPosition(1, 0, 0);
  ren[0]->GetActiveCamera()->SetViewUp(0, 0, -1);
  ren[0]->ResetCamera();

  ren[0]->GetActiveCamera()->Azimuth(120);
  ren[0]->GetActiveCamera()->Elevation(30);
  ren[0]->GetActiveCamera()->Dolly(1.1);
  ren[0]->ResetCameraClippingRange();

  renwin->Render();
  ren[0]->ResetCamera();
  renwin->Render();

  // Start
  interactor->Initialize();
  interactor->Start();

  return EXIT_SUCCESS;
}

namespace {
vtkSmartPointer<vtkPolyData> ReadPolyData(const char* fileName)
{
  vtkSmartPointer<vtkPolyData> polyData;
  std::string extension =
      vtksys::SystemTools::GetFilenameExtension(std::string(fileName));
  if (extension == ".ply")
  {
    vtkNew<vtkPLYReader> reader;
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".vtp")
  {
    vtkNew<vtkXMLPolyDataReader> reader;
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".vtk")
  {
    vtkNew<vtkPolyDataReader> reader;
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".obj")
  {
    vtkNew<vtkOBJReader> reader;
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".stl")
  {
    vtkNew<vtkSTLReader> reader;
    reader->SetFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else if (extension == ".g")
  {
    vtkNew<vtkBYUReader> reader;
    reader->SetGeometryFileName(fileName);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else
  {
    vtkNew<vtkSphereSource> sphere;
    sphere->SetPhiResolution(11);
    sphere->SetThetaResolution(11);

    sphere->Update();
    polyData = sphere->GetOutput();
  }
  vtkNew<vtkCleanPolyData> clean;
  clean->SetInputData(polyData);
  clean->Update();
  return clean->GetOutput();
}
} // namespace

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(NormalsDemo)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonCore
  vtkCommonDataModel
  vtkFiltersCore
  vtkFiltersSources
  vtkIOGeometry
  vtkIOLegacy
  vtkIOPLY
  vtkIOXML
  vtkInteractionStyle
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  vtkRenderingOpenGL2
  QUIET
)

if (NOT VTK_FOUND)
  message("Skipping NormalsDemo: ${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(NormalsDemo MACOSX_BUNDLE NormalsDemo.cxx )
  target_link_libraries(NormalsDemo PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(NormalsDemo MACOSX_BUNDLE NormalsDemo.cxx )
  target_link_libraries(NormalsDemo PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS NormalsDemo
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build NormalsDemo

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

cd NormalsDemo/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:

./NormalsDemo

WINDOWS USERS

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