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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 <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 3.12 FATAL_ERROR)

project(NormalsDemo)

find_package(VTK COMPONENTS 
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "NormalsDemo: Unable to find the VTK build folder.")
endif()

# 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(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}
)

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.