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Scalars

vtk-examples/Cxx/VTKConcepts/Scalars

Question

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Code

Scalars.cxx

#include <vtkDoubleArray.h>
#include <vtkFloatArray.h>
#include <vtkNew.h>
#include <vtkPointData.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>

void TypeSpecific();
void NonTypeSpecific();

int main(int, char*[])
{
  TypeSpecific();
  NonTypeSpecific();

  return EXIT_SUCCESS;
}

void TypeSpecific()
{
  // Create a point set
  vtkNew<vtkPoints> points;
  points->InsertNextPoint(0, 0, 0);
  points->InsertNextPoint(1, 0, 0);

  vtkNew<vtkPolyData> polydata;
  polydata->SetPoints(points);

  vtkNew<vtkDoubleArray> weights;
  weights->SetNumberOfValues(2);
  weights->SetValue(0, 1);
  weights->SetValue(1, 2);

  polydata->GetPointData()->SetScalars(weights);

  double weight =
      dynamic_cast<vtkDoubleArray*>(polydata->GetPointData()->GetScalars())
          ->GetValue(0);
  std::cout << "double weight: " << weight << std::endl;

  /*
  // This causes a crash because the array is not a vtkFloatArray
  double weightf =
  dynamic_cast<vtkFloatArray*>(polydata->GetPointData()->GetScalars())->GetValue(0);
  std::cout << "float weight: " << weightf << std::endl;
  */
}

void NonTypeSpecific()
{
  // Create a point set
  vtkNew<vtkPoints> points;
  points->InsertNextPoint(0, 0, 0);
  points->InsertNextPoint(1, 0, 0);

  vtkNew<vtkPolyData> polydata;
  polydata->SetPoints(points);

  vtkNew<vtkDoubleArray> weights;
  weights->SetNumberOfValues(2);
  weights->SetValue(0, 1);
  weights->SetValue(1, 2);

  polydata->GetPointData()->SetScalars(weights);

  double weight = polydata->GetPointData()->GetScalars()->GetComponent(0, 0);
  std::cout << "double weight: " << weight << std::endl;

  double weightf = polydata->GetPointData()->GetScalars()->GetComponent(0, 0);
  std::cout << "float weight: " << weightf << std::endl;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(Scalars)

find_package(VTK COMPONENTS 
  CommonCore
  CommonDataModel
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "Scalars: 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(Scalars MACOSX_BUNDLE Scalars.cxx )
  target_link_libraries(Scalars PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS Scalars
  MODULES ${VTK_LIBRARIES}
)

Download and Build Scalars

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

cd Scalars/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:

./Scalars

WINDOWS USERS

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