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DeleteCells

Repository source: DeleteCells

Description

This example demonstrates how to delete a cell from a vtkPolyData. This is a three-step process: first, build upward-links from points to cells; second, mark cells for deletion; third, delete the marked cells. The first step is necessary to create a data structure suitable for efficient delete operations. Creating this data structure is computationally expensive, so it is only carried out before operations that need it, e.g. those that require changes to the topology.

Question

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Code

DeleteCells.cxx

#include <vtkActor.h>
#include <vtkCellArray.h>
#include <vtkLine.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

int main(int, char*[])
{
  vtkNew<vtkPoints> points;
  points->InsertNextPoint(0, 0, 0);
  points->InsertNextPoint(1, 0, 0);
  points->InsertNextPoint(1, 1, 0);
  points->InsertNextPoint(0, 1, 0);

  vtkNew<vtkLine> line0;
  line0->GetPointIds()->SetId(0, 0);
  line0->GetPointIds()->SetId(1, 1);

  vtkNew<vtkLine> line1;
  line1->GetPointIds()->SetId(0, 1);
  line1->GetPointIds()->SetId(1, 2);

  vtkNew<vtkLine> line2;
  line2->GetPointIds()->SetId(0, 2);
  line2->GetPointIds()->SetId(1, 3);

  vtkNew<vtkCellArray> lines;
  lines->InsertNextCell(line0);
  lines->InsertNextCell(line1);
  lines->InsertNextCell(line2);

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

  // Tell the polydata to build 'upward' links from points to cells.
  polydata->BuildLinks();
  // Mark a cell as deleted.
  polydata->DeleteCell(1);
  // Remove the marked cell.
  polydata->RemoveDeletedCells();

  // Visualize
  vtkNew<vtkNamedColors> colors;

  vtkNew<vtkPolyDataMapper> mapper;
  mapper->SetInputDataObject(polydata);

  vtkNew<vtkActor> actor;
  actor->SetMapper(mapper);
  actor->GetProperty()->SetColor(colors->GetColor3d("Peacock").GetData());
  actor->GetProperty()->SetLineWidth(4);

  vtkNew<vtkRenderer> renderer;
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(renderer);
  renderWindow->SetWindowName("DeleteCells");

  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  renderWindowInteractor->SetRenderWindow(renderWindow);
  renderer->AddActor(actor);
  renderer->SetBackground(colors->GetColor3d("Silver").GetData());

  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(DeleteCells)

find_package(VTK COMPONENTS 
  CommonColor
  CommonCore
  CommonDataModel
  InteractionStyle
  RenderingContextOpenGL2
  RenderingCore
  RenderingFreeType
  RenderingGL2PSOpenGL2
  RenderingOpenGL2
)

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

Download and Build DeleteCells

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

cd DeleteCells/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:

./DeleteCells

WINDOWS USERS

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