ZBuffer

// This demo creates depth map for a polydata instance by extracting
// exact ZBuffer values.
#include <vtkSmartPointer.h>

#include <vtkPolyDataMapper.h>
#include <vtkActor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkXMLPolyDataReader.h>
#include <vtkBMPWriter.h>
#include <vtkWindowToImageFilter.h>
#include <vtkImageShiftScale.h>

int main(int argc, char *argv[])
{
  if (argc < 3)
  {
      std::cout << "Usage: " << argv[0]
                << " input(.vtp) output(.bmp)"
                << std::endl;
      return EXIT_FAILURE;
  }

  vtkSmartPointer<vtkPolyDataMapper> mapper =
    vtkSmartPointer<vtkPolyDataMapper>::New();
  vtkSmartPointer<vtkActor> actor =
    vtkSmartPointer<vtkActor>::New();
  vtkSmartPointer<vtkRenderer> renderer =
    vtkSmartPointer<vtkRenderer>::New();
  vtkSmartPointer<vtkRenderWindow> renWin =
    vtkSmartPointer<vtkRenderWindow>::New();
  vtkSmartPointer<vtkRenderWindowInteractor> interactor =
    vtkSmartPointer<vtkRenderWindowInteractor>::New();
  vtkSmartPointer<vtkXMLPolyDataReader> fileReader =
    vtkSmartPointer<vtkXMLPolyDataReader>::New();
  vtkSmartPointer<vtkWindowToImageFilter> filter =
    vtkSmartPointer<vtkWindowToImageFilter>::New();
  vtkSmartPointer<vtkBMPWriter> imageWriter =
    vtkSmartPointer<vtkBMPWriter>::New();
  vtkSmartPointer<vtkImageShiftScale> scale =
    vtkSmartPointer<vtkImageShiftScale>::New();

  // Read .vtp file
  fileReader->SetFileName(argv[1]);

  //Build visualization enviroment
  mapper->SetInputConnection(fileReader->GetOutputPort());
  actor->SetMapper(mapper);
  renderer->AddActor(actor);
  renWin->AddRenderer(renderer);
  interactor->SetRenderWindow(renWin);
  renWin->Render();

  // Create Depth Map
  filter->SetInput(renWin);
#if VTK_MAJOR_VERSION > 8 || VTK_MAJOR_VERSION == 8 && VTK_MINOR_VERSION >= 1
  filter->SetScale(1);
#else
  filter->SetMagnification(1);
#endif
  filter->SetInputBufferTypeToZBuffer();        //Extract z buffer value

  scale->SetOutputScalarTypeToUnsignedChar();
  scale->SetInputConnection(filter->GetOutputPort());
  scale->SetShift(0);
  scale->SetScale(-255);

  // Write depth map as a .bmp image
  imageWriter->SetFileName(argv[2]);
  imageWriter->SetInputConnection(scale->GetOutputPort());
  imageWriter->Write();

  return EXIT_SUCCESS;
}

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(ZBuffer)

find_package(VTK COMPONENTS 
  vtkCommonCore
  vtkIOImage
  vtkIOXML
  vtkImagingCore
  vtkInteractionStyle
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingOpenGL2 QUIET)
if (NOT VTK_FOUND)
  message("Skipping ZBuffer: ${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(ZBuffer MACOSX_BUNDLE ZBuffer.cxx )
  target_link_libraries(ZBuffer PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(ZBuffer MACOSX_BUNDLE ZBuffer.cxx )
  target_link_libraries(ZBuffer PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS ZBuffer
    MODULES ${VTK_LIBRARIES}
    )
endif () 

cd ZBuffer/build 

cmake ..

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

make

./ZBuffer