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3230 :: Ideas for calling CGAL from Nim?

• Stefan_Salewski (orginal) [2017-10-08T10:15:12+02:00] view original

  For example consider this code:

  ++
  // https://doc.cgal.org/latest/Triangulation_2/index.html#Section_2D_Triangulations_Constrained_Delaunay
  
  #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
  #include <CGAL/Constrained_Delaunay_triangulation_2.h>
  #include <cassert>
  #include <iostream>
  typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
  typedef CGAL::Exact_predicates_tag                               Itag;
  typedef CGAL::Constrained_Delaunay_triangulation_2<K, CGAL::Default, Itag> CDT;
  typedef CDT::Point          Point;
  int
  main( )
  {
    CDT cdt;
    std::cout << "Inserting a grid of 5x5 constraints " << std::endl;
    for (int i = 1; i < 6; ++i)
      cdt.insert_constraint( Point(0,i), Point(6,i));
    for (int j = 1; j < 6; ++j)
      cdt.insert_constraint( Point(j,0), Point(j,6));
    assert(cdt.is_valid());
    int count = 0;
    for (CDT::Finite_edges_iterator eit = cdt.finite_edges_begin();
         eit != cdt.finite_edges_end();
         ++eit)
      if (cdt.is_constrained(*eit)) ++count;
    std::cout << "The number of resulting constrained edges is  ";
    std::cout <<  count << std::endl;
    return 0;
  }
  
  Run

  I can compile this with

  
  cgal_create_CMakeLists -s executable
  cmake -DCGAL_DIR=/usr/lib64/cmake .
  make
  Run

  or with a plain

  
  g++ -lCGAL -lgmp executable.cpp
  
  Run

  I have used CGAL and BOOST some years ago from Ruby, which was some work, but I can not remember details currently. I think for Nim the ordinary wrapper approach with c2nim makes not much sense because CGAL is using so many C++ templates. So I guess I have to use emit and/or importcpp and compile the whole project to C++? Or maybe wrap the C++ code in plain C functions before calling it from Nim?

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• Tiberium (orginal) [2017-10-08T14:35:31+02:00] view original

  c2nim already supports C++ templates

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• Stefan_Salewski (orginal) [2017-10-13T10:11:45+02:00] view original

  Yesterday I tried a very similar approach as I used for Ruby:

  ++
  // g++ -c -lCGAL -lgmp cdt.cpp
  // ar rvs cdt.a cdt.o
  #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
  #include <CGAL/Constrained_Delaunay_triangulation_2.h>
  //#include <cassert>
  //#include <iostream>
  typedef CGAL::Exact_predicates_inexact_constructions_kernel K;
  typedef CGAL::Exact_predicates_tag                               Itag;
  typedef CGAL::Constrained_Delaunay_triangulation_2<K, CGAL::Default, Itag> CDT;
  typedef CDT::Point          Point;
  
  extern "C" void *newCDT();
  extern "C" void insertConstraint(CDT *cdt, double x0, double y0, double x1, double y1);
  extern "C" int numConstraints(CDT *cdt);
  
  void *newCDT()
  {
    CDT *cdt;
    cdt = new CDT;
    return cdt;
  }
  
  void insertConstraint(CDT *cdt, double x0, double y0, double x1, double y1)
  {
      cdt->insert_constraint( Point(x0, y0), Point(x1, y1));
  }
  
  int numConstraints(CDT *cdt)
  {
    int count = 0;
    for (CDT::Finite_edges_iterator eit = cdt->finite_edges_begin();
         eit != cdt->finite_edges_end();
         ++eit)
      if (cdt->is_constrained(*eit)) ++count;
    return count;
  }
  Run

  #nim cpp --passL:cdt.a --passL:-lCGAL --passL:-lgmp cdt.nim
  
  type
    CDT = ptr object
  
  proc newCDT(): CDT {.importc.}
  
  proc insertConstraint(cdt: CDT; x0, y0, x1, y1: cdouble) {.importc.}
  
  proc numConstraints(cdt: CDT): cint {.importc.}
  
  var cdt = newCDT()
  
  for i in 1 ..< 6:
    cdt.insertConstraint(0.cdouble, i.cdouble, 6.cdouble, i.cdouble)
  for j in 1 ..< 6:
    cdt.insertConstraint(j.cdouble, 0.cdouble, j.cdouble, 6.cdouble)
  
  echo cdt.numConstraints
  Run

  Seems to compile and work. I have to invoke nim compiler with cpp -- initially I assumed that cpp backand is not necessary due to extern "C"

  
  g++ -c -lCGAL -lgmp cdt.cpp
  ar rvs cdt.a cdt.o
  nim cpp --passL:cdt.a --passL:-lCGAL --passL:-lgmp cdt.nim
  
  Run

  I assume this will not work with llvm backend. Of course releasing memory with GC is still work in progress, for Triangulation data structure it is not really simple, because Triangulation is some sort of container, so objects can live inside triangulation and at the same time outside in Nim world. I think I did it wrong for Ruby some years ago -- never fixed, as it was working for me...

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