Segfault when triangulating a mesh (on Windows only)

[stla]

pentagrammicPrism.off.txt

Hello,

This is a non-triangle mesh and when I try to triangulate it (via R), this crashes the session on Windows, but not on Linux. However I didn't try with this OFF file, I enter the vertex coordinates and the face indices in R. I'm using CGAL 5.6 and there was no such problem with the previous version.

Is it enough for you to test, or do you want a full reproducible code?

[sloriot]

A minimal c++ example would actually help, thanks.

[stla]

Here is a minimal code. I have not tested it yet (cause compiling my DLL takes a while and I don't know how to compile to exe).

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Polygon_mesh_processing/IO/polygon_mesh_io.h>
#include <CGAL/Surface_mesh.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel EK;
typedef CGAL::Surface_mesh<EK::Point_3> EMesh;
namespace PMP = CGAL::Polygon_mesh_processing;

int main() {
  EMesh mesh;
  const bool readoff = CGAL::IO::read_OFF("pentagrammicPrism.off", mesh);
  if(!readoff) {
    std::cout << "read_OFF has failed.";
    return 1;
  }
  const bool success = PMP::triangulate_faces(mesh);
  if(!success) {
    std::cout << "Triangulation has failed.";
    return 1;
  }
  return 0;
}

[afabri]

I had to add

#include <CGAL/Polygon_mesh_processing/triangulate_faces.h>

It does not crash. Neither in Debug nor in Release. I am in the master branch on github.

[stla]

Ok thanks. That is strange. I didn't try with the OFF file yet, I will.

Below is the code I use to construct this mesh. I didn't run it yet.

#include <CGAL/Exact_predicates_exact_constructions_kernel.h>
#include <CGAL/Polygon_mesh_processing/triangulate_faces.h>
#include <CGAL/Surface_mesh.h>

typedef CGAL::Exact_predicates_exact_constructions_kernel EK;
typedef EK::Point_3                                       Point;
typedef CGAL::Surface_mesh<Point>                         EMesh;
typedef boost::graph_traits<EMesh>::face_descriptor       face_descriptor;
namespace PMP = CGAL::Polygon_mesh_processing;

int main() {
  // vertices -----------------------------------------------------------------
  const double rho = sqrt((5 - sqrt(5))/10);
  const double R = sqrt((25 - 11*sqrt(5))/10);
  const double pi = M_PI;
  std::vector<Point> vertices;
  for(int i = 0; i < 5; i++) {
    vertices.push_back(Point(rho*cos(2*i*pi/5), rho*sin(2*i*pi/5), 0.1))
  }
  for(int i = 0; i < 5; i++) {
    vertices.push_back(Point(rho*cos(2*i*pi/5), rho*sin(2*i*pi/5), -0.1))
  }
  for(int i = 0; i < 5; i++) {
    vertices.push_back(Point(R*cos(2*i*pi/5 + pi/5), R*sin(2*i*pi/5 + pi/5), 0.1))
  }
  for(int i = 0; i < 5; i++) {
    vertices.push_back(Point(R*cos(2*i*pi/5 + pi/5), R*sin(2*i*pi/5 + pi/5), -0.1))
  }
  // faces --------------------------------------------------------------------
  std::vector<std::vector<int>> triangles = 
    {
      {14, 0, 10}, 
      {10, 1, 11}, 
      {11, 2, 12},
      {12, 3, 13},
      {13, 4, 14},
      {15, 5, 19},
      {16, 6, 15},
      {17, 7, 16},
      {18, 8, 17},
      {19, 9, 18}
    };
  std::vector<std::vector<int>> rectangles =
  {
    {0, 5, 15, 10},
    {1, 6, 16, 11},
    {2, 7, 17, 12},
    {3, 8, 18, 13},
    {4, 9, 19, 14},
    {6, 1, 10, 15},
    {7, 2, 11, 16},
    {8, 3, 12, 17},
    {9, 4, 13, 18},
    {5, 0, 14, 19}
  };
  std::vector<std::vector<int>> pentagons =
  {
    {10, 11, 12, 13, 14},
    {19, 18, 17, 16, 15}
  };
  // mesh ---------------------------------------------------------------------
  EMesh mesh;
  const int nverts = vertices.size();
  for(int i = 0; i < nverts; i++) {
    mesh.add_vertex(vertices[i]);
  }
  const int ntriangles = triangles.size();
  for(int i = 0; i < ntriangles; i++) {
    std::vector<int> intface = triangles[i];
    std::vector<EMesh::Vertex_index> face;
    face.reserve(3);
    for(int k = 0; k < 3; k++) {
      face.emplace_back(CGAL::SM_Vertex_index(intface[k]));
    }
    face_descriptor fd = mesh.add_face(face);
    if(fd == EMesh::null_face()) {
      std::cout << "Cannot add triangle " + std::to_string(i) + ".";
      return 1;
    }
  }
  const int nrectangles = rectangles.size();
  for(int i = 0; i < nrectangles; i++) {
    std::vector<int> intface = rectangles[i];
    std::vector<EMesh::Vertex_index> face;
    face.reserve(4);
    for(int k = 0; k < 4; k++) {
      face.emplace_back(CGAL::SM_Vertex_index(intface[k]));
    }
    face_descriptor fd = mesh.add_face(face);
    if(fd == EMesh::null_face()) {
      std::cout << "Cannot add rectangle " + std::to_string(i) + ".";
      return 1;
    }
  }
  const int npentagons = pentagons.size();
  for(int i = 0; i < npentagons; i++) {
    std::vector<int> intface = pentagons[i];
    std::vector<EMesh::Vertex_index> face;
    face.reserve(5);
    for(int k = 0; k < 5; k++) {
      face.emplace_back(CGAL::SM_Vertex_index(intface[k]));
    }
    face_descriptor fd = mesh.add_face(face);
    if(fd == EMesh::null_face()) {
      std::cout << "Cannot add pentagon " + std::to_string(i) + ".";
      return 1;
    }
  }
  // triangulation
  const bool success = PMP::triangulate_faces(mesh);
  if(!success) {
    std::cout << "Triangulation has failed.";
    return 1;
  }
  return 0;
}

[stla]

Makes no sense... I also observed no crash when doing PMP::triangulate_faces only. My actual triangulation step also has a visitor, so I tried with this visitor and no crash... So I put some std::cout everywhere in my code to locate the occurence of the crash and now there's no crash anymore! I'm going to check again the package on the CRAN website, but if there's no crash anymore this would be really mysterious because the only thing I changed is the std::cout.