remove return_empty_on_invalid_input

and show in an example how to check preconditions

Constrained_triangulation_3/examples/Constrained_triangulation_3/ccdt_3_check_preconditions.cpp

@@ -1,11 +1,18 @@
 #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
 
-#include <CGAL/IO/polygon_mesh_io.h>
-#include <CGAL/IO/write_MEDIT.h>
 #include <CGAL/Surface_mesh/Surface_mesh.h>
+#include <CGAL/Polygon_mesh_processing/triangulate_faces.h>
+#include <CGAL/Polygon_mesh_processing/self_intersections.h>
+#include <CGAL/boost/graph/copy_face_graph.h>
+#include <CGAL/Polygon_mesh_processing/polygon_mesh_to_polygon_soup.h>
+
 #include <CGAL/make_conforming_constrained_Delaunay_triangulation_3.h>
 
 #include <CGAL/draw_constrained_triangulation_3.h>
+#include <CGAL/IO/polygon_mesh_io.h>
+#include <CGAL/IO/write_MEDIT.h>
+
+#include <vector>
 
 using K = CGAL::Exact_predicates_inexact_constructions_kernel;
 using Point = K::Point_3;
@@ -13,13 +20,36 @@ using Surface_mesh = CGAL::Surface_mesh<Point>;
 
 namespace PMP = CGAL::Polygon_mesh_processing;
 
+// Function to verify preconditions for a mesh input
+bool verify_preconditions_mesh(const Surface_mesh& mesh)
+{
+  if(CGAL::is_triangle_mesh(mesh))
+    return !CGAL::Polygon_mesh_processing::does_self_intersect(mesh);
+
+  Surface_mesh triangle_mesh;
+  CGAL::copy_face_graph(mesh, triangle_mesh);
+  bool tri_ok = CGAL::Polygon_mesh_processing::triangulate_faces(triangle_mesh);
+  if(!tri_ok)
+    return false;
+
+  return !CGAL::Polygon_mesh_processing::does_self_intersect(triangle_mesh);
+}
+
+// Function to verify preconditions for a polygon soup input
+template <typename PointRange, typename PolygonRange>
+bool verify_preconditions_soup(const PointRange& points, const PolygonRange& polygons)
+{
+  return !CGAL::Polygon_mesh_processing::does_polygon_soup_self_intersect(points, polygons);
+}
+
 int main(int argc, char* argv[])
 {
   const auto filename = (argc > 1) ? argv[1]
                        : CGAL::data_file_path("meshes/mpi_and_sphere.off");
 
   CGAL::Surface_mesh<K::Point_3> mesh;
-  if(!CGAL::IO::read_polygon_mesh(filename, mesh)) {
+  if(!CGAL::IO::read_polygon_mesh(filename, mesh))
+  {
     std::cerr << "Error: cannot read file " << filename << std::endl;
     return EXIT_FAILURE;
   }
@@ -27,8 +57,25 @@ int main(int argc, char* argv[])
   std::cout << "Number of facets in " << filename << ": "
             << mesh.number_of_faces() << "\n";
 
-  auto ccdt = CGAL::make_conforming_constrained_Delaunay_triangulation_3(mesh,
-                CGAL::parameters::return_empty_on_invalid_input(true));
+  // Verify preconditions for the mesh input
+  if(!verify_preconditions_mesh(mesh))
+  {
+    // If the mesh is not a valid triangle mesh or has self-intersections,
+    // convert it to a polygon soup and verify the preconditions for the soup
+    std::vector<K::Point_3> points;
+    std::vector<std::vector<std::size_t>> polygons;
+    CGAL::Polygon_mesh_processing::polygon_mesh_to_polygon_soup(mesh, points, polygons);
+    if(!verify_preconditions_soup(points, polygons))
+    {
+      std::cerr << "Error: input polygon soup is not a valid input for CCDT_3\n";
+      return EXIT_FAILURE;
+    }
+
+    std::cerr << "Error: input mesh is not a valid input for CCDT_3\n";
+    return EXIT_FAILURE;
+  }
+
+  auto ccdt = CGAL::make_conforming_constrained_Delaunay_triangulation_3(mesh);
 
   if(ccdt.number_of_constrained_facets() == 0)
   {

Constrained_triangulation_3/include/CGAL/Conforming_constrained_Delaunay_triangulation_3.h

@@ -638,18 +638,6 @@ public:
     // ----------------------------------
     using parameters::choose_parameter;
     using parameters::get_parameter;
-#ifndef CGAL_CDT_3_DISABLE_INPUT_CHECKS
-    const bool return_empty_on_invalid_input =
-        choose_parameter(get_parameter(np, internal_np::return_empty_on_invalid_input), false);
-
-    if (choose_parameter(get_parameter(np, internal_np::do_self_intersection_tests), true))
-    {
-      CGAL_precondition_msg(return_empty_on_invalid_input || preconditions_verified_mesh(mesh, np),
-                            "Conforming_constrained_Delaunay_triangulation_3: mesh self-intersects");
-    }
-
-    if(return_empty_on_invalid_input && !preconditions_verified_mesh(mesh, np)) return;
-#endif
 
     auto mesh_vp_map = choose_parameter(get_parameter(np, internal_np::vertex_point), get(CGAL::vertex_point, mesh));
 
@@ -777,15 +765,6 @@ public:
     // ----------------------------------
     using parameters::choose_parameter;
     using parameters::get_parameter;
-#ifndef CGAL_CDT_3_DISABLE_INPUT_CHECKS
-    const bool return_empty_on_invalid_input =
-        choose_parameter(get_parameter(np, internal_np::return_empty_on_invalid_input), false);
-
-    CGAL_precondition_msg(return_empty_on_invalid_input || preconditions_verified_soup(points, polygons, np),
-                          "Conforming_constrained_Delaunay_triangulation_3: polygon soup self-intersects");
-
-    if(return_empty_on_invalid_input && !preconditions_verified_soup(points, polygons, np)) return;
-#endif
 
     using PointRange_const_iterator = typename PointRange::const_iterator;
     using PointRange_value_type = typename std::iterator_traits<PointRange_const_iterator>::value_type;

Constrained_triangulation_3/include/CGAL/make_conforming_constrained_Delaunay_triangulation_3.h

@@ -43,16 +43,19 @@ namespace CGAL {
 
   By default, each face of the input is considered a polygonal constraint for the triangulation. The
   named parameter `plc_face_id` can be used to describe larger polygonal constraints, possibly with holes. If
-  used, this parameter must be a property map that associates each face of the input with a patch
-  identifier. Faces with the same patch identifier are considered part of the same surface patch. Each of these
+  used, this parameter must be a property map that associates each face of the input with a PLC face
+  identifier. Faces with the same face identifier are considered part of the same surface patch. Each of these
   surface patches (defined as the union of the input faces with a given patch identifier) is expected to be a polygon or
   a polygon with holes, with coplanar vertices (or nearly coplanar up to the precision of the number type used).
 
   The generated triangulation will conform to the faces of the input, or to the surface patches
   described by the `plc_face_id` property map if provided.
 
+  In the case where the input contains a non-planar PLC face, building the triangulation may fail with an exception
+  of type `CGAL::Non_planar_plc_facet_exception`.
 
   \pre The input data must not be coplanar.
+  \pre The input data must not have self-intersections.
 
   Template Parameters        {#make_conforming_constrained_Delaunay_triangulation_3_template_parameters}
   -------------------
@@ -121,16 +124,6 @@ namespace CGAL {
  *                   Faces of `mesh` with the same patch identifier are considered part of the same PLC face.}
  *   \cgalParamNEnd
  *
- *   \cgalParamNBegin{return_empty_on_invalid_input}
- *     \cgalParamDescription{a Boolean activating the check of preconditions on the input
- *                           before starting to construct the triangulation.
- *                           If the check is activated and the preconditions are not satisfied,
- *                           an empty triangulation is immediately returned.}
- *     \cgalParamType{Boolean}
- *     \cgalParamDefault{`false`}
- *     \cgalParamExtra{If this parameter is set to `false` and the preconditions are not satisfied, the algorithm may throw an exception or crash.}
- *   \cgalParamNEnd
- *
  *   \cgalParamNBegin{geom_traits}
  *     \cgalParamDescription{an instance of a geometric traits class}
  *     \cgalParamType{`Traits` as defined above in the section \ref make_conforming_constrained_Delaunay_triangulation_3_returned_type}
@@ -199,16 +192,6 @@ auto make_conforming_constrained_Delaunay_triangulation_3(const PolygonMesh &mes
  *   \cgalParamExtra{Otherwise facets with the same patch identifier are considered part of the same PLC face.}
  *   \cgalParamNEnd
  *
- *   \cgalParamNBegin{return_empty_on_invalid_input}
- *     \cgalParamDescription{a Boolean activating the check of preconditions on the input
- *                           before starting to construct the triangulation.
- *                           If the check is activated and the preconditions are not satisfied,
- *                           an empty triangulation is immediately returned.}
- *     \cgalParamType{Boolean}
- *     \cgalParamDefault{`false`}
- *     \cgalParamExtra{If this parameter is set to `false` and the preconditions are not satisfied, the algorithm may throw an exception or crash.}
- *   \cgalParamNEnd
- *
  *   \cgalParamNBegin{geom_traits}
  *     \cgalParamDescription{an instance of a geometric traits class}
  *     \cgalParamType{`Traits` as defined above in the section \ref make_conforming_constrained_Delaunay_triangulation_3_returned_type}

STL_Extension/include/CGAL/STL_Extension/internal/parameters_interface.h

@@ -325,9 +325,6 @@ CGAL_add_named_parameter(preserve_order_t, preserve_order, preserve_order)
 CGAL_add_named_parameter(adjust_directions_t, adjust_directions, adjust_directions)
 CGAL_add_named_parameter(segment_t, segment_map, segment_map)
 
-// List of named parameters using in Constrained_triangulation_3
-CGAL_add_named_parameter(return_empty_on_invalid_input_t, return_empty_on_invalid_input, return_empty_on_invalid_input)
-
 // List of named parameters used in Mesh_2 package
 CGAL_add_named_parameter_with_compatibility(seeds_t, seeds, seeds)
 CGAL_add_named_parameter_with_compatibility(domain_is_initialized_t, domain_is_initialized, domain_is_initialized)