Handle copy of non manifold umbrella in a Face_filtered_graph (#8682)

CGAL · Jan 9, 2025 · 8be09c9 · 8be09c9
2 parents 06fa730 + 1e06a88
commit 8be09c9
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Showing 2 changed files with 125 additions and 4 deletions.
diff --git a/BGL/include/CGAL/boost/graph/copy_face_graph.h b/BGL/include/CGAL/boost/graph/copy_face_graph.h
@@ -178,6 +178,7 @@ void copy_face_graph_impl(const SourceMesh& sm, TargetMesh& tm,
   }
 
   // detect if there are some non-manifold umbrellas and fix missing halfedge target pointers
+  std::map<sm_vertex_descriptor, std::vector<tm_halfedge_descriptor>> nm_umbrella_map;
   typedef typename std::vector<tm_edge_descriptor>::iterator edge_iterator;
   for (edge_iterator it=new_edges.begin(); it!=new_edges.end(); ++it)
   {
@@ -199,17 +200,38 @@ void copy_face_graph_impl(const SourceMesh& sm, TargetMesh& tm,
             // we recover tm_v using the halfedge associated to the target vertex of
             // the halfedge in sm corresponding to nh_t. This is working because we
             // set the vertex halfedge pointer to the "same" halfedges.
-            tm_vertex_descriptor tm_v =
-              target( get(hs_to_ht, halfedge(target(get(ht_to_hs, nh_t), sm), sm)), tm);
-            for(tm_halfedge_descriptor ht : halfedges_around_target(nh_t, tm))
-              set_target(ht, tm_v, tm);
+
+            sm_vertex_descriptor vs = target(get(ht_to_hs, nh_t), sm);
+            sm_halfedge_descriptor hs = halfedge(vs, sm);
+            if (hs == boost::graph_traits<SourceMesh>::null_halfedge())
+            {  // special case for Face_filtered_graph with a non-manifold input with not all umbrellas selected
+              nm_umbrella_map[vs].push_back(nh_t);
+            }
+            else
+            {
+              tm_vertex_descriptor tm_v = target( get(hs_to_ht, hs), tm);
+              for(tm_halfedge_descriptor ht : halfedges_around_target(nh_t, tm))
+                set_target(ht, tm_v, tm);
+            }
           }
           nh_t = opposite(nh_t, tm);
         }
       }
       break;
     }
   }
+
+  for (const auto& vs_and_hts : nm_umbrella_map)
+  {
+    sm_vertex_descriptor v_sm = vs_and_hts.first;
+    tm_vertex_descriptor v_tm = add_vertex(tm);
+    *v2v++=std::make_pair(v_sm, v_tm);
+    set_halfedge(v_tm, vs_and_hts.second.front(), tm);
+    put(tm_vpm, v_tm, conv(get(sm_vpm, v_sm)));
+
+    for (tm_halfedge_descriptor h_tm : vs_and_hts.second)
+      set_target(h_tm, v_tm, tm);
+  }
 }
 
 } // end of namespace internal

diff --git a/BGL/test/BGL/test_Face_filtered_graph.cpp b/BGL/test/BGL/test_Face_filtered_graph.cpp
@@ -498,6 +498,103 @@ void test_invalid_selections()
   assert(!many_umbrellas_fg.is_selection_valid());
 }
 
+
+void non_manifoldness_test1()
+{
+  // works out-of-the-box because Face_filtered_graph handles already non-manifold cycles
+  SM mesh;
+  SM::Vertex_index v0=add_vertex(mesh);
+  SM::Vertex_index v1=add_vertex(mesh);
+  SM::Vertex_index v2=add_vertex(mesh);
+  SM::Vertex_index v3=add_vertex(mesh);
+  SM::Vertex_index v4=add_vertex(mesh);
+  SM::Vertex_index v5=add_vertex(mesh);
+  SM::Vertex_index v6=add_vertex(mesh);
+
+  SM::Face_index f0=mesh.add_face(v0,v1,v2);
+  SM::Face_index f1=mesh.add_face(v0,v3,v4);
+  SM::Face_index f2=mesh.add_face(v0,v5,v6);
+  SM::Halfedge_index h = halfedge(f0,mesh);
+  while(target(h, mesh)!=v0)
+    h=next(h,mesh);
+  set_halfedge(v0, h, mesh);
+
+  std::vector<SM::Face_index> selection = {f1, f2};
+  CGAL::Face_filtered_graph<SM> ffg(mesh, selection);
+
+  SM out;
+  CGAL::copy_face_graph(ffg, out);
+
+  assert(vertices(out).size()==5);
+  assert(faces(out).size()==2);
+}
+
+void non_manifoldness_test2()
+{
+  SM mesh;
+  SM::Vertex_index v0=add_vertex(mesh);
+  SM::Vertex_index v0b=add_vertex(mesh);
+  SM::Vertex_index v0t=add_vertex(mesh);
+
+  SM::Vertex_index v1=add_vertex(mesh);
+  SM::Vertex_index v2=add_vertex(mesh);
+  SM::Vertex_index v3=add_vertex(mesh);
+
+  SM::Vertex_index v4=add_vertex(mesh);
+  SM::Vertex_index v5=add_vertex(mesh);
+  SM::Vertex_index v6=add_vertex(mesh);
+
+  SM::Vertex_index v7=add_vertex(mesh);
+  SM::Vertex_index v8=add_vertex(mesh);
+  SM::Vertex_index v9=add_vertex(mesh);
+
+  SM::Face_index f00=mesh.add_face(v1,v2,v0);
+  SM::Face_index f01=mesh.add_face(v2,v3,v0);
+  SM::Face_index f02=mesh.add_face(v3,v1,v0);
+
+  SM::Face_index f10=mesh.add_face(v4,v5,v0b);
+  SM::Face_index f11=mesh.add_face(v5,v6,v0b);
+  SM::Face_index f12=mesh.add_face(v6,v4,v0b);
+
+  SM::Face_index f20=mesh.add_face(v7,v8,v0t);
+  SM::Face_index f21=mesh.add_face(v8,v9,v0t);
+  SM::Face_index f22=mesh.add_face(v9,v7,v0t);
+
+  assert(f00!=SM::Face_index());
+  assert(f01!=SM::Face_index());
+  assert(f02!=SM::Face_index());
+  assert(f10!=SM::Face_index());
+  assert(f11!=SM::Face_index());
+  assert(f12!=SM::Face_index());
+  assert(f20!=SM::Face_index());
+  assert(f21!=SM::Face_index());
+  assert(f22!=SM::Face_index());
+
+  #define UPDATE_V(fX, vX) \
+  { SM::Halfedge_index h = halfedge(fX,mesh);\
+  while(target(h, mesh)!=vX) h=next(h,mesh);\
+  set_target(h, v0, mesh); }
+
+  UPDATE_V(f10, v0b)
+  UPDATE_V(f11, v0b)
+  UPDATE_V(f12, v0b)
+  UPDATE_V(f20, v0t)
+  UPDATE_V(f21, v0t)
+  UPDATE_V(f22, v0t)
+
+  remove_vertex(v0b, mesh);
+  remove_vertex(v0t, mesh);
+
+  std::vector<SM::Face_index> selection = {f10, f11, f12, f20, f21, f22};
+  CGAL::Face_filtered_graph<SM> ffg(mesh, selection);
+
+  SM out;
+  CGAL::copy_face_graph(ffg, out);
+
+  assert(vertices(out).size()==7);
+  assert(faces(out).size()==6);
+}
+
 int main()
 {
   test_graph_range(poly_data());
@@ -511,6 +608,8 @@ int main()
 #endif
 
   test_invalid_selections();
+  non_manifoldness_test1();
+  non_manifoldness_test2();
 
   // Make a tetrahedron and test the adapter for a patch that only contains 2 faces
   typedef CGAL::Face_filtered_graph<SM> SM_Adapter;