From 965d4fd48d27d4182625a811c3a25e455d6c5427 Mon Sep 17 00:00:00 2001
From: Andreas Fabri <andreas.fabri@geometryfactory.com>
Date: Tue, 22 Aug 2023 17:01:46 +0100
Subject: [PATCH] WIP: When we delete a face we have to transfer its isolated
 vertices

---
 Nef_2/include/CGAL/Nef_2/PM_const_decorator.h |  7 ++++---
 Nef_2/include/CGAL/Nef_2/PM_overlayer.h       | 16 +++++++++++++---
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/Nef_2/include/CGAL/Nef_2/PM_const_decorator.h b/Nef_2/include/CGAL/Nef_2/PM_const_decorator.h
index de2eb257997..3078ac12e6a 100644
--- a/Nef_2/include/CGAL/Nef_2/PM_const_decorator.h
+++ b/Nef_2/include/CGAL/Nef_2/PM_const_decorator.h
@@ -434,9 +434,10 @@ check_integrity_and_topological_planarity(bool faces) const
   /* check the source links of out edges and count isolated vertices */
   for (vit = vertices_begin() ; vit != vend; ++vit) {
     if ( is_isolated(vit) ) {
-      if ( faces )
-        CGAL_assertion_msg( vit->face() != Face_const_handle(),
-                            VI(vit).c_str());
+        if (faces) {
+            CGAL_assertion_msg(vit->face() != Face_const_handle(),
+                VI(vit).c_str());
+        }
       ++iso_vert_num;
     } else {
       CGAL_assertion_msg( vit->halfedge() != Halfedge_const_handle(),
diff --git a/Nef_2/include/CGAL/Nef_2/PM_overlayer.h b/Nef_2/include/CGAL/Nef_2/PM_overlayer.h
index a28160ed477..0b822458150 100644
--- a/Nef_2/include/CGAL/Nef_2/PM_overlayer.h
+++ b/Nef_2/include/CGAL/Nef_2/PM_overlayer.h
@@ -626,8 +626,11 @@ avoid the simplification for edge pairs referenced by |e|.}*/
   for(v = this->vertices_begin(); v != vend; v=vn) { CGAL_NEF_TRACEN("at vertex "<<PV(v));
     vn=v; ++vn;
     if ( is_isolated(v) ) {
-      if ( mark(v) == mark(face(v)) ) delete_vertex_only(v);
-      else set_isolated_vertex(face(v),v);
+      if (mark(v) == mark(face(v))) {
+        delete_vertex_only(v);
+      } else {
+        set_isolated_vertex(face(v), v);
+      }
     } else { // v not isolated
       Halfedge_handle e2 = first_out_edge(v), e1 = previous(e2);
       Point p1 = point(source(e1)), p2 = point(v),
@@ -643,7 +646,14 @@ avoid the simplification for edge pairs referenced by |e|.}*/
   for (f = this->faces_begin(); f != fend; f=fn) {
     fn=f; ++fn;
     Union_find_handle pit = Pitem[f];
-    if ( unify_faces.find(pit) != pit ) delete_face(f);
+    if (unify_faces.find(pit) != pit) {
+      Union_find_handle root = unify_faces.find(pit);
+      for(Isolated_vertex_iterator ivi = isolated_vertices_begin(f); ivi != isolated_vertices_end(f); ++ivi){
+        v->set_face(*root);
+        link_as_isolated_vertex(*root,v);
+      }
+      delete_face(f);
+    }
   }