From: David Wells <drwells@email.unc.edu>
Date: Sun, 15 Jul 2018 18:43:03 +0000 (-0400)
Subject: Permit merging empty triangulations.
X-Git-Tag: v9.1.0-rc1~874^2~1
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=269d6770bb74662d3ff398ac0bcaaba8ada44a58;p=dealii.git

Permit merging empty triangulations.

This is useful when we build triangulations by repeatedly merging triangulations
in a loop.
---

diff --git a/source/grid/grid_generator.cc b/source/grid/grid_generator.cc
index 4181dc1a7e..313a3302f0 100644
--- a/source/grid/grid_generator.cc
+++ b/source/grid/grid_generator.cc
@@ -4145,6 +4145,18 @@ namespace GridGenerator
                        const double duplicated_vertex_tolerance,
                        const bool   copy_manifold_ids)
   {
+    // if either Triangulation is empty then merging is just a copy.
+    if (triangulation_1.n_cells() == 0)
+      {
+        result.copy_triangulation(triangulation_2);
+        return;
+      }
+    if (triangulation_2.n_cells() == 0)
+      {
+        result.copy_triangulation(triangulation_1);
+        return;
+      }
+
     Assert(triangulation_1.n_levels() == 1,
            ExcMessage("The input triangulations must be non-empty "
                       "and must not be refined."));