1 files changed, 38 insertions, 11 deletions

diff --git a/source/blender/blenkernel/intern/cdderivedmesh.c b/source/blender/blenkernel/intern/cdderivedmesh.c
index b7ad135fa72..7ac046c092f 100644
--- a/source/blender/blenkernel/intern/cdderivedmesh.c
+++ b/source/blender/blenkernel/intern/cdderivedmesh.c
@@ -2408,6 +2408,11 @@ void CDDM_calc_normals_tessface(DerivedMesh *dm)
  * this is a really horribly written function.  ger. - joeedh
  *
  * note, CDDM_recalc_tessellation has to run on the returned DM if you want to access tessfaces.
+ *
+ * Note: This function is currently only used by the Mirror modifier, so it
+ *       skips any faces that have all vertices merged (to avoid creating pairs
+ *       of faces sharing the same set of vertices). If used elsewhere, it may
+ *       be necessary to make this functionality optional.
  */
 DerivedMesh *CDDM_merge_verts(DerivedMesh *dm, const int *vtargetmap)
 {
@@ -2451,14 +2456,11 @@ DerivedMesh *CDDM_merge_verts(DerivedMesh *dm, const int *vtargetmap)
 			newv[i] = newv[vtargetmap[i]];
 		}
 	}
-	
-	/* find-replace merged vertices with target vertices */
-	ml = cddm->mloop;
-	for (i = 0; i < totloop; i++, ml++) {
-		if (vtargetmap[ml->v] != -1) {
-			ml->v = vtargetmap[ml->v];
-		}
-	}
+
+	/* Don't remap vertices in cddm->mloop, because we need to know the original
+	 * indices in order to skip faces with all vertices merged.
+	 * The "update loop indices..." section further down remaps vertices in mloop.
+	 */
 
 	/* now go through and fix edges and faces */
 	med = cddm->medge;
@@ -2492,6 +2494,24 @@ DerivedMesh *CDDM_merge_verts(DerivedMesh *dm, const int *vtargetmap)
 		
 		ml = cddm->mloop + mp->loopstart;
 
+		/* skip faces with all vertices merged */
+		{
+			int all_vertices_merged = TRUE;
+
+			for (j = 0; j < mp->totloop; j++, ml++) {
+				if (vtargetmap[ml->v] == -1) {
+					all_vertices_merged = FALSE;
+					break;
+				}
+			}
+
+			if (UNLIKELY(all_vertices_merged)) {
+				continue;
+			}
+		}
+
+		ml = cddm->mloop + mp->loopstart;
+
 		c = 0;
 		for (j = 0; j < mp->totloop; j++, ml++) {
 			med = cddm->medge + ml->e;
@@ -2650,7 +2670,7 @@ void CDDM_calc_edges(DerivedMesh *dm)
 	EdgeHashIterator *ehi;
 	MPoly *mp = cddm->mpoly;
 	MLoop *ml;
-	MEdge *med;
+	MEdge *med, *origmed;
 	EdgeHash *eh = BLI_edgehash_new();
 	int v1, v2;
 	int *eindex;
@@ -2683,6 +2703,7 @@ void CDDM_calc_edges(DerivedMesh *dm)
 	CustomData_add_layer(&edgeData, CD_MEDGE, CD_CALLOC, NULL, numEdges);
 	CustomData_add_layer(&edgeData, CD_ORIGINDEX, CD_CALLOC, NULL, numEdges);
 
+	origmed = cddm->medge;
 	med = CustomData_get_layer(&edgeData, CD_MEDGE);
 	index = CustomData_get_layer(&edgeData, CD_ORIGINDEX);
 
@@ -2693,8 +2714,14 @@ void CDDM_calc_edges(DerivedMesh *dm)
 		BLI_edgehashIterator_getKey(ehi, &med->v1, &med->v2);
 		j = GET_INT_FROM_POINTER(BLI_edgehashIterator_getValue(ehi));
 
-		med->flag = ME_EDGEDRAW | ME_EDGERENDER;
-		*index = j == 0 ? ORIGINDEX_NONE : eindex[j - 1];
+		if (j == 0) {
+			med->flag = ME_EDGEDRAW | ME_EDGERENDER;
+			*index = ORIGINDEX_NONE;
+		}
+		else {
+			med->flag = ME_EDGEDRAW | ME_EDGERENDER | origmed[j - 1].flag;
+			*index = eindex[j - 1];
+		}
 
 		BLI_edgehashIterator_setValue(ehi, SET_INT_IN_POINTER(i));
 	}