From b202bf05646b89c8b1f9f24a1d0f9750914997b1 Mon Sep 17 00:00:00 2001
From: Campbell Barton <ideasman42@gmail.com>
Date: Wed, 30 Nov 2011 07:11:29 +0000
Subject: [PATCH] fix [#29450] Mirror Vertex Groups issue

---
 source/blender/blenkernel/BKE_deform.h        |  1 +
 source/blender/blenkernel/intern/deform.c     | 25 +++++++++++++++++++
 source/blender/editors/object/object_vgroup.c | 14 ++++++++---
 3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/source/blender/blenkernel/BKE_deform.h b/source/blender/blenkernel/BKE_deform.h
index 3e643fe961c..2dcafd769d8 100644
--- a/source/blender/blenkernel/BKE_deform.h
+++ b/source/blender/blenkernel/BKE_deform.h
@@ -57,6 +57,7 @@ float  defvert_find_weight(const struct MDeformVert *dvert, const int group_num)
 float  defvert_array_find_weight_safe(const struct MDeformVert *dvert, int index, int group_num);
 
 void defvert_copy(struct MDeformVert *dvert_r, const struct MDeformVert *dvert);
+void defvert_copy_index(struct MDeformVert *dv_dst, const struct MDeformVert *dv_src, const int defgroup);
 void defvert_sync(struct MDeformVert *dvert_r, const struct MDeformVert *dvert, int use_verify);
 void defvert_sync_mapped(struct MDeformVert *dvert_r, const struct MDeformVert *dvert, const int *flip_map, const int flip_map_len, const int use_verify);
 void defvert_remap (struct MDeformVert *dvert, int *map);
diff --git a/source/blender/blenkernel/intern/deform.c b/source/blender/blenkernel/intern/deform.c
index 0c3c78f6eef..021433dee9e 100644
--- a/source/blender/blenkernel/intern/deform.c
+++ b/source/blender/blenkernel/intern/deform.c
@@ -94,6 +94,31 @@ void defvert_copy (MDeformVert *dvert_r, const MDeformVert *dvert)
 	}
 }
 
+/* copy an index from one dvert to another
+ * - do nothing if neither are set.
+ * - add destination weight if needed.
+ */
+void defvert_copy_index (MDeformVert *dv_dst, const MDeformVert *dv_src, const int defgroup)
+{
+	MDeformWeight *dw_src, *dw_dst;
+
+	dw_src= defvert_find_index(dv_src, defgroup);
+
+	if (dw_src) {
+		/* source is valid, verify destination */
+		dw_dst= defvert_verify_index(dv_dst, defgroup);
+		dw_dst->weight= dw_src->weight;
+	}
+	else {
+		/* source was NULL, assign zero, could also remove */
+		dw_dst= defvert_find_index(dv_dst, defgroup);
+
+		if (dw_dst) {
+			dw_dst->weight= 0.0f;
+		}
+	}
+}
+
 /* only sync over matching weights, don't add or remove groups
  * warning, loop within loop.
  */
diff --git a/source/blender/editors/object/object_vgroup.c b/source/blender/editors/object/object_vgroup.c
index d6300dc1fe3..16073434cc7 100644
--- a/source/blender/editors/object/object_vgroup.c
+++ b/source/blender/editors/object/object_vgroup.c
@@ -1576,13 +1576,21 @@ static void dvert_mirror_op(MDeformVert *dvert, MDeformVert *dvert_mirr,
 		}
 	}
 	else {
-		/* dvert should always be the target */
+		/* dvert should always be the target, only swaps pointer */
 		if(sel_mirr) {
 			SWAP(MDeformVert *, dvert, dvert_mirr);
 		}
 
-		if(mirror_weights)
-			defvert_copy(dvert, dvert_mirr);
+		if(mirror_weights) {
+			if (all_vgroups) {
+				defvert_copy(dvert, dvert_mirr);
+			}
+			else {
+				defvert_copy_index(dvert, dvert_mirr, act_vgroup);
+			}
+		}
+
+		/* flip map already modified for 'all_vgroups' */
 		if(flip_vgroups) {
 			defvert_flip(dvert, flip_map, flip_map_len);
 		}