Fix group flipping when syncing mirror weights

Corrects mirror syncing for invert, levels & smooth.

Note that the code changed to process mirroring even if both verts are selected,
since group flipping can mean that is still meaningful.

source/blender/blenkernel/BKE_deform.h

@@ -76,7 +76,13 @@ void defvert_copy(struct MDeformVert *dvert_dst, const struct MDeformVert *dvert
 void defvert_copy_subset(
         struct MDeformVert *dvert_dst, const struct MDeformVert *dvert_src,
         const bool *vgroup_subset, const int vgroup_tot);
-void defvert_copy_index(struct MDeformVert *dvert_dst, const struct MDeformVert *dvert_src, const int defgroup);
+void defvert_mirror_subset(
+        struct MDeformVert *dvert_dst, const struct MDeformVert *dvert_src,
+        const bool *vgroup_subset, const int vgroup_tot,
+        const int *flip_map, const int flip_map_len);
+void defvert_copy_index(
+        struct MDeformVert       *dvert_dst, const int defgroup_dst,
+        const struct MDeformVert *dvert_src, const int defgroup_src);
 void defvert_sync(struct MDeformVert *dvert_dst, const struct MDeformVert *dvert_src, const bool use_verify);
 void defvert_sync_mapped(
         struct MDeformVert *dvert_dst, const struct MDeformVert *dvert_src,

source/blender/blenkernel/intern/deform.c

@@ -119,7 +119,25 @@ void defvert_copy_subset(
 	int defgroup;
 	for (defgroup = 0; defgroup < vgroup_tot; defgroup++) {
 		if (vgroup_subset[defgroup]) {
-			defvert_copy_index(dvert_dst, dvert_src, defgroup);
+			defvert_copy_index(dvert_dst, defgroup, dvert_src, defgroup);
+		}
+	}
+}
+
+/**
+ * Overwrite weights filtered by vgroup_subset and with mirroring specified by the flip map
+ * - do nothing if neither are set.
+ * - add destination weight if needed
+ */
+void defvert_mirror_subset(
+        MDeformVert *dvert_dst, const MDeformVert *dvert_src,
+        const bool *vgroup_subset, const int vgroup_tot,
+        const int *flip_map, const int flip_map_len)
+{
+	int defgroup;
+	for (defgroup = 0; defgroup < vgroup_tot && defgroup < flip_map_len; defgroup++) {
+		if (vgroup_subset[defgroup] && (dvert_dst != dvert_src || flip_map[defgroup] != defgroup)) {
+			defvert_copy_index(dvert_dst, flip_map[defgroup], dvert_src, defgroup);
 		}
 	}
 }
@@ -148,20 +166,22 @@ void defvert_copy(MDeformVert *dvert_dst, const MDeformVert *dvert_src)
  * - do nothing if neither are set.
  * - add destination weight if needed.
  */
-void defvert_copy_index(MDeformVert *dvert_dst, const MDeformVert *dvert_src, const int defgroup)
+void defvert_copy_index(
+        MDeformVert       *dvert_dst, const int defgroup_dst,
+        const MDeformVert *dvert_src, const int defgroup_src)
 {
 	MDeformWeight *dw_src, *dw_dst;
 
-	dw_src = defvert_find_index(dvert_src, defgroup);
+	dw_src = defvert_find_index(dvert_src, defgroup_src);
 
 	if (dw_src) {
 		/* source is valid, verify destination */
-		dw_dst = defvert_verify_index(dvert_dst, defgroup);
+		dw_dst = defvert_verify_index(dvert_dst, defgroup_dst);
 		dw_dst->weight = dw_src->weight;
 	}
 	else {
 		/* source was NULL, assign zero, could also remove */
-		dw_dst = defvert_find_index(dvert_dst, defgroup);
+		dw_dst = defvert_find_index(dvert_dst, defgroup_dst);
 
 		if (dw_dst) {
 			dw_dst->weight = 0.0f;

source/blender/editors/object/object_vgroup.c

@@ -257,7 +257,6 @@ void ED_vgroup_parray_mirror_sync(Object *ob,
 	BMEditMesh *em = BKE_editmesh_from_object(ob);
 	MDeformVert **dvert_array_all = NULL;
 	int dvert_tot_all;
-	int i;
 
 	/* get an array of all verts, not only selected */
 	if (ED_vgroup_parray_alloc(ob->data, &dvert_array_all, &dvert_tot_all, false) == false) {
@@ -268,22 +267,26 @@ void ED_vgroup_parray_mirror_sync(Object *ob,
 		BM_mesh_elem_table_ensure(em->bm, BM_VERT);
 	}
 
-	for (i = 0; i < dvert_tot; i++) {
-		if (dvert_array[i] == NULL) {
-			/* its unselected, check if its mirror is */
-			int i_sel = ED_mesh_mirror_get_vert(ob, i);
-			if ((i_sel != -1) && (i_sel != i) && (dvert_array[i_sel])) {
+	int flip_map_len;
+	const int *flip_map = defgroup_flip_map(ob, &flip_map_len, true);
+
+	for (int i_src = 0; i_src < dvert_tot; i_src++) {
+		if (dvert_array[i_src] != NULL) {
+			/* its selected, check if its mirror exists */
+			int i_dst = ED_mesh_mirror_get_vert(ob, i_src);
+			if (i_dst != -1 && dvert_array_all[i_dst] != NULL) {
 				/* we found a match! */
-				MDeformVert *dv_src = dvert_array[i_sel];
-				MDeformVert *dv_dst = dvert_array_all[i];
+				const MDeformVert *dv_src = dvert_array[i_src];
+				MDeformVert       *dv_dst = dvert_array_all[i_dst];
 
-				defvert_copy_subset(dv_dst, dv_src, vgroup_validmap, vgroup_tot);
+				defvert_mirror_subset(dv_dst, dv_src, vgroup_validmap, vgroup_tot, flip_map, flip_map_len);
 
-				dvert_array[i] = dvert_array_all[i];
+				dvert_array[i_dst] = dvert_array_all[i_dst];
 			}
 		}
 	}
 
+	MEM_freeN((void *)flip_map);
 	MEM_freeN(dvert_array_all);
 }
 
@@ -2123,7 +2126,7 @@ static void dvert_mirror_op(MDeformVert *dvert, MDeformVert *dvert_mirr,
 				defvert_copy(dvert, dvert_mirr);
 			}
 			else {
-				defvert_copy_index(dvert, dvert_mirr, act_vgroup);
+				defvert_copy_index(dvert, act_vgroup, dvert_mirr, act_vgroup);
 			}
 		}