Fix T47788: Symmetrize flips multi-res data

Symmetrize was unusable with multi-res data,
add an option for the bmesh operator not to flip the multi-res depth.

source/blender/bmesh/intern/bmesh_core.c

@@ -1044,13 +1044,18 @@ static int UNUSED_FUNCTION(bm_loop_length)(BMLoop *l)
  *
  * BMESH_TODO: reinsert validation code.
  *
+ * \param cd_loop_mdisp_offset: Cached result of `CustomData_get_offset(&bm->ldata, CD_MDISPS)`.
+ * \param use_loop_mdisp_flip: When set, flip the Z-depth of the mdisp,
+ * (use when flipping normals, disable when mirroring, eg: symmetrize).
+ *
  * \return Success
  */
-static bool bm_loop_reverse_loop(BMesh *bm, BMFace *f
+static bool bm_loop_reverse_loop(
+        BMesh *bm, BMFace *f,
 #ifdef USE_BMESH_HOLES
-                                , BMLoopList *lst
+        BMLoopList *lst,
 #endif
-                                )
+        const int cd_loop_mdisp_offset, const bool use_loop_mdisp_flip)
 {
 
 #ifdef USE_BMESH_HOLES
@@ -1060,7 +1065,6 @@ static bool bm_loop_reverse_loop(BMesh *bm, BMFace *f
 #endif
 
 	const int len = f->len;
-	const int cd_loop_mdisp_offset = CustomData_get_offset(&bm->ldata, CD_MDISPS);
 	BMLoop *l_iter, *oldprev, *oldnext;
 	BMEdge **edar = BLI_array_alloca(edar, len);
 	int i, j, edok;
@@ -1100,15 +1104,19 @@ static bool bm_loop_reverse_loop(BMesh *bm, BMFace *f
 					SWAP(float, co_a[0], co_a[1]);
 					SWAP(float, co_b[0], co_b[1]);
 
-					co_a[2] *= -1.0f;
+					if (use_loop_mdisp_flip) {
-					co_b[2] *= -1.0f;
+						co_a[2] *= -1.0f;
+						co_b[2] *= -1.0f;
+					}
 				}
 
 				co_a = co[x * sides + x];
 
 				SWAP(float, co_a[0], co_a[1]);
 
-				co_a[2] *= -1.0f;
+				if (use_loop_mdisp_flip) {
+					co_a[2] *= -1.0f;
+				}
 			}
 		}
 	}
@@ -1155,12 +1163,14 @@ static bool bm_loop_reverse_loop(BMesh *bm, BMFace *f
 /**
  * \brief Flip the faces direction
  */
-bool bmesh_loop_reverse(BMesh *bm, BMFace *f)
+bool bmesh_loop_reverse(
+        BMesh *bm, BMFace *f,
+        const int cd_loop_mdisp_offset, const bool use_loop_mdisp_flip)
 {
 #ifdef USE_BMESH_HOLES
-	return bm_loop_reverse_loop(bm, f, f->loops.first);
+	return bm_loop_reverse_loop(bm, f, f->loops.first, cd_loop_mdisp_offset, use_loop_mdisp_flip);
 #else
-	return bm_loop_reverse_loop(bm, f);
+	return bm_loop_reverse_loop(bm, f, cd_loop_mdisp_offset, use_loop_mdisp_flip);
 #endif
 }
 

source/blender/bmesh/intern/bmesh_core.h

@@ -75,7 +75,9 @@ void    bmesh_vert_separate(
         BMesh *bm, BMVert *v, BMVert ***r_vout, int *r_vout_len,
         const bool copy_select);
 
-bool    bmesh_loop_reverse(BMesh *bm, BMFace *f);
+bool    bmesh_loop_reverse(
+        BMesh *bm, BMFace *f,
+        const int cd_loop_mdisp_offset, const bool use_loop_mdisp_flip);
 
 BMFace *BM_faces_join(BMesh *bm, BMFace **faces, int totface, const bool do_del);
 void    BM_vert_separate(

source/blender/bmesh/intern/bmesh_mods.c

@@ -244,7 +244,8 @@ BMFace *BM_faces_join_pair(BMesh *bm, BMFace *f_a, BMFace *f_b, BMEdge *e, const
 	BLI_assert(l_a && l_b);
 
 	if (l_a->v == l_b->v) {
-		bmesh_loop_reverse(bm, f_b);
+		const int cd_loop_mdisp_offset = CustomData_get_offset(&bm->ldata, CD_MDISPS);
+		bmesh_loop_reverse(bm, f_b, cd_loop_mdisp_offset, true);
 	}
 	
 	return BM_faces_join(bm, faces, 2, do_del);

source/blender/bmesh/intern/bmesh_opdefines.c

@@ -243,6 +243,7 @@ static BMOpDefine bmo_reverse_faces_def = {
 	"reverse_faces",
 	/* slots_in */
 	{{"faces", BMO_OP_SLOT_ELEMENT_BUF, {BM_FACE}},    /* input faces */
+	 {"flip_multires", BMO_OP_SLOT_BOOL},  /* maintain multi-res offset */
 	 {{'\0'}},
 	},
 	{{{'\0'}}},  /* no output */

source/blender/bmesh/intern/bmesh_polygon.c

@@ -702,10 +702,18 @@ void BM_face_calc_center_mean_vcos(
  * Reverses the winding of a face.
  * \note This updates the calculated normal.
  */
+void BM_face_normal_flip_ex(
+        BMesh *bm, BMFace *f,
+        const int cd_loop_mdisp_offset, const bool use_loop_mdisp_flip)
+{
+	bmesh_loop_reverse(bm, f, cd_loop_mdisp_offset, use_loop_mdisp_flip);
+	negate_v3(f->no);
+}
+
 void BM_face_normal_flip(BMesh *bm, BMFace *f)
 {
-	bmesh_loop_reverse(bm, f);
+	const int cd_loop_mdisp_offset = CustomData_get_offset(&bm->ldata, CD_MDISPS);
-	negate_v3(f->no);
+	BM_face_normal_flip_ex(bm, f, cd_loop_mdisp_offset, true);
 }
 
 /* detects if two line segments cross each other (intersects).

source/blender/bmesh/intern/bmesh_polygon.h

@@ -62,6 +62,9 @@ bool  BM_vert_calc_normal(const BMVert *v, float r_no[3]);
 void  BM_vert_normal_update(BMVert *v) ATTR_NONNULL();
 void  BM_vert_normal_update_all(BMVert *v) ATTR_NONNULL();
 
+void  BM_face_normal_flip_ex(
+        BMesh *bm, BMFace *f,
+        const int cd_loop_mdisp_offset, const bool use_loop_mdisp_flip) ATTR_NONNULL();
 void  BM_face_normal_flip(BMesh *bm, BMFace *f) ATTR_NONNULL();
 bool  BM_face_point_inside_test(const BMFace *f, const float co[3]) ATTR_WARN_UNUSED_RESULT ATTR_NONNULL();
 

source/blender/bmesh/operators/bmo_extrude.c

@@ -773,6 +773,7 @@ void bmo_solidify_face_region_exec(BMesh *bm, BMOperator *op)
 
 	/* Flip original faces (so the shell is extruded inward) */
 	BMO_op_init(bm, &reverseop, op->flag, "reverse_faces");
+	BMO_slot_bool_set(reverseop.slots_in, "flip_multires", true);
 	BMO_slot_copy(op,         slots_in, "geom",
 	              &reverseop, slots_in, "faces");
 	BMO_op_exec(bm, &reverseop);

source/blender/bmesh/operators/bmo_symmetrize.c

@@ -79,6 +79,9 @@ void bmo_symmetrize_exec(BMesh *bm, BMOperator *op)
 
 
 	BMO_op_callf(bm, op->flag, "scale verts=%S vec=%v", &op_dupe, "geom.out", scale);
+
+	/* important 'flip_multires' is disabled,
+	 * otherwise multi-res data will be reversed, see: T47788 */
 	BMO_op_callf(bm, op->flag, "reverse_faces faces=%S", &op_dupe, "geom.out");
 
 

source/blender/bmesh/operators/bmo_utils.c

@@ -111,11 +111,13 @@ void bmo_rotate_exec(BMesh *bm, BMOperator *op)
 
 void bmo_reverse_faces_exec(BMesh *bm, BMOperator *op)
 {
+	const int cd_loop_mdisp_offset = CustomData_get_offset(&bm->ldata, CD_MDISPS);
+	const bool use_loop_mdisp_flip = BMO_slot_bool_get(op->slots_in, "flip_multires");
 	BMOIter siter;
 	BMFace *f;
 
 	BMO_ITER (f, &siter, op->slots_in, "faces", BM_FACE) {
-		BM_face_normal_flip(bm, f);
+		BM_face_normal_flip_ex(bm, f, cd_loop_mdisp_offset, use_loop_mdisp_flip);
 	}
 }
 

source/blender/editors/mesh/editmesh_tools.c

@@ -1470,8 +1470,12 @@ static int edbm_flip_normals_exec(bContext *C, wmOperator *op)
 	Object *obedit = CTX_data_edit_object(C);
 	BMEditMesh *em = BKE_editmesh_from_object(obedit);
 	
-	if (!EDBM_op_callf(em, op, "reverse_faces faces=%hf", BM_ELEM_SELECT))
+	if (!EDBM_op_callf(
+	        em, op, "reverse_faces faces=%hf flip_multires=%b",
+	        BM_ELEM_SELECT, true))
+	{
 		return OPERATOR_CANCELLED;
+	}
 	
 	EDBM_update_generic(em, true, false);
 
@@ -1639,8 +1643,9 @@ static int edbm_normals_make_consistent_exec(bContext *C, wmOperator *op)
 	if (!EDBM_op_callf(em, op, "recalc_face_normals faces=%hf", BM_ELEM_SELECT))
 		return OPERATOR_CANCELLED;
 
-	if (RNA_boolean_get(op->ptr, "inside"))
+	if (RNA_boolean_get(op->ptr, "inside")) {
-		EDBM_op_callf(em, op, "reverse_faces faces=%hf", BM_ELEM_SELECT);
+		EDBM_op_callf(em, op, "reverse_faces faces=%hf flip_multires=%b", BM_ELEM_SELECT, true);
+	}
 
 	EDBM_update_generic(em, true, false);