Mesh: Add operator to flip quad tessellation

This adds a new operator: bpy.ops.mesh.flip_quad_tessellation()

This operator rotates the internal loops of the selected quads, allowing
the user to control tessellation without destructively altering the
mesh.

{F14201995}

This operator can be found in the "Face" menu (Ctrl+F) under "Face
Data".

{F14201997}

Reviewed By: campbellbarton, dbystedt

Differential Revision: https://developer.blender.org/D17056

release/scripts/startup/bl_ui/space_view3d.py

@@ -4274,7 +4274,10 @@ class VIEW3D_MT_edit_mesh_faces_data(Menu):
 
         layout.separator()
 
+        layout.operator("mesh.flip_quad_tessellation")
+
         if with_freestyle:
+            layout.separator()
             layout.operator("mesh.mark_freestyle_face").clear = False
             layout.operator("mesh.mark_freestyle_face", text="Clear Freestyle Face").clear = True
 

source/blender/bmesh/intern/bmesh_opdefines.c

@@ -270,6 +270,23 @@ static BMOpDefine bmo_reverse_faces_def = {
    BMO_OPTYPE_FLAG_NORMALS_CALC),
 };
 
+/*
+ * Flip Quad Tessellation
+ *
+ * Flip the tessellation direction of the selected quads.
+*/
+static BMOpDefine bmo_flip_quad_tessellation_def = {
+  "flip_quad_tessellation",
+  /* slot_in */
+  {
+    {"faces", BMO_OP_SLOT_ELEMENT_BUF, {BM_FACE}},
+    {{'\0'}}
+  },
+  {{{'\0'}}}, /* no output */
+  bmo_flip_quad_tessellation_exec,
+  (BMO_OPTYPE_FLAG_UNTAN_MULTIRES | BMO_OPTYPE_FLAG_NORMALS_CALC),
+};
+
 /*
  * Edge Bisect.
  *
@@ -2128,6 +2145,7 @@ const BMOpDefine *bmo_opdefines[] = {
     &bmo_extrude_face_region_def,
     &bmo_extrude_vert_indiv_def,
     &bmo_find_doubles_def,
+    &bmo_flip_quad_tessellation_def,
     &bmo_grid_fill_def,
     &bmo_inset_individual_def,
     &bmo_inset_region_def,

source/blender/bmesh/intern/bmesh_operators_private.h

@@ -88,3 +88,4 @@ void bmo_triangulate_exec(BMesh *bm, BMOperator *op);
 void bmo_unsubdivide_exec(BMesh *bm, BMOperator *op);
 void bmo_weld_verts_exec(BMesh *bm, BMOperator *op);
 void bmo_wireframe_exec(BMesh *bm, BMOperator *op);
+void bmo_flip_quad_tessellation_exec(BMesh *bm, BMOperator *op);

source/blender/bmesh/intern/bmesh_polygon.h

@@ -177,6 +177,7 @@ void BM_face_normal_flip_ex(BMesh *bm,
                             int cd_loop_mdisp_offset,
                             bool use_loop_mdisp_flip) ATTR_NONNULL();
 void BM_face_normal_flip(BMesh *bm, BMFace *f) ATTR_NONNULL();
+
 /**
  * BM POINT IN FACE
  *

source/blender/bmesh/operators/bmo_utils.c

@@ -147,6 +147,22 @@ void bmo_reverse_faces_exec(BMesh *bm, BMOperator *op)
 #define SEL_FLAG 1
 #define SEL_ORIG 2
 
+void bmo_flip_quad_tessellation_exec(BMesh *bm, BMOperator *op)
+{
+  BMOIter siter;
+  BMFace *f;
+  bool changed = false;
+  BMO_ITER (f, &siter, op->slots_in, "faces", BM_FACE) {
+    if (f->len == 4) {
+      f->l_first = f->l_first->next;
+      changed = true;
+    }
+  }
+  if (changed) {
+    bm->elem_index_dirty |= BM_LOOP;
+  }
+}
+
 static void bmo_face_flag_set_flush(BMesh *bm, BMFace *f, const short oflag, const bool value)
 {
   BMLoop *l_iter;

source/blender/editors/mesh/editmesh_tools.c

@@ -2227,6 +2227,18 @@ static void edbm_flip_normals_custom_loop_normals(Object *obedit, BMEditMesh *em
               });
 }
 
+static void edbm_flip_quad_tessellation(wmOperator *op, Object *obedit, BMEditMesh *em)
+{
+  if (EDBM_op_callf(em, op, "flip_quad_tessellation faces=%hf", BM_ELEM_SELECT)) {
+    EDBM_update(obedit->data,
+                &(const struct EDBMUpdate_Params){
+                    .calc_looptri = true,
+                    .calc_normals = false,
+                    .is_destructive = false,
+                });
+  }
+}
+
 static void edbm_flip_normals_face_winding(wmOperator *op, Object *obedit, BMEditMesh *em)
 {
 
@@ -2253,6 +2265,27 @@ static void edbm_flip_normals_face_winding(wmOperator *op, Object *obedit, BMEdi
   }
 }
 
+static int edbm_flip_quad_tessellation_exec(bContext *C, wmOperator *op)
+{
+  const Scene *scene = CTX_data_scene(C);
+  ViewLayer *view_layer = CTX_data_view_layer(C);
+  uint objects_len = 0;
+  Object **objects = BKE_view_layer_array_from_objects_in_edit_mode_unique_data(
+      scene, view_layer, CTX_wm_view3d(C), &objects_len);
+
+  for (uint ob_index = 0; ob_index < objects_len; ob_index++) {
+    Object *obedit = objects[ob_index];
+    BMEditMesh *em = BKE_editmesh_from_object(obedit);
+    if (em->bm->totfacesel == 0) {
+      continue;
+    }
+    edbm_flip_quad_tessellation(op, obedit, em);
+  }
+
+  MEM_freeN(objects);
+  return OPERATOR_FINISHED;
+}
+
 static int edbm_flip_normals_exec(bContext *C, wmOperator *op)
 {
   const bool only_clnors = RNA_boolean_get(op->ptr, "only_clnors");
@@ -9934,4 +9967,18 @@ void MESH_OT_mod_weighted_strength(struct wmOperatorType *ot)
       "Strength to use for assigning or selecting face influence for weighted normal modifier");
 }
 
+void MESH_OT_flip_quad_tessellation(struct wmOperatorType *ot)
+{
+  /* identifiers */
+  ot->name = "Flip Quad Tessellation";
+  ot->description = "Flips the tessellation of selected quads";
+  ot->idname = "MESH_OT_flip_quad_tessellation";
+
+  ot->exec = edbm_flip_quad_tessellation_exec;
+  ot->poll = ED_operator_editmesh;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+}
+
 /** \} */

source/blender/editors/mesh/mesh_intern.h

@@ -294,6 +294,7 @@ void MESH_OT_set_normals_from_faces(struct wmOperatorType *ot);
 void MESH_OT_average_normals(struct wmOperatorType *ot);
 void MESH_OT_smooth_normals(struct wmOperatorType *ot);
 void MESH_OT_mod_weighted_strength(struct wmOperatorType *ot);
+void MESH_OT_flip_quad_tessellation(struct wmOperatorType *ot);
 
 /* *** editmesh_mask_extract.c *** */
 

source/blender/editors/mesh/mesh_ops.c

@@ -193,6 +193,7 @@ void ED_operatortypes_mesh(void)
   WM_operatortype_append(MESH_OT_average_normals);
   WM_operatortype_append(MESH_OT_smooth_normals);
   WM_operatortype_append(MESH_OT_mod_weighted_strength);
+  WM_operatortype_append(MESH_OT_flip_quad_tessellation);
 }
 
 #if 0 /* UNUSED, remove? */