Refactor: UI: Replace uiLayoutRadial with class method uiLayout::menu_pie

This converts the public `uiLayoutRadial` function to an object oriented
API (`uiLayout::menu_pie`), matching the python API.
This reduces the difference between the C++ API with the python version,
its also helps while converting code from python to C++ code (or vice-versa),
making it almost seamless.

`uiLayout::menu_pie` now returns an `uiLayout` reference instead of a pointer.
New calls to this method should use references too.

Part of: #117604

Pull Request: https://projects.blender.org/blender/blender/pulls/138563

source/blender/editors/include/UI_interface_layout.hh

@@ -155,6 +155,13 @@ struct uiLayout : uiItem {
   /** Add a new list box sub-layout. */
   uiLayout &list_box(uiList *ui_list, PointerRNA *actptr, PropertyRNA *actprop);
 
+  /**
+   * Add a pie menu layout, buttons are arranged around a center.
+   * Only one pie menu per layout root can be added, if it's already initialized it will be
+   * returned instead of adding a new one.
+   */
+  uiLayout &menu_pie();
+
   /** Add a new overlap sub-layout. */
   uiLayout &overlap();
 
@@ -396,9 +403,6 @@ void uiLayoutListItemAddPadding(uiLayout *layout);
 
 bool uiLayoutEndsWithPanelHeader(const uiLayout &layout);
 
-/** Pie menu layout: Buttons are arranged around a center. */
-uiLayout *uiLayoutRadial(uiLayout *layout);
-
 enum class LayoutSeparatorType : int8_t {
   Auto,
   Space,

source/blender/editors/interface/interface_layout.cc

@@ -106,7 +106,7 @@ enum class ItemType : int8_t {
   LayoutAbsolute,
   LayoutSplit,
   LayoutOverlap,
-  LayoutRadial,
+  LayoutRadial, /* AKA: menu pie. */
 
   LayoutRoot,
 #if 0
@@ -837,7 +837,7 @@ static void ui_item_enum_expand_exec(uiLayout *layout,
   uiLayout *layout_radial = nullptr;
   if (radial) {
     if (layout->root_->layout == layout) {
-      layout_radial = uiLayoutRadial(layout);
+      layout_radial = &layout->menu_pie();
       UI_block_layout_set_current(block, layout_radial);
     }
     else {
@@ -1486,7 +1486,7 @@ void uiItemsFullEnumO_items(uiLayout *layout,
   const bool radial = ui_layout_is_radial(layout);
 
   if (radial) {
-    target = uiLayoutRadial(layout);
+    target = &layout->menu_pie();
   }
   else if ((uiLayoutGetLocalDir(layout) == UI_LAYOUT_HORIZONTAL) && (flag & UI_ITEM_R_ICON_ONLY)) {
     target = layout;
@@ -5141,30 +5141,30 @@ static uiLayoutItemBx *ui_layout_box(uiLayout *layout, int type)
   return box;
 }
 
-uiLayout *uiLayoutRadial(uiLayout *layout)
+uiLayout &uiLayout::menu_pie()
 {
   /* radial layouts are only valid for radial menus */
-  if (layout->root_->type != UI_LAYOUT_PIEMENU) {
-    return ui_item_local_sublayout(layout, layout, false);
+  if (root_->type != UI_LAYOUT_PIEMENU) {
+    return *ui_item_local_sublayout(this, this, false);
   }
 
   /* only one radial wheel per root layout is allowed, so check and return that, if it exists */
-  for (uiItem *item : layout->root_->layout->items_) {
+  for (uiItem *item : root_->layout->items_) {
     if (item->type_ == uiItemType::LayoutRadial) {
       uiLayout *litem = static_cast<uiLayout *>(item);
-      UI_block_layout_set_current(layout->root_->block, litem);
-      return litem;
+      UI_block_layout_set_current(root_->block, litem);
+      return *litem;
     }
   }
 
   uiLayout *litem = MEM_new<uiLayout>(__func__);
-  ui_litem_init_from_parent(litem, layout, false);
+  ui_litem_init_from_parent(litem, this, false);
 
   litem->type_ = uiItemType::LayoutRadial;
 
-  UI_block_layout_set_current(layout->root_->block, litem);
+  UI_block_layout_set_current(root_->block, litem);
 
-  return litem;
+  return *litem;
 }
 
 uiLayout &uiLayout::box()

source/blender/editors/interface/regions/interface_region_menu_pie.cc

@@ -232,7 +232,7 @@ wmOperatorStatus UI_pie_menu_invoke_from_operator_enum(bContext *C,
   pie = UI_pie_menu_begin(C, IFACE_(title.c_str()), ICON_NONE, event);
   layout = UI_pie_menu_layout(pie);
 
-  layout = uiLayoutRadial(layout);
+  layout = &layout->menu_pie();
   uiItemsEnumO(layout, opname, propname);
 
   UI_pie_menu_end(C, pie);
@@ -266,7 +266,7 @@ wmOperatorStatus UI_pie_menu_invoke_from_rna_enum(bContext *C,
 
   layout = UI_pie_menu_layout(pie);
 
-  layout = uiLayoutRadial(layout);
+  layout = &layout->menu_pie();
   uiItemFullR(layout, &r_ptr, r_prop, RNA_NO_INDEX, 0, UI_ITEM_R_EXPAND, std::nullopt, ICON_NONE);
 
   UI_pie_menu_end(C, pie);
@@ -316,7 +316,7 @@ static void ui_pie_menu_level_invoke(bContext *C, void *argN, void *arg2)
   uiPieMenu *pie = UI_pie_menu_begin(C, IFACE_(lvl->title), lvl->icon, win->eventstate);
   uiLayout *layout = UI_pie_menu_layout(pie);
 
-  layout = uiLayoutRadial(layout);
+  layout = &layout->menu_pie();
 
   PointerRNA ptr;
 

source/blender/makesrna/intern/rna_ui_api.cc

@@ -910,6 +910,11 @@ static uiLayout *rna_uiLayoutGridFlow(uiLayout *layout,
   return &layout->grid_flow(row_major, columns_len, even_columns, even_rows, align);
 }
 
+static uiLayout *rna_uiLayoutMenuPie(uiLayout *layout)
+{
+  return &layout->menu_pie();
+}
+
 void rna_uiLayoutPanelProp(uiLayout *layout,
                            bContext *C,
                            ReportList *reports,
@@ -1400,7 +1405,7 @@ void RNA_api_ui_layout(StructRNA *srna)
   RNA_def_boolean(func, "align", false, "", "Align buttons to each other");
 
   /* radial/pie layout */
-  func = RNA_def_function(srna, "menu_pie", "uiLayoutRadial");
+  func = RNA_def_function(srna, "menu_pie", "rna_uiLayoutMenuPie");
   parm = RNA_def_pointer(func, "layout", "UILayout", "", "Sub-layout to put items in");
   RNA_def_function_return(func, parm);
   RNA_def_function_ui_description(func,