Keep track of submenu index in parent context menu

this improves the Id's generated for submenus, as they will depend on
the index in their parent, rather than their position. This avoids
recreating an Id for the same conceptual submenu, only drawn at a
different position.

Author: mankinskin

egui/src/context_menu.rs

@@ -144,14 +144,16 @@ pub struct MenuEntry {
     text: String,
     icon: String,
     state: EntryState,
+    index: usize,
 }
 impl MenuEntry {
     #[allow(clippy::needless_pass_by_value)]
-    fn new(text: impl ToString, icon: impl ToString, state: EntryState) -> Self {
+    fn new(text: impl ToString, icon: impl ToString, state: EntryState, index: usize) -> Self {
         Self {
             text: text.to_string(),
             icon: icon.to_string(),
             state,
+            index,
         }
     }
     #[allow(clippy::needless_pass_by_value)]
@@ -167,7 +169,8 @@ impl MenuEntry {
         let MenuEntry {
             text,
             icon,
-            state
+            state,
+            ..
         } = self;
 
         let text_style = TextStyle::Button;
@@ -223,14 +226,14 @@ pub struct SubMenu<'a> {
 }
 impl<'a> SubMenu<'a> {
     #[allow(clippy::needless_pass_by_value)]
-    fn new(text: impl ToString, parent_state: &'a mut MenuState) -> Self {
+    fn new(text: impl ToString, parent_state: &'a mut MenuState, index: usize) -> Self {
         Self {
-            entry: MenuEntry::new(text, "⏵", EntryState::Active),
+            entry: MenuEntry::new(text, "⏵", EntryState::Active, index),
             parent_state,
         }
     }
     pub fn show(self, ui: &mut Ui, add_contents: impl FnOnce(&mut Ui, &mut MenuState)) -> Response {
-        let sub_id = ui.id().with(format!("{:?}", ui.placer.cursor().min));
+        let sub_id = ui.id().with(self.entry.index);
         let button = self.entry.show_with_state(ui, EntryState::submenu(self.parent_state, sub_id));
         self.parent_state
             .submenu_button_interaction(ui, sub_id, &button);
@@ -244,29 +247,36 @@ pub struct MenuState {
     sub_menu: Option<(Id, Box<MenuState>)>,
     rect: Rect,
     response: MenuResponse,
+    entry_count: usize,
 }
 impl MenuState {
     /// close menu hierarchy
     pub fn close(&mut self) {
         self.response = MenuResponse::Close;
     }
     /// create a menu item
-    pub fn item(&self, text: impl ToString) -> MenuEntry {
-        MenuEntry::new(text, "", EntryState::entry(self))
+    pub fn item(&mut self, text: impl ToString) -> MenuEntry {
+        MenuEntry::new(text, "", EntryState::entry(self), self.next_entry_index())
     }
     /// create a menu item with an icon
-    pub fn item_with_icon(&self, text: impl ToString, icon: impl ToString) -> MenuEntry {
-        MenuEntry::new(text, icon, EntryState::entry(self))
+    pub fn item_with_icon(&mut self, text: impl ToString, icon: impl ToString) -> MenuEntry {
+        MenuEntry::new(text, icon, EntryState::entry(self), self.next_entry_index())
+    }
+    fn next_entry_index(&mut self) -> usize {
+        self.entry_count += 1;
+        self.entry_count-1
     }
     /// create a sub-menu
     pub fn submenu(&'_ mut self, text: impl ToString) -> SubMenu<'_> {
-        SubMenu::new(text, self)
+        let index = self.next_entry_index();
+        SubMenu::new(text, self, index)
     }
     fn new(position: Pos2) -> Self {
         Self {
             rect: Rect::from_min_size(position, Vec2::ZERO),
             sub_menu: None,
             response: MenuResponse::Stay,
+            entry_count: 0,
         }
     }
     /// sense button interaction opening and closing submenu
@@ -303,6 +313,7 @@ impl MenuState {
         id: Id,
         add_contents: impl FnOnce(&mut Ui, &mut MenuState),
     ) -> Response {
+        self.entry_count = 0;
         crate::menu::menu_ui(
             ctx,
             id,