Standard widgets: Popover and Menu. (#21636)

# Objective

- Splitting out the non-BSN parts of the work on popup menus.

## Solution

- Added Popover and Menu components.

## Testing

- Manual testing using example.

## Showcase

<img width="311" height="261" alt="popup"
src="https://github.com/user-attachments/assets/ab9e8959-65bc-45d3-aa36-9d56cc09ea9d"
/>

---------

Co-authored-by: Viktor Gustavsson <[email protected]>

Author: viridia

crates/bevy_input_focus/src/tab_navigation.rs

@@ -166,12 +166,12 @@ pub struct TabNavigation<'w, 's> {
 }
 
 impl TabNavigation<'_, '_> {
-    /// Navigate to the desired focusable entity.
+    /// Navigate to the desired focusable entity, relative to the current focused entity.
     ///
     /// Change the [`NavAction`] to navigate in a different direction.
     /// Focusable entities are determined by the presence of the [`TabIndex`] component.
     ///
-    /// If no focusable entities are found, then this function will return either the first
+    /// If there is no currently focused entity, then this function will return either the first
     /// or last focusable entity, depending on the direction of navigation. For example, if
     /// `action` is `Next` and no focusable entities are found, then this function will return
     /// the first focusable entity.
@@ -198,13 +198,46 @@ impl TabNavigation<'_, '_> {
                 })
         });
 
+        self.navigate_internal(focus.0, action, tabgroup)
+    }
+
+    /// Initialize focus to a focusable child of a container, either the first or last
+    /// depending on [`NavAction`]. This assumes that the parent entity has a [`TabGroup`]
+    /// component.
+    ///
+    /// Focusable entities are determined by the presence of the [`TabIndex`] component.
+    pub fn initialize(
+        &self,
+        parent: Entity,
+        action: NavAction,
+    ) -> Result<Entity, TabNavigationError> {
+        // If there are no tab groups, then there are no focusable entities.
+        if self.tabgroup_query.is_empty() {
+            return Err(TabNavigationError::NoTabGroups);
+        }
+
+        // Look for the tab group on the parent entity.
+        match self.tabgroup_query.get(parent) {
+            Ok(tabgroup) => self.navigate_internal(None, action, Some((parent, tabgroup.1))),
+            Err(_) => Err(TabNavigationError::NoTabGroups),
+        }
+    }
+
+    pub fn navigate_internal(
+        &self,
+        focus: Option<Entity>,
+        action: NavAction,
+        tabgroup: Option<(Entity, &TabGroup)>,
+    ) -> Result<Entity, TabNavigationError> {
         let navigation_result = self.navigate_in_group(tabgroup, focus, action);
 
         match navigation_result {
             Ok(entity) => {
-                if focus.0.is_some() && tabgroup.is_none() {
+                if let Some(previous_focus) = focus
+                    && tabgroup.is_none()
+                {
                     Err(TabNavigationError::NoTabGroupForCurrentFocus {
-                        previous_focus: focus.0.unwrap(),
+                        previous_focus,
                         new_focus: entity,
                     })
                 } else {
@@ -218,7 +251,7 @@ impl TabNavigation<'_, '_> {
     fn navigate_in_group(
         &self,
         tabgroup: Option<(Entity, &TabGroup)>,
-        focus: &InputFocus,
+        focus: Option<Entity>,
         action: NavAction,
     ) -> Result<Entity, TabNavigationError> {
         // List of all focusable entities found.
@@ -268,7 +301,7 @@ impl TabNavigation<'_, '_> {
             }
         });
 
-        let index = focusable.iter().position(|e| Some(e.0) == focus.0);
+        let index = focusable.iter().position(|e| Some(e.0) == focus);
         let count = focusable.len();
         let next = match (index, action) {
             (Some(idx), NavAction::Next) => (idx + 1).rem_euclid(count),

crates/bevy_math/src/rects/rect.rs

@@ -356,6 +356,20 @@ impl Rect {
         }
     }
 
+    /// Return the area of this rectangle.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use bevy_math::Rect;
+    /// let r = Rect::new(0., 0., 10., 10.); // w=10 h=10
+    /// assert_eq!(r.area(), 100.0);
+    /// ```
+    #[inline]
+    pub fn area(&self) -> f32 {
+        self.width() * self.height()
+    }
+
     /// Returns self as [`IRect`] (i32)
     #[inline]
     pub fn as_irect(&self) -> IRect {

crates/bevy_ui_widgets/Cargo.toml

@@ -12,6 +12,7 @@ keywords = ["bevy"]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.18.0-dev" }
 bevy_a11y = { path = "../bevy_a11y", version = "0.18.0-dev" }
+bevy_camera = { path = "../bevy_camera", version = "0.18.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.18.0-dev" }
 bevy_input = { path = "../bevy_input", version = "0.18.0-dev" }
 bevy_input_focus = { path = "../bevy_input_focus", version = "0.18.0-dev" }

crates/bevy_ui_widgets/src/lib.rs

@@ -20,13 +20,16 @@
 
 mod button;
 mod checkbox;
+mod menu;
 mod observe;
+pub mod popover;
 mod radio;
 mod scrollbar;
 mod slider;
 
 pub use button::*;
 pub use checkbox::*;
+pub use menu::*;
 pub use observe::*;
 pub use radio::*;
 pub use scrollbar::*;
@@ -35,15 +38,19 @@ pub use slider::*;
 use bevy_app::{PluginGroup, PluginGroupBuilder};
 use bevy_ecs::{entity::Entity, event::EntityEvent};
 
+use crate::popover::PopoverPlugin;
+
 /// A plugin group that registers the observers for all of the widgets in this crate. If you don't want to
 /// use all of the widgets, you can import the individual widget plugins instead.
 pub struct UiWidgetsPlugins;
 
 impl PluginGroup for UiWidgetsPlugins {
     fn build(self) -> PluginGroupBuilder {
         PluginGroupBuilder::start::<Self>()
+            .add(PopoverPlugin)
             .add(ButtonPlugin)
             .add(CheckboxPlugin)
+            .add(MenuPlugin)
             .add(RadioGroupPlugin)
             .add(ScrollbarPlugin)
             .add(SliderPlugin)