Add Area::sense and improve hit-testing of buttons in menus (#4234)

Previously, putting the cursor in the gap between two menu buttons would
not hover any of the buttons, but the click-sensitive menu itself. Now
the menu is no longer click-sensitive.

crates/egui/src/containers/area.rs

@@ -61,6 +61,7 @@ impl State {
 #[derive(Clone, Copy, Debug)]
 pub struct Area {
     pub(crate) id: Id,
+    sense: Option<Sense>,
     movable: bool,
     interactable: bool,
     enabled: bool,
@@ -78,6 +79,7 @@ impl Area {
     pub fn new(id: Id) -> Self {
         Self {
             id,
+            sense: None,
             movable: true,
             interactable: true,
             constrain: false,
@@ -114,7 +116,7 @@ impl Area {
         self
     }
 
-    /// moveable by dragging the area?
+    /// Moveable by dragging the area?
     #[inline]
     pub fn movable(mut self, movable: bool) -> Self {
         self.movable = movable;
@@ -139,6 +141,15 @@ impl Area {
         self
     }
 
+    /// Explicitly set a sense.
+    ///
+    /// If not set, this will default to `Sense::drag()` if movable, `Sense::click()` if interactable, and `Sense::hover()` otherwise.
+    #[inline]
+    pub fn sense(mut self, sense: Sense) -> Self {
+        self.sense = Some(sense);
+        self
+    }
+
     /// `order(Order::Foreground)` for an Area that should always be on top
     #[inline]
     pub fn order(mut self, order: Order) -> Self {
@@ -255,6 +266,7 @@ impl Area {
     pub(crate) fn begin(self, ctx: &Context) -> Prepared {
         let Self {
             id,
+            sense,
             movable,
             order,
             interactable,
@@ -299,13 +311,15 @@ impl Area {
         // interact right away to prevent frame-delay
         let mut move_response = {
             let interact_id = layer_id.id.with("move");
-            let sense = if movable {
-                Sense::drag()
-            } else if interactable {
-                Sense::click() // allow clicks to bring to front
-            } else {
-                Sense::hover()
-            };
+            let sense = sense.unwrap_or_else(|| {
+                if movable {
+                    Sense::drag()
+                } else if interactable {
+                    Sense::click() // allow clicks to bring to front
+                } else {
+                    Sense::hover()
+                }
+            });
 
             let move_response = ctx.create_widget(WidgetRect {
                 id: interact_id,

crates/egui/src/menu.rs

@@ -149,7 +149,8 @@ pub(crate) fn menu_ui<'c, R>(
         .order(Order::Foreground)
         .fixed_pos(pos)
         .constrain_to(ctx.screen_rect())
-        .interactable(true);
+        .interactable(true)
+        .sense(Sense::hover());
 
     let area_response = area.show(ctx, |ui| {
         set_menu_style(ui.style_mut());