Remove highlight_this_frame

crates/egui/src/context.rs

@@ -900,6 +900,14 @@ impl Context {
         self.write(move |ctx| writer(&mut ctx.viewport().frame_state))
     }
 
+    /// Read-only access to the [`FrameState`] from the previous frame.
+    ///
+    /// This is swapped at the end of each frame.
+    #[inline]
+    pub(crate) fn prev_frame_state<R>(&self, reader: impl FnOnce(&FrameState) -> R) -> R {
+        self.write(move |ctx| reader(&ctx.viewport().prev_frame_state))
+    }
+
     /// Read-only access to [`Fonts`].
     ///
     /// Not valid until first call to [`Context::run()`].
@@ -1108,7 +1116,8 @@ impl Context {
             enabled,
         } = widget_rect;
 
-        let highlighted = self.frame_state(|fs| fs.highlight_this_frame.contains(&id));
+        // previous frame + "highlight next frame" == "highlight this frame"
+        let highlighted = self.prev_frame_state(|fs| fs.highlight_next_frame.contains(&id));
 
         let mut res = Response {
             ctx: self.clone(),

crates/egui/src/frame_state.rs

@@ -70,10 +70,7 @@ pub struct FrameState {
     #[cfg(feature = "accesskit")]
     pub accesskit_state: Option<AccessKitFrameState>,
 
-    /// Highlight these widgets this next frame. Read from this.
-    pub highlight_this_frame: IdSet,
-
-    /// Highlight these widgets the next frame. Write to this.
+    /// Highlight these widgets the next frame.
     pub highlight_next_frame: IdSet,
 
     #[cfg(debug_assertions)]
@@ -92,7 +89,6 @@ impl Default for FrameState {
             scroll_delta: Vec2::default(),
             #[cfg(feature = "accesskit")]
             accesskit_state: None,
-            highlight_this_frame: Default::default(),
             highlight_next_frame: Default::default(),
 
             #[cfg(debug_assertions)]
@@ -114,7 +110,6 @@ impl FrameState {
             scroll_delta,
             #[cfg(feature = "accesskit")]
             accesskit_state,
-            highlight_this_frame,
             highlight_next_frame,
 
             #[cfg(debug_assertions)]
@@ -139,7 +134,7 @@ impl FrameState {
             *accesskit_state = None;
         }
 
-        *highlight_this_frame = std::mem::take(highlight_next_frame);
+        highlight_next_frame.clear();
     }
 
     /// How much space is still available after panels has been added.