Add egui::cache::FramePublisher

crates/egui/src/cache/frame_publisher.rs

@@ -0,0 +1,61 @@
+use std::hash::Hash;
+
+use super::CacheTrait;
+
+/// Stores a key:value pair for the duration of this frame and the next.
+pub struct FramePublisher<Key: Eq + Hash, Value> {
+    generation: u32,
+    cache: ahash::HashMap<Key, (u32, Value)>,
+}
+
+impl<Key: Eq + Hash, Value> Default for FramePublisher<Key, Value> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<Key: Eq + Hash, Value> FramePublisher<Key, Value> {
+    pub fn new() -> Self {
+        Self {
+            generation: 0,
+            cache: Default::default(),
+        }
+    }
+
+    /// Publish the value. It will be available for the duration of the and the next frame.
+    pub fn set(&mut self, key: Key, value: Value) {
+        self.cache.insert(key, (self.generation, value));
+    }
+
+    /// Retrieve a value if it was publiushed this or the previous frame.
+    pub fn get(&self, key: &Key) -> Option<&Value> {
+        self.cache.get(key).map(|(_, value)| value)
+    }
+
+    /// Must be called once per frame to clear the cache.
+    pub fn evict_cache(&mut self) {
+        let current_generation = self.generation;
+        self.cache.retain(|_key, cached| {
+            cached.0 == current_generation // only keep those that were used this frame
+        });
+        self.generation = self.generation.wrapping_add(1);
+    }
+}
+
+impl<Key, Value> CacheTrait for FramePublisher<Key, Value>
+where
+    Key: 'static + Eq + Hash + Send + Sync,
+    Value: 'static + Send + Sync,
+{
+    fn update(&mut self) {
+        self.evict_cache();
+    }
+
+    fn len(&self) -> usize {
+        self.cache.len()
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+        self
+    }
+}

crates/egui/src/cache/mod.rs

@@ -13,7 +13,9 @@
 mod cache_storage;
 mod cache_trait;
 mod frame_cache;
+mod frame_publisher;
 
 pub use cache_storage::CacheStorage;
 pub use cache_trait::CacheTrait;
 pub use frame_cache::{ComputerMut, FrameCache};
+pub use frame_publisher::FramePublisher;