Add Memory::caches for caching things from one frame to the next

CHANGELOG.md

@@ -14,6 +14,7 @@ NOTE: [`eframe`](eframe/CHANGELOG.md), [`egui_web`](egui_web/CHANGELOG.md), [`eg
 * Add feature `"serialize"` separatedly from `"persistence"`.
 * Add `egui::widgets::global_dark_light_mode_buttons` to easily add buttons for switching the egui theme.
 * `TextEdit` can now be used to show text which can be selectedd and copied, but not edited.
+* Add `Memory::caches` for caching things from one frame to the next.
 
 ### Changed 🔧
 * Label text will now be centered, right-aligned and/or justified based on the layout.

Cargo.lock

@@ -831,7 +831,9 @@ dependencies = [
 name = "egui"
 version = "0.14.2"
 dependencies = [
+ "ahash",
  "epaint",
+ "nohash-hasher",
  "ron",
  "serde",
  "serde_json",

egui/Cargo.toml

@@ -24,8 +24,10 @@ all-features = true
 
 [dependencies]
 epaint = { version = "0.14.0", path = "../epaint", default-features = false }
-serde = { version = "1", features = ["derive", "rc"], optional = true }
+ahash = "0.7"
+nohash-hasher = "0.2"
 ron = { version = "0.6.4", optional = true }
+serde = { version = "1", features = ["derive", "rc"], optional = true }
 
 [features]
 default = ["default_fonts", "single_threaded"]

egui/src/memory.rs

@@ -19,6 +19,7 @@ use crate::{any, area, window, Id, InputState, LayerId, Pos2, Rect, Style};
 pub struct Memory {
     pub options: Options,
 
+    // ------------------------------------------
     /// This map stores current states for widgets that don't require `Id`.
     /// This will be saved between different program runs if you use the `persistence` feature.
     #[cfg(feature = "persistence")]
@@ -30,7 +31,7 @@ pub struct Memory {
     pub data: any::TypeMap,
 
     /// Same as `data`, but this data will not be saved between runs.
-    #[cfg_attr(feature = "persistence", serde(skip))]
+    #[cfg_attr(feature = "serde", serde(skip))]
     pub data_temp: any::TypeMap,
 
     /// This map stores current states for all widgets with custom `Id`s.
@@ -44,9 +45,37 @@ pub struct Memory {
     pub id_data: any::AnyMap<Id>,
 
     /// Same as `id_data`, but this data will not be saved between runs.
-    #[cfg_attr(feature = "persistence", serde(skip))]
+    #[cfg_attr(feature = "serde", serde(skip))]
     pub id_data_temp: any::AnyMap<Id>,
 
+    // ------------------------------------------
+    /// Can be used to cache computations from one frame to another.
+    ///
+    /// This is for saving CPU when you have something that may take 1-100ms to compute.
+    /// Things that are very slow (>100ms) should instead be done async (i.e. in another thread)
+    /// so as not to lock the UI thread.
+    ///
+    /// ```
+    /// use egui::util::cache::{ComputerMut, FrameCache};
+    ///
+    /// #[derive(Default)]
+    /// struct CharCounter {}
+    /// impl ComputerMut<&str, usize> for CharCounter {
+    ///     fn compute(&mut self, s: &str) -> usize {
+    ///         s.chars().count() // you probably want to cache something more expensive than this
+    ///     }
+    /// }
+    /// type CharCountCache<'a> = FrameCache<usize, CharCounter>;
+    ///
+    /// # let mut ctx = egui::CtxRef::default();
+    /// let mut memory = ctx.memory();
+    /// let cache = memory.caches.cache::<CharCountCache<'_>>();
+    /// assert_eq!(cache.get("hello"), 5);
+    /// ```
+    #[cfg_attr(feature = "serde", serde(skip))]
+    pub caches: crate::util::cache::CacheStorage,
+
+    // ------------------------------------------
     /// new scale that will be applied at the start of the next frame
     pub(crate) new_pixels_per_point: Option<f32>,
 
@@ -286,6 +315,7 @@ impl Memory {
         input: &InputState,
         used_ids: &epaint::ahash::AHashMap<Id, Rect>,
     ) {
+        self.caches.update();
         self.areas.end_frame();
         self.interaction.focus.end_frame(used_ids);
         self.drag_value.end_frame(input);

egui/src/util/cache.rs

@@ -1,41 +1,164 @@
-use epaint::util::hash;
+//! Computing the same thing each frame can be expensive,
+//! so often you want to save the result from the previous frame and reuse it.
+//!
+//! Enter [`FrameCache`]: it caches the results of a computation for one frame.
+//! If it is still used next frame, it is not recomputed.
+//! If it is not used next frame, it is evicted from the cache to save memory.
 
-const SIZE: usize = 1024; // must be small for web/WASM build (for unknown reason)
+/// Something that does an expensive computation that we want to cache
+/// to save us from recomputing it each frame.
+pub trait ComputerMut<Key, Value>: 'static + Send + Sync {
+    fn compute(&mut self, key: Key) -> Value;
+}
 
-/// Very stupid/simple key-value cache. TODO: improve
+/// Caches the results of a computation for one frame.
-#[derive(Clone)]
+/// If it is still used next frame, it is not recomputed.
-pub struct Cache<K, V>([Option<(K, V)>; SIZE]);
+/// If it is not used next frame, it is evicted from the cache to save memory.
+pub struct FrameCache<Value, Computer> {
+    generation: u32,
+    computer: Computer,
+    cache: nohash_hasher::IntMap<u64, (u32, Value)>,
+}
 
-impl<K, V> Default for Cache<K, V>
+impl<Value, Computer> Default for FrameCache<Value, Computer>
 where
-    K: Copy,
+    Computer: Default,
-    V: Copy,
 {
     fn default() -> Self {
-        Self([None; SIZE])
+        Self::new(Computer::default())
     }
 }
 
-impl<K, V> std::fmt::Debug for Cache<K, V> {
+impl<Value, Computer> FrameCache<Value, Computer> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    pub fn new(computer: Computer) -> Self {
-        write!(f, "Cache")
+        Self {
-    }
+            generation: 0,
-}
+            computer,
-
+            cache: Default::default(),
-impl<K, V> Cache<K, V>
-where
-    K: std::hash::Hash + PartialEq,
-{
-    pub fn get(&self, key: &K) -> Option<&V> {
-        let bucket = (hash(key) % (SIZE as u64)) as usize;
-        match &self.0[bucket] {
-            Some((k, v)) if k == key => Some(v),
-            _ => None,
         }
     }
 
-    pub fn set(&mut self, key: K, value: V) {
+    /// Must be called once per frame to clear the [`Galley`] cache.
-        let bucket = (hash(&key) % (SIZE as u64)) as usize;
+    pub fn evice_cache(&mut self) {
-        self.0[bucket] = Some((key, value));
+        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<Value, Computer> FrameCache<Value, Computer> {
+    /// Get from cache (if the same key was used last frame)
+    /// or recompute and store in the cache.
+    pub fn get<Key>(&mut self, key: Key) -> Value
+    where
+        Key: Copy + std::hash::Hash,
+        Value: Clone,
+        Computer: ComputerMut<Key, Value>,
+    {
+        let hash = crate::util::hash(key);
+
+        match self.cache.entry(hash) {
+            std::collections::hash_map::Entry::Occupied(entry) => {
+                let cached = entry.into_mut();
+                cached.0 = self.generation;
+                cached.1.clone()
+            }
+            std::collections::hash_map::Entry::Vacant(entry) => {
+                let value = self.computer.compute(key);
+                entry.insert((self.generation, value.clone()));
+                value
+            }
+        }
+    }
+}
+
+#[allow(clippy::len_without_is_empty)]
+pub trait CacheTrait: 'static + Send + Sync {
+    /// Call once per frame to evict cache.
+    fn update(&mut self);
+
+    /// Number of values currently in the cache.
+    fn len(&self) -> usize;
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any;
+}
+
+impl<Value: 'static + Send + Sync, Computer: 'static + Send + Sync> CacheTrait
+    for FrameCache<Value, Computer>
+{
+    fn update(&mut self) {
+        self.evice_cache()
+    }
+
+    fn len(&self) -> usize {
+        self.cache.len()
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
+        self
+    }
+}
+
+/// ```
+/// use egui::util::cache::{CacheStorage, ComputerMut, FrameCache};
+///
+/// #[derive(Default)]
+/// struct CharCounter {}
+/// impl ComputerMut<&str, usize> for CharCounter {
+///     fn compute(&mut self, s: &str) -> usize {
+///         s.chars().count()
+///     }
+/// }
+/// type CharCountCache<'a> = FrameCache<usize, CharCounter>;
+///
+/// # let mut cache_storage = CacheStorage::default();
+/// let mut cache = cache_storage.cache::<CharCountCache<'_>>();
+/// assert_eq!(cache.get("hello"), 5);
+/// ```
+#[derive(Default)]
+pub struct CacheStorage {
+    caches: ahash::AHashMap<std::any::TypeId, Box<dyn CacheTrait>>,
+}
+
+impl CacheStorage {
+    pub fn cache<FrameCache: CacheTrait + Default>(&mut self) -> &mut FrameCache {
+        self.caches
+            .entry(std::any::TypeId::of::<FrameCache>())
+            .or_insert_with(|| Box::new(FrameCache::default()))
+            .as_any_mut()
+            .downcast_mut::<FrameCache>()
+            .unwrap()
+    }
+
+    /// Total number of cached values
+    fn num_values(&self) -> usize {
+        self.caches.values().map(|cache| cache.len()).sum()
+    }
+
+    /// Call once per frame to evict cache.
+    pub fn update(&mut self) {
+        for cache in self.caches.values_mut() {
+            cache.update();
+        }
+    }
+}
+
+impl Clone for CacheStorage {
+    fn clone(&self) -> Self {
+        // We return an empty cache that can be filled in again.
+        Self::default()
+    }
+}
+
+impl std::fmt::Debug for CacheStorage {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(
+            f,
+            "FrameCacheStorage[{} caches with {} elements]",
+            self.caches.len(),
+            self.num_values()
+        )
     }
 }

egui/src/util/fixed_cache.rs

@@ -0,0 +1,41 @@
+use epaint::util::hash;
+
+const FIXED_CACHE_SIZE: usize = 1024; // must be small for web/WASM build (for unknown reason)
+
+/// Very stupid/simple key-value cache. TODO: improve
+#[derive(Clone)]
+pub(crate) struct FixedCache<K, V>([Option<(K, V)>; FIXED_CACHE_SIZE]);
+
+impl<K, V> Default for FixedCache<K, V>
+where
+    K: Copy,
+    V: Copy,
+{
+    fn default() -> Self {
+        Self([None; FIXED_CACHE_SIZE])
+    }
+}
+
+impl<K, V> std::fmt::Debug for FixedCache<K, V> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Cache")
+    }
+}
+
+impl<K, V> FixedCache<K, V>
+where
+    K: std::hash::Hash + PartialEq,
+{
+    pub fn get(&self, key: &K) -> Option<&V> {
+        let bucket = (hash(key) % (FIXED_CACHE_SIZE as u64)) as usize;
+        match &self.0[bucket] {
+            Some((k, v)) if k == key => Some(v),
+            _ => None,
+        }
+    }
+
+    pub fn set(&mut self, key: K, value: V) {
+        let bucket = (hash(&key) % (FIXED_CACHE_SIZE as u64)) as usize;
+        self.0[bucket] = Some((key, value));
+    }
+}

egui/src/util/mod.rs

@@ -1,8 +1,10 @@
 //! Miscellaneous tools used by the rest of egui.
 
-pub(crate) mod cache;
+pub mod cache;
+pub(crate) mod fixed_cache;
 mod history;
 pub mod undoer;
 
-pub(crate) use cache::Cache;
 pub use history::History;
+
+pub use epaint::util::{hash, hash_with};

egui/src/widgets/color_picker.rs

@@ -1,6 +1,6 @@
 //! Color picker widgets.
 
-use crate::util::Cache;
+use crate::util::fixed_cache::FixedCache;
 use crate::*;
 use epaint::{color::*, *};
 
@@ -322,7 +322,7 @@ pub fn color_picker_color32(ui: &mut Ui, srgba: &mut Color32, alpha: Alpha) -> b
         .ctx()
         .memory()
         .data_temp
-        .get_or_default::<Cache<Color32, Hsva>>()
+        .get_or_default::<FixedCache<Color32, Hsva>>()
         .get(srgba)
         .cloned()
         .unwrap_or_else(|| Hsva::from(*srgba));
@@ -334,7 +334,7 @@ pub fn color_picker_color32(ui: &mut Ui, srgba: &mut Color32, alpha: Alpha) -> b
     ui.ctx()
         .memory()
         .data_temp
-        .get_mut_or_default::<Cache<Color32, Hsva>>()
+        .get_mut_or_default::<FixedCache<Color32, Hsva>>()
         .set(*srgba, hsva);
 
     response
@@ -386,7 +386,7 @@ pub fn color_edit_button_srgba(ui: &mut Ui, srgba: &mut Color32, alpha: Alpha) -
         .ctx()
         .memory()
         .data_temp
-        .get_or_default::<Cache<Color32, Hsva>>()
+        .get_or_default::<FixedCache<Color32, Hsva>>()
         .get(srgba)
         .cloned()
         .unwrap_or_else(|| Hsva::from(*srgba));
@@ -398,7 +398,7 @@ pub fn color_edit_button_srgba(ui: &mut Ui, srgba: &mut Color32, alpha: Alpha) -
     ui.ctx()
         .memory()
         .data_temp
-        .get_mut_or_default::<Cache<Color32, Hsva>>()
+        .get_mut_or_default::<FixedCache<Color32, Hsva>>()
         .set(*srgba, hsva);
 
     response

epaint/src/text/fonts.rs

@@ -405,7 +405,7 @@ struct GalleyCache {
 
 impl GalleyCache {
     fn layout(&mut self, fonts: &Fonts, job: LayoutJob) -> Arc<Galley> {
-        let hash = crate::util::hash_with(&job, ahash::AHasher::new_with_keys(123, 456)); // TODO: even faster hasher?
+        let hash = crate::util::hash(&job); // TODO: even faster hasher?
 
         match self.cache.entry(hash) {
             std::collections::hash_map::Entry::Occupied(entry) => {