Optimization: introduce IdMap

egui/src/animation_manager.rs

@@ -1,10 +1,8 @@
-use epaint::ahash::AHashMap;
-
-use crate::{emath::remap_clamp, Id, InputState};
+use crate::{emath::remap_clamp, Id, IdMap, InputState};
 
 #[derive(Clone, Default)]
 pub(crate) struct AnimationManager {
-    bools: AHashMap<Id, BoolAnim>,
+    bools: IdMap<BoolAnim>,
 }
 
 #[derive(Clone, Debug)]

egui/src/frame_state.rs

@@ -1,5 +1,4 @@
 use crate::*;
-use epaint::ahash;
 
 /// State that is collected during a frame and then cleared.
 /// Short-term (single frame) memory.
@@ -7,7 +6,7 @@ use epaint::ahash;
 pub(crate) struct FrameState {
     /// All `Id`s that were used this frame.
     /// Used to debug `Id` clashes of widgets.
-    pub(crate) used_ids: ahash::AHashMap<Id, Rect>,
+    pub(crate) used_ids: IdMap<Rect>,
 
     /// Starts off as the screen_rect, shrinks as panels are added.
     /// The `CentralPanel` does not change this.

egui/src/id.rs

@@ -67,3 +67,56 @@ impl std::fmt::Debug for Id {
         write!(f, "{:X}", self.0)
     }
 }
+
+// ----------------------------------------------------------------------------
+
+// Idea taken from the `nohash_hasher` crate.
+#[derive(Default)]
+pub struct IdHasher(u64);
+
+impl std::hash::Hasher for IdHasher {
+    fn write(&mut self, _: &[u8]) {
+        unreachable!("Invalid use of IdHasher")
+    }
+
+    fn write_u8(&mut self, _n: u8) {
+        unreachable!("Invalid use of IdHasher")
+    }
+    fn write_u16(&mut self, _n: u16) {
+        unreachable!("Invalid use of IdHasher")
+    }
+    fn write_u32(&mut self, _n: u32) {
+        unreachable!("Invalid use of IdHasher")
+    }
+    fn write_u64(&mut self, n: u64) {
+        self.0 = n
+    }
+    fn write_usize(&mut self, _n: usize) {
+        unreachable!("Invalid use of IdHasher")
+    }
+
+    fn write_i8(&mut self, _n: i8) {
+        unreachable!("Invalid use of IdHasher")
+    }
+    fn write_i16(&mut self, _n: i16) {
+        unreachable!("Invalid use of IdHasher")
+    }
+    fn write_i32(&mut self, _n: i32) {
+        unreachable!("Invalid use of IdHasher")
+    }
+    fn write_i64(&mut self, _n: i64) {
+        unreachable!("Invalid use of IdHasher")
+    }
+    fn write_isize(&mut self, _n: isize) {
+        unreachable!("Invalid use of IdHasher")
+    }
+
+    fn finish(&self) -> u64 {
+        self.0
+    }
+}
+
+pub type BuilIdHasher = std::hash::BuildHasherDefault<IdHasher>;
+
+/// `IdMap<V>` is a `HashMap<Id, V>` optimized by knowing that `Id` has good entropy, and doesn't need more hashing.
+pub type IdMap<V> = std::collections::HashMap<Id, V, BuilIdHasher>;

egui/src/layers.rs

@@ -2,7 +2,6 @@
 //! are sometimes painted behind or in front of other things.
 
 use crate::{Id, *};
-use epaint::ahash::AHashMap;
 use epaint::mutex::Mutex;
 use epaint::{ClippedShape, Shape};
 use std::sync::Arc;
@@ -154,7 +153,7 @@ impl PaintList {
 }
 
 #[derive(Clone, Default)]
-pub(crate) struct GraphicLayers([AHashMap<Id, Arc<Mutex<PaintList>>>; Order::COUNT]);
+pub(crate) struct GraphicLayers([IdMap<Arc<Mutex<PaintList>>>; Order::COUNT]);
 
 impl GraphicLayers {
     pub fn list(&mut self, layer_id: LayerId) -> &Arc<Mutex<PaintList>> {

egui/src/lib.rs

@@ -387,7 +387,7 @@ pub use {
         output::{self, CursorIcon, Output, WidgetInfo},
     },
     grid::Grid,
-    id::Id,
+    id::{Id, IdMap},
     input_state::{InputState, MultiTouchInfo, PointerState},
     layers::{LayerId, Order},
     layout::*,

egui/src/memory.rs

@@ -1,6 +1,6 @@
-use std::collections::{HashMap, HashSet};
+use std::collections::HashSet;
 
-use crate::{any, area, window, Id, InputState, LayerId, Pos2, Rect, Style};
+use crate::{any, area, window, Id, IdMap, InputState, LayerId, Pos2, Rect, Style};
 
 // ----------------------------------------------------------------------------
 
@@ -259,7 +259,7 @@ impl Focus {
         }
     }
 
-    pub(crate) fn end_frame(&mut self, used_ids: &epaint::ahash::AHashMap<Id, Rect>) {
+    pub(crate) fn end_frame(&mut self, used_ids: &IdMap<Rect>) {
         if let Some(id) = self.id {
             // Allow calling `request_focus` one frame and not using it until next frame
             let recently_gained_focus = self.id_previous_frame != Some(id);
@@ -310,11 +310,7 @@ impl Memory {
         }
     }
 
-    pub(crate) fn end_frame(
-        &mut self,
-        input: &InputState,
-        used_ids: &epaint::ahash::AHashMap<Id, Rect>,
-    ) {
+    pub(crate) fn end_frame(&mut self, input: &InputState, used_ids: &IdMap<Rect>) {
         self.caches.update();
         self.areas.end_frame();
         self.interaction.focus.end_frame(used_ids);
@@ -465,7 +461,7 @@ impl Memory {
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "serde", serde(default))]
 pub struct Areas {
-    areas: HashMap<Id, area::State>,
+    areas: IdMap<area::State>,
     /// Back-to-front. Top is last.
     order: Vec<LayerId>,
     visible_last_frame: HashSet<LayerId>,