Remove 64 bit atomics in main crate (#8037)

This allows the base egui crate to run on platforms without 64 bit
atomics

* Addresses <https://github.com/emilk/egui/issues/7692>, but does not
address the `egui_extras` crate

* [x] I have followed the instructions in the PR template

crates/egui/src/load/texture_loader.rs

@@ -1,5 +1,3 @@
-use std::sync::atomic::{AtomicU64, Ordering::Relaxed};
-
 use emath::Vec2;
 
 use super::{
@@ -17,7 +15,7 @@ struct PrimaryKey {
 type Bucket = HashMap<Option<SizeHint>, Entry>;
 
 struct Entry {
-    last_used: AtomicU64,
+    last_used: u64,
 
     /// Size of the original SVG, if any, or the texel size of the image if not an SVG.
     source_size: Vec2,
@@ -25,10 +23,15 @@ struct Entry {
     handle: TextureHandle,
 }
 
+#[derive(Default)]
+struct State {
+    pass_index: u64,
+    cache: HashMap<PrimaryKey, Bucket>,
+}
+
 #[derive(Default)]
 pub struct DefaultTextureLoader {
-    pass_index: AtomicU64,
-    cache: Mutex<HashMap<PrimaryKey, Bucket>>,
+    state: Mutex<State>,
 }
 
 impl TextureLoader for DefaultTextureLoader {
@@ -55,7 +58,9 @@ impl TextureLoader for DefaultTextureLoader {
             None
         };
 
-        let mut cache = self.cache.lock();
+        let mut state = self.state.lock();
+        let State { pass_index, cache } = &mut *state;
+
         let bucket = cache
             .entry(PrimaryKey {
                 uri: uri.to_owned(),
@@ -63,10 +68,8 @@ impl TextureLoader for DefaultTextureLoader {
             })
             .or_default();
 
-        if let Some(texture) = bucket.get(&svg_size_hint) {
-            texture
-                .last_used
-                .store(self.pass_index.load(Relaxed), Relaxed);
+        if let Some(texture) = bucket.get_mut(&svg_size_hint) {
+            texture.last_used = *pass_index;
             let texture = SizedTexture::new(texture.handle.id(), texture.source_size);
             Ok(TexturePoll::Ready { texture })
         } else {
@@ -79,7 +82,7 @@ impl TextureLoader for DefaultTextureLoader {
                     bucket.insert(
                         svg_size_hint,
                         Entry {
-                            last_used: AtomicU64::new(self.pass_index.load(Relaxed)),
+                            last_used: *pass_index,
                             source_size,
                             handle,
                         },
@@ -104,33 +107,37 @@ impl TextureLoader for DefaultTextureLoader {
     fn forget(&self, uri: &str) {
         log::trace!("forget {uri:?}");
 
-        self.cache.lock().retain(|key, _value| key.uri != uri);
+        self.state.lock().cache.retain(|key, _value| key.uri != uri);
     }
 
     fn forget_all(&self) {
         log::trace!("forget all");
 
-        self.cache.lock().clear();
+        self.state.lock().cache.clear();
     }
 
     fn end_pass(&self, pass_index: u64) {
-        self.pass_index.store(pass_index, Relaxed);
-        let mut cache = self.cache.lock();
+        let mut state = self.state.lock();
+        state.pass_index = pass_index;
+
+        let State { pass_index, cache } = &mut *state;
+
         cache.retain(|_key, bucket| {
             if 2 <= bucket.len() {
                 // There are multiple textures of the same URI (e.g. SVGs of different scales).
                 // This could be because someone has an SVG in a resizable container,
                 // and so we get a lot of different sizes of it.
                 // This could wast VRAM, so we remove the ones that are not used in this frame.
-                bucket.retain(|_, texture| pass_index <= texture.last_used.load(Relaxed) + 1);
+                bucket.retain(|_, texture| *pass_index <= texture.last_used + 1);
             }
             !bucket.is_empty()
         });
     }
 
     fn byte_size(&self) -> usize {
-        self.cache
+        self.state
             .lock()
+            .cache
             .values()
             .map(|bucket| {
                 bucket

crates/epaint/src/text/fonts.rs

@@ -3,7 +3,7 @@ use std::{
     collections::BTreeMap,
     sync::{
         Arc,
-        atomic::{AtomicU64, Ordering},
+        atomic::{AtomicUsize, Ordering},
     },
 };
 
@@ -439,7 +439,7 @@ impl FontFaceKey {
     pub const INVALID: Self = Self(0);
 
     fn new() -> Self {
-        static KEY_COUNTER: AtomicU64 = AtomicU64::new(1);
+        static KEY_COUNTER: AtomicUsize = AtomicUsize::new(1);
         Self(crate::util::hash(
             KEY_COUNTER.fetch_add(1, Ordering::Relaxed),
         ))