Make Context::request_repaint safe to call from any thread.

Closes https://github.com/emilk/egui/issues/1379

CHANGELOG.md

@@ -9,7 +9,7 @@ NOTE: [`epaint`](epaint/CHANGELOG.md), [`eframe`](eframe/CHANGELOG.md), [`egui_w
 ### Added ⭐
 * Added `Shape::Callback` for backend-specific painting ([#1351](https://github.com/emilk/egui/pull/1351)).
 * Added `Frame::canvas` ([#1362](https://github.com/emilk/egui/pull/1362)).
-* `Context::request_repaint` will wake up UI thread, if integrations has called `Context::set_request_repaint_callback` ([#1366](https://github.com/emilk/egui/pull/1366)).
+* `Context::request_repaint` will wake up UI thread, if integrations has called `Context::with_repaint_callback` ([#1366](https://github.com/emilk/egui/pull/1366)).
 * Added `Ui::push_id` ([#1374](https://github.com/emilk/egui/pull/1374)).
 
 ### Changed 🔧

egui-winit/src/epi.rs

@@ -229,12 +229,11 @@ pub struct EpiIntegration {
 impl EpiIntegration {
     pub fn new(
         integration_name: &'static str,
+        egui_ctx: egui::Context,
         max_texture_side: usize,
         window: &winit::window::Window,
         persistence: crate::epi::Persistence,
     ) -> Self {
-        let egui_ctx = egui::Context::default();
-
         *egui_ctx.memory() = persistence.load_memory().unwrap_or_default();
 
         let prefer_dark_mode = prefer_dark_mode();

egui/src/context.rs

@@ -1,5 +1,8 @@
 // #![warn(missing_docs)]
 
+use std::sync::atomic::AtomicU32;
+use std::sync::atomic::Ordering::SeqCst;
+
 use crate::{
     animation_manager::AnimationManager, data::output::PlatformOutput, frame_state::FrameState,
     input_state::*, layers::GraphicLayers, memory::Options, output::FullOutput, TextureHandle, *,
@@ -27,6 +30,25 @@ impl Default for WrappedTextureManager {
 
 // ----------------------------------------------------------------------------
 
+struct RepaintInfo {
+    /// While positive, keep requesting repaints. Decrement at the end of each frame.
+    repaint_requests: AtomicU32,
+    request_repaint_callbacks: Option<Box<dyn Fn() + Send + Sync>>,
+}
+
+impl Default for RepaintInfo {
+    fn default() -> Self {
+        Self {
+            // Start with painting an extra frame to compensate for some widgets
+            // that take two frames before they "settle":
+            repaint_requests: 1.into(),
+            request_repaint_callbacks: None,
+        }
+    }
+}
+
+// ----------------------------------------------------------------------------
+
 #[derive(Default)]
 struct ContextImpl {
     /// `None` until the start of the first frame.
@@ -45,10 +67,6 @@ struct ContextImpl {
     output: PlatformOutput,
 
     paint_stats: PaintStats,
-
-    /// While positive, keep requesting repaints. Decrement at the end of each frame.
-    repaint_requests: u32,
-    request_repaint_callbacks: Option<Box<dyn Fn() + Send + Sync>>,
 }
 
 impl ContextImpl {
@@ -142,33 +160,41 @@ impl ContextImpl {
 ///     paint(full_output.textures_delta, clipped_primitives);
 /// }
 /// ```
-#[derive(Clone)]
+#[derive(Clone, Default)]
-pub struct Context(Arc<RwLock<ContextImpl>>);
+pub struct Context {
+    ctx: Arc<RwLock<ContextImpl>>,
+    repaint_info: Arc<RepaintInfo>,
+}
 
 impl std::cmp::PartialEq for Context {
     fn eq(&self, other: &Context) -> bool {
-        Arc::ptr_eq(&self.0, &other.0)
+        Arc::ptr_eq(&self.ctx, &other.ctx)
-    }
-}
-
-impl Default for Context {
-    fn default() -> Self {
-        Self(Arc::new(RwLock::new(ContextImpl {
-            // Start with painting an extra frame to compensate for some widgets
-            // that take two frames before they "settle":
-            repaint_requests: 1,
-            ..ContextImpl::default()
-        })))
     }
 }
 
 impl Context {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Construct a [`Context`] with a callback that is called when the user calls
+    /// [`Context::request_repaint`].
+    pub fn with_repaint_callback(callback: impl Fn() + Send + Sync + 'static) -> Self {
+        Self {
+            ctx: Default::default(),
+            repaint_info: Arc::new(RepaintInfo {
+                request_repaint_callbacks: Some(Box::new(callback)),
+                ..Default::default()
+            }),
+        }
+    }
+
     fn read(&self) -> RwLockReadGuard<'_, ContextImpl> {
-        self.0.read()
+        self.ctx.read()
     }
 
     fn write(&self) -> RwLockWriteGuard<'_, ContextImpl> {
-        self.0.write()
+        self.ctx.write()
     }
 
     /// Run the ui code for one frame.
@@ -539,25 +565,16 @@ impl Context {
     /// Call as many times as you wish, only one repaint will be issued.
     ///
     /// If called from outside the UI thread, the UI thread will wake up and run,
-    /// provided the egui integration has set that up via [`Self::set_request_repaint_callback`]
+    /// provided the egui integration has set that up via [`Self::with_repaint_callback`]
     /// (this will work on `eframe`).
     pub fn request_repaint(&self) {
         // request two frames of repaint, just to cover some corner cases (frame delays):
-        let mut ctx = self.write();
+        self.repaint_info.repaint_requests.store(2, SeqCst);
-        ctx.repaint_requests = 2;
+        if let Some(callback) = &self.repaint_info.request_repaint_callbacks {
-        if let Some(callback) = &ctx.request_repaint_callbacks {
             (callback)();
         }
     }
 
-    /// For integrations: this callback will be called when an egui user calls [`Self::request_repaint`].
-    ///
-    /// This lets you wake up a sleeping UI thread.
-    pub fn set_request_repaint_callback(&self, callback: impl Fn() + Send + Sync + 'static) {
-        let callback = Box::new(callback);
-        self.write().request_repaint_callbacks = Some(callback);
-    }
-
     /// Tell `egui` which fonts to use.
     ///
     /// The default `egui` fonts only support latin and cyrillic alphabets,
@@ -776,8 +793,8 @@ impl Context {
 
         let platform_output: PlatformOutput = std::mem::take(&mut self.output());
 
-        let needs_repaint = if self.read().repaint_requests > 0 {
+        let needs_repaint = if self.repaint_info.repaint_requests.load(SeqCst) > 0 {
-            self.write().repaint_requests -= 1;
+            self.repaint_info.repaint_requests.fetch_sub(1, SeqCst);
             true
         } else {
             false

egui_glow/src/epi_backend.rs

@@ -46,20 +46,21 @@ pub fn run(app_name: &str, native_options: &epi::NativeOptions, app_creator: epi
     let mut painter = crate::Painter::new(gl.clone(), None, "")
         .unwrap_or_else(|error| panic!("some OpenGL error occurred {}\n", error));
 
+    let event_loop_proxy = parking_lot::Mutex::new(event_loop.create_proxy());
+    let egui_ctx = egui::Context::with_repaint_callback({
+        move || {
+            event_loop_proxy.lock().send_event(RequestRepaintEvent).ok();
+        }
+    });
+
     let mut integration = egui_winit::epi::EpiIntegration::new(
         "egui_glow",
+        egui_ctx,
         painter.max_texture_side(),
         gl_window.window(),
         persistence,
     );
 
-    {
-        let event_loop_proxy = parking_lot::Mutex::new(event_loop.create_proxy());
-        integration.egui_ctx.set_request_repaint_callback(move || {
-            event_loop_proxy.lock().send_event(RequestRepaintEvent).ok();
-        });
-    }
-
     let mut app = app_creator(&epi::CreationContext {
         egui_ctx: integration.egui_ctx.clone(),
         integration_info: integration.frame.info(),

egui_web/src/backend.rs

@@ -159,14 +159,12 @@ impl AppRunner {
 
         let needs_repaint: std::sync::Arc<NeedRepaint> = Default::default();
 
-        let egui_ctx = egui::Context::default();
+        let egui_ctx = egui::Context::with_repaint_callback({
-
-        {
             let needs_repaint = needs_repaint.clone();
-            egui_ctx.set_request_repaint_callback(move || {
+            move || {
                 needs_repaint.0.store(true, SeqCst);
-            });
             }
+        });
 
         load_memory(&egui_ctx);
         if prefer_dark_mode == Some(true) {