fix some corner cases for repaint requests

egui/src/containers/area.rs

@@ -190,7 +190,6 @@ impl Prepared {
         if move_interact.active {
             state.pos += input.mouse.delta;
             state.vel = input.mouse.velocity;
-            ctx.request_repaint();
         } else {
             let stop_speed = 20.0; // Pixels per second.
             let friction_coeff = 1000.0; // Pixels per second squared.
@@ -225,6 +224,7 @@ impl Prepared {
             || !ctx.memory().areas.visible_last_frame(&layer)
         {
             ctx.memory().areas.move_to_top(layer);
+            ctx.request_repaint();
         }
         ctx.memory().areas.set_state(layer, state);
 

egui/src/containers/collapsing_header.rs

@@ -104,7 +104,6 @@ impl State {
         let openness = self.openness(ui);
         let animate = 0.0 < openness && openness < 1.0;
         if animate {
-            ui.ctx().request_repaint();
             Some(ui.add_custom(|child_ui| {
                 let max_height = if self.open {
                     if let Some(full_height) = self.open_height {

egui/src/containers/resize.rs

@@ -128,6 +128,8 @@ impl Resize {
         let id = self.id.unwrap_or_else(|| ui.make_child_id("resize"));
 
         let mut state = ui.memory().resize.get(&id).cloned().unwrap_or_else(|| {
+            ui.ctx().request_repaint(); // counter frame delay
+
             let default_size = self.default_size.max(self.min_size);
 
             State {

egui/src/context.rs

@@ -1,4 +1,7 @@
-use std::sync::Arc;
+use std::sync::{
+    atomic::{AtomicU32, Ordering::SeqCst},
+    Arc,
+};
 
 use {
     ahash::AHashMap,
@@ -38,6 +41,9 @@ pub struct Context {
     used_ids: Mutex<AHashMap<Id, Pos2>>,
 
     paint_stats: Mutex<PaintStats>,
+
+    /// While positive, keep requesting repaints. Decrement at the end of each frame.
+    repaint_requests: AtomicU32,
 }
 
 impl Clone for Context {
@@ -53,6 +59,7 @@ impl Clone for Context {
             output: Mutex::new(self.output.lock().clone()),
             used_ids: Mutex::new(self.used_ids.lock().clone()),
             paint_stats: Mutex::new(*self.paint_stats.lock()),
+            repaint_requests: self.repaint_requests.load(SeqCst).into(),
         }
     }
 }
@@ -82,7 +89,9 @@ impl Context {
     /// If this is called at least once in a frame, then there will be another frame right after this.
     /// Call as many times as you wish, only one repaint will be issued.
     pub fn request_repaint(&self) {
-        self.output().needs_repaint = true;
+        // request two frames of repaint, just to cover some corner cases (frame delays):
+        let times_to_repaint = 2;
+        self.repaint_requests.store(times_to_repaint, SeqCst);
     }
 
     pub fn input(&self) -> &InputState {
@@ -95,7 +104,7 @@ impl Context {
         &*self
             .fonts
             .as_ref()
-            .expect("No fonts available until first call to Contex::begin_frame()`")
+            .expect("No fonts available until first call to Context::begin_frame()`")
     }
 
     /// Not valid until first call to `begin_frame()`
@@ -105,7 +114,7 @@ impl Context {
     }
 
     /// Will become active at the start of the next frame.
-    /// `pixels_per_point` will be ignored (overwitten at start of each frame with the contents of input)
+    /// `pixels_per_point` will be ignored (overwritten at start of each frame with the contents of input)
     pub fn set_fonts(&self, font_definitions: FontDefinitions) {
         *self.font_definitions.lock() = font_definitions;
     }
@@ -180,7 +189,13 @@ impl Context {
         }
 
         self.memory().end_frame();
-        let output: Output = std::mem::take(&mut self.output());
+
+        let mut output: Output = std::mem::take(&mut self.output());
+        if self.repaint_requests.load(SeqCst) > 0 {
+            self.repaint_requests.fetch_sub(1, SeqCst);
+            output.needs_repaint = true;
+        }
+
         let paint_jobs = self.paint();
         (output, paint_jobs)
     }
@@ -574,7 +589,7 @@ impl paint::PaintOptions {
 impl PaintStats {
     pub fn ui(&self, ui: &mut Ui) {
         ui.add(label!("Jobs: {}", self.num_jobs))
-            .tooltip_text("Number of separate clip rectanlges");
+            .tooltip_text("Number of separate clip rectangles");
         ui.add(label!("Primitives: {}", self.num_primitives))
             .tooltip_text("Boxes, circles, text areas etc");
         ui.add(label!("Vertices: {}", self.num_vertices));

egui/src/types.rs

@@ -18,9 +18,9 @@ pub struct Output {
     /// Response to Event::Copy or Event::Cut. Ignore if empty.
     pub copied_text: String,
 
-    /// Set to `true` to request another repaint right after this one.
-    /// This is only used in reactive backends (i.e. backends where we repaint on new input).
-    /// For instance, you may want to set this to `true` while there is an animation.
+    /// If `true`, Egui or a user is indicating that the UI needs immediate repaint (e.g. on the next frame).
+    /// This happens for instance when there is an animation, or if a user has called `Context::request_repaint()`.
+    /// Don't set this manually, but call `Context::request_repaint()` instead.
     pub needs_repaint: bool,
 }