Fix: request_repaint_after works even when called from background thread (#2939)

* Refactor repaint logic

* request_repaint_after also fires the request_repaint callback

* Bug fixes

* Add test to egui_demo_app

* build_demo_web: build debug unless --release is specified

* Fix the web backend too

* Run special clippy for wasm, forbidding some types/methods

* Remove wasm_bindgen_check.sh

* Fix typos

* Revert "Remove wasm_bindgen_check.sh"

This reverts commit 92dde25344.

* Only run cranky/clippy once

crates/egui_demo_app/src/backend_panel.rs

@@ -1,5 +1,3 @@
-use egui::Widget;
-
 /// How often we repaint the demo app by default
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 enum RunMode {
@@ -43,6 +41,7 @@ impl Default for RunMode {
 
 // ----------------------------------------------------------------------------
 
+#[derive(Default)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "serde", serde(default))]
 pub struct BackendPanel {
@@ -52,9 +51,6 @@ pub struct BackendPanel {
     // go back to [`RunMode::Reactive`] mode each time we start
     run_mode: RunMode,
 
-    #[cfg_attr(feature = "serde", serde(skip))]
-    repaint_after_seconds: f32,
-
     /// current slider value for current gui scale
     #[cfg_attr(feature = "serde", serde(skip))]
     pixels_per_point: Option<f32>,
@@ -65,19 +61,6 @@ pub struct BackendPanel {
     egui_windows: EguiWindows,
 }
 
-impl Default for BackendPanel {
-    fn default() -> Self {
-        Self {
-            open: false,
-            run_mode: Default::default(),
-            repaint_after_seconds: 1.0,
-            pixels_per_point: None,
-            frame_history: Default::default(),
-            egui_windows: Default::default(),
-        }
-    }
-}
-
 impl BackendPanel {
     pub fn update(&mut self, ctx: &egui::Context, frame: &mut eframe::Frame) {
         self.frame_history
@@ -90,9 +73,6 @@ impl BackendPanel {
             }
             RunMode::Reactive => {
                 // let the computer rest for a bit
-                ctx.request_repaint_after(std::time::Duration::from_secs_f32(
-                    self.repaint_after_seconds,
-                ));
             }
         }
     }
@@ -271,17 +251,27 @@ impl BackendPanel {
         } else {
             ui.label("Only running UI code when there are animations or input.");
 
-            ui.horizontal(|ui| {
-                ui.spacing_mut().item_spacing.x = 0.0;
-                ui.label("(but at least every ");
-                egui::DragValue::new(&mut self.repaint_after_seconds)
-                    .clamp_range(0.1..=10.0)
-                    .speed(0.1)
-                    .suffix(" s")
-                    .ui(ui)
-                    .on_hover_text("Repaint this often, even if there is no input.");
-                ui.label(")");
-            });
+            // Add a test for `request_repaint_after`, but only in debug
+            // builds to keep the noise down in the official demo.
+            if cfg!(debug_assertions) {
+                ui.collapsing("More…", |ui| {
+                    ui.horizontal(|ui| {
+                        ui.label("Frame number:");
+                        ui.monospace(ui.ctx().frame_nr().to_string());
+                    });
+                    if ui
+                        .button("Wait 2s, then request repaint after another 3s")
+                        .clicked()
+                    {
+                        log::info!("Waiting 2s before requesting repaint...");
+                        let ctx = ui.ctx().clone();
+                        call_after_delay(std::time::Duration::from_secs(2), move || {
+                            log::info!("Request a repaint in 3s...");
+                            ctx.request_repaint_after(std::time::Duration::from_secs(3));
+                        });
+                    }
+                });
+            }
         }
     }
 }
@@ -394,3 +384,28 @@ impl EguiWindows {
             });
     }
 }
+
+// ----------------------------------------------------------------------------
+
+#[cfg(not(target_arch = "wasm32"))]
+fn call_after_delay(delay: std::time::Duration, f: impl FnOnce() + Send + 'static) {
+    std::thread::spawn(move || {
+        std::thread::sleep(delay);
+        f();
+    });
+}
+
+#[cfg(target_arch = "wasm32")]
+fn call_after_delay(delay: std::time::Duration, f: impl FnOnce() + Send + 'static) {
+    use wasm_bindgen::prelude::*;
+    let window = web_sys::window().unwrap();
+    let closure = Closure::once(f);
+    let delay_ms = delay.as_millis() as _;
+    window
+        .set_timeout_with_callback_and_timeout_and_arguments_0(
+            closure.as_ref().unchecked_ref(),
+            delay_ms,
+        )
+        .unwrap();
+    closure.forget(); // We must forget it, or else the callback is canceled on drop
+}

crates/egui_demo_app/src/frame_history.rs

@@ -33,12 +33,6 @@ impl FrameHistory {
     }
 
     pub fn ui(&mut self, ui: &mut egui::Ui) {
-        ui.label(format!(
-            "Total frames painted: {}",
-            self.frame_times.total_count()
-        ))
-        .on_hover_text("Includes this frame.");
-
         ui.label(format!(
             "Mean CPU usage: {:.2} ms / frame",
             1e3 * self.mean_frame_time()