Add Context::request_repaint_after (#1694)

eframe/src/native/run.rs

@@ -120,7 +120,7 @@ pub fn run_glow(
 
             let egui::FullOutput {
                 platform_output,
-                needs_repaint,
+                repaint_after,
                 textures_delta,
                 shapes,
             } = integration.update(app.as_mut(), window);
@@ -148,9 +148,18 @@ pub fn run_glow(
 
             *control_flow = if integration.should_quit() {
                 winit::event_loop::ControlFlow::Exit
-            } else if needs_repaint {
+            } else if repaint_after.is_zero() {
                 window.request_redraw();
                 winit::event_loop::ControlFlow::Poll
+            } else if let Some(repaint_after_instant) =
+                std::time::Instant::now().checked_add(repaint_after)
+            {
+                // if repaint_after is something huge and can't be added to Instant,
+                // we will use `ControlFlow::Wait` instead.
+                // technically, this might lead to some weird corner cases where the user *WANTS*
+                // winit to use `WaitUntil(MAX_INSTANT)` explicitly. they can roll their own
+                // egui backend impl i guess.
+                winit::event_loop::ControlFlow::WaitUntil(repaint_after_instant)
             } else {
                 winit::event_loop::ControlFlow::Wait
             };
@@ -167,7 +176,6 @@ pub fn run_glow(
                 std::thread::sleep(std::time::Duration::from_millis(10));
             }
         };
-
         match event {
             // Platform-dependent event handlers to workaround a winit bug
             // See: https://github.com/rust-windowing/winit/issues/987
@@ -209,7 +217,12 @@ pub fn run_glow(
                 painter.destroy();
             }
             winit::event::Event::UserEvent(RequestRepaintEvent) => window.request_redraw(),
-            _ => (),
+            winit::event::Event::NewEvents(winit::event::StartCause::ResumeTimeReached {
+                ..
+            }) => {
+                window.request_redraw();
+            }
+            _ => {}
         }
     });
 }
@@ -298,7 +311,7 @@ pub fn run_wgpu(
 
             let egui::FullOutput {
                 platform_output,
-                needs_repaint,
+                repaint_after,
                 textures_delta,
                 shapes,
             } = integration.update(app.as_mut(), window);
@@ -319,9 +332,18 @@ pub fn run_wgpu(
 
             *control_flow = if integration.should_quit() {
                 winit::event_loop::ControlFlow::Exit
-            } else if needs_repaint {
+            } else if repaint_after.is_zero() {
                 window.request_redraw();
                 winit::event_loop::ControlFlow::Poll
+            } else if let Some(repaint_after_instant) =
+                std::time::Instant::now().checked_add(repaint_after)
+            {
+                // if repaint_after is something huge and can't be added to Instant,
+                // we will use `ControlFlow::Wait` instead.
+                // technically, this might lead to some weird corner cases where the user *WANTS*
+                // winit to use `WaitUntil(MAX_INSTANT)` explicitly. they can roll their own
+                // egui backend impl i guess.
+                winit::event_loop::ControlFlow::WaitUntil(repaint_after_instant)
             } else {
                 winit::event_loop::ControlFlow::Wait
             };
@@ -395,6 +417,11 @@ pub fn run_wgpu(
                 painter.destroy();
             }
             winit::event::Event::UserEvent(RequestRepaintEvent) => window.request_redraw(),
+            winit::event::Event::NewEvents(winit::event::StartCause::ResumeTimeReached {
+                ..
+            }) => {
+                window.request_redraw();
+            }
             _ => (),
         }
     });

eframe/src/web/backend.rs

@@ -251,10 +251,10 @@ impl AppRunner {
         Ok(())
     }
 
-    /// Returns `true` if egui requests a repaint.
+    /// Returns how long to wait until the next repaint.
     ///
     /// Call [`Self::paint`] later to paint
-    pub fn logic(&mut self) -> Result<(bool, Vec<egui::ClippedPrimitive>), JsValue> {
+    pub fn logic(&mut self) -> Result<(std::time::Duration, Vec<egui::ClippedPrimitive>), JsValue> {
         let frame_start = now_sec();
 
         resize_canvas_to_screen_size(self.canvas_id(), self.app.max_size_points());
@@ -266,7 +266,7 @@ impl AppRunner {
         });
         let egui::FullOutput {
             platform_output,
-            needs_repaint,
+            repaint_after,
             textures_delta,
             shapes,
         } = full_output;
@@ -288,7 +288,7 @@ impl AppRunner {
         }
 
         self.frame.info.cpu_usage = Some((now_sec() - frame_start) as f32);
-        Ok((needs_repaint, clipped_primitives))
+        Ok((repaint_after, clipped_primitives))
     }
 
     pub fn clear_color_buffer(&self) {

eframe/src/web/events.rs

@@ -9,11 +9,12 @@ pub fn paint_and_schedule(
         let mut runner_lock = runner_ref.lock();
         if runner_lock.needs_repaint.fetch_and_clear() {
             runner_lock.clear_color_buffer();
-            let (needs_repaint, clipped_primitives) = runner_lock.logic()?;
+            let (repaint_after, clipped_primitives) = runner_lock.logic()?;
             runner_lock.paint(&clipped_primitives)?;
-            if needs_repaint {
+            if repaint_after.is_zero() {
                 runner_lock.needs_repaint.set_true();
             }
+            // TODO: schedule a repaint after `repaint_after` when it is not zero
             runner_lock.auto_save();
         }