From 49dbf2c14658cb5f2aafdbb75d826d8ba8fedc31 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?=
 <hector0193@gmail.com>
Date: Tue, 9 Jun 2020 15:45:57 +0200
Subject: [PATCH] Request a redraw only on relevant events

---
 examples/integration/src/main.rs | 21 ++++++++++++---------
 glutin/src/application.rs        |  4 ++++
 native/src/program/state.rs      | 11 +++++++----
 winit/src/application.rs         |  4 ++++
 4 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/examples/integration/src/main.rs b/examples/integration/src/main.rs
index db8b4366..4c4b6d84 100644
--- a/examples/integration/src/main.rs
+++ b/examples/integration/src/main.rs
@@ -119,16 +119,19 @@ pub fn main() {
                 }
             }
             Event::MainEventsCleared => {
-                // We update iced
-                let _ = state.update(
-                    None,
-                    viewport.logical_size(),
-                    &mut renderer,
-                    &mut debug,
-                );
+                // If there are events pending
+                if !state.is_queue_empty() {
+                    // We update iced
+                    let _ = state.update(
+                        None,
+                        viewport.logical_size(),
+                        &mut renderer,
+                        &mut debug,
+                    );
 
-                // and request a redraw
-                window.request_redraw();
+                    // and request a redraw
+                    window.request_redraw();
+                }
             }
             Event::RedrawRequested(_) => {
                 if resized {
diff --git a/glutin/src/application.rs b/glutin/src/application.rs
index c777a13b..4f36114c 100644
--- a/glutin/src/application.rs
+++ b/glutin/src/application.rs
@@ -95,6 +95,10 @@ pub fn run<A, E, C>(
 
     event_loop.run(move |event, _, control_flow| match event {
         event::Event::MainEventsCleared => {
+            if state.is_queue_empty() {
+                return;
+            }
+
             let command = runtime.enter(|| {
                 state.update(
                     clipboard.as_ref().map(|c| c as _),
diff --git a/native/src/program/state.rs b/native/src/program/state.rs
index 8716d8b9..bb428198 100644
--- a/native/src/program/state.rs
+++ b/native/src/program/state.rs
@@ -88,6 +88,13 @@ where
         self.queued_messages.push(message);
     }
 
+    /// Returns whether the event queue of the [`State`] is empty or not.
+    ///
+    /// [`State`]: struct.State.html
+    pub fn is_queue_empty(&self) -> bool {
+        self.queued_events.is_empty() && self.queued_messages.is_empty()
+    }
+
     /// Processes all the queued events and messages, rebuilding and redrawing
     /// the widgets of the linked [`Program`] if necessary.
     ///
@@ -102,10 +109,6 @@ where
         renderer: &mut P::Renderer,
         debug: &mut Debug,
     ) -> Option<Command<P::Message>> {
-        if self.queued_events.is_empty() && self.queued_messages.is_empty() {
-            return None;
-        }
-
         let mut user_interface = build_user_interface(
             &mut self.program,
             self.cache.take().unwrap(),
diff --git a/winit/src/application.rs b/winit/src/application.rs
index 73ac72b2..a5d00407 100644
--- a/winit/src/application.rs
+++ b/winit/src/application.rs
@@ -150,6 +150,10 @@ pub fn run<A, E, C>(
 
     event_loop.run(move |event, _, control_flow| match event {
         event::Event::MainEventsCleared => {
+            if state.is_queue_empty() {
+                return;
+            }
+
             let command = runtime.enter(|| {
                 state.update(
                     clipboard.as_ref().map(|c| c as _),