From 44e63b0bbe4aaa419d69c4d2c5e1934795d5e833 Mon Sep 17 00:00:00 2001
From: Maan2003 <manmeetmann2003@gmail.com>
Date: Wed, 19 May 2021 12:53:50 +0530
Subject: [PATCH] [web backend] Make sure we only request animation once per
 frame

Earlier we call `requestAnimationFrame` every time on `invalidate_rect`
or `request_anim_frame`. This lead to even `render()` being called many
times per frame and hence poor performance.
---
 druid-shell/src/platform/web/window.rs | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/druid-shell/src/platform/web/window.rs b/druid-shell/src/platform/web/window.rs
index 4ba6237c00..28bbe28be9 100644
--- a/druid-shell/src/platform/web/window.rs
+++ b/druid-shell/src/platform/web/window.rs
@@ -113,6 +113,7 @@ struct WindowState {
     invalid: RefCell<Region>,
     click_counter: ClickCounter,
     active_text_input: Cell<Option<TextFieldToken>>,
+    rendering_soon: Cell<bool>,
 }
 
 // TODO: support custom cursors
@@ -444,6 +445,7 @@ impl WindowBuilder {
             invalid: RefCell::new(Region::EMPTY),
             click_counter: ClickCounter::default(),
             active_text_input: Cell::new(None),
+            rendering_soon: Cell::new(false),
         });
 
         setup_web_callbacks(&window);
@@ -632,10 +634,14 @@ impl WindowHandle {
     fn render_soon(&self) {
         if let Some(s) = self.0.upgrade() {
             let state = s.clone();
-            s.request_animation_frame(move || {
-                state.render();
-            })
-            .expect("Failed to request animation frame");
+            if !state.rendering_soon.get() {
+                state.rendering_soon.set(true);
+                s.request_animation_frame(move || {
+                    state.rendering_soon.set(false);
+                    state.render();
+                })
+                .expect("Failed to request animation frame");
+            }
         }
     }