From 63867295115e6bd2e9e4c0e55d321bca3f118703 Mon Sep 17 00:00:00 2001
From: Tommy Nguyen <4123478+tido64@users.noreply.github.com>
Date: Mon, 29 Jun 2020 23:33:39 +0200
Subject: [PATCH] Alleviate excessive layout jittering when resizing window
 (#439)

---
 React/Base/RCTRootView.m | 42 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/React/Base/RCTRootView.m b/React/Base/RCTRootView.m
index 172e5c573b9a3f..6913cdc92f69cb 100644
--- a/React/Base/RCTRootView.m
+++ b/React/Base/RCTRootView.m
@@ -37,6 +37,10 @@
 #import "RCTDevMenu.h"
 #endif // ]TODO(OSS Candidate ISS#2710739)
 
+#if TARGET_OS_OSX // [TODO(macOS ISS#2323203)
+#define RCT_LAYOUT_THROTTLE 0.25
+#endif // ]TODO(macOS ISS#2323203)
+
 NSString *const RCTContentDidAppearNotification = @"RCTContentDidAppearNotification";
 
 @interface RCTUIManager (RCTRootView)
@@ -52,6 +56,11 @@ @implementation RCTRootView
   RCTRootContentView *_contentView;
   BOOL _passThroughTouches;
   CGSize _intrinsicContentSize;
+
+#if TARGET_OS_OSX // [TODO(macOS ISS#2323203)
+  NSDate *_lastLayout;
+  BOOL _throttleLayout;
+#endif // ]TODO(macOS ISS#2323203)
 }
 
 - (instancetype)initWithBridge:(RCTBridge *)bridge
@@ -79,6 +88,10 @@ - (instancetype)initWithBridge:(RCTBridge *)bridge
     _loadingViewFadeDuration = 0.25;
     _sizeFlexibility = RCTRootViewSizeFlexibilityNone;
 
+#if TARGET_OS_OSX // [TODO(macOS ISS#2323203)
+    _lastLayout = [NSDate new];
+#endif // ]TODO(macOS ISS#2323203)
+
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(bridgeDidReload)
                                                  name:RCTJavaScriptWillStartLoadingNotification
@@ -173,6 +186,35 @@ - (CGSize)sizeThatFits:(CGSize)size
   return fitSize;
 }
 
+#if TARGET_OS_OSX // [TODO(macOS ISS#2323203)
+// TODO: https://github.com/microsoft/react-native-macos/issues/459
+// This is a workaround for window resizing events overloading the shadow queue:
+//  - https://github.com/microsoft/react-native-macos/issues/322
+//  - https://github.com/microsoft/react-native-macos/issues/422
+// We should revisit this issue when we switch over to Fabric.
+- (void)layout
+{
+  if (self.window != nil && !_throttleLayout) {
+    NSTimeInterval interval = [[NSDate date] timeIntervalSinceDate:_lastLayout];
+    if (interval >= RCT_LAYOUT_THROTTLE) {
+      _lastLayout = [NSDate new];
+      [self layoutSubviews];
+    } else {
+      _throttleLayout = YES;
+      __weak typeof(self) weakSelf = self;
+      int64_t delta = (RCT_LAYOUT_THROTTLE - interval) * NSEC_PER_SEC;
+      dispatch_after(dispatch_time(DISPATCH_TIME_NOW, delta), dispatch_get_main_queue(), ^{
+        typeof(self) strongSelf = weakSelf;
+        if (strongSelf != nil) {
+          strongSelf->_throttleLayout = NO;
+          [strongSelf setNeedsLayout];
+        }
+      });
+    }
+  }
+}
+#endif // ]TODO(macOS ISS#2323203)
+
 - (void)layoutSubviews
 {
   [super layoutSubviews];