From fc8b468d84f1fef5bf5183dd0b36d9411d454ea7 Mon Sep 17 00:00:00 2001
From: Kaushik Iska <iska.kaushik@gmail.com>
Date: Sat, 26 Sep 2020 06:47:26 -0700
Subject: [PATCH] [macOS] Set the display refresh rate (flutter/engine#21095)

Fixes: https://github.com/flutter/flutter/issues/49222
---
 .../macos/framework/Source/FlutterEngine.mm   | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm b/engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm
index 36b24f3424d..6210378110d 100644
--- a/engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm
+++ b/engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm
@@ -281,6 +281,7 @@ static bool OnAcquireExternalTexture(FlutterEngine* engine,
 
   [self sendUserLocales];
   [self updateWindowMetrics];
+  [self updateDisplayConfig];
   return YES;
 }
 
@@ -317,6 +318,31 @@ static bool OnAcquireExternalTexture(FlutterEngine* engine,
   return _resourceContext;
 }
 
+- (void)updateDisplayConfig {
+  if (!_engine) {
+    return;
+  }
+
+  CVDisplayLinkRef displayLinkRef;
+  CGDirectDisplayID mainDisplayID = CGMainDisplayID();
+  CVDisplayLinkCreateWithCGDisplay(mainDisplayID, &displayLinkRef);
+  CVTime nominal = CVDisplayLinkGetNominalOutputVideoRefreshPeriod(displayLinkRef);
+  if (!(nominal.flags & kCVTimeIsIndefinite)) {
+    double refreshRate = static_cast<double>(nominal.timeScale) / nominal.timeValue;
+
+    FlutterEngineDisplay display;
+    display.struct_size = sizeof(display);
+    display.display_id = mainDisplayID;
+    display.refresh_rate = round(refreshRate);
+
+    std::vector<FlutterEngineDisplay> displays = {display};
+    FlutterEngineNotifyDisplayUpdate(_engine, kFlutterEngineDisplaysUpdateTypeStartup,
+                                     displays.data(), displays.size());
+  }
+
+  CVDisplayLinkRelease(displayLinkRef);
+}
+
 - (void)updateWindowMetrics {
   if (!_engine) {
     return;