From fc7f9f87e51dba8c3d8a04f99380868e7f15686f Mon Sep 17 00:00:00 2001
From: Sam Johnson <sam@scj.me>
Date: Tue, 10 Sep 2024 17:54:41 +0000
Subject: [PATCH] Bug 1912338 - Consistently hide macOS titlebar separator for
 full screen windows. r=mac-reviewers,bradwerth

In bug 1906034, I attempted to preserve the workaround for the white line issue from bug 1700211, but it did not prevent the white line from appearing. Hiding the separator in response to full-screen events avoids the issue.

Differential Revision: https://phabricator.services.mozilla.com/D221576
---
 widget/cocoa/nsCocoaWindow.mm | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/widget/cocoa/nsCocoaWindow.mm b/widget/cocoa/nsCocoaWindow.mm
index df9782494c7e..708b79ebf59e 100644
--- a/widget/cocoa/nsCocoaWindow.mm
+++ b/widget/cocoa/nsCocoaWindow.mm
@@ -2843,6 +2843,14 @@ void nsCocoaWindow::CocoaWindowDidResize() {
     [titlebarContainerView setTransparent:NO];
   }
 
+  if (@available(macOS 11.0, *)) {
+    // In order to work around a drawing bug with titlebarAppearsTransparent
+    // windows in full screen mode, disable titlebar separators for full
+    // screen windows. The drawing bug was filed as FB9056136. See bug 1700211
+    // and bug 1912338 for more details.
+    window.titlebarSeparatorStyle = NSTitlebarSeparatorStyleNone;
+  }
+
   if (!mGeckoWindow) {
     return;
   }