From 5d5b5c14a9f432624b66a3dcf5789a5a8ed26372 Mon Sep 17 00:00:00 2001
From: 0AnshuAditya0 <anshubaka2004@gmail.com>
Date: Fri, 26 Dec 2025 13:36:17 +0530
Subject: [PATCH] Fix Qt HighGUI lifecycle issue when external QApplication
 exists

Respect QApplication::quitOnLastWindowClosed() before calling qApp->quit().
This prevents OpenCV from unintentionally terminating externally managed
Qt applications when the last HighGUI window is closed.

Fixes #28291
---
 modules/highgui/src/window_QT.cpp | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/modules/highgui/src/window_QT.cpp b/modules/highgui/src/window_QT.cpp
index 3746acb171..d327ad6603 100644
--- a/modules/highgui/src/window_QT.cpp
+++ b/modules/highgui/src/window_QT.cpp
@@ -854,14 +854,17 @@ GuiReceiver::GuiReceiver() : bTimeOut(false), nb_windows(0)
 
 void GuiReceiver::isLastWindow()
 {
-    if (--nb_windows <= 0)
+    if (qApp->quitOnLastWindowClosed())
     {
-        delete guiMainThread;//delete global_control_panel too
-        guiMainThread = NULL;
-
-        if (doesExternalQAppExist)
+        if (--nb_windows <= 0)
         {
-            qApp->quit();
+            delete guiMainThread; // delete global_control_panel too
+            guiMainThread = NULL;
+
+            if (doesExternalQAppExist)
+            {
+                qApp->quit();
+            }
         }
     }
 }