From 4b21b332ee4388fdd4e9654c6e818e56e09a4f85 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Morten=20S=C3=B8rvig?= <morten.sorvig@qt.io>
Date: Mon, 4 Sep 2023 13:42:02 +0200
Subject: [PATCH] Always run screen change side effects
MIME-Version: 1.0
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processWindowScreenChangedEvent() returns early if the
screen for the (top-level) window has already been updated,
for instance by a call to handleScreenRemoved(). This was
preventing us from updating the DPR and window geometry.

Move the code a slot connected to QWindow::screenChange,
which gets emitted for all windows (also child windows),
whenever the screen changes.

Fixes: QTBUG-116232
Change-Id: I44701fd001ab1fd54efe9c8451c6a58cfc0b285f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
(cherry picked from commit 89ce65c2d01e77c1cf49bb8579f63b60480e0186)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/gui/kernel/qguiapplication.cpp | 11 -----------
 src/gui/kernel/qwindow.cpp         | 13 +++++++++++++
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 9c09bc2d4ac..c5f03719e4b 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -2604,17 +2604,6 @@ void QGuiApplicationPrivate::processWindowScreenChangedEvent(QWindowSystemInterf
         else // Fall back to default behavior, and try to find some appropriate screen
             topLevelWindow->setScreen(nullptr);
     }
-
-    // We may have changed scaling; trigger resize event if needed,
-    // except on Windows, where we send resize events during WM_DPICHANGED
-    // event handling. FIXME: unify DPI change handling across all platforms.
-#ifndef Q_OS_WIN
-    if (window->handle()) {
-        QWindowSystemInterfacePrivate::GeometryChangeEvent gce(window, QHighDpi::fromNativePixels(window->handle()->geometry(), window));
-        processGeometryChangeEvent(&gce);
-    }
-#endif
-    QWindowPrivate::get(window)->updateDevicePixelRatio();
 }
 
 void QGuiApplicationPrivate::processWindowDevicePixelRatioChangedEvent(QWindowSystemInterfacePrivate::WindowDevicePixelRatioChangedEvent *wde)
diff --git a/src/gui/kernel/qwindow.cpp b/src/gui/kernel/qwindow.cpp
index 7750c70ba1e..0d524b8692b 100644
--- a/src/gui/kernel/qwindow.cpp
+++ b/src/gui/kernel/qwindow.cpp
@@ -227,6 +227,19 @@ void QWindowPrivate::init(QScreen *targetScreen)
 
     requestedFormat = QSurfaceFormat::defaultFormat();
     devicePixelRatio = connectScreen->devicePixelRatio();
+
+    QObject::connect(q, &QWindow::screenChanged, q, [q, this](QScreen *){
+        // We may have changed scaling; trigger resize event if needed,
+        // except on Windows, where we send resize events during WM_DPICHANGED
+        // event handling. FIXME: unify DPI change handling across all platforms.
+#ifndef Q_OS_WIN
+        if (q->handle()) {
+            QWindowSystemInterfacePrivate::GeometryChangeEvent gce(q, QHighDpi::fromNativePixels(q->handle()->geometry(), q));
+            QGuiApplicationPrivate::processGeometryChangeEvent(&gce);
+        }
+#endif
+        updateDevicePixelRatio();
+    });
 }
 
 /*!