macOS: Stop relying on balanced CGDisplay reconfiguration callbacks

We were using CGDisplay callbacks to determine when a screen reconfiguration
had happened, and when it had propagated to changes in NSScreen.screens,
so that we could update our QScreen view of the world.

Unfortunately the CGDisplay callbacks were not deterministic enough to
use as a signal for when a reconfigure had completed.

Since we can't rely on NSApplicationDidChangeScreenParametersNotification
either (it comes in too late), we're now resorting to updating our QScreens
at every chance we get:

 - On every CGDisplay reconfiguration ending
 - On QCocoaWindow::windowDidChangeScreen() as a result of AppKit
   moving the window.
 - On NSApplicationDidChangeScreenParametersNotification
 - On QCocoaScreen::get() as a last resort

Since the result of these updates are only reflected as QScreen property
updates or QGuiApplication signals if a change actually occurred, it should
be safe to update early and often.

Task-number: QTBUG-77656
Fixes: QTBUG-80193
Pick-to: 6.2 6.1 5.15
Change-Id: I98334a66767736d94ad2fcb169e65f0d8bc71a30
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

1 files changed, 7 insertions, 4 deletions

diff --git a/src/plugins/platforms/cocoa/qcocoawindow.mm b/src/plugins/platforms/cocoa/qcocoawindow.mm
index ee1689c2f4..7270e7c23c 100644
--- a/src/plugins/platforms/cocoa/qcocoawindow.mm
+++ b/src/plugins/platforms/cocoa/qcocoawindow.mm
@@ -1268,11 +1268,15 @@ void QCocoaWindow::windowDidChangeScreen()
         return;
 
     // Note: When a window is resized to 0x0 Cocoa will report the window's screen as nil
-    auto *currentScreen = QCocoaScreen::get(m_view.window.screen);
+    NSScreen *nsScreen = m_view.window.screen;
+
+    qCDebug(lcQpaWindow) << window() << "did change" << nsScreen;
+    QCocoaScreen::updateScreens();
+
     auto *previousScreen = static_cast<QCocoaScreen*>(screen());
+    auto *currentScreen = QCocoaScreen::get(nsScreen);
 
-    Q_ASSERT_X(!m_view.window.screen || currentScreen,
-        "QCocoaWindow", "Failed to get QCocoaScreen for NSScreen");
+    qCDebug(lcQpaWindow) << "Screen changed for" << window() << "from" << previousScreen << "to" << currentScreen;
 
     // Note: The previous screen may be the same as the current screen, either because
     // a) the screen was just reconfigured, which still results in AppKit sending an
@@ -1285,7 +1289,6 @@ void QCocoaWindow::windowDidChangeScreen()
     // device-pixel ratio may have changed, and needs to be delivered to all
     // windows, both top level and child windows.
 
-    qCDebug(lcQpaWindow) << "Screen changed for" << window() << "from" << previousScreen << "to" << currentScreen;
     QWindowSystemInterface::handleWindowScreenChanged<QWindowSystemInterface::SynchronousDelivery>(
         window(), currentScreen ? currentScreen->screen() : nullptr);