1 files changed, 37 insertions, 4 deletions
diff --git a/src/plugins/platforms/cocoa/qnswindowdelegate.mm b/src/plugins/platforms/cocoa/qnswindowdelegate.mm
index 057a4c2943..97309ea990 100644
--- a/src/plugins/platforms/cocoa/qnswindowdelegate.mm
+++ b/src/plugins/platforms/cocoa/qnswindowdelegate.mm
@@ -39,21 +39,24 @@
 
 #include "qnswindowdelegate.h"
 #include "qcocoahelpers.h"
+#include "qcocoawindow.h"
 #include "qcocoascreen.h"
 
 #include <QDebug>
+#include <QtCore/private/qcore_mac_p.h>
 #include <qpa/qplatformscreen.h>
 #include <qpa/qwindowsysteminterface.h>
 
 static QRegExp whitespaceRegex = QRegExp(QStringLiteral("\\s*"));
 
-@implementation QNSWindowDelegate
+@implementation QNSWindowDelegate {
+    QCocoaWindow *m_cocoaWindow;
+}
 
-- (id)initWithQCocoaWindow:(QCocoaWindow *)cocoaWindow
+- (instancetype)initWithQCocoaWindow:(QCocoaWindow *)cocoaWindow
 {
-    if (self = [super init])
+    if ((self = [self init]))
         m_cocoaWindow = cocoaWindow;
-
     return self;
 }
 
@@ -103,6 +106,36 @@ static QRegExp whitespaceRegex = QRegExp(QStringLiteral("\\s*"));
     return QCocoaScreen::mapToNative(maximizedFrame);
 }
 
+#pragma clang diagnostic push
+// NSDisableScreenUpdates and NSEnableScreenUpdates are deprecated, but the
+// NSAnimationContext API that replaces them doesn't handle the use-case of
+// cross-thread screen update synchronization.
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+- (NSSize)windowWillResize:(NSWindow *)window toSize:(NSSize)frameSize
+{
+    qCDebug(lcQpaWindow) << window << "will resize to" << QSizeF::fromCGSize(frameSize)
+        << "- disabling screen updates temporarily";
+
+    // There may be separate threads rendering to CA layers in this window,
+    // and if any of them do a swap while the resize is still in progress,
+    // the visual bounds of that layer will be updated before the visual
+    // bounds of the window frame, resulting in flickering while resizing.
+
+    // To prevent this we disable screen updates for the whole process until
+    // the resize is complete, which makes the whole thing visually atomic.
+    NSDisableScreenUpdates();
+
+    return frameSize;
+}
+
+- (void)windowDidResize:(NSNotification *)notification
+{
+    NSWindow *window = notification.object;
+    qCDebug(lcQpaWindow) << window << "was resized - re-enabling screen updates";
+    NSEnableScreenUpdates();
+}
+#pragma clang diagnostic pop
+
 - (BOOL)window:(NSWindow *)window shouldPopUpDocumentPathMenu:(NSMenu *)menu
 {
     Q_UNUSED(window);