macOS: Invalidate backingstore and trigger expose on color space changes

Fixes: QTBUG-77749
Change-Id: I677a71152e4a218c08d8863d4f886d158a79e809
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/plugins/platforms/cocoa/qcocoabackingstore.h

@@ -54,6 +54,8 @@ class QCocoaBackingStore : public QRasterBackingStore
 protected:
     QCocoaBackingStore(QWindow *window);
     QCFType<CGColorSpaceRef> colorSpace() const;
+    QMacNotificationObserver m_backingPropertiesObserver;
+    virtual void backingPropertiesChanged() = 0;
 };
 
 class QNSWindowBackingStore : public QCocoaBackingStore
@@ -69,6 +71,7 @@ private:
     bool windowHasUnifiedToolbar() const;
     QImage::Format format() const override;
     void redrawRoundedBottomCorners(CGRect) const;
+    void backingPropertiesChanged() override;
 };
 
 class QCALayerBackingStore : public QCocoaBackingStore
@@ -115,6 +118,8 @@ private:
     bool recreateBackBufferIfNeeded();
     bool prepareForFlush();
 
+    void backingPropertiesChanged() override;
+
     std::list<std::unique_ptr<GraphicsBuffer>> m_buffers;
 };
 

src/plugins/platforms/cocoa/qcocoabackingstore.mm

@@ -51,6 +51,17 @@ QT_BEGIN_NAMESPACE
 QCocoaBackingStore::QCocoaBackingStore(QWindow *window)
     : QRasterBackingStore(window)
 {
+    // Ideally this would be plumbed from the platform layer to QtGui, and
+    // the QBackingStore would be recreated, but we don't have that code yet,
+    // so at least make sure we invalidate our backingstore when the backing
+    // properties (color space e.g.) are changed.
+    NSView *view = static_cast<QCocoaWindow *>(window->handle())->view();
+    m_backingPropertiesObserver = QMacNotificationObserver(view.window,
+        NSWindowDidChangeBackingPropertiesNotification, [this]() {
+            qCDebug(lcQpaBackingStore) << "Backing properties for"
+                << this->window() << "did change";
+            backingPropertiesChanged();
+        });
 }
 
 QCFType<CGColorSpaceRef> QCocoaBackingStore::colorSpace() const
@@ -299,6 +310,11 @@ void QNSWindowBackingStore::redrawRoundedBottomCorners(CGRect windowRect) const
 #endif
 }
 
+void QNSWindowBackingStore::backingPropertiesChanged()
+{
+    m_image = QImage();
+}
+
 // ----------------------------------------------------------------------------
 
 // https://stackoverflow.com/a/52722575/2761869
@@ -574,6 +590,12 @@ QImage QCALayerBackingStore::toImage() const
     return imageCopy;
 }
 
+void QCALayerBackingStore::backingPropertiesChanged()
+{
+    m_buffers.clear();
+    m_buffers.resize(1);
+}
+
 QPlatformGraphicsBuffer *QCALayerBackingStore::graphicsBuffer() const
 {
     return m_buffers.back().get();

src/plugins/platforms/cocoa/qcocoawindow.h

@@ -161,6 +161,7 @@ public:
     Q_NOTIFICATION_HANDLER(NSWindowDidOrderOffScreenNotification) void windowDidOrderOffScreen();
     Q_NOTIFICATION_HANDLER(NSWindowDidChangeOcclusionStateNotification) void windowDidChangeOcclusionState();
     Q_NOTIFICATION_HANDLER(NSWindowDidChangeScreenNotification) void windowDidChangeScreen();
+    Q_NOTIFICATION_HANDLER(NSWindowDidChangeBackingPropertiesNotification) void windowDidChangeBackingProperties();
     Q_NOTIFICATION_HANDLER(NSWindowWillCloseNotification) void windowWillClose();
 
     bool windowShouldClose();

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -1261,6 +1261,17 @@ void QCocoaWindow::windowDidChangeScreen()
         currentScreen->requestUpdate();
     }
 }
+/*
+    The window's backing scale factor or color space has changed.
+*/
+void QCocoaWindow::windowDidChangeBackingProperties()
+{
+    // Ideally we would plumb this thought QPA in a way that lets clients
+    // invalidate their own caches, and recreate QBackingStore. For now we
+    // trigger an expose, and let QCocoaBackingStore deal with its own
+    // buffer invalidation.
+    [m_view setNeedsDisplay:YES];
+}
 
 void QCocoaWindow::windowWillClose()
 {