qtbug-113394.diff

commit d62ac93bba020a79d131c3a1eba3973d7525860d
Author: Colin Snover <github.com@zetafleet.com>
Date:   Thu May 4 17:29:32 2023 -0500

    Debounce macOS font change notifications
    
    Many notifications of this type may be received at once so it is
    necessary to debounce them:
    
    https://www.mail-archive.com/cocoa-dev@lists.apple.com/msg73901.html
    
    These notifications can be triggered by font fallback resolution,
    not just by users adding fonts manually, so it is especially
    important to debounce since regenerating the font database is an
    expensive operation that triggers layout invalidation every time it
    happens.
    
    Other software that listens for font changes tends to use the newer
    kCTFontManagerRegisteredFontsChangedNotification (added in 10.6),
    but this also appears to send multiple notifications so there does
    not seem to be any obvious benefit to switching.
    
    Fixes: QTBUG-113394
    Change-Id: I7fbafaba47459acebb242e0e08859c422ecf0df5

diff --git a/src/gui/text/coretext/qcoretextfontdatabase.mm b/src/gui/text/coretext/qcoretextfontdatabase.mm
index 61c662cd..ca207a30 100644
--- a/src/gui/text/coretext/qcoretextfontdatabase.mm
+++ b/src/gui/text/coretext/qcoretextfontdatabase.mm
@@ -78,9 +78,12 @@
     : m_hasPopulatedAliases(false)
 {
 #if defined(Q_OS_MACOS)
-    m_fontSetObserver = QMacNotificationObserver(nil, NSFontSetChangedNotification, [] {
-        qCDebug(lcQpaFonts) << "Fonts have changed";
-        QPlatformFontDatabase::repopulateFontDatabase();
+    m_fontSetObserver = QMacNotificationObserver(nil, NSFontSetChangedNotification, [this] {
+        if (!m_fontSetDebounceTimer.isActive())
+            qCDebug(lcQpaFonts) << "Fonts have changed";
+
+        // The timeout length was selected arbitrarily
+        m_fontSetDebounceTimer.start(25, this);
     });
 #endif
 }
@@ -90,6 +93,18 @@
     qDeleteAll(m_themeFonts);
 }
 
+#if defined(Q_OS_MACOS)
+void QCoreTextFontDatabase::timerEvent(QTimerEvent *event)
+{
+    if (event->timerId() == m_fontSetDebounceTimer.timerId()) {
+        m_fontSetDebounceTimer.stop();
+        qCDebug(lcQpaFonts) << "Font change notifications have settled";
+        QPlatformFontDatabase::repopulateFontDatabase();
+    }
+    QObject::timerEvent(event);
+}
+#endif
+
 CTFontDescriptorRef descriptorForFamily(const QString &familyName)
 {
     return CTFontDescriptorCreateWithAttributes(CFDictionaryRef(@{
diff --git a/src/gui/text/coretext/qcoretextfontdatabase_p.h b/src/gui/text/coretext/qcoretextfontdatabase_p.h
index 74c3f30b..c81c510b 100644
--- a/src/gui/text/coretext/qcoretextfontdatabase_p.h
+++ b/src/gui/text/coretext/qcoretextfontdatabase_p.h
@@ -21,6 +21,11 @@
 #include <qpa/qplatformtheme.h>
 #include <private/qcore_mac_p.h>
 
+#if defined(Q_OS_MACOS)
+#include <QtCore/qbasictimer.h>
+#include <QtCore/qobject.h>
+#endif
+
 Q_FORWARD_DECLARE_CF_TYPE(CTFontDescriptor);
 Q_FORWARD_DECLARE_CF_TYPE(CTFont);
 
@@ -29,7 +34,11 @@ QT_DECL_METATYPE_EXTERN_TAGGED(QCFType<CFURLRef>, QCFType_CFURLRef, Q_GUI_EXPORT
 
 QT_BEGIN_NAMESPACE
 
-class Q_GUI_EXPORT QCoreTextFontDatabase : public QPlatformFontDatabase
+class Q_GUI_EXPORT QCoreTextFontDatabase :
+#if defined(Q_OS_MACOS)
+    public QObject,
+#endif
+    public QPlatformFontDatabase
 {
 public:
     QCoreTextFontDatabase();
@@ -63,7 +72,11 @@ private:
     bool m_hasPopulatedAliases;
 
 #if defined(Q_OS_MACOS)
+protected:
+    void timerEvent(QTimerEvent *event) override;
+private:
     QMacNotificationObserver m_fontSetObserver;
+    QBasicTimer m_fontSetDebounceTimer;
 #endif
 };