CoreText: Warn the user when family alias lookup slows down the application

If the user specifies a font family in their application that doesn't
exist in the system, or one that uses the localized family name, we
will end up resolving the family alias for all fonts in the system,
which typically adds 600-800ms of startup time. Let the user know
when this happens.

Change-Id: Id8d6f55028e37f681ec4a686df25d33240b5a30f
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

2 files changed, 46 insertions, 6 deletions

diff --git a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
index 201a82864f..4887a501ba 100644
--- a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
+++ b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase.mm
@@ -48,6 +48,8 @@
 #import <UIKit/UIFont.h>
 #endif
 
+#include <QtCore/qelapsedtimer.h>
+
 #include "qcoretextfontdatabase_p.h"
 #include "qfontengine_coretext_p.h"
 #if QT_CONFIG(settings)
@@ -113,39 +115,77 @@ QCoreTextFontDatabase::~QCoreTextFontDatabase()
 
 void QCoreTextFontDatabase::populateFontDatabase()
 {
+    qCDebug(lcQpaFonts) << "Populating font database...";
+    QElapsedTimer elapsed;
+    if (lcQpaFonts().isDebugEnabled())
+        elapsed.start();
+
     QCFType<CFArrayRef> familyNames = CTFontManagerCopyAvailableFontFamilyNames();
     for (NSString *familyName in familyNames.as<const NSArray *>())
         QPlatformFontDatabase::registerFontFamily(QString::fromNSString(familyName));
 
+    qCDebug(lcQpaFonts) << "Populating available families took" << elapsed.restart() << "ms";
+
     // Force creating the theme fonts to get the descriptors in m_systemFontDescriptors
     if (m_themeFonts.isEmpty())
         (void)themeFonts();
 
+    qCDebug(lcQpaFonts) << "Resolving theme fonts took" << elapsed.restart() << "ms";
+
     Q_FOREACH (CTFontDescriptorRef fontDesc, m_systemFontDescriptors)
         populateFromDescriptor(fontDesc);
 
+    qCDebug(lcQpaFonts) << "Populating system descriptors took" << elapsed.restart() << "ms";
+
     Q_ASSERT(!m_hasPopulatedAliases);
 }
 
-bool QCoreTextFontDatabase::populateFamilyAliases()
+bool QCoreTextFontDatabase::populateFamilyAliases(const QString &missingFamily)
 {
 #if defined(Q_OS_MACOS)
     if (m_hasPopulatedAliases)
         return false;
 
+    // There's no API to go from a localized family name to its non-localized
+    // name, so we have to resort to enumerating all the available fonts and
+    // doing a reverse lookup.
+
+    qCDebug(lcQpaFonts) << "Populating family aliases...";
+    QElapsedTimer elapsed;
+    elapsed.start();
+
+    QString nonLocalizedMatch;
     QCFType<CFArrayRef> familyNames = CTFontManagerCopyAvailableFontFamilyNames();
+    NSFontManager *fontManager = NSFontManager.sharedFontManager;
     for (NSString *familyName in familyNames.as<const NSArray *>()) {
-        NSFontManager *fontManager = [NSFontManager sharedFontManager];
         NSString *localizedFamilyName = [fontManager localizedNameForFamily:familyName face:nil];
         if (![localizedFamilyName isEqual:familyName]) {
-            QPlatformFontDatabase::registerAliasToFontFamily(
-                QString::fromNSString(familyName),
-                QString::fromNSString(localizedFamilyName));
+            QString nonLocalizedFamily = QString::fromNSString(familyName);
+            QString localizedFamily = QString::fromNSString(localizedFamilyName);
+            QPlatformFontDatabase::registerAliasToFontFamily(nonLocalizedFamily, localizedFamily);
+            if (localizedFamily == missingFamily)
+                nonLocalizedMatch = nonLocalizedFamily;
         }
     }
     m_hasPopulatedAliases = true;
+
+    if (lcQpaFonts().isWarningEnabled()) {
+        QString warningMessage;
+        QDebug msg(&warningMessage);
+
+        msg << "Populating font family aliases took" << elapsed.restart() << "ms.";
+        if (!nonLocalizedMatch.isNull())
+            msg << "Replace uses of" << missingFamily << "with its non-localized name" << nonLocalizedMatch;
+        else
+            msg << "Replace uses of missing font family" << missingFamily << "with one that exists";
+        msg << "to avoid this cost.";
+
+        qCWarning(lcQpaFonts) << qPrintable(warningMessage);
+    }
+
     return true;
 #else
+    Q_UNUSED(missingFamily);
     return false;
 #endif
 }
diff --git a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase_p.h b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase_p.h
index 45e74b99be..69ff454d1e 100644
--- a/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase_p.h
+++ b/src/platformsupport/fontdatabases/mac/qcoretextfontdatabase_p.h
@@ -71,7 +71,7 @@ public:
     QCoreTextFontDatabase();
     ~QCoreTextFontDatabase();
     void populateFontDatabase() override;
-    bool populateFamilyAliases() override;
+    bool populateFamilyAliases(const QString &missingFamily) override;
     void populateFamily(const QString &familyName) override;
     void invalidate() override;