[QFontDatabase] Defer the fallback families list initialization

Use the same trick the WebKit related path has used for years:
if there is no explicit list that takes a precedence over the
default one (i.e. QFont("Arial,SimHei")), then defer the fallback
families list initialization until it gets requested.

Change-Id: If5a74294bdebb24865c619bc0d7328b3e706de76
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@theqtcompany.com>

2 files changed, 22 insertions, 20 deletions

diff --git a/src/gui/text/qfontdatabase.cpp b/src/gui/text/qfontdatabase.cpp
index 6b7a9837cb..af03778e22 100644
--- a/src/gui/text/qfontdatabase.cpp
+++ b/src/gui/text/qfontdatabase.cpp
@@ -756,7 +756,7 @@ QString qt_resolveFontFamilyAlias(const QString &alias)
     return alias;
 }
 
-static QStringList fallbackFamilies(const QString &family, QFont::Style style, QFont::StyleHint styleHint, QChar::Script script)
+QStringList qt_fallbacksForFamily(const QString &family, QFont::Style style, QFont::StyleHint styleHint, QChar::Script script)
 {
     // make sure that the db has all fallback families
     QStringList retList = QGuiApplicationPrivate::platformIntegration()->fontDatabase()->fallbacksForFamily(family,style,styleHint,script);
@@ -884,17 +884,19 @@ QFontEngine *loadEngine(int script, const QFontDef &request,
     QFontEngine *engine = loadSingleEngine(script, request, family, foundry, style, size);
     Q_ASSERT(!engine || engine->type() != QFontEngine::Multi);
     if (engine && !(request.styleStrategy & QFont::NoFontMerging) && !engine->symbol) {
-        QStringList fallbacks = request.fallBackFamilies;
+        QPlatformFontDatabase *pfdb = QGuiApplicationPrivate::platformIntegration()->fontDatabase();
+        QFontEngineMulti *pfMultiEngine = pfdb->fontEngineMulti(engine, QChar::Script(script));
+        if (!request.fallBackFamilies.isEmpty()) {
+            QStringList fallbacks = request.fallBackFamilies;
 
-        QFont::StyleHint styleHint = QFont::StyleHint(request.styleHint);
-        if (styleHint == QFont::AnyStyle && request.fixedPitch)
-            styleHint = QFont::TypeWriter;
+            QFont::StyleHint styleHint = QFont::StyleHint(request.styleHint);
+            if (styleHint == QFont::AnyStyle && request.fixedPitch)
+                styleHint = QFont::TypeWriter;
 
-        fallbacks += fallbackFamilies(family->name, QFont::Style(style->key.style), styleHint, QChar::Script(script));
+            fallbacks += qt_fallbacksForFamily(family->name, QFont::Style(style->key.style), styleHint, QChar::Script(script));
 
-        QPlatformFontDatabase *pfdb = QGuiApplicationPrivate::platformIntegration()->fontDatabase();
-        QFontEngineMulti *pfMultiEngine = pfdb->fontEngineMulti(engine, QChar::Script(script));
-        pfMultiEngine->setFallbackFamiliesList(fallbacks);
+            pfMultiEngine->setFallbackFamiliesList(fallbacks);
+        }
         engine = pfMultiEngine;
 
         // Cache Multi font engine as well in case we got the single
@@ -2560,10 +2562,10 @@ QFontEngine *QFontDatabase::findFont(const QFontDef &request, int script)
                 styleHint = QFont::TypeWriter;
 
             QStringList fallbacks = request.fallBackFamilies
-                                  + fallbackFamilies(request.family,
-                                                     QFont::Style(request.style),
-                                                     styleHint,
-                                                     QChar::Script(script));
+                                  + qt_fallbacksForFamily(request.family,
+                                                          QFont::Style(request.style),
+                                                          styleHint,
+                                                          QChar::Script(script));
             if (script > QChar::Script_Common)
                 fallbacks += QString(); // Find the first font matching the specified script.
 
diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 6f5d178655..f9d924d10a 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -1590,15 +1590,15 @@ QFontEngineMulti::~QFontEngineMulti()
     }
 }
 
+QStringList qt_fallbacksForFamily(const QString &family, QFont::Style style, QFont::StyleHint styleHint, QChar::Script script);
+
 void QFontEngineMulti::ensureFallbackFamiliesQueried()
 {
-    if (QPlatformIntegration *integration = QGuiApplicationPrivate::platformIntegration()) {
-        const QStringList fallbackFamilies = integration->fontDatabase()->fallbacksForFamily(fontDef.family,
-                                                                                             QFont::Style(fontDef.style),
-                                                                                             QFont::AnyStyle,
-                                                                                             QChar::Script(m_script));
-        setFallbackFamiliesList(fallbackFamilies);
-    }
+    QFont::StyleHint styleHint = QFont::StyleHint(fontDef.styleHint);
+    if (styleHint == QFont::AnyStyle && fontDef.fixedPitch)
+        styleHint = QFont::TypeWriter;
+
+    setFallbackFamiliesList(qt_fallbacksForFamily(fontDef.family, QFont::Style(fontDef.style), styleHint, QChar::Script(m_script)));
 }
 
 void QFontEngineMulti::setFallbackFamiliesList(const QStringList &fallbackFamilies)