Fix text issues when using typographic names

By default, only the legacy family names are populated on Windows,
since we are using GDI to do the population.

The actual typographic names are added later as aliases when
the font is loaded.

This can cause us to fail matching a font against its typographic
name before it has been loaded and e.g .in Qt Quick we will cache
the glyph indexes for a fallback font instead. If the font is later
loaded and aliases are populated, we will use the cached glyph
indexes and get seemingly random glyphs displayed.

We reuse the mechanism invented for CoreText to do lazy population
of aliases. The population will now happen when the first non-match
occurs, and a second attempt will be made after we populate aliases.

[ChangeLog][Windows] Fixes an issue where fonts would sometimes not
fail to work when selected using typographic names.

Fixes: QTBUG-84786
Pick-to: 5.15
Change-Id: Ic7b65cde26ddcbf1a257f1673b9af37154660c2f
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

2 files changed, 17 insertions, 0 deletions

diff --git a/src/gui/text/windows/qwindowsfontdatabase.cpp b/src/gui/text/windows/qwindowsfontdatabase.cpp
index b5e0997015..36d8da0ce8 100644
--- a/src/gui/text/windows/qwindowsfontdatabase.cpp
+++ b/src/gui/text/windows/qwindowsfontdatabase.cpp
@@ -651,6 +651,21 @@ static int QT_WIN_CALLBACK storeFont(const LOGFONT *logFont, const TEXTMETRIC *t
     return 1;
 }
 
+bool QWindowsFontDatabase::populateFamilyAliases(const QString &missingFamily)
+{
+    Q_UNUSED(missingFamily);
+
+    if (m_hasPopulatedAliases)
+        return false;
+
+    QStringList families = QFontDatabase::families();
+    for (const QString &family : families)
+        populateFamily(family);
+    m_hasPopulatedAliases = true;
+
+    return true;
+}
+
 void QWindowsFontDatabase::populateFamily(const QString &familyName)
 {
     qCDebug(lcQpaFonts) << familyName;
diff --git a/src/gui/text/windows/qwindowsfontdatabase_p.h b/src/gui/text/windows/qwindowsfontdatabase_p.h
index b870d6c4a0..b4b367b1e7 100644
--- a/src/gui/text/windows/qwindowsfontdatabase_p.h
+++ b/src/gui/text/windows/qwindowsfontdatabase_p.h
@@ -80,6 +80,7 @@ public:
 
     void populateFontDatabase() override;
     void populateFamily(const QString &familyName) override;
+    bool populateFamilyAliases(const QString &missingFamily) override;
     QFontEngine *fontEngine(const QFontDef &fontDef, void *handle) override;
     QFontEngine *fontEngine(const QByteArray &fontData, qreal pixelSize, QFont::HintingPreference hintingPreference) override;
     QStringList fallbacksForFamily(const QString &family, QFont::Style style, QFont::StyleHint styleHint, QChar::Script script) const override;
@@ -126,6 +127,7 @@ private:
 
     static unsigned m_fontOptions;
     QStringList m_eudcFonts;
+    bool m_hasPopulatedAliases = false;
 };
 
 #ifndef QT_NO_DEBUG_STREAM