Windows: Default to DirectWrite font backend

The GDI font backend is missing support for certain modern features,
and has a lot of work arounds for missing APIs. DirectWrite is the
modern way to handle fonts on Windows, so we make this the default
now, but keep the old backend as a fail safe.

Fixes: QTBUG-119420
Change-Id: I0ea5cdfdcd759ccc894efb01b2410826c44aa1ea
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Lars Knoll <lars@knoll.priv.no>

src/gui/kernel/qguiapplication.cpp

@@ -587,13 +587,10 @@ static QWindowGeometrySpecification windowGeometrySpecification = Q_WINDOW_GEOME
             \c none disables them.
 
         \li \c {fontengine=freetype}, uses the FreeType font engine.
-        \li \c {fontengine=directwrite}, uses the experimental DirectWrite
-               font database and defaults to using the DirectWrite font
+        \li \c {fontengine=gdi}, uses the legacy GDI-based
+               font database and defaults to using the GDI font
                engine (which is otherwise only used for some font types
-               or font properties.) This affects font selection and aims
-               to provide font naming more consistent with other platforms,
-               but does not support all font formats, such as Postscript
-               Type-1 or Microsoft FNT fonts.
+               or font properties.) (Since Qt 6.8).
         \li \c {menus=[native|none]}, controls the use of native menus.
 
                Native menus are implemented using Win32 API and are simpler than
@@ -607,7 +604,8 @@ static QWindowGeometrySpecification windowGeometrySpecification = Q_WINDOW_GEOME
         \li \c {nocolorfonts} Turn off DirectWrite Color fonts
                (since Qt 5.8).
 
-        \li \c {nodirectwrite} Turn off DirectWrite fonts (since Qt 5.8).
+        \li \c {nodirectwrite} Turn off DirectWrite fonts (since Qt 5.8). This implicitly
+               also selects the GDI font engine.
 
         \li \c {nomousefromtouch} Ignores mouse events synthesized
                from touch events by the operating system.

src/plugins/platforms/windows/qwindowsintegration.cpp

@@ -142,8 +142,8 @@ static inline unsigned parseOptions(const QStringList &paramList,
     unsigned options = 0;
     for (const QString &param : paramList) {
         if (param.startsWith(u"fontengine=")) {
-            if (param.endsWith(u"directwrite")) {
-                options |= QWindowsIntegration::FontDatabaseDirectWrite;
+            if (param.endsWith(u"gdi")) {
+                options |= QWindowsIntegration::FontDatabaseGDI;
             } else if (param.endsWith(u"freetype")) {
                 options |= QWindowsIntegration::FontDatabaseFreeType;
             } else if (param.endsWith(u"native")) {
@@ -482,17 +482,17 @@ QWindowsStaticOpenGLContext *QWindowsIntegration::staticOpenGLContext()
 QPlatformFontDatabase *QWindowsIntegration::fontDatabase() const
 {
     if (!d->m_fontDatabase) {
-#if QT_CONFIG(directwrite3)
-        if (d->m_options & QWindowsIntegration::FontDatabaseDirectWrite)
-            d->m_fontDatabase = new QWindowsDirectWriteFontDatabase;
-        else
-#endif
 #ifndef QT_NO_FREETYPE
         if (d->m_options & QWindowsIntegration::FontDatabaseFreeType)
             d->m_fontDatabase = new QWindowsFontDatabaseFT;
         else
 #endif // QT_NO_FREETYPE
-        d->m_fontDatabase = new QWindowsFontDatabase();
+#if QT_CONFIG(directwrite3)
+        if (!(d->m_options & (QWindowsIntegration::FontDatabaseGDI | QWindowsIntegration::DontUseDirectWriteFonts)))
+            d->m_fontDatabase = new QWindowsDirectWriteFontDatabase;
+        else
+#endif
+            d->m_fontDatabase = new QWindowsFontDatabase;
     }
     return d->m_fontDatabase;
 }

src/plugins/platforms/windows/qwindowsintegration.h

@@ -45,7 +45,7 @@ class QWindowsIntegration : public QPlatformIntegration
         DontUseWMPointer = 0x400,
         DetectAltGrModifier = 0x800,
         RtlEnabled = 0x1000,
-        FontDatabaseDirectWrite = 0x2000
+        FontDatabaseGDI = 0x2000
     };
 
     explicit QWindowsIntegration(const QStringList &paramList);