GTK2 theme should use GTK configured font variant

This patch makes the GTK2 theme read the font configuration and use
that as the default system font.

Task-number: QTBUG-39643
Change-Id: Ieacf8968e54f34c6d44669350d349c9a96ed6cc5
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>

src/platformsupport/themes/genericunix/qgenericunixthemes.cpp

@@ -519,15 +519,23 @@ const char *QGnomeTheme::name = "gnome";
 class QGnomeThemePrivate : public QPlatformThemePrivate
 {
 public:
-    QGnomeThemePrivate()
-        : systemFont(QLatin1Literal(defaultSystemFontNameC), defaultSystemFontSize)
-        , fixedFont(QStringLiteral("monospace"), systemFont.pointSize())
+    QGnomeThemePrivate() : fontsConfigured(false) { }
+    void configureFonts(QString gtkFontName) const
     {
+        Q_ASSERT(!fontsConfigured);
+        const int split = gtkFontName.lastIndexOf(QChar::Space);
+        float size = gtkFontName.mid(split+1).toFloat();
+        QString fontName = gtkFontName.left(split);
+
+        systemFont = QFont(fontName, size);
+        fixedFont = QFont(QLatin1String("monospace"), systemFont.pointSize());
         fixedFont.setStyleHint(QFont::TypeWriter);
+        fontsConfigured = true;
     }
 
-    const QFont systemFont;
-    QFont fixedFont;
+    mutable QFont systemFont;
+    mutable QFont fixedFont;
+    mutable bool fontsConfigured;
 };
 
 QGnomeTheme::QGnomeTheme()
@@ -565,9 +573,11 @@ QVariant QGnomeTheme::themeHint(QPlatformTheme::ThemeHint hint) const
 const QFont *QGnomeTheme::font(Font type) const
 {
     Q_D(const QGnomeTheme);
+    if (!d->fontsConfigured)
+        d->configureFonts(gtkFontName());
     switch (type) {
     case QPlatformTheme::SystemFont:
-        return  &d->systemFont;
+        return &d->systemFont;
     case QPlatformTheme::FixedFont:
         return &d->fixedFont;
     default:
@@ -575,6 +585,11 @@ const QFont *QGnomeTheme::font(Font type) const
     }
 }
 
+QString QGnomeTheme::gtkFontName() const
+{
+    return QStringLiteral("%1 %2").arg(QLatin1String(defaultSystemFontNameC)).arg(defaultSystemFontSize);
+}
+
 QString QGnomeTheme::standardButtonText(int button) const
 {
     switch (button) {

src/platformsupport/themes/genericunix/qgenericunixthemes_p.h

@@ -111,6 +111,8 @@ public:
     virtual const QFont *font(Font type) const;
     QString standardButtonText(int button) const Q_DECL_OVERRIDE;
 
+    virtual QString gtkFontName() const;
+
     static const char *name;
 };
 

src/plugins/platformthemes/gtk2/qgtk2theme.cpp

@@ -85,6 +85,14 @@ QVariant QGtk2Theme::themeHint(QPlatformTheme::ThemeHint hint) const
     }
 }
 
+QString QGtk2Theme::gtkFontName() const
+{
+    QString cfgFontName = gtkSetting("gtk-font-name");
+    if (!cfgFontName.isEmpty())
+        return cfgFontName;
+    return QGnomeTheme::gtkFontName();
+}
+
 bool QGtk2Theme::usePlatformNativeDialog(DialogType type) const
 {
     switch (type) {

src/plugins/platformthemes/gtk2/qgtk2theme.h

@@ -51,7 +51,8 @@ class QGtk2Theme : public QGnomeTheme
 public:
     QGtk2Theme();
 
-    QVariant themeHint(ThemeHint hint) const;
+    virtual QVariant themeHint(ThemeHint hint) const Q_DECL_OVERRIDE;
+    virtual QString gtkFontName() const Q_DECL_OVERRIDE;
 
     bool usePlatformNativeDialog(DialogType type) const;
     QPlatformDialogHelper *createPlatformDialogHelper(DialogType type) const;