QGtkStyle: add getIconThemeName() helper function

Add QGtkStyle::getIconThemeName() static helper function
(which uses GtkSettings to retrieve the theme name) and use it in
QGuiPlatformPlugin::systemIconThemeName() when desktop is GNOME.

In modern distributions like Debian and Ubuntu, the
/desktop/gnome/interface GConf schema is no longer installed,
so the old method for retrieving icon theme name no longer works.

Qt 5 already uses GtkSettings for this thing, although the code
is in a different place.

Change-Id: Ib13d4809b55dd55dc1fa0bc2c4b1552f13feb030
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>

2 files changed, 23 insertions, 0 deletions

diff --git a/src/gui/styles/qgtkstyle_p.cpp b/src/gui/styles/qgtkstyle_p.cpp
index 302cf09..67b3245 100644
--- a/src/gui/styles/qgtkstyle_p.cpp
+++ b/src/gui/styles/qgtkstyle_p.cpp
@@ -686,6 +686,28 @@ QString QGtkStylePrivate::getThemeName()
     return themeName;
 }
 
+QString QGtkStylePrivate::getIconThemeName() {
+    if (!gtk_settings_get_default) {
+        // enforce the "0" suffix, so we'll open libgtk-x11-2.0.so.0
+        QLibrary libgtk(QLS("gtk-x11-2.0"), 0, 0);
+        libgtk.setLoadHints(QLibrary::ImprovedSearchHeuristics);
+        gtk_init = (Ptr_gtk_init)libgtk.resolve("gtk_init");
+        gtk_settings_get_default = (Ptr_gtk_settings_get_default)libgtk.resolve("gtk_settings_get_default");
+    }
+    if (!gtk_settings_get_default) {
+        return QString();
+    }
+    x11ErrorHandler qt_x_errhandler = XSetErrorHandler(0);
+    gtk_init(NULL, NULL);
+    XSetErrorHandler(qt_x_errhandler);
+    GtkSettings *settings = gtk_settings_get_default();
+    gchararray value;
+    g_object_get(settings, "gtk-icon-theme-name", &value, NULL);
+    QString result = QString::fromUtf8(value);
+    g_free(value);
+    return result;
+}
+
 // Get size of the arrow controls in a GtkSpinButton
 int QGtkStylePrivate::getSpinboxArrowSize() const
 {
diff --git a/src/gui/styles/qgtkstyle_p.h b/src/gui/styles/qgtkstyle_p.h
index b4ab589..1be5aa4 100644
--- a/src/gui/styles/qgtkstyle_p.h
+++ b/src/gui/styles/qgtkstyle_p.h
@@ -339,6 +339,7 @@ public:
     static QString getGConfString(const QString &key, const QString &fallback = QString());
 
     static QString getThemeName();
+    static QString getIconThemeName();
     virtual int getSpinboxArrowSize() const;
 
     static void setupGtkFileChooser(GtkWidget* gtkFileChooser, QWidget *parent,