[gtk+/gtk-3-16] fontchooser: Use gtk-fontconfig-timestamp setting

[Matthias Clasen <matthiasc src gnome org>]

commit d2df0aa7ca175f20a983e2bc7b8e94056b8a627b
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Mon May 4 13:25:27 2015 +0100

    fontchooser: Use gtk-fontconfig-timestamp setting
    
    We can use the GtkSettings:gtk-fontconfig-timestamp property to decide
    whether or not we should reload fonts on style and screen changes. This
    should avoid doing a lot of work with large font collections when only
    the theme has changed.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=748782

 gtk/gtkfontchooserwidget.c |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkfontchooserwidget.c b/gtk/gtkfontchooserwidget.c
index 5fc82b2..9e22fbc 100644
--- a/gtk/gtkfontchooserwidget.c
+++ b/gtk/gtkfontchooserwidget.c
@@ -95,6 +95,8 @@ struct _GtkFontChooserWidgetPrivate
   GtkFontFilterFunc filter_func;
   gpointer          filter_data;
   GDestroyNotify    filter_data_destroy;
+
+  guint last_fontconfig_timestamp;
 };
 
 /* This is the initial fixed height and the top padding of the preview entry */
@@ -633,6 +635,21 @@ gtk_font_chooser_widget_load_fonts (GtkFontChooserWidget *fontchooser)
   gint n_families, i;
   PangoFontFamily **families;
   gchar *family_and_face;
+  guint fontconfig_timestamp;
+
+  g_object_get (gtk_widget_get_settings (GTK_WIDGET (fontchooser)),
+                "gtk-fontconfig-timestamp", &fontconfig_timestamp,
+                NULL);
+
+  /* The fontconfig timestamp is only set on systems with fontconfig; every
+   * other platform will set it to 0. For those systems, we fall back to
+   * reloading the fonts every time.
+   */
+  if (fontconfig_timestamp != 0 &&
+      priv->last_fontconfig_timestamp == fontconfig_timestamp)
+    return;
+
+  priv->last_fontconfig_timestamp = fontconfig_timestamp;
 
   list_store = GTK_LIST_STORE (priv->model);