gnome-desktop-thumbnail.c: Check for a filesystem-supplied preview

icon before running thumbnailers.

Some devices that transfer media files can also provide a preview
icon for these files, saving the thumbnailer having to load the
original files in order to create a preview (which can block
file managers from loading the remaining files).

Author: mtwebster

libcinnamon-desktop/gnome-desktop-thumbnail.c

@@ -1175,6 +1175,58 @@ expand_thumbnailing_script (const char *script,
   return NULL;
 }
 
+static GdkPixbuf *
+get_preview_thumbnail (const char *uri,
+                       int         size)
+{
+    GdkPixbuf *pixbuf;
+    GFile *file;
+    g_autoptr(GFileInfo) file_info = NULL;
+    GInputStream *input_stream;
+    GObject *object;
+
+    g_return_val_if_fail (uri != NULL, NULL);
+
+    input_stream = NULL;
+
+    file = g_file_new_for_uri (uri);
+
+    /* First see if we can get an input stream via preview::icon  */
+    file_info = g_file_query_info (file,
+                                   G_FILE_ATTRIBUTE_PREVIEW_ICON,
+                                   G_FILE_QUERY_INFO_NONE,
+                                   NULL,  /* GCancellable */
+                                   NULL); /* return location for GError */
+    g_object_unref (file);
+
+    if (file_info == NULL)
+      return NULL;
+
+    object = g_file_info_get_attribute_object (file_info,
+                                               G_FILE_ATTRIBUTE_PREVIEW_ICON);
+
+    if (!object)
+      return NULL;
+    if (!G_IS_LOADABLE_ICON (object)) {
+      return NULL;
+    }
+
+    input_stream = g_loadable_icon_load (G_LOADABLE_ICON (object),
+                                         0,     /* size */
+                                         NULL,  /* return location for type */
+                                         NULL,  /* GCancellable */
+                                         NULL); /* return location for GError */
+
+    if (!input_stream)
+      return NULL;
+
+    pixbuf = gdk_pixbuf_new_from_stream_at_scale (input_stream,
+                                                  size, size,
+                                                  TRUE, NULL, NULL);
+    g_object_unref (input_stream);
+    return pixbuf;
+}
+
 /**
  * gnome_desktop_thumbnail_factory_generate_thumbnail:
  * @factory: a #GnomeDesktopThumbnailFactory
@@ -1217,6 +1269,10 @@ gnome_desktop_thumbnail_factory_generate_thumbnail (GnomeDesktopThumbnailFactory
 
   pixbuf = NULL;
 
+  pixbuf = get_preview_thumbnail (uri, size);
+  if (pixbuf != NULL)
+    return pixbuf;
+
   script = NULL;
   g_mutex_lock (&factory->priv->lock);