stack: assert for some assumptions

diff --git a/gtk/gtkstack.c b/gtk/gtkstack.c
index b97ebb54bb52895f3375b1ded14bf031eec4dd2e..cafa2a263bb0930cf73fb136a04dc1934ca92610 100644 (file)
--- a/gtk/gtkstack.c
+++ b/gtk/gtkstack.c
@@ -2166,6 +2166,9 @@ gtk_stack_snapshot_cube (GtkWidget   *widget,
   GtkStackPrivate *priv = gtk_stack_get_instance_private (stack);
   double progress = gtk_progress_tracker_get_progress (&priv->tracker, FALSE);
 
+  g_assert (priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_ROTATE_RIGHT ||
+            priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_ROTATE_LEFT);
+
   if (priv->active_transition_type == GTK_STACK_TRANSITION_TYPE_ROTATE_RIGHT)
     progress = 1 - progress;