interval: Add is_valid() method

The is_valid() method checks if the Interval has an initial and final
values and it's not still uninitialized.

clutter/clutter-interval.c

@@ -1065,3 +1065,27 @@ clutter_interval_compute (ClutterInterval *interval,
 
   return NULL;
 }
+
+/**
+ * clutter_interval_is_valid:
+ * @interval: a #ClutterInterval
+ *
+ * Checks if the @interval has a valid initial and final values.
+ *
+ * Return value: %TRUE if the #ClutterInterval has an initial and
+ *   final values, and %FALSE otherwise
+ *
+ * Since: 1.12
+ */
+gboolean
+clutter_interval_is_valid (ClutterInterval *interval)
+{
+  ClutterIntervalPrivate *priv;
+
+  g_return_val_if_fail (CLUTTER_IS_INTERVAL (interval), FALSE);
+
+  priv = interval->priv;
+
+  return G_IS_VALUE (&priv->values[INITIAL]) &&
+         G_IS_VALUE (&priv->values[FINAL]);
+}

clutter/clutter-interval.h

@@ -133,6 +133,9 @@ gboolean         clutter_interval_compute_value      (ClutterInterval *interval,
 const GValue *   clutter_interval_compute            (ClutterInterval *interval,
                                                       gdouble          factor);
 
+CLUTTER_AVAILABLE_IN_1_12
+gboolean         clutter_interval_is_valid           (ClutterInterval *interval);
+
 G_END_DECLS
 
 #endif /* __CLUTTER_INTERVAL_H__ */

clutter/clutter.symbols

@@ -794,6 +794,7 @@ clutter_interval_get_initial_value
 clutter_interval_get_interval
 clutter_interval_get_type
 clutter_interval_get_value_type
+clutter_interval_is_valid
 clutter_interval_new
 clutter_interval_new_with_values
 clutter_interval_peek_final_value