app: add gimp_gegl_node_is_source_operation()

... which determines if a node is a source operation.

app/gegl/gimp-gegl-utils.c

@@ -119,6 +119,21 @@ gimp_gegl_progress_connect (GeglNode     *node,
                           (GDestroyNotify) g_free);
 }
 
+gboolean
+gimp_gegl_node_is_source_operation (GeglNode *node)
+{
+  GeglOperation *operation;
+
+  g_return_val_if_fail (GEGL_IS_NODE (node), FALSE);
+
+  operation = gegl_node_get_gegl_operation (node);
+
+  if (! operation)
+    return FALSE;
+
+  return GEGL_IS_OPERATION_SOURCE (operation);
+}
+
 gboolean
 gimp_gegl_node_is_point_operation (GeglNode *node)
 {

app/gegl/gimp-gegl-utils.h

@@ -32,6 +32,7 @@ void         gimp_gegl_progress_connect             (GeglNode            *node,
                                                      GimpProgress        *progress,
                                                      const gchar         *text);
 
+gboolean     gimp_gegl_node_is_source_operation     (GeglNode            *node);
 gboolean     gimp_gegl_node_is_point_operation      (GeglNode            *node);
 
 const Babl * gimp_gegl_node_get_format              (GeglNode            *node,