Sets whether @widget should be mapped along with its when its parent is mapped and @widget has been shown with gtk_widget_show(). The child visibility can be set for widget before it is added to a container with gtk_widget_set_parent(), to avoid mapping children unnecessary before immediately unmapping them. However it will be reset to its default state of %TRUE when the widget is removed from a container. Note that changing the child visibility of a widget does not queue a resize on the widget. Most of the time, the size of a widget is computed from all visible children, whether or not they are mapped. If this is not the case, the container can queue a resize itself. This function is only useful for container implementations and never should be called by an application.