Hides or shows the widget depending on the value of visible. If visible is true the widget will be shown. If it is false it will be hidden.
The optional parameter all can be used to hide or show all children under the widget. If all is true, show_all() or hide_all() will be called instead of show() or hide() .
set_visible() returns true if the widget is now visible and false.
See also: show() , hide() , is_visible()