Sets the visual that should be used for by widget and its children for
creating #GdkWindows. The visual must be on the same #GdkScreen as
returned by gtk_widget_get_screen(), so handling the
#GtkWidget::screen-changed signal is necessary.
Setting a new @visual will not cause @widget to recreate its windows,
so you should call this function before @widget is realized.
Sets the visual that should be used for by widget and its children for creating #GdkWindows. The visual must be on the same #GdkScreen as returned by gtk_widget_get_screen(), so handling the #GtkWidget::screen-changed signal is necessary.
Setting a new @visual will not cause @widget to recreate its windows, so you should call this function before @widget is realized.