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.Widget.getScreen, 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.Widget.getScreen, 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.