Gtk.Widget.prototype.set_visual

function set_visual(visual:Gdk.Visual):void {
    // Gjs wrapper for gtk_widget_set_visual()
}

Sets the visual that should be used for by widget and its children for creating #GdkWindows. The visual must be on the same Gdk.Screen as returned by Gtk.Widget.prototype.get_screen, so handling the Gtk.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.