Window placement can be influenced using this enumeration.
|0||Gtk::WIN_POS_NONE||No influence is made on placement.|
|1||Gtk::WIN_POS_CENTER||Windows should be placed in the center of the screen.|
|2||Gtk::WIN_POS_MOUSE||Windows should be placed at the current mouse position.|
|3||Gtk::WIN_POS_CENTER_ALWAYS||Keep window centered as it changes size, etc.|
|4||Gtk::WIN_POS_CENTER_ON_PARENT||Center the window on its transient parent (see set_transient_for() ).|