Windows should be placed in the center of the screen.
Keep window centered as it changes size, etc.
Center the window on its transient
parent (see gtk_window_set_transient_for()).
Windows should be placed at the current mouse position.
No influence is made on placement.
Window placement can be influenced using this enumeration. Note that using #GTK_WIN_POS_CENTER_ALWAYS is almost always a bad idea. It won’t necessarily work well with all window managers or on all windowing systems.