GtkWindow::get_frame_dimensions
Returns an array containing the widths of the frame window for the toplevel. The array returned contains the left, top, right, and bottom widths in that order.
Note: This is a special-purpose function intended for the framebuffer
port. It does not return the width of the window decorations. Use
get_frame_extents() for that
purpose.
See also: set_frame_dimensions()