def add_global_overlay(o):
    GLOBAL_OVERLAYS.append(o)
def remove_global_overlay(o):
    if o in GLOBAL_OVERLAYS:
        GLOBAL_OVERLAYS.remove(o)
def set_global_overlays(olist):
    for _ in range(len(GLOBAL_OVERLAYS)):
        GLOBAL_OVERLAYS.remove(GLOBAL_OVERLAYS[0])
    GLOBAL_OVERLAYS.extend(olist)