arrows_renderer = arrow_x = arrow_y = None

FOV_ARROWS = { \
    "50um[0.0]": [20.0]   \
}


FOV_ARROWS_SIZE=100
FOV_ARROWS_ORIGIN=Point(image.getData().width/4, image.getData().height*3/4)
FOV_FUTURE=None
    
def  update_arrows():
    global arrows_renderer, arrow_x, arrow_y 
    if arrows_renderer is not None:
        fov = microscope.get_preset_label()
        args = FOV_ARROWS.get(fov, None)
        if args is not None:
            angle=args[0]
            x,y = FOV_ARROWS_ORIGIN.x, FOV_ARROWS_ORIGIN.y            
            a=math.radians(angle)
            xa,ya=int(x+FOV_ARROWS_SIZE*math.cos(a)),  int(y-FOV_ARROWS_SIZE*math.sin(a))
            arrow_x.update(FOV_ARROWS_ORIGIN, Point(xa,ya))
            angle=angle+90
            a=math.radians(angle)
            xa,ya=int(x+FOV_ARROWS_SIZE*math.cos(a)),  int(y-FOV_ARROWS_SIZE*math.sin(a))
            arrow_y.update(FOV_ARROWS_ORIGIN, Point(xa,ya))
        else:
            arrow_x.update(FOV_ARROWS_ORIGIN, FOV_ARROWS_ORIGIN)
            arrow_y.update(FOV_ARROWS_ORIGIN, FOV_ARROWS_ORIGIN)            
            
def  task_update_arrows():  
    global arrows_renderer
    while arrows_renderer is not None:
        try:
            if arrows_renderer.isShowing():
                update_arrows()
                time.sleep(5.0)
            time.sleep(1.0)
        except:         
            pass
            

def start_arrows(renderer=None):
    global arrows_renderer, arrow_x, arrow_y, FOV_FUTURE
    if arrows_renderer is None:
        arrows_renderer = renderer if renderer else show_panel(image)
        arrow_x = Overlays.Arrow(Pen(Color.GREEN))
        arrow_y = Overlays.Arrow(Pen(Color.GREEN.darker().darker()))
        arrows_renderer.addOverlays([arrow_x,arrow_y])
        #update_arrows()
        FOV_FUTURE = fork(task_update_arrows,)[0]
    

def stop_arrows(renderer=None):
    global arrows_renderer, arrow_x, arrow_y, FOV_FUTURE
    if arrows_renderer is not None:
        arrows_renderer.removeOverlays([arrow_x,arrow_y])
    arrows_renderer=None
    FOV_FUTURE.cancel(True)
    try:
        join(FOV_FUTURE)
    except:
        pass