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def on_enter(self):
    self.animate_logo()
    clock.schedule_once(self.transition_to_main_screen, 3)  # adjust transition time as needed

def animate_logo(self):
    logo_image = self.logo_image
    if logo_image:
        anim = animation(size_hint_x=1.2, duration=0.5)
        anim.bind(on_complete=self.animate_logo_back)
        anim.start(logo_image)

def animate_logo_back(self, *args):
    logo_image = self.logo_image
    if logo_image:
        anim = animation(size_hint_x=1, duration=0.5)
        anim.start(logo_image)

def transition_to_main_screen(self, dt):
    self.manager.current = 'main_screen'  # replace 'main_screen' with your main screen name

def login(self):
    # implement your login logic here
    username = self.ids.username_field.text
    password = self.ids.password_field.text
    # ... (check credentials, navigate to appropriate screen)

def show_signup_screen(self):
    self.manager.current = 'signup_screen'  # replace with your signup screen name

def build(self):
    sm = ScreenManager()
    sm.add_widget(SplashScreen(name='splash_screen'))
    sm.add_widget(MainScreen(name='main_screen'))  # Add your main screen
    sm.current = 'splash_screen'
    return sm