docs: def on_event(self, event):
          """Pygame event processing callback method.
  
          :param event: Event to process.
          """
          if self.state > 0:
              if event.type == MOUSEBUTTONDOWN:
                  key = self.layout.get_key_at(pygame.mouse.get_pos())
                  if key is not None:
                      self.on_key_down(key)
              elif event.type == MOUSEBUTTONUP:
                  self.on_key_up()
              elif event.type == KEYDOWN:
                  value = pygame.key.name(event.key)
                  # TODO : Find from layout (consider checking layout key space ?)
              elif event.type == KEYUP:
                  value = pygame.key.name(event.key)