Why do objects move with a delay when moving_ip in Pygame?

Question

Python

Greetings. I placed the objects in the paygame (these are sprites in a group) in random places, getting random coordinates. Then I want to change these coordinates to create a chaotic movement in random directions. When I changed them like this: rect.x += 1, then I reset the previously assigned random coordinates to 0 x and the changes occurred from x = 0 for all objects. I remembered move_ip. But I don't understand why it works like this:

Depending on the set value, there is a delay before the start of movement, then the objects begin to move and accelerate after an equal time interval (measured by counting out loud and bending the fingers).

class Object(Sprite):

  def __init__(self, screen, settings):
    super().__init__()
    
    self.screen = screen
    self.screen_rect = self.screen.get_rect()

    self.settings              = settings
    self.objects_amount = settings.objects_amount 
    self.image 		= pg.image.load('img/image.png').convert_alpha()
    self.rect 		        = self.image.get_rect()
    self.x 			= float(self.rect.x)
    self.y 			= float(self.rect.y)
    self.width 		= self.rect.width
    self.height 		= self.rect.height

  def get_random_position(self):
    """ Получаю список рандомных координат x и y """

    start_position  = self.width
    x_end_position  = self.settings.screen_width  - self.width
    y_end_position  = self.settings.screen_height - self.height
    pos_x = random.randint(start_position, x_end_position)
    pos_y = random.randint(start_position, y_end_position)

    return pos_x, pos_y

  def set_random_position(self, humans_amount):
    """ установить рандомные координаты """

    positions_list  = []
    width 			= self.rect.width
    height 			= self.rect.height

    for i in range(objects_amount):

      if not positions_list: # если пустой, то добавить первое значение 
        rand_x, rand_y = self.get_random_position()
        positions_list.append((rand_x, rand_y))
        
      elif positions_list:
        rand_x, rand_y = self.get_random_position()
        positions_list.append((rand_x, rand_y))

    return positions_list

(I create the group outside the main loop in the main file. Sprites are also placed outside the main loop, that is, once.) In the main loop, fpsClock.tick(60) is specified

Important:

def update(self):
    self.x += 0.01
    self.rect.move_ip(self.x,self.x) # одинаковые значения просто пока разбираюсь

With a value of 0.01, after about 2 seconds, the objects start moving, then after another couple of seconds, the speed increases by 2 times. With a value of 0.1, there is practically no delay (some fractions of a second), and there is an acceleration every second

. Why does it work like this? Is this normal or have I messed something up? move_ip moves the object to the specified coordinates, the update function is called in the main loop, and I understand why the acceleration occurs. But where does the delay come from? How is it determined that 0.01 is an interval of about 2 seconds, and 0.1 is a second? If you set it to 0.001, then the delay will be about 14 seconds.
Please explain how this is all calculated and how to remove the delay when setting low values, such as 0.01 and 0.001

Answer 1

You have 60 FPS, which means 60 update calls per second, which means x every second increases by - 0.6px (0.01 * 60). It is also worth considering that integer arithmetic is used in pygame.Rect calculations , i.e. move_ip won't move your character if current x < 1. So while x gets to 1, you end up with a delay of ~2 seconds. If we take the increment as 0.001, then the increase will be 0.06px, and x will gain one in ~16 seconds (1 / 0.06) and only after 16 seconds the character will start moving. To avoid delay, as you might have guessed, you need to initially set x to one