OOP pygame movement issues

Question

I am just getting started with pygame. My Player instances position does not update on the surface even though it's x value is changed accordingly.

'''__main__.py'''
import script

if __name__ == '__main__':
    script.setup()
    script.update()

-

'''script.py'''
import pygame
from player import Player
from enemy import Enemy
from ball import Ball


def setup():
    global window, player, enemy, ball

    pygame.init()
    pygame.display.set_caption('Pong')
    window = pygame.display.set_mode((800, 600))

    player = Player(40, window.get_height() / 2 - 100 / 2, 20, 100)
    enemy = Enemy(window.get_width() - 40 - 20, window.get_height() / 2 - 100 / 2, 20, 100)


def draw():
    player.update()
    enemy.update()
    pygame.display.update()

    player.draw(window)
    enemy.draw(window)

def update():

    running = True
    while running:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                running = False


        keys = pygame.key.get_pressed()

        if keys[pygame.K_UP]:
            player.up = True
        if keys[pygame.K_DOWN]:
            player.down = True

        if not keys[pygame.K_UP]:
            player.up = False
        if not keys[pygame.K_DOWN]:
            player.down = False

        draw()


    pygame.quit()

-

'''player.py'''
import pygame

class Player:
    '''Player'''
    def __init__(self, x, y, width, height):
        self.x = x
        self.y = y
        self.width = width
        self.height = height
        self.color = (255, 255, 255)
        self.rect = (self.x, self.y, self.width, self.height)
        self.vel = 10
        self.up = False
        self.down = False

    def draw(self, surface):
        pygame.draw.rect(surface, self.color, self.rect)

    def update(self):
        if self.up:
            self.x -= self.vel
        if self.down:
            self.x += self.vel

The instance's x value changes when I press up or down, but for some reason it does not get drawn on screen. I have tried moving the draw method and the player.update method but can't seem to get it to work properly.

petraszd petraszd · Accepted Answer · 2019-12-01T15:11:47

Look at the Player.draw method. It draws using self.rect.

The problem with your update method is that it never updates self.rect. So self.rect stays the same as after constructor.

Remove self.rect as attribute and replace it with either simple method (Option A) or property (Option B):

class Player:
    # Options A:
    def get_rect(self):
        return (self.x, self.y, self.width, self.height)

    # Option B:
    @property
    def rect(self):
        return (self.x, self.y, self.width, self.height)

Or update self.rect inside update method. But I do not recommend that. Having it separately was a reason why you got your no-changing-position-bug in the first place.

OOP pygame movement issues

1 Answers