Why does my pygame.draw.rect() keep drawing in the main code without the background?

Question

Here is the code with the background in the main code. I cannot figure out what is wrong.

    import pygame
    import random
    pygame.init()

    width, height = 800, 400
    win = pygame.display.set_mode((width, height))
    pygame.display.set_caption("Dungeon Crawler")

    bg_img = pygame.image.load('background_image.png')
    bg_img = pygame.transform.scale(bg_img, (width, height))

    player_x = 100
    player_y = 100
    player_width = 50
    player_height = 50
    player_speed = 5


    run = True
    clock = pygame.time.Clock()

    while run:
        clock.tick(60)  # 60 FPS
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False

        win.blit(bg_img, (0, 0))
        pygame.display.update()
    
         keys = pygame.key.get_pressed()
        if keys[pygame.K_LEFT] and player_x > 0:
            player_x -= player_speed
        if keys[pygame.K_RIGHT] and player_x < width - player_width:
            player_x += player_speed
        if keys[pygame.K_UP] and player_y > 0:
            player_y -= player_speed
        if keys[pygame.K_DOWN] and player_y < height - player_height:
            player_y += player_speed



        pygame.draw.rect(win, (0, 255, 0), (player_x, player_y, player_width, player_height))

        pygame.display.update()

    pygame.quit()

The cubes flicker in and out with the background, whereas when you move the win.blit(bg_img, (0, 0)) and pygame.display.update() out of the main code, (just under num_enemies = 6), the cube becomes like a long, stretched green snake... Please can somebody tell me what is wrong with the code? I am a noob still, I have tried chatGPT but it does not supply the level of knowledge I can get from other coders. Please help, this is my first time using pygame (within the last couple of weeks) and I really need some help. If you have more information about pygame that I could use to make a game, please tell me. Anyway, thanks in advance. (Yes you can copy and paste into idle or such, it is not too far into development, and thanks)

I tried doing a number of things, such as moving it around to other locations in the code, figuring out why but it did not work. Help please.

Your "main render loop" shouldn't update the display twice. – tkausl Aug 21 '23 at 22:54 — tkausl, Aug 21 '23 at 22:54

score 0 · Accepted Answer · answered Aug 22 '23 at 02:23

That's because you are calling pygame.display.update() more than once in your game loop. You should only call this function after you're done drawing on the window. Here is the fixed version:

import pygame
import random
pygame.init()

width, height = 800, 400
win = pygame.display.set_mode((width, height))
pygame.display.set_caption("Dungeon Crawler")

bg_img = pygame.image.load('background_image.png')
bg_img = pygame.transform.scale(bg_img, (width, height))

player_x = 100
player_y = 100
player_width = 50
player_height = 50
player_speed = 5


run = True
clock = pygame.time.Clock()

while run:
    clock.tick(60)  # 60 FPS
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    win.blit(bg_img, (0, 0))
    # Removed pygame.display.update() here

    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT] and player_x > 0:
        player_x -= player_speed
    if keys[pygame.K_RIGHT] and player_x < width - player_width:
        player_x += player_speed
    if keys[pygame.K_UP] and player_y > 0:
        player_y -= player_speed
    if keys[pygame.K_DOWN] and player_y < height - player_height:
        player_y += player_speed



    pygame.draw.rect(win, (0, 255, 0), (player_x, player_y, player_width, player_height))

    pygame.display.update()

pygame.quit()

Why does my pygame.draw.rect() keep drawing in the main code without the background?

1 Answers1