Pygame Surface updates non-sequentially

Question

I am attempting to implement a simple Pygame script that is supposed to:

First, check for when the user presses the Space key;
On Space keypress, display some text; then
Pauses for 2 seconds and then update the screen to its original state.

Note that all of the above events must occur sequentially, and cannot be out of order.

I am encountering problems where the program first pauses, then displays the text only appears for a split second (or not at all) before the screen updates to its original state.

The program seems to have skipped over step 2 and proceeded with the pause in step 3 before displaying text. My code is as follows:

import pygame
import sys
from pygame.locals import *

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)

pygame.init()
wS = pygame.display.set_mode((500, 500), 0, 32)


# Method works as intended by itself
def create_text(x, y, phrase, color):
    """
    Create and displays text onto the globally-defined `wS` Surface
    (params in docstring omitted)
    """
    # Assume that the font file exists and is successfully found
    font_obj = pygame.font.Font("./roboto_mono.ttf", 32)
    text_surface_obj = font_obj.render(phrase, True, color)
    text_rect_obj = text_surface_obj.get_rect()
    text_rect_obj.center = (x, y)
    wS.blit(text_surface_obj, text_rect_obj)


while True:
    wS.fill(BLACK)
    for event in pygame.event.get():
        if event.type == KEYDOWN and event.key == K_SPACE:

            # Snippet containing unexpected behavior
            create_text(250, 250, "Hello world!", WHITE)
            pygame.display.update()
            pygame.time.delay(2000)
            # Snippet end

        if event.type == QUIT:
            pygame.quit()
            sys.exit(0)
    pygame.display.update()

Thanks in advance!

Try to remove the two lines under `pygame.time.delay(2000)`. It looks like they're unnecessary and could cause the problem. — skrx, May 31 '18 at 09:19
@skrx Once I've removed the two lines below the `delay()` method call, I do see the `Hello World!` text getting blitted; however, it only gets displayed for an instant (one frame?) as opposed to the intended 2 seconds. — Jerrybibo, May 31 '18 at 09:22
That's odd. The execution of the program should be stopped after the `delay` call. BTW, I had trouble to reproduce the bug in the first place. I think I saw it once for a very short time but couldn't reproduce it again. Perhaps it would be better to restructure the program and use one of these [timers](https://stackoverflow.com/questions/30720665/countdown-timer-in-pygame). — skrx, May 31 '18 at 09:38

score 9 · Accepted Answer · 2018-07-16T23:52:48.267

For some reason the program worked for me with the only thing I changed was the font. This is the same as what @Omega0x013 is doing, but you have an unlimited framerate. It works because FPS.tick() returns the amount of time since it was last called, if you don't specify a frame rate, it does not hold the program.

import pygame
import sys
from pygame.locals import *
displayText = False
WHITE = (255, 255, 255)
BLACK = (0, 0, 0)

pygame.init()
wS = pygame.display.set_mode((500, 500), 0, 32)


# Method works as intended by itself
def create_text(x, y, phrase, color):
    """
    Create and displays text onto the globally-defined `wS` Surface
    (params in docstring omitted)
    """
    # Assume that the font file exists and is successfully found

    font_obj = pygame.font.Font(None,30)
    text_surface_obj = font_obj.render(phrase, True, color)
    text_rect_obj = text_surface_obj.get_rect()
    text_rect_obj.center = (x, y)
    wS.blit(text_surface_obj, text_rect_obj)

FPS = pygame.time.Clock()
while True:
    wS.fill(BLACK)
    for event in pygame.event.get():
        if event.type == KEYDOWN and event.key == K_SPACE:
            totalTime = 0
            FPS.tick()
            displayText = True

        if event.type == QUIT:
            pygame.quit()
            sys.exit(0)
    if displayText:
        totalTime += FPS.tick()
        create_text(250, 250, "Hello world!", WHITE)
        if totalTime >= 2000:
            displayText = False
    pygame.display.update()

Wow, this solution is perfect for my usage. Thanks! (Also, shouldn't it be OK if the `FPS.tick()` call is removed from the event loop?) — Jerrybibo, Jul 17 '18 at 02:05
The Fps.Tick() returns the amount of time since it was last called. If I press space then 5 seconds later I press space again and call FPS.tick() it will return 5 seconds, meaning the screen will instantly turn black, by keeping it in the event loop, whenever i press space, the time is reset. — , Jul 17 '18 at 02:28

score 8 · Answer 2 · edited Jul 16 '18 at 17:06

you should try this:

import pygame
import sys
from pygame.locals import *

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)

pygame.init()
wS = pygame.display.set_mode((500, 500), 0, 32)
clock = pygame.time.Clock()

showing = False
timer = 0
# Method works as intended by itself
def create_text(x, y, phrase, color):
    """
    Create and displays text onto the globally-defined `wS` Surface
    (params in docstring omitted)
    """
    # Assume that the font file exists and is successfully found
    font_obj = pygame.font.Font("./roboto_mono.ttf", 32)
    text_surface_obj = font_obj.render(phrase, True, color)
    text_rect_obj = text_surface_obj.get_rect()
    text_rect_obj.center = (x, y)
    wS.blit(text_surface_obj, text_rect_obj)


while True:
    wS.fill(BLACK)
    for event in pygame.event.get():
        if event.type == KEYDOWN and event.key == K_SPACE:
            showing = True
            timer = 0

        if event.type == QUIT:
            pygame.quit()
            sys.exit(0)

    if showing:
        timer += 1
        create_text(250, 250, "Hello world!", WHITE)

    if timer == 20:
        timer = 0
        showing = False

    pygame.display.update()
    clock.tick(100)

what this does is every time you press space it shows the text for 2s by showing it, counting 2000ms and then not showing it.

The indentation is a little off, you might want to fix that. Also, I understand that this is not specified within the question, but `pygame.Clock.tick()` comes with the drawback of a limited framerate. I would lean more towards a solution that does not involve such limitations. — Jerrybibo, Jul 16 '18 at 16:56
This solution worked if I unindented the last 2 `if` clauses to the same level as the `for event` loop; I upvoted your answer. But I'm also looking for a more elegant solution that doesn't rely on `pygame.Clock.tick()`. — Jerrybibo, Jul 16 '18 at 17:02
i would agree that there are limitations to pygame.Clock.tick() @Jerrybibo, but it makes the time that it takes constant and measurable for exactly two seconds. — Omega0x013, Jul 16 '18 at 17:04

Pygame Surface updates non-sequentially

2 Answers2