[pygame] Bug: Circle tearing with mouse clicks within the window.

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Michael Baca

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Dec 14, 2020, 10:00:37 PM12/14/20
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Python 3.8.6
Pygame 2.0.0
Xubuntu 20.10
Nvidia 1060 6GB

The following code, when run, causes an issue where the circle starts to tear as it moves across the screen if I click on the active window. Where I click seems to matter also, as the tearing can be adjusted by clicking at various points from top to bottom. I'm not checking for mouse events in the code, but I would imagine their still being tracked.

The tearing continues to happen after I've stopped and ran it again as well. It does go back to normal after a few tries. But the effects seem to stay in memory.

I wasn't sure where to send bugs, the website led me here. I hope this is the right place.

# ----------------------------------------
import pygame as pg

# init game space
pg.init()

screen = pg.display.set_mode((600, 400))
pg.display.set_caption("Ball Moving")

playerX = 50
playerY = 50
player_Width = 30
player_Height = 30
playerVelocity = 0.5

# Color Constants
BLUE = (0, 0, 255)

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

    # update screen
    keys = pg.key.get_pressed()
    if keys[pg.K_LEFT]:
        playerX -= playerVelocity
    if keys[pg.K_RIGHT]:
        playerX += playerVelocity
    if keys[pg.K_UP]:
        playerY -= playerVelocity
    if keys[pg.K_DOWN]:
        playerY += playerVelocity

    screen.fill(WHITE)
    pg.draw.circle(screen, (BLUE), (playerX, playerY), player_Width, 0)
    pg.display.flip()

pg.display.quit()
pg.quit()

Michael Lutynski

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Dec 14, 2020, 11:19:05 PM12/14/20
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Hello Michael and welcome to the community :)


I tried your code on my Linux setup: Python 3.8.5, Pygame 2.0.0, SDL 2.0.12, KDE neon 5.20.04, Mesa DRI Intel HD Graphics 3000...


After adding the missing


     WHITE = (255, 255, 255)


and running your code, I didn't notice tearing as I moved the circle around. But for me, KDE uses KWin, which is a composited window manager. Is Xubuntu using XFWM? I'm going out on a limb, but I think that is not a composited WM, and might have a different interaction with X11 and appear differently. Have you experimented with installing a different distro, like Kubuntu, then login and run your test and see if it behaves differently?

~ Michael

Greg Ewing

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Dec 15, 2020, 12:31:12 AM12/15/20
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On 15/12/20 4:00 pm, Michael Baca wrote:
> The following code, when run, causes an issue where the circle starts to
> tear as it moves across the screen

You could try

screen = pg.display.set_mode((600, 400),
flags = pg.HWSURFACE | pg.DOUBLEBUF)

According to the docs, this will cause screen.flip() to wait for
a vertical retrace.

--
Greg
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