I am stuck on a screen tearing problem for about a week now.
Here is my problem: I would like to make a program that can display a sequence of PNG pictures really fast (at a rate of 30 fps or more). To do this I use the pygame library, especially pygame.display.blit
and pygame.display.flip
.
Here is an example of the code (with a homemade delay function):
import time
import pygame
screen=pygame.display.set_mode(size, pygame.FULLSCREEN)
nbPicturesToLoad=12
pictures=range(nbPicturesToLoad)
for i in range(nbPicturesToLoad):
pictures[i]=pygame.image.load(pictureName).convert() //Here pictureName depends on the value of i
(...)
for i in range(nbPicturesToLoad):
timer1=time.time()
screen.blit(pictures[i], (0,0))
pygame.display.flip()
timer2=time.time()
timer=timer2-timer1
while(timer<0.03333):
timer2=time.time()
timer=timer2-timer1
The timer allows me to have the same refresh rate on the screen.
My problem is that one can see with their own eyes that there is a screen tearing problem (https://en.wikipedia.org/wiki/Screen_tearing).
On the pygame documentation they recommend to use other flags for the screen init (pygame.HWSURFACE and pygame.DOUBLEBUF
, http://www.pygame.org/docs/ref/display, y.set_mode
). Apparently these could help to correct the screen tearing problems. But when I use these flags I see no screen tearing correction.
I've seen somewhere that pygame can't handle vsync on X11, which would explain why I see no difference with the HWSURFACE and DOUBLEBUF flags.
Has anyone ever encountered this vsync issue on the Raspberry Pi? Is there a parameter to put in the "config.txt" file? Does anyone have a way to get real vsync information to avoid these screen tearing effects?
I've seen that pyglet could handle vsync in the created windows, but for unknown reasons I can't display images in the pyglet window and I'm really not sure if it would fix the problem, especially if a Raspberry can't handle vsync right now.