Blur algorithm works badly when the pitch is not equal to width*bytes_per_pixel.

[yunline]

import pygame
import sys

pygame.font.init()

font=pygame.font.SysFont('Arial',100)

pygame.display.init()
dsf=pygame.display.set_mode((1280,720))

sf=font.render('HelloWorld',1,(255,255,255))#.convert_alpha()
print(sf)
print(sf.get_pitch())
print(sf.get_width()*sf.get_bitsize()//8)

sf_blur=pygame.transform.box_blur(sf,10)

dsf.fill((0,150,0))
dsf.blit(sf,(0,0,1,1))
dsf.blit(sf_blur,(640,0,1,1))
pygame.display.update()

while 1:
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            sys.exit()

pygame-ce 2.2.0.dev1 (SDL 2.0.22, Python 3.10.6)
<Surface(487x115x32 SW)>
2016
1948

And, when I use the convert_alpha() to convert the surface, the bug disappeared:

pygame-ce 2.2.0.dev1 (SDL 2.0.22, Python 3.10.6)
<Surface(487x115x32 SW)>
1948
1948