fixed pixelarray indexing to prevent segfault reported in #2275

[oddbookworm]

fixes #2275

[oddbookworm]

Further note:
It is also possible to segfault by trying to just index into that created pixelarray. This fixes both and the regression test has both cases

[Starbuck5]

I think this may be more complicated.

If I create a PixelArray from a normal Surface and access the shape attribute, I get (w, h). With the example code in the issue, I get (w,). However, if I flip the dimension that it is zero dimensional in, everything works perfectly fine and it raises an IndexError as I would expect.

>>> weird_surface = pygame.Surface((0,5))
>>> pixarray = pygame.PixelArray(weird_surface)
>>> pixarray.shape
(0, 5)
>>> pixarray[0]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: array index out of range

So the problem is that the code is using 0 in shape[1] as a special value in places to indicate the dimensionality of the data? And this just happens to be slotting into that? Maybe the special value should be replaced with -1, which would never come from a Surface's dimensions.

[simplyrohan]

Another thing I found was that when the 0d value is in the Y value, then the shape of the pixel array does not include the Y value at all...

import pygame
test_surf1 = pygame.Surface((0, 5))
test_surf2 = pygame.Surface((5,0))
pixarr1 = pygame.PixelArray(test_surf1)
pixarr2 = pygame.PixelArray(test_surf2)
print(pixarr1.shape, pixarr2.shape)

Outputs:
(0, 5) (5,)

Also, calling any magic method on the broken PixelArray will cause it to segfault. This means that the issue isn't only in the indexing.

Furthermore, the make_surface method of the broken PixelArray will simply hang indefinitely. It also does not close with KeyboardInterrupt. I had to force quit the terminal...

[oddbookworm]

My most recent commit makes it impossible to create that pixelarray in the first place. I'll keep looking at how to solve the issue in a less strict way, but this should at least prevent any segfault conditions for now

[MyreMylar]

LGTM 👍

I think not being able to create an array of pixels for a surface with absolutely no pixels is a perfectly acceptable solution to this issue.

[ankith26]

thanks 👍