[pygame] Surfarray.array_alpha() bugfix, py2exe/py2app segfault

[Zack Schilling <zack.schilling@xxxxxxxxx>]

I'm not sure if my last message went though because I had not yet  
signed up for the mailing list before sending it, but I have an update  
on the issue. Sorry for the length, I'm just trying to be as helpful  
as possible to the pygame developers and not just slap a bandage on my  
problem.

In Pygame 1.8.1 and the latest 1.9.0 unstable, I've been having  
trouble using the surfarray module's pixels_alpha() and array_alpha()  
functions. I'm using 32bpp images with per-pixel alpha and I'm trying  
to work with the alpha data in numpy.

At first I couldn't get surfarray.array_alpha() to return a proper  
array (it returned all opaque values, surfarray.pixels_alpha() worked  
fine). Since pixels_alpha() worked fine, I figured I'd use it instead.  
That was fine, except it segfaulted when I tried to package up my  
script using py2exe or py2app. You can get a minimal testcase that  
shows everything I'm talking about here: http://dl-client.getdropbox.com/u/107712/alpha.zip

So I went to find out why array_alpha wasn't working properly. I  
investigated in the pygame source and found the culprit in "pygame/ 
_numpysurfarray.py"

The following code, intended to catch 8 bit images or images without  
alpha values, was erroneously catching my perpixel  images.

    if surface.get_bytesize () == 1 or not surface.get_alpha ():
        # 1 bpp surfaces and surfaces without alpha are always fully
        # opaque.

The fix is simple, make sure that the image is less than 32bpp AND  
missing an alpha channel before giving up on it.

    if surface.get_bytesize () == 1 or (not surface.get_alpha () and  
surface.get_bytesize () < 4):
        # 1 bpp surfaces and surfaces without alpha are always fully
        # opaque.

A pygame developer should make and commit that change. Once I fixed  
that issue, everything worked as expected... as long as I ran the  
script from the command line. Now if I used either array_alpha() or  
pixels_alpha() in a py2exe/p2app program, I got a segmentation fault!  
( just like before the change with pixels_alpha() )

I tracked the segfault through the array_alpha function to the array2d  
function in "pygame/_numpysurfarray.py".

    # Taken from Alex Holkner's pygame-ctypes package. Thanks a lot.
    data = surface.get_buffer ().raw

From there, the line to run last before the segfault seems to  
reference the compiled C surface module. I looked into the module  
(surface.c) but I don't see anything obvious. I also checked the raw  
getter in _bufferproxy.c but I'm a bit over my head at this point. Why  
would the code run fine on the command line but segfault if bundled  
up? It's not an issue with Numpy because it works fine bundled into an  
exe or app. Pygame typically bundles well also.

I've tried all different configurations. Everything is up to date and  
working properly as far as I can tell. Python 2.5, Numpy 1.2.1. Both  
Windows XP and Mac OS X. Numpy works fine on its own in both scripts  
and exe/apps.

Again, here is a minimal test case that demonstrates all these issues:
http://dl-client.getdropbox.com/u/107712/alpha.zip

MAIN.PY:

#Import Modules
import os, pygame, numpy
from pygame.locals import *
from numpy import *

def main():
   pygame.init()
   screen = pygame.display.set_mode((500,500))
   image = pygame.image.load("alpha.png")
   image = image.convert_alpha()

   # Setup the pygame array system to use numpy
   pygame.surfarray.use_arraytype('numpy')

   # Copy the images' alpha values to numpy arrays
   a = pygame.surfarray.pixels_alpha(image)
   b = pygame.surfarray.array_alpha(image)
	
   print array2string(a)
   print array2string(b)
   return 0

#this calls the 'main' function when this script is executed
if __name__ == '__main__': main()