Re: [pygame] [BUG] SRCALPHA - unexpected behaviour.

[Lenard Lindstrom <len-l@xxxxxxxxx>]

René Dudfield wrote:
> Thanks Brian.
>
> I think there is one issue with raising an error though.  The flags
> are just 'hints' and not all installations support each flag.
>   

Pygame does the alpha to alpha software surface blits. From what I can 
tell SDL code takes care of other software blits. How SDL deals with 
blits to hardware I did not find out. So only alpha blits to hardware 
would be questionable.

> SRCALPHA is only supported on 32 bit surfaces (I think). 
I thought SRCALPHA was necessary to make surface alpha and colorkey to 
work. But while testing that assumption I found this:

>python
Python 2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32 bit 
(Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import pygame
>>> print pygame.__version__
1.8.0rc3
>>> s = pygame.Surface((100, 100), pygame.SRCALPHA, 24)
>>> s.fill((255, 0, 0))
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
pygame.error: display Surface quit
>>> s.get_bitsize()
Fatal Python error: (pygame parachute) Segmentation Fault

This application has requested the Runtime to terminate it in an unusual 
way.
Please contact the application's support team for more information.

C:\user\projects\Python25
>

This also happens after pygame.init() is called. Curiously, if I 
initialize pygame first and let the surface default to 24 bits, my 
display setting, pygame.SRCALPHA is ignored:

>>> import pygame
>>> pygame.init()
(6, 0)
>>> s = pygame.Surface((100, 100), pygame.SRCALPHA)
>>> s.get_flags()
0
>>> s.get_bitsize()
24
>>> s.fill((255, 0, 0))
<rect(0, 0, 100, 100)>
>>>

And I found that colorkey and surface alpha do work without SRCALPHA.

>  So if the
> underlying video subsystem decides that it should return 16 bit
> surfaces (for example), then the SRCALPHA flag should correctly have
> no effect.
>
>
> On 8/20/07, Brian Fisher <brian@xxxxxxxxxxxxxxxxxxx> wrote:
>   
> > Being able to have this succeed without error:
> >    surf = pygame.Surface((100, 100), pygame.SRCALPHA)
> > and get a surface that doesn't have SRCALPHA set seems like a clear
> > and obvious bug to me. I'd say the best fix would be to always use
> > SRCALPHA if requested, and raise an error if the request couldn't be
> > satisfied. attached is a patch to svn pyame that seems to do that (it
> > passes the test in svn for this, anyways)
> >
> > ------
> >
> > ... However I'm also seeing that this:
> >    surf = pygame.Surface((100, 100), flags=pygame.SRCALPHA, depth=32)
> > is returning a surface without alpha set. So it seems like the Surface
> > constructor doesn't support keyword arguments at all.
> >
> > I've tested python 2.3 on windows, pygame 1.7 and svn pygame. I've
> > also tried python 2.5 on macOSX, pygame 1.7
> >
> > I have no idea how to fix this, but I've attached a patch to the surface test
> >
> >
> >     


--
Lenard Lindstrom
<len-l@xxxxxxxxx>