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

["Brian Fisher" <brian@xxxxxxxxxxxxxxxxxxx>]

I disagree that an error is bad in that case.

It's exactly because the video subsystem may make choices for you that
I think raising an error is the right thing to do. Raising an error
will make it so that when your art doesn't draw right, the program
will know. Also, raising an error doesn't prevent you from handling
that case as a programmer either - you can always catch the exception
and try again with no alpha.
Raising an error is the pythonic thing to do - it exposes problems
instead of hiding them. Finding hidden problems is slow and not fun.

Moreover, with respect to the "flags are just hints" point, as a user
of pygame, I can confidently say that when I say I want alpha
blending, it is much more than a "hint", I am demanding alpha
blending. All the rest of the flags though, are still like "hints",
and the patch doesn't change that (it doesn't confirm HWSURFACE, for
instance)

Finally, 16-bit surfaces support alpha, no problem. Running the
attached script to see for yourself.


On 8/19/07, René Dudfield <renesd@xxxxxxxxx> 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.
> SRCALPHA is only supported on 32 bit surfaces (I think).  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
> >
> >
>

import pygame
pygame.display.init()
screen = pygame.display.set_mode((320,256),0, 16)

alpha_surface = pygame.Surface((100,100), pygame.SRCALPHA, 16)
alpha_surface.fill((255,255,0,128))

no_alpha_surface = pygame.Surface((100,100), 0, 16)
no_alpha_surface.fill((255,255,0,128))

screen.fill((0,0,0))
screen.blit(alpha_surface,(0,0))
screen.blit(no_alpha_surface,(200,0))
pygame.display.update()

while 1:
    for event in pygame.event.get():
            if event.type == pygame.KEYDOWN:
                if event.key == 27:
                    raise SystemExit
    pygame.display.update()