Re: [pygame] Pygame alpha blits and self blitting

[René Dudfield <renesd@xxxxxxxxx>]

hi,

can we make it all SRCALPHA self blits done with pygame?  Because I
think the SDL colorkey blits should be lots faster.


cheers.




On Sun, Feb 15, 2009 at 4:04 AM, Lenard Lindstrom <len-l@xxxxxxxxx> wrote:
> Well, it turns out Pygame passes colorkey target surface blits to SDL. So it
> is SDL that is failing to handle self blits properly. However, I now have
> Pygame blits working correctly, and they can replace the faulty SDL blits as
> well. So as an interim solution, until SDL is fixed (*), all SRCALPHA
> destination surface blits will be handled by Pygame. Now to verify the
> Pygame blit code.
>
> Lenard
>
> (*) There is activity in the SDL SVN trunk so it may already be fixed.
>
>
> Lenard Lindstrom wrote:
>>
>> Hi Brian,
>>
>> Brian Fisher wrote:
>
> [snip]
>>
>>> My point is, the reason why I advocated raising an exception are gone
>>> (i.e. the windows crashing is fixed), so I personally think that should be
>>> off the table.
>>>
>> True enough. This is in the domain of Pygame, so we can actually do
>> something about it.
>>
>>> I'd say making the blit work as expected with a special case would be
>>> great.
>>
>> It will be more than just the colorkey blit that need special casing. I
>> recently added ten new blit loops to handle blend blits to 24 bit surfaces.
>> None of them are special cased. I am hoping the solution is as simple as
>> adjusting some pointers and stride values. Having a duplicate of every blit
>> routine in alphablit.c would be too cumbersome in my opinion.
>>
> [snip]
>>
>>> On Fri, Feb 13, 2009 at 1:14 PM, Lenard Lindstrom <len-l@xxxxxxxxx
>>> <mailto:len-l@xxxxxxxxx>> wrote:
>>>
>>>    Hi everyone,
>>>
>>>    While checking out Mozilla bug 19 (*) I found that blitting a
>>>    surface with colorkey to itself causes repetition of the source
>>>    image. I have attached an example. This is a known problem with
>>>    copy algorithms. SDL blits have special code to handle it.
>>>    Pygame's blits do not. The concerns over self blits were discussed
>>>    in the bug 19 related thread (**), but I could find no conclusion
>>>    as to whether to support it or raise an exception and provide
>>>    explicit scroll routines instead. Pygame has many special case
>>>    blit loops to be considered.
>>>
>>>    Lenard
>>>
>>>    (*) http://pygame.motherhamster.org/bugzilla/show_bug.cgi?id=19
>>>    (**)
>>>    http://thread.gmane.org/gmane.comp.python.pygame/15390/focus=15407
>>>
>>
>
>
> --
> Lenard Lindstrom
> <len-l@xxxxxxxxx>
>
>