Re: [pygame] Another blitting surface to itself crash

[Lenard Lindstrom <len-l@xxxxxxxxx>]

I believe I found the bug. And it was already fixed for SDL 1.3 (I 
cannot confirm it is also fixed for 1.2.13 in SVN since the site is 
down.) There should be a licensing requirement to do assembly level 
programming :-). The optimized reverse blit uses an i386 string move 
instruction. The direction of the copy is controlled by a register flag. 
A cleared flag causes a forward copy, the data pointers are incremented. 
A set flag causes a reverse copy, decrementing data pointers. The flag 
was set by the SDL copy code, but not cleared afterwards. And the flag 
doesn't reset itself apparently. So the set flag sat there like an armed 
bomb until the next string copy instruction was executed.

Lenard


Lenard Lindstrom wrote:
> That seems to be it. Try out the modified SDL.dll for Pythons 2.4. and 
> 2.5:
>
> http://www3.telus.net/len_l/pygame/SDL-self-blit.zip
>
> md5sum:
> 59a283f9383d6b5512c236d98e39c97b *SDL-self-blit.zip
>
> Lenard
>
>
> Lenard Lindstrom wrote:
> > I will. But it will be hand-customized.
> >
> > Lenard
> >
> >
> > Brian Fisher wrote:
> > > Hey Lenard,
> > > Can you build SDL with mingw in a way that the inlined assembly 
> > > won't be used? (i.e. so that it uses the same source that VisualC 
> > > does to build)


--
Lenard Lindstrom
<len-l@xxxxxxxxx>