[SDL] SDL_BlitSurface on MacOSX 10.3.9

[Michael Ryan Bannon]

Some further information (I'm really hoping somebody might be able to help 
me with this...)
The problem, I believe, has something to do with the alpha blending.  Each 
surface has the following done before the blit:

surface->format->Amask = 0; // turns off per-pixel alpha; note that surface 
is an SDL_Surface
SDL_SetAlpha(surface, SDL_SRCALPHA, constantAlpha);

"cosntantAlpha" is a number between 0 and 255.  Now, if I set the Amask 
parameter to 1, the SDL_SetAlpha call is ignored (I assume) because SDL 
thinks that each pixel now has an individual alpha.  When I do this, there's 
no more 2nd background, which is what I want, but at the same time there's 
obviously no alpha blending.

So, I've determined that per-surface alpha blending has something to do with 
it (along with Mac OS 10.3.9).  Aside from that I'm stumped.

Thanks,

ryan


"Michael Ryan Bannon" <ryan.bannon at humagade.com> wrote in message 
news:e7pgkp$o7a$1 at sea.gmane.org...
> Hello,
>
> I'm using SDL_BlitSurface to blend two 800x600 backgrounds.  One 
> background stays at an alpha at 255 and goes to 0 while the other one, on 
> top of it, goes from 0 to 255 at the same rate.  Everything works fine 
> except for one odd anomoly: my code works fine on MacOSX 10.4.6 version 
> but not on my 10.3.9.  On the 10.3.9 machine, the back image (the one 
> starting at 255) is shifted to the right about 5 pixels.  I even tried to 
> simplfy it by doing the following:
>
> SDL_BlitSurface(srcSurface, NULL, targetSurface, NULL);
>
> I can remedy the problem by setting the position of the backgrounds to the 
> right one pixel.
>
> SDL_Rect rect;
> rect.x = 1;
> rect.y = 0;
> ...
> SDL_BlitSurface(srcSurface, NULL, m_targetSurface, rect);
>
> This works on both OSs, however I would then have a small black line on 
> the left side of my window.
> Has anybody seen this problem before or have any idea what might be 
> causing it?  I can provide more info if needed.
>
> Thanks,
>
> Ryan