[SDL] SDL_BlitSurface on MacOSX 10.3.9

[Michael Ryan Bannon]

What I'm doing for now is just making sure that the surfaces all have the 
same bits per pixel, so that solves my problem.

Thanks,

Ryan

"Michael Ryan Bannon" <mrbannon at swen.uwaterloo.ca> wrote in message 
news:e8tim0$jgd$1 at sea.gmane.org...
> So, is this a bug in SDL or am I doing something wrong?  Has anybody 
> tested the code?
>
> Thanks,
>
> Ryan
>
> "Michael Ryan Bannon" <mrbannon at swen.uwaterloo.ca> wrote in message 
> news:e8jdmu$8j8$1 at sea.gmane.org...
>> Hello,
>>
>> I finally found out what was causing the problem.  Now my question is the 
>> following: is it an SDL problem or a problem with my code?
>> First, here's a sample:
>>
>> #include <SDL/SDL.h>
>>
>> #include <SDL_image/SDL_image.h>
>>
>>
>>
>> int main(int argc, char*argv[])
>>
>> {
>>
>>     // Initialize SDL with the given driverName.  This driver is 
>> specified by setting the
>>
>>     // environment variable, "SDL_VIDEODRIVER" to driverName.
>>
>>    SDL_Init(SDL_INIT_VIDEO);
>>
>>     SDL_putenv("SDL_VIDEODRIVER=Quartz");
>>
>>
>>
>>    // Create surfaces.
>>
>>    SDL_Surface* pSurfaceOne = IMG_Load("/1.jpg");
>>
>>     SDL_Surface *pSurfaceTwo = IMG_Load("/2.jpg");
>>
>>
>>
>>    // Convert surfaces.
>>
>>    SDL_Surface* pConversionSurface = SDL_CreateRGBSurface(SDL_SWSURFACE, 
>> 1, 1, 32, 0xff000000, 0x00ff0000, 0x0000ff00, 0x000000ff);
>>
>>    SDL_Surface* pSurfaceOneConverted = SDL_ConvertSurface(pSurfaceOne, 
>> pConversionSurface->format, SDL_SWSURFACE);
>>
>>    SDL_Surface* pSurfaceTwoConverted = SDL_ConvertSurface(pSurfaceTwo, 
>> pConversionSurface->format, SDL_SWSURFACE);
>>
>>
>>
>>    // Create window and display surface.
>>
>>     SDL_Surface* pDisplaySurface = SDL_SetVideoMode(800, 600, 32, 
>> SDL_SWSURFACE);
>>
>>
>>
>>    // Display
>>
>>    int alpha = 0;
>>
>>    while(true)
>>
>>    {
>>
>>        // Set alpha.
>>
>>        alpha += 10;
>>
>>        if(alpha > 255)
>>
>>        {
>>
>>            alpha = 0;
>>
>>            SDL_Surface* temp = pSurfaceOneConverted;
>>
>>            pSurfaceOneConverted = pSurfaceTwoConverted;
>>
>>            pSurfaceTwoConverted = temp;
>>
>>        }
>>
>>
>>
>>        // Apply to surfaces and blit.
>>
>>        pSurfaceOneConverted->format->Amask = 0;
>>
>>        pSurfaceTwoConverted->format->Amask = 0;
>>
>>        SDL_SetAlpha(pSurfaceTwoConverted, SDL_SRCALPHA, 255 - alpha);
>>
>>        SDL_BlitSurface(pSurfaceTwoConverted, NULL, pDisplaySurface, 
>> NULL);
>>
>>        SDL_SetAlpha(pSurfaceOneConverted, SDL_SRCALPHA, alpha);
>>
>>        SDL_BlitSurface(pSurfaceOneConverted, NULL, pDisplaySurface, 
>> NULL);
>>
>>
>>
>>        // Update the surface.
>>
>>        SDL_Flip(pDisplaySurface);
>>
>>    }
>>
>>    return 0;
>>
>> }
>>
>>
>> So, to restate the issue...I'm running this code on two different 
>> machines. The first is a Mac OS 10.4.6 2GHz Intel Duo running XCode 2.3. 
>> I'm using SDL 1.2.11 UB.
>> The second machine is a Mac OS 10.3.9 PowerPC...no XCode (I was doing a 
>> remote debug).
>>
>> The above sample (with the SDLMain stuff used, of course) would run as 
>> expected on the 10.4.6 machine.  That is, one background would fade out 
>> while the other faded in.  When they had finished their fades, they would 
>> fade backwards...and so on.  This sample did NOT run as expected on the 
>> 10.3.9 machine.  There seems to be an extra rendering every time an alpha 
>> value (not 0 or 255) is present and this extra rendering is put about 5 
>> pixels to the right and on top of the proper rendering.
>>
>> The cause of this is the surface conversion.  If you get rid of the 
>> conversion code, it will run as expected on both machines.  Should this 
>> code always work as expected, regardless of machine?  I would assume not, 
>> but I don't understand the surface conversion that well.
>>
>> I'm more than happy to provide any other information.  And any help is 
>> greatly appreciated.
>>
>> Thanks,
>>
>> Ryan
>>
>> ps - I just put 1.jpg and 2.jpg in the root for convenience.  They're 
>> 800x600 jpegs...that's all.
>>
>> "Torsten Giebl" <wizard at syntheticsw.com> wrote in message 
>> news:3617.141.99.122.11.1151530170.squirrel at mail.syntheticsw.com...
>>> Hello !
>>>
>>>
>>>> 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.
>>>
>>> Please put together a minimal example that
>>> shows the problem.
>>>
>>>
>>> CU