[SDL] SDL_BlitSurface on MacOSX 10.3.9

[Michael Ryan Bannon]

Actually, that doesn't solve the problem.  The alpha blending really slows 
down if I do that.

"Michael Ryan Bannon" <mrbannon at swen.uwaterloo.ca> wrote in message 
news:e90h34$73u$1 at sea.gmane.org...
> What I'm doing for now is just making sure that the surfaces all have the 
> same bits per pixel, so that solves my problem.
>
> Thanks,
>
> Ryan
>
> "Michael Ryan Bannon" <mrbannon at swen.uwaterloo.ca> wrote in message 
> news:e8tim0$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