[SDL] Checking pixel color w/ transparent color

[Ricardo Amores Hernández]

Damiano escribió:

I think you must lock the surface in order to use getPixel()

Hum, i´ve just read the docs and yes, you MUST lock the surface. Taken 
from the docs:

> Hello,
> 
> I'd like to know how I could check if a pixel at a specifed (x, y) position
> in an SDL_Surface is transparent. The SDL_Surface comes from a
> TTF_RenderText function call by the way.
> 
> I've tried this but it doesn't seem to work :
> 
> SDL_Surface *img = TTF_RenderText...(...);

    if ( SDL_MUSTLOCK(screen) )
         if ( SDL_LockSurface(screen) < 0 ) {
             fprintf(stderr, "Can't lock screen: %s\n", SDL_GetError());
             return;
         }


> // getpixel() taken from the doc
> // at 'Chapter 2'

> Uint32 pixel = getpixel(img, x, y);


if ( SDL_MUSTLOCK(screen) )
         SDL_UnlockSurface(screen);

> if ( pixel == img->format->colorkey )
>     printf("Pixel @ (%d, %d) is transparent\n", x, y);
> }
> Can you help me ?
> 
> Thanks,
> 

Hope it works now.
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      Ricardo Amores Hernández
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	MSN: zheo_ (at) hotmail (dot) es
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