[SDL] Trouble (I think) with alpha channel using SDL_ttf

[David Bruce]

Hi,

I've taken over a project that has a function (see below) that is supposed to 
return a SDL_Surface* containing text with a black outline.  The surface 
surrounding the text is supposed to be transparent.  However, the entire 
SDL_Surface comes out transparent.  I have tested having the function return 
some of the intermediate surfaces, and everything other than the "tmp" 
surfaces immediately returned by TTF_RenderUTF8_Blended() comes out 
transparent. Do I need to do something with SDL_SetAlpha() on the "tmp" 
surfaces before I blit them to the "out" surface?



#if SDL_BYTEORDER == SDL_BIG_ENDIAN
#define rmask 0xff000000
#define gmask 0x00ff0000
#define bmask 0x0000ff00
#define amask 0x000000ff
#else
#define rmask 0x000000ff
#define gmask 0x0000ff00
#define bmask 0x00ff0000
#define amask 0xff000000
#endif


SDL_Surface* black_outline(unsigned char *t, TTF_Font *font, SDL_Color *c) {
	SDL_Surface *out, *tmp, *tmp2;
	SDL_Rect dstrect;

	tmp = font, t, black);

	tmp2 = SDL_CreateRGBSurface(SDL_SWSURFACE,
                                                     (tmp->w)+5,
                                                     (tmp->h)+5,
                                                      32, 
                                                      rmask, gmask,
                                                      bmask, amask);

	out = SDL_DisplayFormatAlpha(tmp2);
	SDL_FreeSurface(tmp2);

	dstrect.w = tmp->w;
	dstrect.h = tmp->h;

        for (dstrect.x = 1; dstrect.x < 4; dstrect.x++)
          for (dstrect.y = 1; dstrect.y < 4; dstrect.y++)
            SDL_BlitSurface( tmp, NULL, out, &dstrect );

        /* NOTE: if I return "out" at this point it is transparent */

	SDL_FreeSurface(tmp);

	/* --- Put the color version of the text on top! --- */
	tmp = TTF_RenderUTF8_Blended(font, t, *c);
	dstrect.x = dstrect.y = 2;
	SDL_BlitSurface(tmp, NULL, out, &dstrect);

	SDL_FreeSurface(tmp);

	/* --- Convert to the screen format for quicker blits --- */

	tmp = SDL_DisplayFormatAlpha(out);
	SDL_FreeSurface(out);

	return tmp;
}

Thanks for any help, and sorry if this is a naive/newbie question. 
-- 
David Bruce