[SDL] SDL_BlitSurface creates "holes" instead of alpha blending

[Johannes Bauer]

Johannes Bauer schrieb:

> What am I doing wrong?

Some code to demonstrate the problem - I still don't see any solution.
This is weird.

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

#include "SDL.h"

SDL_Surface *init(int Width, int Height) {
   Uint32 RMask, GMask, BMask, AMask;
#if SDL_BYTEORDER == SDL_BIG_ENDIAN
   RMask = 0xff000000;
   GMask = 0x00ff0000;
   BMask = 0x0000ff00;
   AMask = 0x000000ff;
#else
   RMask = 0x000000ff;
   GMask = 0x0000ff00;
   BMask = 0x00ff0000;
   AMask = 0xff000000;
#endif

   SDL_Surface *SubSurface = SDL_CreateRGBSurface(SDL_SWSURFACE |
SDL_SRCALPHA, Width, Height, 32, RMask, GMask, BMask, AMask);
//   SDL_SetAlpha(SubSurface, SDL_SRCALPHA, SDL_ALPHA_OPAQUE);
   return SubSurface;
}

void dump(SDL_Surface *x) {
   Uint8 r, g, b, a;
   SDL_GetRGBA(((Uint32*)x->pixels)[0], x->format, &r, &g, &b, &a);
   printf("RGBA %2x %2x %2x %2x\n", r, g, b, a);
}

int main(int argc, char **argv) {

   SDL_Init(SDL_INIT_VIDEO);

   {
      SDL_Surface *src, *dst;
      src = init(1, 1);
      dst = init(1, 1);

      ((Uint32*)(src->pixels))[0] = 0x11223344;
      ((Uint32*)(dst->pixels))[0] = 0x0;
      SDL_BlitSurface(src, NULL, dst, NULL);

      dump(src);
      dump(dst);

      SDL_FreeSurface(src);
      SDL_FreeSurface(dst);
   }

   SDL_Quit();
   return 0;
}

So it should blit "src" on "dst". What it outputs is:

RGBA 44 33 22 11
RGBA  0  0  0  0

This is *way* weird. Shouldn't it output something like
RGBA  3  2  1  0

I'm pretty desperate right now. This is like the *most* basic primitive
SDL offers and I get it to work most of the time (my game works,
actually) - but currently I'm incredibly stuck. Did it all just work by
accident so far?

Greetings,
Johannes