TRANSPARENCE DIRECTDRAW (SIMULÉE)

// La fonction principale
void MakeTransparent(LPDIRECTDRAWSURFACE4 surf, DWORD colKey)
{
  DDSURFACEDESC2 ddsd;
  HRESULT ret;
  DWORD *primary_buffer;
  LONG lpitch;

  // Accès direct aux pixels

  STRUCT_INIT(ddsd);
  ddsd.dwFlags = DDSD_CAPS | DDSD_WIDTH | DDSD_HEIGHT;
  ret = surf->GetSurfaceDesc(&ddsd);
  if( ret == DDERR_INVALIDOBJECT || 
      ret == DDERR_INVALIDPARAMS )
    return;
  if( surf->Lock(NULL, &ddsd, 
                 DDLOCK_SURFACEMEMORYPTR | 
                 DDLOCK_WAIT, NULL) != DD_OK )
    return;
  primary_buffer = (DWORD*)ddsd.lpSurface;
  lpitch = ddsd.lPitch >> 2;

  // Boucle sur la surface et c'est tout !

  for(DWORD y=0; y<ddsd.dwHeight; y++)
  {
    for(DWORD x=0; x<ddsd.dwWidth; x++)
    {
      if( y % 2 == 0 )
      {
        if( x % 2 != 0 )
	  primary_buffer[(y * lpitch) + x] = colKey;
      }
      else
      {
        if( x % 2 == 0 )
	  primary_buffer[(y * lpitch) + x] = colKey;
      }
    }
  }

  surf->Unlock(NULL);
}