大神帮帮忙~~~SDL SDL_ConvertSurface 转换失败

bmp 位图转换想转成ARGB1555 ,用 SDL_ConvertSurface 这个函数一直转换的位深是24~而ARGB的位深对应的是16位~
代码如下

SDL_PixelFormat *fmt; //pixel format information strcut
    fmt = (SDL_PixelFormat*)malloc(sizeof(SDL_PixelFormat));
    memset(fmt,0,sizeof(SDL_PixelFormat));
    fmt.BitsPerPixel = 16;
    fmt.BytesPerPixel = 2;
   
    fmt->Amask = 0x8000;
    fmt->Rmask = 0x7E00;          //ARGB1555
    fmt->Gmask = 0x03E0;
    fmt->Bmask = 0x001f;
   
    fmt->Ashift = 15;
    fmt->Rshift = 10;
    fmt->Gshift = 4;
    fmt->Bshift = 0;
    fmt->colorkey = 0xffffffff;
    fmt->alpha = 0xff;
    SDL_Surface *temp = SDL_ConvertSurface(text,fmt,SDL_SWSURFACE);

用的SDL库是老库1.2的库