// borrowed from Wine

static DWORD get_font_data(FT_Face ft_face, DWORD tag, DWORD offset, LPVOID buf, DWORD cbData, INT ttc_item_offset)
{
    FT_ULong len;
    FT_Error err;

    if (!FT_IS_SFNT(ft_face))
        return GDI_ERROR;

    if (!buf)
        len = 0;
    else
        len = cbData;

    if (ttc_item_offset)
    {
        if (tag == TTAG_ttcf)
            tag = 0;
        else if (tag == 0)
            offset += ttc_item_offset;
    }

    if (buf && len)
    {
        FT_ULong needed = 0;
        err = FT_Load_Sfnt_Table(ft_face, tag, offset, NULL, &needed);
        if (!err && needed < len)
            len = needed;
    }
    err = FT_Load_Sfnt_Table(ft_face, tag, offset, buf, &len);
    if (err)
        return GDI_ERROR;
    return len;
}