2009.04.07 13:44 "Re: [Tiff] Writing tiff to in-memory buffer", by Christian Henning

Ok, my read function was wrong. Since I only want to write into the buffer the read procedure should return 0 and not the size read. Fixing that gives me a valid TIFF*. I also need to setup my seek_proc to prohibit it from seeking on an empty ostream. Doing though would raise the failbit. I don't understand why TIFFClientOpen is calling seek_proc( 0,0). It seems redundant to me.

This code is working:
static tsize_t read_proc( thandle_t fd
                        , tdata_t buf
                        , tsize_t size
                        )
{
    return 0;
}

static tsize_t write_proc( thandle_t handle
                         , tdata_t   buf
                         , tsize_t   size

                         )
{
    std::ostream* os = reinterpret_cast< std::ostream* >( handle );

    os->write( reinterpret_cast< char const*>( buf )
             , static_cast<std::streamsize>( size )
             );

    return size;
}

static toff_t seek_proc( thandle_t handle
                       , toff_t off
                       , int i
                       )
{
    std::ostream* os = reinterpret_cast< std::ostream* >( handle );

    std::ostream::streamoff size = os->tellp();
    if( size == -1 ) return 0;

    os->seekp( off
             , i == SEEK_SET
             ? std::ios::beg
             : ( i == SEEK_CUR
                 ? std::ios::cur
                 : std::ios::end )
              );

    return off;
}

static int close_proc( thandle_t handle )
{
    std::ostream* os = reinterpret_cast< std::ostream* >( handle );
    os->operator<< ( std::flush );

    return 0;
}

static toff_t size_proc( thandle_t handle )
{
    return 0;
}

void error_handler( const char* module, const char* fmt, va_list ap )
{
}

int main()
{

    TIFFSetErrorHandler(error_handler);

    stringstream ss( ios_base::in | ios_base::out | ios_base::binary );

    TIFF* t = TIFFClientOpen( "dummy"
                            , "w"
                            , ss
                            , read_proc
                            , write_proc
                            , seek_proc
                            , close_proc
                            , size_proc
                            , NULL
                            , NULL
                            );
}

On Mon, Apr 6, 2009 at 2:45 PM, Bob Friesenhahn <bfriesen@simple.dallas.tx.us> wrote:

> On Mon, 6 Apr 2009, Christian Henning wrote:
>>>

>>> It should be useful to use contrib/stream/tiffstream.cpp from the libtiff >>> source distribution as a reference.  The version which will be included

>>> in
>>> libtiff4 is updated to standard C++.
>>
>> Seems I need to recompile libtiff and start debugging. Does the code
>> work on your machine?
>

> I don't know if your code would work on my machine and I have also never > actually tested contrib/stream/tiffstream.cpp.

>
> I am now also reminded that there is a libtiff/tif_stream.cxx which is

> included in libtiff's C++ library.  I have spent some time updating this > source file for libtiff4 (but without actually testing it).

>

> As far as the viability of TIFFClientOpen() goes, GraphicsMagick has been > using it for many years without any problems.

>

> The error message you are seeing suggests that libtiff requests to read back > from the file it is writing and perhaps your wrapper functions do not

> adequately support this.

Bob
--
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/