Graphics::MNG version 0.04
==========================
NAME
Graphics::MNG - Perl extension for the MNG library from Gerard Juyn (gerard@libmng.com)
SYNOPSIS
# OO-interface
use Graphics::MNG;
my $it=['user data'];
my $obj = new Graphics::MNG ( ); # w/o user data
my $obj = new Graphics::MNG ( undef ); # w/o user data
my $obj = new Graphics::MNG ( $it ); # w/ user data
my $obj = Graphics::MNG::new( ); # w/o name w/o data
my $obj = Graphics::MNG::new('Graphics::MNG' ); # w/ name w/o data
my $obj = Graphics::MNG::new('Graphics::MNG',$it); # w/ name w/ data
$obj->set_userdata(['user data']);
my $data = $obj->get_userdata();
print @$data[0],"\n";
undef $obj;
# functional interface
use Graphics::MNG qw( :fns );
my $handle = initialize( ['more user data'] );
die "Can't get an MNG handle" if ( MNG_NULL == $handle );
my $rv = reset( $handle );
die "Can't reset the MNG handle" unless ( MNG_NOERROR == $rv );
my $data = get_userdata( $handle );
print @$data[0],"\n";
$rv = cleanup( $handle );
die "handle not NULL" unless ( MNG_NULL == $handle );
DESCRIPTION
This is alpha stage software. Use at your own risk.
Please visit http://www.libmng.com/ to learn all about the new
MNG format.
MNG (which stands for Multiple Network Graphics) is an extension
of the PNG format, which is already gaining popularity over the
GIF format. MNG adds the aspect of animation that PNG lacks.
The Gd module (by Lincoln Stein) supports PNG formats, but MNG is
more complicated. It would be cumbersome to add support to the Gd
interface for MNG.
Gerard Juyn as been kind enough to bring us a C-library that
supports MNG, so now I thought I'd do my part in bringing you a
Perl interface to that library.
The Graphics::MNG module is an attempt to provide an "accurate"
interface to the MNG graphics library. This means that the Perl
methods supported in this module should look very much like the
functions in the MNG library interface.
This module supports both a functional and an OO interface to the
MNG library.
EXPORT
Everthing under the :constants tag is exported by default.
Ideally, you'll use one of the incantations of new() to get
yourself an object reference, and you'll call methods on that.
EXPORTABLE CONSTANTS
:all -- everything
:callback_types -- enum list of callback types (MNG_TYPE_*)
:canvas -- constants for canvas ops (MNG_CANVAS_*)
:canvas_fns -- functions for canvas ops (MNG_CANVAS_*)
:chunk_fns -- functions for chunk ops (getchunk_*,putchunk_*)
:chunk_names -- constants for chunk ops (MNG_UINT_*)
:chunk_properties -- constants for chunk ops
:compile_options -- constants describing how this extension was built
:constants -- constants which are commonly used
(MNG_FALSE, MNG_TRUE,
MNG_NOERROR, MNG_NULL, MNG_INVALIDHANDLE)
:errors -- constants returned as error values
:fns -- functions for the MNG functional interface
:misc -- constants misc. (MNG_SUSPEND*)
:version -- functions to return various version numbers
(MNG,PNG,draft,etc.)
:IJG -- constants IJG parameters for compression
:ZLIB -- constants zlib compression params for deflateinit2
INTERFACE FUNCTIONS/METHODS
The OO-I/F is the same as the functional interface, except that you
new() your handle into existence, and you undef() it out. Also,
you don't pass it as the first parameter to any of the methods --
that's done for you when you use the -> calling syntax to call a
method.
There are a *lot* of interface functions in the MNG library. I'd
love to list them all here, but you're really better off opening up
the libmng.h file, related documentation, or the Graphics/MNG.pm file
and looking at the list of exported methods. I'll try to make a
list here of the methods that deviate in interface characteristics
from those found in the MNG library itself.
I doubt that I've implemented the Perl interface correctly for all
of them. You will find bugs. Sorry about that.
In some cases it is convenient to change the Perl interface to make
it more convenient to use from within Perl. A good example of this
is any mng_get*() methods that returned values via pointers in the
parameter list. Most or all of these will return a list of values
(with the status as the first element), and will only accept the
input parameters. On error, only the status code is returned.
The method getlasterror() behaves in a similiar manner, except that
it will return the list of parameters only when there is an error.
Otherwise, it just returns the status (in this case MNG_NOERROR).
The method initialize() currently takes only one argument -- a
scalar (typically a reference) to user data. If the MNG library is
not compiled with MNG_INTERNAL_MEMMNGMT, then this Perl interface
will provide default memory allocation support. You can use other
interface methods to enable/disable trace support.
I've also added some new methods to the interface:
my ($name, $type) = getchunk_name([$hHandle,] $iChunktype);
my ($rv, $href) = getchunk_info($hHandle, $hChunk, $iChunktype)
my ($rv) = putchunk_info($hHandle, [$iChunktype,] \%chunkHash)
-getchunk_name():
This method takes the chunktype and returns the ASCII name of the
chunk, and also a string containing the hexadecimal representation of
the chunktype. The $hHandle arg is optional (to support the OO-I/F),
and is not used. Consider this to be a class method.
-getchunk_info():
This method uses the $iChunktype parameter to look up the correct
getchunk_*() method to call on the $hHandle object to get the chunk
information related to $hChunk. It returns a list of status and a
hash reference containing all of the chunk information. If called in
a scalar context, an array reference containing this list is returned.
The key names of the hash correspond to the libmng parameter names for
the appropriate mng_getchunk_*() function.
There are two additional fields added to the returned hash:
'iChunktype' : the type as passed in by $iChunktype
'pChunkname' : the chunk name (from getchunk_name($iChunktype))
This hash reference can be passed directly to putchunk_info().
-putchunk_info():
This method uses the $iChunktype parameter to look up the correct
putchunk_*() method to call on the $hHandle object. The key names
of the hash must correspond to the libmng parameter names for the
mng_putchunk_*() function that will be called.
If the $iChunktype parameter is excluded, then the hash is examined
for a field named 'iChunktype'.
If any fields are excluded, they default to '0', which (before
presentation to the libmng interface) will translate to a string for
array and pointer types, and will translate to zero for integer types.
This seems safe because most arrays and pointer types are accompanied
by a length field, which will also default to zero if it is excluded.
This method is mostly useful for directly copying chunks from one file
to another in conjunction with the getchunk_info() method.
LIMITATIONS
The MNG library is designed around the concept of callbacks. I've
tried to make the Perl interface closely model the library interface.
That means that you'll be working with callback functions. Depending
on your point of view, that's a limitation.
If you want to write a file with the MNG library, you'll have to
call create() before writing chunks. That's just how libmng works.
If you forget, you'll be disappointed with the results.
This Perl module is in the alpha stage of development. That means
that you'll be lucky to compile it, let alone use it effectively
without tripping over bugs.
The MNG library may have limitations of its own, please visit the MNG
homepage to learn about them.
PREREQUISITES/DEPENDENCIES
You'll need a compiled MNG library, complete with header files, in
order to build this Perl module.
MNG requires some or all of the following support libraries:
- lcms (little CMS)
- libjpeg
- libz
Specifically, I compile the MNG library (static library, NOT a DLL)
using MSVC++ with the following compilation flags:
MNG_FULL_CMS, MNG_INTERNAL_MEMMNGMT, NON_WINDOWS,
MNG_BUILD_SO, MNG_SUPPORT_TRACE
INSTALLATION
Since this is alpha software...
- compile the MNG as a static library (Win32) or as a shared library
- edit Makefile.PL as appropriate for your header file and lib paths
Then you can install this module by typing the following:
perl Makefile.PL
make
make test
make install
TESTING
There is a suite of tests packaged with this module. Test #0 is
really just a setup script that has been pieced together from other
sources. It uses pure PERL to generate a test case MNG file for
later tests. If you have GD, it will also generate the necessary
PNG images.
Since all of the output of this script is already packaged in the
distribution, you probably won't need to run it. It's just there
for your reference and my convenience.
The last couple of tests actually read and write MNG files. There
are some good examples in there, it's worth checking out.
If you're on cygwin, 'make test' may not work correctly. If it
complains about not being able to open up t/*.t, just type this
at the command prompt in the Graphics/MNG directory:
perl -Mblib test.pl
KNOWN BUGS
I have successfully read and written MNG files with this interface.
If you can't write (simple) MNG files, you may be doing something
wrong. See the section LIMITATIONS for related topics.
You may have noticed that the "mng_" prefix has been removed from
all of the functions. This was done to make the OO-I/F look
prettier. However, if you import the functional interface, you'll
get read() and write() in your namespace, thus clashing with Perl's
built-in functions. I may change the name for these in the future
(i.e. an interface deviation). In the meantime, I suggest that you
use sysread() and syswrite() in your callbacks. Even better, use
the OO-I/F and don't import qw(:fns).
I'm developing exclusively on Win32 for now, although everything
*should* work well for any other platform that the MNG library
supports.
I'm pretty sure that I have *not* gotten all of the appropriate
#ifdef protection around parts of the XS code that may be affected
by MNG compilation flags.
CHANGES AND FUTURE DEVELOPMENT
This is alpha software. Expect the worst. Hope for the best.
For any functions that return or accept an array of integers or
structs, I plan (eventually) to provide a Perl interface that accepts
an array of integers or structs (the structs themselves probably being
represented as arrays or hashes). Right now, you'll need to pack()
and unpack() the string.
I may add a convenience method to insert PNG or JNG files into the
MNG stream. This would make use of getchunk_*() and putchunk_*()
methods.
AUTHOR
David P. Mott (dpmott@sep.com)
SUPPORT
I'd love to support this interface full time, but my work schedule
won't allow that. If you see a problem, try to fix it. If you can
fix it, write a test case for it. If you get all of that done, send
me the fix and the test case, and I'll include it in the next release.
If you can't fix it, or don't know how to test it, go ahead and send
me some email. I'll see what I can do.
If you want to maintain this module, by all means mail me and I'll
get you set up.
Releases will happen approximately whenever I feel like I have
something worthwhile to release, or whenever I get a whole bunch of
email from people like you demanding a release.
COPYRIGHT AND LICENCE
The Graphics::MNG module is Copyright (c) 2001 David P. Mott, USA
(dpmott@sep.com)
All rights reserved.
This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself (i.e. GPL or Artistic).
See the the Perl README file for more details.
(maybe here: http://www.perldoc.com/perl5.6.1/README.html)
For more info on GNU software and the GPL see http://www.gnu.org/
For more info on the Artistic license see
http://www.perl.com/perl/misc/Artistic.html
THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
L<perl>.
The PNG homepage: http://www.libpng.org/pub/png/
The MNG homepage: http://www.libmng.com/
The PNG specification: http://www.libpng.org/pub/png/spec/
The MNG specification: http://www.libpng.org/pub/mng/spec/
The JPEG homepage: http://www.ijg.org/
The Lcms homepage: http://www.littlecms.com/
The Zlib homepage: http://www.gzip.org/zlib/
The GD module: [download it from your favorite CPAN server]
The GD homepage: http://www.boutell.com/gd/
The Freetype homepage: http://www.freetype.org/