readme.txt - for libpng 0.90

This is the fourth beta version of libpng 1.0.  The changes from
libpng-0.89 include bug fixes, a C++ wrapper for png.h, some
additions to the API, as well as internal changes to the library.

**
Note that some of the changes to the png_info structure render
this version of the library binary incompatible with libpng-0.89
if you are using a shared library.  Re-compiling the application
should be enough to remove this problem.
**

The additions to 0.89 include the ability to read from a PNG stream
which has had some (or all) of the signature bytes read by the
calling application.  This also allows the reading of embedded PNG
streams that do not have the PNG file signature.  As well, it is
now possible to set the library action on the detection of chunk
CRC errors.  It is possible to set different actions based on
whether the error occurred in a critical or an ancillary chunk.

The callback functions for the error/warning messages have changed
since the 0.88 release because their implementation was broken,
and it was thought best to change the API itself (which was only
introduced in libpng-0.88 itself) to alert the user to the change,
rather than mislead the user into thinking their application was
OK after re-compiling.  This means that calls to png_set_message_fn()
no longer exist, because the previously suggested method of calling
them before png_read_init() or png_write_init() is now ineffective.

The preferred method of setting the error and warning callbacks
has been incorporated into the allocation of the png_struct and
info_struct itself, which allow them to be safely used during the
initialization of the structure, as well as to keep the size of
the png_struct internal to the library, rather than at compile time
of the application.  This will hopefully remove any problems with
dynamically linked libraries, and should be considered the preferred
method of creating these structures, although the previous
initialization API is still available for compatibility.  See libpng.txt
for more information on the new API.

The changes made to the library, and bugs fixed are based on discussions
on the PNG implementation mailing list <png-implement@dworking.wustl.edu>
and not on material submitted to Guy.

For a detailed description on using libpng, read libpng.txt.  For
usage information and restrictions (what little they are) on libpng,
see png.h.  For a description on using zlib (the compression library
used by libpng) and zlib's restrictions, see zlib.h

I have included a general makefile, as well as several machine and compiler
specific ones, but you may have to modify one for your own needs.

You should use zlib 1.0.4 or later to run this, but it MAY work with
versions as old as zlib 0.95.  Even so, there are bugs in older zlib
versions which can cause the output of invalid compression streams for
some images.  You will definitely need zlib 1.0.4 or later if you are
taking advantage of the MS-DOS "far" structure allocation for the small
and medium memory models.  You should also note that zlib is a
compression library that is useful for more things than just PNG files.
You can use zlib as a drop-in replacement for fread() and fwrite() if
you are so inclined.

zlib should be available at the same place that libpng is.
If not, it should be at ftp.uu.net in /graphics/png
Eventually, it will be at ftp.uu.net in /pub/archiving/zip/zlib

You may also want a copy of the PNG specification.  It is available
as an Internet Draft, and RFC, and a W3C Recommendation.  Failing
these resources you can try ftp.uu.net in the /graphics/png directory.

This code is currently being archived at ftp.uu.net in the
/graphics/png directory, and on CompuServe, Lib 20 (PNG SUPPORT)
at GO GRAPHSUP.  If you can't find it in any of those places,
e-mail me, and I'll help you find it.

If you have any code changes, requests, problems, etc., please e-mail
them to me.  Also, I'd appreciate any make files or project files,
and any modifications you needed to make to get libpng to compile,
along with a #define variable to tell what compiler/system you are on.
If you needed to add transformations to libpng, or wish libpng would
provide the image in a different way, drop me a note (and code, if
possible), so I can consider supporting the transformation.
Finally, if you get any warning messages when compiling libpng
(note: not zlib), and they are easy to fix, I'd appreciate the
fix.  Please mention "libpng" somewhere in the subject line.  Thanks.

This release was created and will be supported by myself (of course
based in a large way on Guy's earlier work), and the PNG group.

adilger@enel.ucalgary.ca
png-implement@dworkin.wustl.edu

You can reach Guy, the original libpng author, at (internet preferred):

internet: schalnat@group42.com
CompuServe: 75501,1625

Please do not send general questions about PNG.  Send them to
the address in the specification.  At the same time, please do
not send libpng questions to that address, send them to me.  I'll
get them in the end anyway.  If you have a question about something
in the PNG specification that is related to using libpng, send it
to me.  Send me any questions that start with "I was using libpng,
and ...".  If in doubt, send questions to me.  I'll bounce them
to others, if necessary.

Please do not send suggestions on how to change PNG.  We have
been discussing PNG for a couple years now, and it is official and
finished.  If you have suggestions for libpng, however, I'll
gladly listen.  Even if your suggestion is not used for version
1.0, it may be used later.

Files in this distribution:

      CHANGES.txt   =>  Description of changes between libpng versions
      README        =>  This file
      TODO          =>  Things not implemented in the current library
      ansi2knr.c    =>  Converts files to K&R style function declarations
      build.bat     =>  MS-DOS batch file for Borland compiler
      descrip.mms   =>  VMS project file
      example.c     =>  Example code for using libpng functions
      libpng.txt    =>  Description of libpng and its functions
      makefile      =>  Defualt makefile
      makefile.aco  =>  ACORN makefile
      makefile.ama  =>  Amiga makefile
      makefile.atr  =>  Atari makefile
      makefile.bor  =>  Borland makefile
      makefile.dj2  =>  DJGPP 2 makefile
      makefile.elf  =>  Unix ELF makefile
      makefile.knr  =>  Makefile which calls ansi2knr to convert files
      makefile.mip  =>  MIPS makefile
      makefile.msc  =>  Microsoft C makefile
      makefile.std  =>  Standard Unix makefile
      makefile.tc   =>  Turbo C makefile
      makevms.com   =>  VMS make program
      png.c         =>  Basic interface functions common to library
      png.h         =>  Library function and interface declarations
      pngconf.h     =>  System specific library configuration
      pngerror.c    =>  Error/warning message I/O functions
      pngmem.c      =>  Memory handling functions
      pngpread.c    =>  Progressive reading functions
      pngrcb.c      =>  Read callback (data handling) low-level functions
      pngread.c     =>  Read data/helper high-level functions
      pngrio.c      =>  Lowest-level data read I/O functions
      pngrtran.c    =>  Read data transformation functions
      pngrutil.c    =>  Read data utility functions
      pngtest.c     =>  Library test program
      pngtest.png   =>  Library test sample image
      pngtrans.c    =>  Common data transformation functions
      pngwio.c      =>  Lowest-level write I/O functions
      pngwrite.c    =>  High-level write functions
      pngwtran.c    =>  Write data transformations
      pngwutil.c    =>  Write utility functions

Good luck, and happy coding.

-Andreas Eric Dilger
 University of Calgary
 Internet: adilger@enel.ucalgary.ca
 Web: www-mddsp.enel.ucalgary.ca/People/adilger/

-Guy Eric Schalnat
 Group 42, Inc.
 Internet: schalnat@group42.com
 CompuServe: 75501,1625
 Web: www.group42.com

