README

[NOTE:  this is still beta version 0.97c; the text below has already
 been updated in anticipation of the imminent 1.0 release.]


README for libpng 1.0

This is the first official release of libpng.  Don't let the fact that
it's the first release fool you.  The libpng library has been in
extensive use and testing for about two years.  However, it's
finally gotten to the stage where there haven't been significant
changes to the API in some time, and people have a bad feeling about
libraries with versions < 1.0.

****
Note that some of the changes to the png_info structure render this
version of the library binary incompatible with libpng-0.89 or
earlier versions if you are using a shared library.  The type of the
"filler" parameter for png_set_filler() has changed from png_byte to
png_uint_32, which will affect shared-library applications that use
this function.

To avoid problems with changes to the internals of png_info_struct,
new APIs have been made available in 0.95 to avoid direct application
access to info_ptr.  These functions are the png_set_<chunk> and
png_get_<chunk> functions.  These functions should be used when
accessing/storing the info_struct data, rather than manipulating it
directly, to avoid such problems in the future.

It is important to note that the APIs do not make current programs
that access the info struct directly incompatible with the new
library.  However, it is strongly suggested that new programs use
the new APIs (as shown in example.c), and older programs be converted
to the new format, to facilitate upgrades in the future.
****

Additions since 0.90 include the ability to compile libpng as a
Windows DLL, and new APIs for accessing data in the info struct.
Experimental functions include the ability to set weighting and cost
factors for row filter selection, direct reads of integers from buffers
on big-endian processors that support misaligned data access, faster
methods of doing alpha composition, and more accurate 16->8 bit color
conversion.

The additions since 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 CRC error occurred in a
critical or an ancillary chunk.

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
examples of libpng in a program, see example.c and pngtest.c.  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       =>  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      =>  Default Unixish 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
      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
      pngset.c      =>  Functions for storing data into the info_struct
      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
 Internet: adilger@enel.ucalgary.ca
 Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/

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