107 lines
4.9 KiB
Plaintext
107 lines
4.9 KiB
Plaintext
readme.txt - for libpng 0.89
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This is a bug fix for the third beta version of libpng 1.0. The
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changes from libpng-0.88 are bug fixes and some changes to the
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API itself to increase robustness with shared libraries. This
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release is based on libpng-0.88, but has been modified from that
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version by Andreas Dilger <adilger@enel.ucalgary.ca> because the
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original author, Guy Schalnat, has not been able to keep up with
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the time demands of maintaining this library.
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The callback functions for the error/warning messages have changed
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since the last release because their implementation was broken,
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and it was thought best to change the API itself (which was only
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introduced in libpng-0.88 itself) to alert the user to the change,
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rather than mislead the user into thinking their application was
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OK after re-compiling. This means that calls to png_set_message_fn()
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no longer exist, because the previously suggested method of calling
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them before png_read_init() or png_write_init() is now ineffective.
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The preferred method of setting the error and warning callbacks
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has been incorporated into the allocation of the png_struct and
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info_struct itself, which allow them to be safely used during the
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initialization of the structure, as well as to keep the size of
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the png_struct internal to the library, rather than at compile time
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of the application. This will hopefully remove any problems with
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dynamically linked libraries, and should be considered the preferred
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method of creating these structures, although the previous
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initialization API is still available for compatibility. See libpng.txt
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for more information on the new API.
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The changes made to the library, and bugs fixed are based on discussions
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on the PNG implementation mailing list <png-implement@dworking.wustl.edu>
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and not on material submitted to Guy.
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For a detailed description on using libpng, read libpng.txt. For
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usage information and restrictions (what little they are) on libpng,
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see png.h. For a description on using zlib (the compression library
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used by libpng) and zlib's restrictions, see zlib.h
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I have included a general makefile, as well as several machine and compiler
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specific ones, but you may have to modify one for your own needs.
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You will need zlib 0.95 or later to run this. zlib is a compression
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library that is useful for more things then just png files. If
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you need a compression library, check out zlib.h. There was a bug in
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zlib <= 0.99 which caused it to generate invalid compression streams
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on some occasions. Later versions of zlib do not have this problem.
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zlib should be available at the same place that libpng is.
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If not, it should be at ftp.uu.net in /graphics/png
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Eventually, it will be at ftp.uu.net in /pub/archiving/zip/zlib
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You may also want a copy of the PNG specification. It should
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be available at the same place you picked up libpng. If it is
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not there, try ftp.uu.net in the /graphics/png directory.
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This code is currently being archived at ftp.uu.net in the
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/graphics/png directory, and on CompuServe, Lib 20 (PNG SUPPORT)
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at GO GRAPHSUP. If you can't find it in any of those places,
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e-mail me, and I'll help you find it.
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If you have any code changes, requests, problems, etc., please e-mail
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them to me. Also, I'd appreciate any make files or project files,
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and any modifications you needed to make to get libpng to compile,
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along with a #define variable to tell what compiler/system you are on.
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If you needed to add transformations to libpng, or wish libpng would
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provide the image in a different way, drop me a note (and code, if
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possible), so I can consider supporting the transformation.
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Finally, if you get any warning messages when compiling libpng
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(note: not zlib), and they are easy to fix, I'd appreciate the
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fix. Please mention "libpng" somewhere in the subject line. Thanks.
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This release was created and will be supported by myself, and the
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PNG group.
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adilger@enel.ucalgary.ca
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png-implement@dworkin.wustl.edu
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You can reach Guy, the original libpng author, at (internet preferred):
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internet: schalnat@group42.com
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CompuServe: 75501,1625
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Please do not send general questions about PNG. Send them to
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the address in the specification. At the same time, please do
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not send libpng questions to that address, send them to me. I'll
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get them in the end anyway. If you have a question about something
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in the PNG specification that is related to using libpng, send it
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to me. Send me any questions that start with "I was using libpng,
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and ...". If in doubt, send questions to me. I'll bounce them
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to others, if necessary.
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Please do not send suggestions on how to change PNG. We have
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been discussing PNG for over a year now, and it is official and
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finished. If you have suggestions for libpng, however, I'll
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gladly listen. Even if your suggestion is not used for version
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1.0, it may be used later.
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Good luck, and happy coding.
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-Guy Eric Schalnat
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Group 42, Inc.
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Internet: schalnat@group42.com
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CompuServe: 75501,1625
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Web: www.group42.com
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