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 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