183 lines
8.5 KiB
Plaintext
183 lines
8.5 KiB
Plaintext
[NOTE: this is still beta version 0.99c; the text below has already
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been updated in anticipation of the imminent 1.0 release.]
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README for libpng 1.0
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This is the first official release of libpng. Don't let the fact that
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it's the first release fool you. The libpng library has been in
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extensive use and testing for about two and a half years. However, it's
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finally gotten to the stage where there haven't been significant
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changes to the API in some time, and people have a bad feeling about
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libraries with versions < 1.0.
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****
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Note that some of the changes to the png_info structure render this
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version of the library binary incompatible with libpng-0.89 or
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earlier versions if you are using a shared library. The type of the
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"filler" parameter for png_set_filler() has changed from png_byte to
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png_uint_32, which will affect shared-library applications that use
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this function.
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To avoid problems with changes to the internals of png_info_struct,
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new APIs have been made available in 0.95 to avoid direct application
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access to info_ptr. These functions are the png_set_<chunk> and
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png_get_<chunk> functions. These functions should be used when
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accessing/storing the info_struct data, rather than manipulating it
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directly, to avoid such problems in the future.
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It is important to note that the APIs do not make current programs
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that access the info struct directly incompatible with the new
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library. However, it is strongly suggested that new programs use
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the new APIs (as shown in example.c), and older programs be converted
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to the new format, to facilitate upgrades in the future.
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****
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Additions since 0.90 include the ability to compile libpng as a
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Windows DLL, and new APIs for accessing data in the info struct.
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Experimental functions include the ability to set weighting and cost
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factors for row filter selection, direct reads of integers from buffers
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on big-endian processors that support misaligned data access, faster
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methods of doing alpha composition, and more accurate 16->8 bit color
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conversion.
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The additions since 0.89 include the ability to read from a PNG stream
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which has had some (or all) of the signature bytes read by the calling
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application. This also allows the reading of embedded PNG streams that
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do not have the PNG file signature. As well, it is now possible to set
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the library action on the detection of chunk CRC errors. It is possible
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to set different actions based on whether the CRC error occurred in a
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critical or an ancillary chunk.
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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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examples of libpng in a program, see example.c and pngtest.c. For usage
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information and restrictions (what little they are) on libpng, see
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png.h. For a description on using zlib (the compression library used by
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libpng) and zlib's restrictions, see zlib.h
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I have included a general makefile, as well as several machine and
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compiler specific ones, but you may have to modify one for your own needs.
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You should use zlib 1.0.4 or later to run this, but it MAY work with
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versions as old as zlib 0.95. Even so, there are bugs in older zlib
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versions which can cause the output of invalid compression streams for
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some images. You will definitely need zlib 1.0.4 or later if you are
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taking advantage of the MS-DOS "far" structure allocation for the small
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and medium memory models. You should also note that zlib is a
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compression library that is useful for more things than just PNG files.
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You can use zlib as a drop-in replacement for fread() and fwrite() if
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you are so inclined.
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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 is available
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as an RFC and a W3C Recommendation. Failing
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these resources you can 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 (of course
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based in a large way on Guy's and Andreas' earlier work), and the PNG group.
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randeg@alumni.rpi.edu
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png-implement@dworkin.wustl.edu
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You can't reach Guy, the original libpng author, at the addresses
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given in previous versions of this document. He and Andreas will read mail
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addressed to the png-implement list, however.
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Please do not send general questions about PNG. Send them to
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the address in the specification (png-group@w3.org). At the same
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time, please do not send libpng questions to that address, send them to me
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or to png-implement@dworkin.wustl.edu. 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 a couple years 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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Files in this distribution:
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CHANGES => Description of changes between libpng versions
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README => This file
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TODO => Things not implemented in the current library
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ansi2knr.c => Converts files to K&R style function declarations
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build.bat => MS-DOS batch file for Borland compiler
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descrip.mms => VMS project file
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example.c => Example code for using libpng functions
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libpng.txt => Description of libpng and its functions
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makefile.aco => ACORN makefile
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makefile.ama => Amiga makefile
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makefile.atr => Atari makefile
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makefile.bor => Borland makefile
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makefile.dec => DEC makefile
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makefile.dj2 => DJGPP 2 makefile
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makefile.elf => Unix ELF makefile
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makefile.knr => Makefile which calls ansi2knr to convert files
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makefile.mip => MIPS makefile
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makefile.msc => Microsoft C makefile
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makefile.sgi => Silicon Graphics Irix makefile
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makefile.std => Standard Unix makefile
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makefile.sun => SUN makefile
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makefile.tc3 => Turbo C 3.0 makefile
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makevms.com => VMS make program
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png.c => Basic interface functions common to library
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png.h => Library function and interface declarations
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pngconf.h => System specific library configuration
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pngerror.c => Error/warning message I/O functions
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pngmem.c => Memory handling functions
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pngpread.c => Progressive reading functions
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pngread.c => Read data/helper high-level functions
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pngrio.c => Lowest-level data read I/O functions
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pngrtran.c => Read data transformation functions
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pngrutil.c => Read data utility functions
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pngset.c => Functions for storing data into the info_struct
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pngtest.c => Library test program
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pngtest.png => Library test sample image
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pngtrans.c => Common data transformation functions
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pngwio.c => Lowest-level write I/O functions
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pngwrite.c => High-level write functions
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pngwtran.c => Write data transformations
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pngwutil.c => Write utility functions
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Good luck, and happy coding.
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-Glenn Randers-Pehrson
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Internet: randeg@alumni.rpi.edu
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Web: http://www.rpi.edu/~randeg/index.html
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-Andreas Eric Dilger
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Internet: adilger@enel.ucalgary.ca
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Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
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-Guy Eric Schalnat
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(formerly of Group 42, Inc)
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Web: http://www.group42.com/
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