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a626cc03 1README for libpng 1.0.3 - January 14, 1999 (shared library 2.1)
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2See the note about version numbers near the top of png.h
3
4See INSTALL for instructions on how to install libpng.
5
6This is the first official release of libpng. Don't let the fact that
7it's the first release fool you. The libpng library has been in
8extensive use and testing for about two and a half years. However, it's
9finally gotten to the stage where there haven't been significant
10changes to the API in some time, and people have a bad feeling about
11libraries with versions < 1.0.
12
13****
14Note that some of the changes to the png_info structure render this
15version of the library binary incompatible with libpng-0.89 or
16earlier versions if you are using a shared library. The type of the
17"filler" parameter for png_set_filler() has changed from png_byte to
18png_uint_32, which will affect shared-library applications that use
19this function.
20
21To avoid problems with changes to the internals of png_info_struct,
22new APIs have been made available in 0.95 to avoid direct application
23access to info_ptr. These functions are the png_set_<chunk> and
24png_get_<chunk> functions. These functions should be used when
25accessing/storing the info_struct data, rather than manipulating it
26directly, to avoid such problems in the future.
27
28It is important to note that the APIs do not make current programs
29that access the info struct directly incompatible with the new
30library. However, it is strongly suggested that new programs use
31the new APIs (as shown in example.c), and older programs be converted
32to the new format, to facilitate upgrades in the future.
33****
34
35Additions since 0.90 include the ability to compile libpng as a
36Windows DLL, and new APIs for accessing data in the info struct.
37Experimental functions include the ability to set weighting and cost
38factors for row filter selection, direct reads of integers from buffers
39on big-endian processors that support misaligned data access, faster
40methods of doing alpha composition, and more accurate 16->8 bit color
41conversion.
42
43The additions since 0.89 include the ability to read from a PNG stream
44which has had some (or all) of the signature bytes read by the calling
45application. This also allows the reading of embedded PNG streams that
46do not have the PNG file signature. As well, it is now possible to set
47the library action on the detection of chunk CRC errors. It is possible
48to set different actions based on whether the CRC error occurred in a
49critical or an ancillary chunk.
50
51The changes made to the library, and bugs fixed are based on discussions
52on the PNG implementation mailing list <png-implement@dworking.wustl.edu>
53and not on material submitted to Guy.
54
55For a detailed description on using libpng, read libpng.txt. For
56examples of libpng in a program, see example.c and pngtest.c. For usage
57information and restrictions (what little they are) on libpng, see
58png.h. For a description on using zlib (the compression library used by
59libpng) and zlib's restrictions, see zlib.h
60
61I have included a general makefile, as well as several machine and
62compiler specific ones, but you may have to modify one for your own needs.
63
64You should use zlib 1.0.4 or later to run this, but it MAY work with
65versions as old as zlib 0.95. Even so, there are bugs in older zlib
66versions which can cause the output of invalid compression streams for
67some images. You will definitely need zlib 1.0.4 or later if you are
68taking advantage of the MS-DOS "far" structure allocation for the small
69and medium memory models. You should also note that zlib is a
70compression library that is useful for more things than just PNG files.
71You can use zlib as a drop-in replacement for fread() and fwrite() if
72you are so inclined.
73
74zlib should be available at the same place that libpng is.
75If not, it should be at ftp.uu.net in /graphics/png
76Eventually, it will be at ftp.uu.net in /pub/archiving/zip/zlib
77
78You may also want a copy of the PNG specification. It is available
79as an RFC and a W3C Recommendation. Failing
80these resources you can try ftp.uu.net in the /graphics/png directory.
81
82This code is currently being archived at ftp.uu.net in the
83/graphics/png directory, and on CompuServe, Lib 20 (PNG SUPPORT)
84at GO GRAPHSUP. If you can't find it in any of those places,
85e-mail me, and I'll help you find it.
86
87If you have any code changes, requests, problems, etc., please e-mail
88them to me. Also, I'd appreciate any make files or project files,
89and any modifications you needed to make to get libpng to compile,
90along with a #define variable to tell what compiler/system you are on.
91If you needed to add transformations to libpng, or wish libpng would
92provide the image in a different way, drop me a note (and code, if
93possible), so I can consider supporting the transformation.
94Finally, if you get any warning messages when compiling libpng
95(note: not zlib), and they are easy to fix, I'd appreciate the
96fix. Please mention "libpng" somewhere in the subject line. Thanks.
97
98This release was created and will be supported by myself (of course
99based in a large way on Guy's and Andreas' earlier work), and the PNG group.
100
101randeg@alumni.rpi.edu
102png-implement@dworkin.wustl.edu
103
104You can't reach Guy, the original libpng author, at the addresses
105given in previous versions of this document. He and Andreas will read mail
106addressed to the png-implement list, however.
107
108Please do not send general questions about PNG. Send them to
109the address in the specification (png-group@w3.org). At the same
110time, please do not send libpng questions to that address, send them to me
111or to png-implement@dworkin.wustl.edu. I'll
112get them in the end anyway. If you have a question about something
113in the PNG specification that is related to using libpng, send it
114to me. Send me any questions that start with "I was using libpng,
115and ...". If in doubt, send questions to me. I'll bounce them
116to others, if necessary.
117
118Please do not send suggestions on how to change PNG. We have
119been discussing PNG for three years now, and it is official and
120finished. If you have suggestions for libpng, however, I'll
121gladly listen. Even if your suggestion is not used for version
1221.0, it may be used later.
123
124Files in this distribution:
125
126 CHANGES => Description of changes between libpng versions
127 README => This file
128 TODO => Things not implemented in the current library
129 ansi2knr.1 => Manual page for ansi2knr
130 ansi2knr.c => Converts files to K&R style function declarations
131 build.bat => MS-DOS batch file for Borland compiler
132 descrip.mms => VMS project file
133 example.c => Example code for using libpng functions
134 libpng.3 => manual page for libpng
135 libpng.txt => Description of libpng and its functions
136 libpngpf.3 => manual page for libpng's private functions
137 png.5 => manual page for the PNG format
138 png.c => Basic interface functions common to library
139 png.h => Library function and interface declarations
140 pngconf.h => System specific library configuration
141 pngerror.c => Error/warning message I/O functions
142 pngget.c => Functions for retrieving info from struct
143 pngmem.c => Memory handling functions
144 pngpread.c => Progressive reading functions
145 pngread.c => Read data/helper high-level functions
146 pngrio.c => Lowest-level data read I/O functions
147 pngrtran.c => Read data transformation functions
148 pngrutil.c => Read data utility functions
149 pngset.c => Functions for storing data into the info_struct
150 pngtest.c => Library test program
151 pngtest.png => Library test sample image
152 pngtrans.c => Common data transformation functions
153 pngwio.c => Lowest-level write I/O functions
154 pngwrite.c => High-level write functions
155 pngwtran.c => Write data transformations
156 pngwutil.c => Write utility functions
157 scripts => Directory containing scripts for building libpng:
158 descrip.mms => VMS makefile for MMS or MMK
159 makefile.std => Generic UNIX makefile
160 makefile.knr => Archaic UNIX Makefile that converts files with ansi2knr
161 makefile.dec => DEC Alpha UNIX makefile
a626cc03 162 makefile.hux => HPUX (10.20 and 11.00) makefile
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163 makefile.sgi => Silicon Graphics IRIX makefile
164 makefile.sun => Sun makefile
165 makefile.s2x => Solaris 2.X makefile (gcc, creates libpng.so.2.1.0)
166 makefile.lnx => Linux/ELF makefile (gcc, creates libpng.so.2.1.0)
167 makefile.mip => MIPS makefile
168 makefile.aco => Acorn makefile
169 makefile.ama => Amiga makefile
170 smakefile.ppc => AMIGA smakefile for SAS C V6.58/7.00 PPC compiler
171 (Requires SCOPTIONS, copied from scripts/SCOPTIONS.ppc)
172 makefile.atr => Atari makefile
173 makefile.bor => Borland makefile
174 build.bat => MS-DOS batch file for Borland compiler
175 makefile.dj2 => DJGPP 2 makefile
176 makefile.msc => Microsoft C makefile
a626cc03 177 makefile.w32 => makefile for Microsoft Visual C++ 4.0 and later
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178 makefile.tc3 => Turbo C 3.0 makefile
179 makefile.os2 => OS/2 Makefile (gcc and emx, requires pngos2.def)
180 makefile.wat => Watcom 10a+ Makefile, 32-bit flat memory model
181 pngos2.def => OS/2 module definition file used by makefile.os2
182 makevms.com => VMS build script
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183 pngdll.mak => To make a png32bd.dll with Borland C++ 4.5
184 pngdef.pas => Defines for a png32bd.dll with Borland C++ 4.5
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185
186Good luck, and happy coding.
187
188-Glenn Randers-Pehrson
189 Internet: randeg@alumni.rpi.edu
190 Web: http://www.rpi.edu/~randeg/index.html
191
192-Andreas Eric Dilger
193 Internet: adilger@enel.ucalgary.ca
194 Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
195
196-Guy Eric Schalnat
197 (formerly of Group 42, Inc)
198 Internet: gschal@infinet.com