216 lines
11 KiB
Plaintext
216 lines
11 KiB
Plaintext
README for libpng version 1.6.19rc02 - October 31, 2015 (shared library 16.0)
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See the note about version numbers near the top of png.h
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See INSTALL for instructions on how to install libpng.
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Libpng comes in several distribution formats. Get libpng-*.tar.gz or
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libpng-*.tar.xz or if you want UNIX-style line endings in the text files,
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or lpng*.7z or lpng*.zip if you want DOS-style line endings.
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Version 0.89 was the first official release of libpng. Don't let the
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fact that it's the first release fool you. The libpng library has been in
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extensive use and testing since mid-1995. By late 1997 it had
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finally gotten to the stage where there hadn'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. Version 1.0.0 was released in
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March 1998.
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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 did not make current programs
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that access the info struct directly incompatible with the new
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library, through libpng-1.2.x. In libpng-1.4.x, which was meant to
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be a transitional release, members of the png_struct and the
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info_struct can still be accessed, but the compiler will issue a
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warning about deprecated usage. Since libpng-1.5.0, direct access
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to these structs is not allowed, and the definitions of the structs
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reside in private pngstruct.h and pnginfo.h header files that are not
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accessible to applications. It is strongly suggested that new
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programs use the new APIs (as shown in example.c and pngtest.c), and
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older programs be converted to the new format, to facilitate upgrades
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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-implement mailing list and not on material submitted
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privately to Guy, Andreas, or Glenn. They will forward any good
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suggestions to the list.
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For a detailed description on using libpng, read libpng-manual.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, or at zlib.net.
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You may also want a copy of the PNG specification. It is available
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as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
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these at http://www.libpng.org/pub/png/documents/
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This code is currently being archived at libpng.sf.net in the
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[DOWNLOAD] area, and at ftp://ftp.simplesystems.org. If you can't find it
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in any of those places, e-mail me, and I'll help you find it.
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I am not a lawyer, but I believe that the Export Control Classification
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Number (ECCN) for libpng is EAR99, which means not subject to export
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controls or International Traffic in Arms Regulations (ITAR) because it
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is open source, publicly available software, that does not contain any
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encryption software. See the EAR, paragraphs 734.3(b)(3) and 734.7(b).
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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
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development group.
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Send comments/corrections/commendations to png-mng-implement at
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lists.sourceforge.net (subscription required; visit
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https://lists.sourceforge.net/lists/listinfo/png-mng-implement
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to subscribe) or to glennrp at users.sourceforge.net
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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
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read mail 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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png-mng-misc at lists.sf.net (subscription required; visit
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https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
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subscribe). 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 twenty 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 immediately,
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it may be used later.
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Files in this distribution:
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ANNOUNCE => Announcement of this version, with recent changes
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CHANGES => Description of changes between libpng versions
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KNOWNBUG => List of known bugs and deficiencies
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LICENSE => License to use and redistribute libpng
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README => This file
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TODO => Things not implemented in the current library
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Y2KINFO => Statement of Y2K compliance
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example.c => Example code for using libpng functions
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libpng.3 => manual page for libpng (includes libpng-manual.txt)
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libpng-manual.txt => Description of libpng and its functions
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libpngpf.3 => manual page for libpng's private functions
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png.5 => manual page for the PNG format
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png.c => Basic interface functions common to library
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png.h => Library function and interface declarations (public)
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pngpriv.h => Library function and interface declarations (private)
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pngconf.h => System specific library configuration (public)
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pngstruct.h => png_struct declaration (private)
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pnginfo.h => png_info struct declaration (private)
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pngdebug.h => debugging macros (private)
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pngerror.c => Error/warning message I/O functions
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pngget.c => Functions for retrieving info from struct
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pngmem.c => Memory handling functions
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pngbar.png => PNG logo, 88x31
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pngnow.png => PNG logo, 98x31
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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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arm => Contains optimized code for the ARM platform
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contrib => Contributions
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examples => Example programs
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gregbook => source code for PNG reading and writing, from
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Greg Roelofs' "PNG: The Definitive Guide",
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O'Reilly, 1999
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libtests => Test programs
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pngminim => Minimal decoder, encoder, and progressive decoder
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programs demonstrating use of pngusr.dfa
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pngminus => Simple pnm2png and png2pnm programs
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pngsuite => Test images
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tools => Various tools
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visupng => Contains a MSVC workspace for VisualPng
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projects => Contains project files and workspaces for
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building a DLL
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owatcom => Contains a WATCOM project for building libpng
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visualc71 => Contains a Microsoft Visual C++ (MSVC)
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workspace for building libpng and zlib
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vstudio => Contains a Microsoft Visual C++ (MSVC)
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workspace for building libpng and zlib
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scripts => Directory containing scripts for building libpng:
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(see scripts/README.txt for the list of scripts)
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Good luck, and happy coding.
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-Glenn Randers-Pehrson (current maintainer, since 1998)
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Internet: glennrp at users.sourceforge.net
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-Andreas Eric Dilger (former maintainer, 1996-1997)
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Internet: adilger at enel.ucalgary.ca
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Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
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-Guy Eric Schalnat (original author and former maintainer, 1995-1996)
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(formerly of Group 42, Inc)
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Internet: gschal at infinet.com
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