| 1 | README for libpng version 1.6.37 - April 14, 2019
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| 2 | =================================================
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| 3 |
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| 4 | See the note about version numbers near the top of png.h.
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| 5 | See INSTALL for instructions on how to install libpng.
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| 6 |
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| 7 | Libpng comes in several distribution formats. Get libpng-*.tar.gz or
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| 8 | libpng-*.tar.xz or if you want UNIX-style line endings in the text
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| 9 | files, or lpng*.7z or lpng*.zip if you want DOS-style line endings.
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| 10 |
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| 11 | Version 0.89 was the first official release of libpng. Don't let the
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| 12 | fact that it's the first release fool you. The libpng library has been
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| 13 | in extensive use and testing since mid-1995. By late 1997 it had
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| 14 | finally gotten to the stage where there hadn't been significant
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| 15 | changes to the API in some time, and people have a bad feeling about
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| 16 | libraries with versions < 1.0. Version 1.0.0 was released in
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| 17 | March 1998.
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| 18 |
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| 19 | ****
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| 20 | Note that some of the changes to the png_info structure render this
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| 21 | version of the library binary incompatible with libpng-0.89 or
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| 22 | earlier versions if you are using a shared library. The type of the
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| 23 | "filler" parameter for png_set_filler() has changed from png_byte to
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| 24 | png_uint_32, which will affect shared-library applications that use
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| 25 | this function.
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| 26 |
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| 27 | To avoid problems with changes to the internals of the png info_struct,
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| 28 | new APIs have been made available in 0.95 to avoid direct application
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| 29 | access to info_ptr. These functions are the png_set_<chunk> and
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| 30 | png_get_<chunk> functions. These functions should be used when
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| 31 | accessing/storing the info_struct data, rather than manipulating it
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| 32 | directly, to avoid such problems in the future.
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| 33 |
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| 34 | It is important to note that the APIs did not make current programs
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| 35 | that access the info struct directly incompatible with the new
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| 36 | library, through libpng-1.2.x. In libpng-1.4.x, which was meant to
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| 37 | be a transitional release, members of the png_struct and the
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| 38 | info_struct can still be accessed, but the compiler will issue a
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| 39 | warning about deprecated usage. Since libpng-1.5.0, direct access
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| 40 | to these structs is not allowed, and the definitions of the structs
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| 41 | reside in private pngstruct.h and pnginfo.h header files that are not
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| 42 | accessible to applications. It is strongly suggested that new
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| 43 | programs use the new APIs (as shown in example.c and pngtest.c), and
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| 44 | older programs be converted to the new format, to facilitate upgrades
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| 45 | in the future.
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| 46 | ****
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| 47 |
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| 48 | Additions since 0.90 include the ability to compile libpng as a
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| 49 | Windows DLL, and new APIs for accessing data in the info struct.
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| 50 | Experimental functions include the ability to set weighting and cost
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| 51 | factors for row filter selection, direct reads of integers from buffers
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| 52 | on big-endian processors that support misaligned data access, faster
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| 53 | methods of doing alpha composition, and more accurate 16->8 bit color
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| 54 | conversion.
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| 55 |
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| 56 | The additions since 0.89 include the ability to read from a PNG stream
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| 57 | which has had some (or all) of the signature bytes read by the calling
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| 58 | application. This also allows the reading of embedded PNG streams that
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| 59 | do not have the PNG file signature. As well, it is now possible to set
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| 60 | the library action on the detection of chunk CRC errors. It is possible
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| 61 | to set different actions based on whether the CRC error occurred in a
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| 62 | critical or an ancillary chunk.
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| 63 |
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| 64 | For a detailed description on using libpng, read libpng-manual.txt.
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| 65 | For examples of libpng in a program, see example.c and pngtest.c. For
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| 66 | usage information and restrictions (what little they are) on libpng,
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| 67 | see png.h. For a description on using zlib (the compression library
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| 68 | used by libpng) and zlib's restrictions, see zlib.h
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| 69 |
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| 70 | I have included a general makefile, as well as several machine and
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| 71 | compiler specific ones, but you may have to modify one for your own
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| 72 | needs.
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| 73 |
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| 74 | You should use zlib 1.0.4 or later to run this, but it MAY work with
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| 75 | versions as old as zlib 0.95. Even so, there are bugs in older zlib
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| 76 | versions which can cause the output of invalid compression streams for
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| 77 | some images.
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| 78 |
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| 79 | You should also note that zlib is a compression library that is useful
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| 80 | for more things than just PNG files. You can use zlib as a drop-in
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| 81 | replacement for fread() and fwrite(), if you are so inclined.
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| 82 |
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| 83 | zlib should be available at the same place that libpng is, or at
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| 84 | https://zlib.net.
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| 85 |
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| 86 | You may also want a copy of the PNG specification. It is available
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| 87 | as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
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| 88 | these at http://www.libpng.org/pub/png/pngdocs.html .
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| 89 |
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| 90 | This code is currently being archived at libpng.sourceforge.io in the
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| 91 | [DOWNLOAD] area, and at http://libpng.download/src .
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| 92 |
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| 93 | This release, based in a large way on Glenn's, Guy's and Andreas'
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| 94 | earlier work, was created and will be supported by myself and the PNG
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| 95 | development group.
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| 96 |
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| 97 | Send comments/corrections/commendations to png-mng-implement at
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| 98 | lists.sourceforge.net (subscription required; visit
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| 99 | https://lists.sourceforge.net/lists/listinfo/png-mng-implement
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| 100 | to subscribe).
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| 101 |
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| 102 | Send general questions about the PNG specification to png-mng-misc
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| 103 | at lists.sourceforge.net (subscription required; visit
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| 104 | https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
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| 105 | subscribe).
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| 106 |
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| 107 | Files in this distribution:
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| 108 |
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| 109 | ANNOUNCE => Announcement of this version, with recent changes
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| 110 | AUTHORS => List of contributing authors
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| 111 | CHANGES => Description of changes between libpng versions
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| 112 | KNOWNBUG => List of known bugs and deficiencies
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| 113 | LICENSE => License to use and redistribute libpng
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| 114 | README => This file
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| 115 | TODO => Things not implemented in the current library
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| 116 | TRADEMARK => Trademark information
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| 117 | example.c => Example code for using libpng functions
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| 118 | libpng.3 => manual page for libpng (includes libpng-manual.txt)
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| 119 | libpng-manual.txt => Description of libpng and its functions
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| 120 | libpngpf.3 => manual page for libpng's private functions
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| 121 | png.5 => manual page for the PNG format
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| 122 | png.c => Basic interface functions common to library
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| 123 | png.h => Library function and interface declarations (public)
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| 124 | pngpriv.h => Library function and interface declarations (private)
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| 125 | pngconf.h => System specific library configuration (public)
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| 126 | pngstruct.h => png_struct declaration (private)
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| 127 | pnginfo.h => png_info struct declaration (private)
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| 128 | pngdebug.h => debugging macros (private)
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| 129 | pngerror.c => Error/warning message I/O functions
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| 130 | pngget.c => Functions for retrieving info from struct
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| 131 | pngmem.c => Memory handling functions
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| 132 | pngbar.png => PNG logo, 88x31
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| 133 | pngnow.png => PNG logo, 98x31
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| 134 | pngpread.c => Progressive reading functions
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| 135 | pngread.c => Read data/helper high-level functions
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| 136 | pngrio.c => Lowest-level data read I/O functions
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| 137 | pngrtran.c => Read data transformation functions
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| 138 | pngrutil.c => Read data utility functions
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| 139 | pngset.c => Functions for storing data into the info_struct
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| 140 | pngtest.c => Library test program
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| 141 | pngtest.png => Library test sample image
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| 142 | pngtrans.c => Common data transformation functions
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| 143 | pngwio.c => Lowest-level write I/O functions
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| 144 | pngwrite.c => High-level write functions
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| 145 | pngwtran.c => Write data transformations
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| 146 | pngwutil.c => Write utility functions
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| 147 | arm => Contains optimized code for the ARM platform
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| 148 | powerpc => Contains optimized code for the PowerPC platform
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| 149 | contrib => Contributions
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| 150 | arm-neon => Optimized code for ARM-NEON platform
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| 151 | powerpc-vsx => Optimized code for POWERPC-VSX platform
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| 152 | examples => Example programs
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| 153 | gregbook => source code for PNG reading and writing, from
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| 154 | Greg Roelofs' "PNG: The Definitive Guide",
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| 155 | O'Reilly, 1999
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| 156 | libtests => Test programs
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| 157 | mips-msa => Optimized code for MIPS-MSA platform
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| 158 | pngminim => Minimal decoder, encoder, and progressive decoder
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| 159 | programs demonstrating use of pngusr.dfa
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| 160 | pngminus => Simple pnm2png and png2pnm programs
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| 161 | pngsuite => Test images
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| 162 | testpngs
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| 163 | tools => Various tools
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| 164 | visupng => Contains a MSVC workspace for VisualPng
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| 165 | intel => Optimized code for INTEL-SSE2 platform
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| 166 | mips => Optimized code for MIPS platform
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| 167 | projects => Contains project files and workspaces for
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| 168 | building a DLL
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| 169 | owatcom => Contains a WATCOM project for building libpng
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| 170 | visualc71 => Contains a Microsoft Visual C++ (MSVC)
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| 171 | workspace for building libpng and zlib
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| 172 | vstudio => Contains a Microsoft Visual C++ (MSVC)
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| 173 | workspace for building libpng and zlib
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| 174 | scripts => Directory containing scripts for building libpng:
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| 175 | (see scripts/README.txt for the list of scripts)
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| 176 |
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| 177 | Good luck, and happy coding!
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| 178 |
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| 179 | * Cosmin Truta (current maintainer, since 2018)
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| 180 | * Glenn Randers-Pehrson (former maintainer, 1998-2018)
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| 181 | * Andreas Eric Dilger (former maintainer, 1996-1997)
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| 182 | * Guy Eric Schalnat (original author and former maintainer, 1995-1996)
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| 183 | (formerly of Group 42, Inc.)
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