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184 lines
9 KiB
Text
184 lines
9 KiB
Text
README for libpng version 1.6.39
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================================
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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 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
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in 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 the 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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For a detailed description on using libpng, read libpng-manual.txt.
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For examples of libpng in a program, see example.c and pngtest.c. For
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usage information and restrictions (what little they are) on libpng,
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see png.h. For a description on using zlib (the compression library
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used by 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
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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.
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You should also note that zlib is a compression library that is useful
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for more things than just PNG files. You can use zlib as a drop-in
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replacement for fread() and fwrite(), if you are so inclined.
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zlib should be available at the same place that libpng is, or at
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https://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/pngdocs.html .
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This code is currently being archived at libpng.sourceforge.io in the
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[DOWNLOAD] area, and at http://libpng.download/src .
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This release, based in a large way on Glenn's, Guy's and Andreas'
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earlier work, was created and will be supported by myself 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).
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Send general questions about the PNG specification to png-mng-misc
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at lists.sourceforge.net (subscription required; visit
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https://lists.sourceforge.net/lists/listinfo/png-mng-misc to
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subscribe).
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Files in this distribution:
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ANNOUNCE => Announcement of this version, with recent changes
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AUTHORS => List of contributing authors
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CHANGES => Description of changes between libpng versions
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INSTALL => Instructions to install libpng
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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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TRADEMARK => Trademark information
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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 (deprecated)
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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/ => Optimized code for the ARM platform
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intel/ => Optimized code for the INTEL-SSE2 platform
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mips/ => Optimized code for the MIPS platform
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powerpc/ => Optimized code for the PowerPC platform
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ci/ => Scripts for continuous integration
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contrib/ => External contributions
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arm-neon/ => Optimized code for the ARM-NEON platform
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mips-msa/ => Optimized code for the MIPS-MSA platform
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powerpc-vsx/ => Optimized code for the POWERPC-VSX platform
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examples/ => Example programs
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gregbook/ => Source code for PNG reading and writing, from
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"PNG: The Definitive Guide" by Greg Roelofs,
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O'Reilly, 1999
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libtests/ => Test programs
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oss-fuzz/ => Files used by the OSS-Fuzz project for fuzz-testing
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libpng
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pngminim/ => Minimal decoder, encoder, and progressive decoder
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programs demonstrating the 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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testpngs/ => Test images
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tools/ => Various tools
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visupng/ => VisualPng, a Windows viewer for PNG images
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projects/ => Project files and workspaces for various IDEs
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owatcom/ => OpenWatcom project
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visualc71/ => Microsoft Visual C++ 7.1 workspace
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vstudio/ => Microsoft Visual Studio workspace
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scripts/ => Scripts and makefiles for building libpng
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(see scripts/README.txt for the complete list)
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tests/ => Test scripts
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Good luck, and happy coding!
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* Cosmin Truta (current maintainer, since 2018)
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* Glenn Randers-Pehrson (former maintainer, 1998-2018)
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* Andreas Eric Dilger (former maintainer, 1996-1997)
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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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