185 lines
9.2 KiB
Plaintext
185 lines
9.2 KiB
Plaintext
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README for libpng version 1.6.43
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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`
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or `libpng-*.tar.xz` if you want UNIX-style line endings in the text
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files, or `lpng*.7z` or `lpng*.zip` if you want DOS-style line endings.
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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`.
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For 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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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 https://libpng.sourceforge.io
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in the 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 and commendations to `png-mng-implement`
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at `lists.sourceforge.net`. (Subscription is 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 is required; visit
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https://lists.sourceforge.net/lists/listinfo/png-mng-misc
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to subscribe.)
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Historical notes
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----------------
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The libpng library has been in extensive use and testing since mid-1995.
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Version 0.89, published a year later, was the first official release.
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By late 1997, it had finally gotten to the stage where there hadn't
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been significant changes to the API in some time, and people have a bad
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feeling about libraries with versions below 1.0. Version 1.0.0 was
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released in March 1998.
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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`
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to `png_uint_32`, which will affect shared-library applications that
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use this function.
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To avoid problems with changes to the internals of the `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
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not 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`),
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and older programs be converted to the new format, to facilitate
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upgrades in the future.
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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 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 included 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-to-8 bit color
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conversion. Some of these experimental functions, such as the weighted
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filter heuristics, have since been removed.
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Files included in this distribution
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-----------------------------------
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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 ARM Neon
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intel/ => Optimized code for INTEL SSE2
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loongarch/ => Optimized code for LoongArch LSX
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mips/ => Optimized code for MIPS MSA and MIPS MMI
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powerpc/ => Optimized code for PowerPC VSX
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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/ => Examples of libpng usage
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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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pngexif/ => Program to inspect the EXIF information in PNG files
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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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