README - platform/external/libpng - Gitiles

 README for libpng version 1.5.0beta47 - August 28, 2010 (shared library 15.0)
 See the note about version numbers near the top of png.h

 See INSTALL for instructions on how to install libpng.

 Libpng comes in several distribution formats.  Get libpng-*.tar.gz,
 libpng-*.tar.xz or libpng-*.tar.bz2 if you want UNIX-style line endings
 in the text files, or lpng*.zip if you want DOS-style line endings.

 Version 0.89 was the first official release of libpng.  Don't let the
 fact that it's the first release fool you.  The libpng library has been in
 extensive use and testing since mid-1995.  By late 1997 it had
 finally gotten to the stage where there hadn't been significant
 changes to the API in some time, and people have a bad feeling about
 libraries with versions < 1.0.  Version 1.0.0 was released in
 March 1998.

 ****
 Note that some of the changes to the png_info structure render this
 version of the library binary incompatible with libpng-0.89 or
 earlier versions if you are using a shared library.  The type of the
 "filler" parameter for png_set_filler() has changed from png_byte to
 png_uint_32, which will affect shared-library applications that use
 this function.

 To avoid problems with changes to the internals of png_info_struct,
 new APIs have been made available in 0.95 to avoid direct application
 access to info_ptr.  These functions are the png_set_<chunk> and
 png_get_<chunk> functions.  These functions should be used when
 accessing/storing the info_struct data, rather than manipulating it
 directly, to avoid such problems in the future.

 It is important to note that the APIs do not make current programs
 that access the info struct directly incompatible with the new
 library.  However, it is strongly suggested that new programs use
 the new APIs (as shown in example.c and pngtest.c), and older programs
 be converted to the new format, to facilitate upgrades in the future.
 ****

 Additions since 0.90 include the ability to compile libpng as a
 Windows DLL, and new APIs for accessing data in the info struct.
 Experimental functions include the ability to set weighting and cost
 factors for row filter selection, direct reads of integers from buffers
 on big-endian processors that support misaligned data access, faster
 methods of doing alpha composition, and more accurate 16->8 bit color
 conversion.

 The additions since 0.89 include the ability to read from a PNG stream
 which has had some (or all) of the signature bytes read by the calling
 application.  This also allows the reading of embedded PNG streams that
 do not have the PNG file signature.  As well, it is now possible to set
 the library action on the detection of chunk CRC errors.  It is possible
 to set different actions based on whether the CRC error occurred in a
 critical or an ancillary chunk.

 The changes made to the library, and bugs fixed are based on discussions
 on the PNG-implement mailing list and not on material submitted
 privately to Guy, Andreas, or Glenn.  They will forward any good
 suggestions to the list.

 For a detailed description on using libpng, read libpng.txt.  For
 examples of libpng in a program, see example.c and pngtest.c.  For usage
 information and restrictions (what little they are) on libpng, see
 png.h.  For a description on using zlib (the compression library used by
 libpng) and zlib's restrictions, see zlib.h

 I have included a general makefile, as well as several machine and
 compiler specific ones, but you may have to modify one for your own needs.

 You should use zlib 1.0.4 or later to run this, but it MAY work with
 versions as old as zlib 0.95.  Even so, there are bugs in older zlib
 versions which can cause the output of invalid compression streams for
 some images.  You will definitely need zlib 1.0.4 or later if you are
 taking advantage of the MS-DOS "far" structure allocation for the small
 and medium memory models.  You should also note that zlib is a
 compression library that is useful for more things than just PNG files.
 You can use zlib as a drop-in replacement for fread() and fwrite() if
 you are so inclined.

 zlib should be available at the same place that libpng is, or at.
 ftp://ftp.info-zip.org/pub/infozip/zlib

 You may also want a copy of the PNG specification.  It is available
 as an RFC, a W3C Recommendation, and an ISO/IEC Standard.  You can find
 these at http://www.libpng.org/pub/png/documents/

 This code is currently being archived at libpng.sf.net in the
 [DOWNLOAD] area, and on CompuServe, Lib 20 (PNG SUPPORT)
 at GO GRAPHSUP.  If you can't find it in any of those places,
 e-mail me, and I'll help you find it.

 If you have any code changes, requests, problems, etc., please e-mail
 them to me.  Also, I'd appreciate any make files or project files,
 and any modifications you needed to make to get libpng to compile,
 along with a #define variable to tell what compiler/system you are on.
 If you needed to add transformations to libpng, or wish libpng would
 provide the image in a different way, drop me a note (and code, if
 possible), so I can consider supporting the transformation.
 Finally, if you get any warning messages when compiling libpng
 (note: not zlib), and they are easy to fix, I'd appreciate the
 fix.  Please mention "libpng" somewhere in the subject line.  Thanks.

 This release was created and will be supported by myself (of course
 based in a large way on Guy's and Andreas' earlier work), and the PNG
 development group.

 Send comments/corrections/commendations to png-mng-implement at
 lists.sourceforge.net (subscription required; visit
 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
 to subscribe) or to glennrp at users.sourceforge.net

 You can't reach Guy, the original libpng author, at the addresses
 given in previous versions of this document.  He and Andreas will
 read mail addressed to the png-implement list, however.

 Please do not send general questions about PNG.  Send them to
 the (png-list at ccrc.wustl.edu, subscription required, write to
 majordomo at ccrc.wustl.edu with "subscribe png-list" in your message).
 On the other hand,
 please do not send libpng questions to that address, send them to me
 or to the png-implement list.  I'll
 get them in the end anyway.  If you have a question about something
 in the PNG specification that is related to using libpng, send it
 to me.  Send me any questions that start with "I was using libpng,
 and ...".  If in doubt, send questions to me.  I'll bounce them
 to others, if necessary.

 Please do not send suggestions on how to change PNG.  We have
 been discussing PNG for nine years now, and it is official and
 finished.  If you have suggestions for libpng, however, I'll
 gladly listen.  Even if your suggestion is not used immediately,
 it may be used later.

 Files in this distribution:

       ANNOUNCE      =>  Announcement of this version, with recent changes
       CHANGES       =>  Description of changes between libpng versions
       KNOWNBUG      =>  List of known bugs and deficiencies
       LICENSE       =>  License to use and redistribute libpng
       README        =>  This file
       TODO          =>  Things not implemented in the current library
       Y2KINFO       =>  Statement of Y2K compliance
       example.c     =>  Example code for using libpng functions
       libpng.3      =>  manual page for libpng (includes libpng.txt)
       libpng.txt    =>  Description of libpng and its functions
       libpngpf.3    =>  manual page for libpng's private functions
       png.5         =>  manual page for the PNG format
       png.c         =>  Basic interface functions common to library
       png.h         =>  Library function and interface declarations (public)
       pngpriv.h     =>  Library function and interface declarations (private)
       pngconf.h     =>  System specific library configuration (public)
       pngstruct.h   =>  png_struct declaration (private)
       pnginfo.h     =>  png_info struct declaration (private)
       pngdebug.h    =>  debugging macros (private)
       pngerror.c    =>  Error/warning message I/O functions
       pngget.c      =>  Functions for retrieving info from struct
       pngmem.c      =>  Memory handling functions
       pngbar.png    =>  PNG logo, 88x31
       pngnow.png    =>  PNG logo, 98x31
       pngpread.c    =>  Progressive reading functions
       pngread.c     =>  Read data/helper high-level functions
       pngrio.c      =>  Lowest-level data read I/O functions
       pngrtran.c    =>  Read data transformation functions
       pngrutil.c    =>  Read data utility functions
       pngset.c      =>  Functions for storing data into the info_struct
       pngtest.c     =>  Library test program
       pngtest.png   =>  Library test sample image
       pngtrans.c    =>  Common data transformation functions
       pngwio.c      =>  Lowest-level write I/O functions
       pngwrite.c    =>  High-level write functions
       pngwtran.c    =>  Write data transformations
       pngwutil.c    =>  Write utility functions
       contrib       =>  Contributions
        gregbook         =>  source code for PNG reading and writing, from
                             Greg Roelofs' "PNG: The Definitive Guide",
                             O'Reilly, 1999
        msvctest     =>  Builds and runs pngtest using a MSVC workspace
        pngminus     =>  Simple pnm2png and png2pnm programs
        pngsuite     =>  Test images
        visupng      =>  Contains a MSVC workspace for VisualPng
       projects      =>  Contains project files and workspaces for
                         building a DLL
        cbuilder5        =>  Contains a Borland workspace for building
                             libpng and zlib
        visualc6         =>  Contains a Microsoft Visual C++ (MSVC)
                             workspace for building libpng and zlib
        visualc71        =>  Contains a Microsoft Visual C++ (MSVC)
                             workspace for building libpng and zlib
        xcode            =>  Contains an Apple xcode
                             workspace for building libpng and zlib
       scripts       =>  Directory containing scripts for building libpng:
                             (see scripts/README.txt for the list of scripts)

 Good luck, and happy coding.

 -Glenn Randers-Pehrson (current maintainer, since 1998)
  Internet: glennrp at users.sourceforge.net

 -Andreas Eric Dilger (former maintainer, 1996-1997)
  Internet: adilger at enel.ucalgary.ca
  Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/

 -Guy Eric Schalnat (original author and former maintainer, 1995-1996)
  (formerly of Group 42, Inc)
  Internet: gschal at infinet.com
	README for libpng version 1.5.0beta47 - August 28, 2010 (shared library 15.0)
	See the note about version numbers near the top of png.h

	See INSTALL for instructions on how to install libpng.

	Libpng comes in several distribution formats. Get libpng-*.tar.gz,
	libpng-.tar.xz or libpng-.tar.bz2 if you want UNIX-style line endings
	in the text files, or lpng*.zip if you want DOS-style line endings.

	Version 0.89 was the first official release of libpng. Don't let the
	fact that it's the first release fool you. The libpng library has been in
	extensive use and testing since mid-1995. By late 1997 it had
	finally gotten to the stage where there hadn't been significant
	changes to the API in some time, and people have a bad feeling about
	libraries with versions < 1.0. Version 1.0.0 was released in
	March 1998.

	****
	Note that some of the changes to the png_info structure render this
	version of the library binary incompatible with libpng-0.89 or
	earlier versions if you are using a shared library. The type of the
	"filler" parameter for png_set_filler() has changed from png_byte to
	png_uint_32, which will affect shared-library applications that use
	this function.

	To avoid problems with changes to the internals of png_info_struct,
	new APIs have been made available in 0.95 to avoid direct application
	access to info_ptr. These functions are the png_set_<chunk> and
	png_get_<chunk> functions. These functions should be used when
	accessing/storing the info_struct data, rather than manipulating it
	directly, to avoid such problems in the future.

	It is important to note that the APIs do not make current programs
	that access the info struct directly incompatible with the new
	library. However, it is strongly suggested that new programs use
	the new APIs (as shown in example.c and pngtest.c), and older programs
	be converted to the new format, to facilitate upgrades in the future.
	****

	Additions since 0.90 include the ability to compile libpng as a
	Windows DLL, and new APIs for accessing data in the info struct.
	Experimental functions include the ability to set weighting and cost
	factors for row filter selection, direct reads of integers from buffers
	on big-endian processors that support misaligned data access, faster
	methods of doing alpha composition, and more accurate 16->8 bit color
	conversion.

	The additions since 0.89 include the ability to read from a PNG stream
	which has had some (or all) of the signature bytes read by the calling
	application. This also allows the reading of embedded PNG streams that
	do not have the PNG file signature. As well, it is now possible to set
	the library action on the detection of chunk CRC errors. It is possible
	to set different actions based on whether the CRC error occurred in a
	critical or an ancillary chunk.

	The changes made to the library, and bugs fixed are based on discussions
	on the PNG-implement mailing list and not on material submitted
	privately to Guy, Andreas, or Glenn. They will forward any good
	suggestions to the list.

	For a detailed description on using libpng, read libpng.txt. For
	examples of libpng in a program, see example.c and pngtest.c. For usage
	information and restrictions (what little they are) on libpng, see
	png.h. For a description on using zlib (the compression library used by
	libpng) and zlib's restrictions, see zlib.h

	I have included a general makefile, as well as several machine and
	compiler specific ones, but you may have to modify one for your own needs.

	You should use zlib 1.0.4 or later to run this, but it MAY work with
	versions as old as zlib 0.95. Even so, there are bugs in older zlib
	versions which can cause the output of invalid compression streams for
	some images. You will definitely need zlib 1.0.4 or later if you are
	taking advantage of the MS-DOS "far" structure allocation for the small
	and medium memory models. You should also note that zlib is a
	compression library that is useful for more things than just PNG files.
	You can use zlib as a drop-in replacement for fread() and fwrite() if
	you are so inclined.

	zlib should be available at the same place that libpng is, or at.
	ftp://ftp.info-zip.org/pub/infozip/zlib

	You may also want a copy of the PNG specification. It is available
	as an RFC, a W3C Recommendation, and an ISO/IEC Standard. You can find
	these at http://www.libpng.org/pub/png/documents/

	This code is currently being archived at libpng.sf.net in the
	[DOWNLOAD] area, and on CompuServe, Lib 20 (PNG SUPPORT)
	at GO GRAPHSUP. If you can't find it in any of those places,
	e-mail me, and I'll help you find it.

	If you have any code changes, requests, problems, etc., please e-mail
	them to me. Also, I'd appreciate any make files or project files,
	and any modifications you needed to make to get libpng to compile,
	along with a #define variable to tell what compiler/system you are on.
	If you needed to add transformations to libpng, or wish libpng would
	provide the image in a different way, drop me a note (and code, if
	possible), so I can consider supporting the transformation.
	Finally, if you get any warning messages when compiling libpng
	(note: not zlib), and they are easy to fix, I'd appreciate the
	fix. Please mention "libpng" somewhere in the subject line. Thanks.

	This release was created and will be supported by myself (of course
	based in a large way on Guy's and Andreas' earlier work), and the PNG
	development group.

	Send comments/corrections/commendations to png-mng-implement at
	lists.sourceforge.net (subscription required; visit
	https://lists.sourceforge.net/lists/listinfo/png-mng-implement
	to subscribe) or to glennrp at users.sourceforge.net

	You can't reach Guy, the original libpng author, at the addresses
	given in previous versions of this document. He and Andreas will
	read mail addressed to the png-implement list, however.

	Please do not send general questions about PNG. Send them to
	the (png-list at ccrc.wustl.edu, subscription required, write to
	majordomo at ccrc.wustl.edu with "subscribe png-list" in your message).
	On the other hand,
	please do not send libpng questions to that address, send them to me
	or to the png-implement list. I'll
	get them in the end anyway. If you have a question about something
	in the PNG specification that is related to using libpng, send it
	to me. Send me any questions that start with "I was using libpng,
	and ...". If in doubt, send questions to me. I'll bounce them
	to others, if necessary.

	Please do not send suggestions on how to change PNG. We have
	been discussing PNG for nine years now, and it is official and
	finished. If you have suggestions for libpng, however, I'll
	gladly listen. Even if your suggestion is not used immediately,
	it may be used later.

	Files in this distribution:

	ANNOUNCE => Announcement of this version, with recent changes
	CHANGES => Description of changes between libpng versions
	KNOWNBUG => List of known bugs and deficiencies
	LICENSE => License to use and redistribute libpng
	README => This file
	TODO => Things not implemented in the current library
	Y2KINFO => Statement of Y2K compliance
	example.c => Example code for using libpng functions
	libpng.3 => manual page for libpng (includes libpng.txt)
	libpng.txt => Description of libpng and its functions
	libpngpf.3 => manual page for libpng's private functions
	png.5 => manual page for the PNG format
	png.c => Basic interface functions common to library
	png.h => Library function and interface declarations (public)
	pngpriv.h => Library function and interface declarations (private)
	pngconf.h => System specific library configuration (public)
	pngstruct.h => png_struct declaration (private)
	pnginfo.h => png_info struct declaration (private)
	pngdebug.h => debugging macros (private)
	pngerror.c => Error/warning message I/O functions
	pngget.c => Functions for retrieving info from struct
	pngmem.c => Memory handling functions
	pngbar.png => PNG logo, 88x31
	pngnow.png => PNG logo, 98x31
	pngpread.c => Progressive reading functions
	pngread.c => Read data/helper high-level functions
	pngrio.c => Lowest-level data read I/O functions
	pngrtran.c => Read data transformation functions
	pngrutil.c => Read data utility functions
	pngset.c => Functions for storing data into the info_struct
	pngtest.c => Library test program
	pngtest.png => Library test sample image
	pngtrans.c => Common data transformation functions
	pngwio.c => Lowest-level write I/O functions
	pngwrite.c => High-level write functions
	pngwtran.c => Write data transformations
	pngwutil.c => Write utility functions
	contrib => Contributions
	gregbook => source code for PNG reading and writing, from
	Greg Roelofs' "PNG: The Definitive Guide",
	O'Reilly, 1999
	msvctest => Builds and runs pngtest using a MSVC workspace
	pngminus => Simple pnm2png and png2pnm programs
	pngsuite => Test images
	visupng => Contains a MSVC workspace for VisualPng
	projects => Contains project files and workspaces for
	building a DLL
	cbuilder5 => Contains a Borland workspace for building
	libpng and zlib
	visualc6 => Contains a Microsoft Visual C++ (MSVC)
	workspace for building libpng and zlib
	visualc71 => Contains a Microsoft Visual C++ (MSVC)
	workspace for building libpng and zlib
	xcode => Contains an Apple xcode
	workspace for building libpng and zlib
	scripts => Directory containing scripts for building libpng:
	(see scripts/README.txt for the list of scripts)

	Good luck, and happy coding.

	-Glenn Randers-Pehrson (current maintainer, since 1998)
	Internet: glennrp at users.sourceforge.net

	-Andreas Eric Dilger (former maintainer, 1996-1997)
	Internet: adilger at enel.ucalgary.ca
	Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/

	-Guy Eric Schalnat (original author and former maintainer, 1995-1996)
	(formerly of Group 42, Inc)
	Internet: gschal at infinet.com