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Imported from libpng-0.96.tar
This commit is contained in:
Andreas Dilger
committed by
Glenn Randers-Pehrson
Glenn Randers-Pehrson
parent
02ad0efbc8
commit
47a0c422ca
90
README
90
README
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readme.txt - for libpng 0.90
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README for libpng 0.96
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This is the fourth beta version of libpng 1.0. The changes from
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libpng-0.89 include bug fixes, a C++ wrapper for png.h, some
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additions to the API, as well as internal changes to the library.
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This is the sixth (and hopefully last) beta release of libpng 1.0.
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The changes from libpng-0.90 include bug fixes, a C++ wrapper for
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png.h, some additions to the API, as well as internal changes to
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the library. See "CHANGES" for a detailed list of differences.
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**
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Note that some of the changes to the png_info structure render
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this version of the library binary incompatible with libpng-0.89
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if you are using a shared library. Re-compiling the application
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should be enough to remove this problem.
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**
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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 which use
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this function.
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The additions to 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
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calling application. This also allows the reading of embedded PNG
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streams that do not have the PNG file signature. As well, it is
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now possible to set the library action on the detection of chunk
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CRC errors. It is possible to set different actions based on
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whether the error occurred in a critical or an ancillary chunk.
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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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****
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The callback functions for the error/warning messages have changed
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since the 0.88 release because their implementation was broken,
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and it was thought best to change the API itself (which was only
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introduced in libpng-0.88 itself) to alert the user to the change,
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rather than mislead the user into thinking their application was
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OK after re-compiling. This means that calls to png_set_message_fn()
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no longer exist, because the previously suggested method of calling
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them before png_read_init() or png_write_init() is now ineffective.
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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 preferred method of setting the error and warning callbacks
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has been incorporated into the allocation of the png_struct and
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info_struct itself, which allow them to be safely used during the
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initialization of the structure, as well as to keep the size of
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the png_struct internal to the library, rather than at compile time
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of the application. This will hopefully remove any problems with
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dynamically linked libraries, and should be considered the preferred
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method of creating these structures, although the previous
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initialization API is still available for compatibility. See libpng.txt
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for more information on the new API.
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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 implementation mailing list <png-implement@dworking.wustl.edu>
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and not on material submitted to Guy.
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For a detailed description on using libpng, read libpng.txt. 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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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 compiler
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specific ones, but you may have to modify one for your own needs.
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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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@@ -113,7 +112,7 @@ gladly listen. Even if your suggestion is not used for version
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Files in this distribution:
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CHANGES.txt => Description of changes between libpng versions
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CHANGES => Description of changes between libpng versions
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README => This file
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TODO => Things not implemented in the current library
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ansi2knr.c => Converts files to K&R style function declarations
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@@ -121,7 +120,7 @@ Files in this distribution:
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descrip.mms => VMS project file
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example.c => Example code for using libpng functions
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libpng.txt => Description of libpng and its functions
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makefile => Defualt makefile
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makefile => Default Unixish makefile
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makefile.aco => ACORN makefile
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makefile.ama => Amiga makefile
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makefile.atr => Atari makefile
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@@ -140,11 +139,11 @@ Files in this distribution:
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pngerror.c => Error/warning message I/O functions
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pngmem.c => Memory handling functions
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pngpread.c => Progressive reading functions
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pngrcb.c => Read callback (data handling) low-level 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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@@ -156,13 +155,12 @@ Files in this distribution:
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Good luck, and happy coding.
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-Andreas Eric Dilger
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University of Calgary
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Internet: adilger@enel.ucalgary.ca
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Web: www-mddsp.enel.ucalgary.ca/People/adilger/
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Web: http://www-mddsp.enel.ucalgary.ca/People/adilger/
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-Guy Eric Schalnat
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Group 42, Inc.
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Internet: schalnat@group42.com
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CompuServe: 75501,1625
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Web: www.group42.com
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Web: http://www.group42.com/
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