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Update the documentation

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Cosmin Truta
2018-07-29 00:33:12 -04:00
parent b729fff4a3
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8 changed files with 180 additions and 462 deletions
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libpng-manual.txt
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@@ -1,7 +1,6 @@
libpng-manual.txt - A description on how to use and modify libpng
libpng version 1.6.35 - July 15, 2018
Updated and distributed by Glenn Randers-Pehrson
Copyright (c) 2018 Cosmin Truta
Copyright (c) 1998-2018 Glenn Randers-Pehrson
This document is released under the libpng license.
@@ -12,7 +11,7 @@ libpng-manual.txt - A description on how to use and modify libpng
libpng versions 0.97, January 1998, through 1.6.35 - July 15, 2018
Updated and distributed by Glenn Randers-Pehrson
Copyright (c) 1998-2017 Glenn Randers-Pehrson
Copyright (c) 1998-2018 Glenn Randers-Pehrson
libpng 1.0 beta 6 - version 0.96 - May 28, 1997
Updated and distributed by Andreas Dilger
@@ -44,7 +43,6 @@ libpng-manual.txt - A description on how to use and modify libpng
XIII. Detecting libpng
XIV. Source code repository
XV. Coding style
XVI. Y2K Compliance in libpng
I. Introduction
@@ -4520,7 +4518,7 @@ When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
having level = 0 will be printed. There aren't any such statements in
this version of libpng, but if you insert some they will be printed.
VII. MNG support
VII. MNG support
The MNG specification (available at http://www.libpng.org/pub/mng) allows
certain extensions to PNG for PNG images that are embedded in MNG datastreams.
@@ -4547,7 +4545,7 @@ or any other MNG chunks; your application must provide its own support for
them. You may wish to consider using libmng (available at
https://www.libmng.com/) instead.
VIII. Changes to Libpng from version 0.88
VIII. Changes to Libpng from version 0.88
It should be noted that versions of libpng later than 0.96 are not
distributed by the original libpng author, Guy Schalnat, nor by
@@ -4602,7 +4600,7 @@ application:
png_uint_32 application_vn = PNG_LIBPNG_VER;
IX. Changes to Libpng from version 1.0.x to 1.2.x
IX. Changes to Libpng from version 1.0.x to 1.2.x
Support for user memory management was enabled by default. To
accomplish this, the functions png_create_read_struct_2(),
@@ -4699,7 +4697,7 @@ which also expands tRNS to alpha was replaced with
png_set_expand_gray_1_2_4_to_8()
which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
Private libpng prototypes and macro definitions were moved from
png.h and pngconf.h into a new pngpriv.h header file.
@@ -4809,7 +4807,7 @@ was renamed to PNG_READ_QUANTIZE_SUPPORTED.
We removed the trailing '.' from the warning and error messages.
XI. Changes to Libpng from version 1.4.x to 1.5.x
XI. Changes to Libpng from version 1.4.x to 1.5.x
From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
function) incorrectly returned a value of type png_uint_32.
@@ -5067,7 +5065,7 @@ even though the default is to use the macros - this allows applications
to choose at app buildtime whether or not to use macros (previously
impossible because the functions weren't in the default build.)
XII. Changes to Libpng from version 1.5.x to 1.6.x
XII. Changes to Libpng from version 1.5.x to 1.6.x
A "simplified API" has been added (see documentation in png.h and a simple
example in contrib/examples/pngtopng.c). The new publicly visible API
@@ -5230,7 +5228,7 @@ attempt to decode the Exif profile; it simply returns a byte array
containing the profile to the calling application which must do its own
decoding.
XIII. Detecting libpng
XIII. Detecting libpng
The png_get_io_ptr() function has been present since libpng-0.88, has never
changed, and is unaffected by conditional compilation macros. It is the
@@ -5255,7 +5253,7 @@ or you can browse it with a web browser at
https://sourceforge.net/p/libpng/code/ci/libpng16/tree/
Patches can be sent to png-mng-implement at lists.sourceforge.net or
you can upload them to the libpng bug tracker at
uploaded to the libpng bug tracker at
https://libpng.sourceforge.io/
@@ -5405,58 +5403,3 @@ We do not use the TAB character for indentation in the C sources.
Lines do not exceed 80 characters.
Other rules can be inferred by inspecting the libpng source.
XVI. Y2K Compliance in libpng
Since the PNG Development group is an ad-hoc body, we can't make
an official declaration.
This is your unofficial assurance that libpng from version 0.71 and
upward through 1.6.35 are Y2K compliant. It is my belief that earlier
versions were also Y2K compliant.
Libpng only has two year fields. One is a 2-byte unsigned integer
that will hold years up to 65535. The other, which is deprecated,
holds the date in text format, and will hold years up to 9999.
The integer is
"png_uint_16 year" in png_time_struct.
The string is
"char time_buffer[29]" in png_struct. This is no longer used
in libpng-1.6.x and will be removed from libpng-1.7.0.
There are seven time-related functions:
png_convert_to_rfc_1123_buffer() in png.c
(formerly png_convert_to_rfc_1152() in error, and
also formerly png_convert_to_rfc_1123())
png_convert_from_struct_tm() in pngwrite.c, called
in pngwrite.c
png_convert_from_time_t() in pngwrite.c
png_get_tIME() in pngget.c
png_handle_tIME() in pngrutil.c, called in pngread.c
png_set_tIME() in pngset.c
png_write_tIME() in pngwutil.c, called in pngwrite.c
All appear to handle dates properly in a Y2K environment. The
png_convert_from_time_t() function calls gmtime() to convert from system
clock time, which returns (year - 1900), which we properly convert to
the full 4-digit year. There is a possibility that applications using
libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
function, or that they are incorrectly passing only a 2-digit year
instead of "year - 1900" into the png_convert_from_struct_tm() function,
but this is not under our control. The libpng documentation has always
stated that it works with 4-digit years, and the APIs have been
documented as such.
The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
integer to hold the year, and can hold years as large as 65535.
zlib, upon which libpng depends, is also Y2K compliant. It contains
no date-related code.
Glenn Randers-Pehrson
libpng maintainer
PNG Development Group