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[libpng15] Added demo of how to deal with unknown chunk location

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to the man page.
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Glenn Randers-Pehrson 2013-04-28 21:10:01 -05:00
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56
libpng-manual.txt
View File

@ -1,6 +1,6 @@
Libpng-manual.txt - A description on how to use and modify libpng Libpng-manual.txt - A description on how to use and modify libpng
libpng version 1.5.16beta04 - April 26, 2013 libpng version 1.5.16beta04 - April 29, 2013
Updated and distributed by Glenn Randers-Pehrson Updated and distributed by Glenn Randers-Pehrson
<glennrp at users.sourceforge.net> <glennrp at users.sourceforge.net>
Copyright (c) 1998-2013 Glenn Randers-Pehrson Copyright (c) 1998-2013 Glenn Randers-Pehrson
@ -11,7 +11,7 @@ Libpng-manual.txt - A description on how to use and modify libpng
Based on: Based on:
libpng versions 0.97, January 1998, through 1.5.16beta04 - April 26, 2013 libpng versions 0.97, January 1998, through 1.5.16beta04 - April 29, 2013
Updated and distributed by Glenn Randers-Pehrson Updated and distributed by Glenn Randers-Pehrson
Copyright (c) 1998-2013 Glenn Randers-Pehrson Copyright (c) 1998-2013 Glenn Randers-Pehrson
@ -31,9 +31,7 @@ Libpng-manual.txt - A description on how to use and modify libpng
I. Introduction I. Introduction
This file describes how to use and modify the PNG reference library This file describes how to use and modify the PNG reference library
(known as libpng) for your own use. There are five sections to this (known as libpng) for your own use. In addition to this
file: introduction, structures, reading, writing, and modification and
configuration notes for various special platforms. In addition to this
file, example.c is a good starting point for using the library, as file, example.c is a good starting point for using the library, as
it is heavily commented and should include everything most people it is heavily commented and should include everything most people
will need. We assume that libpng is already installed; see the will need. We assume that libpng is already installed; see the
@ -3037,13 +3035,45 @@ from PNG time to an RFC 1123 format string.
Writing unknown chunks Writing unknown chunks
You can use the png_set_unknown_chunks function to queue up chunks You can use the png_set_unknown_chunks function to queue up private chunks
for writing. You give it a chunk name, raw data, and a size; that's for writing. You give it a chunk name, location, raw data, and a size. You
all there is to it. The chunks will be written by the next following also must use png_set_keep_unknown_chunks() to ensure that libpng will
png_write_info_before_PLTE, png_write_info, or png_write_end function. handle them. That's all there is to it. The chunks will be written by the
Any chunks previously read into the info structure's unknown-chunk next following png_write_info_before_PLTE, png_write_info, or png_write_end
list will also be written out in a sequence that satisfies the PNG function, depending upon the specified location. Any chunks previously
specification's ordering rules. read into the info structure's unknown-chunk list will also be written out
in a sequence that satisfies the PNG specification's ordering rules.
Here is an example of writing two private chunks, prVt and miNE:
#ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
/* Set unknown chunk data */
png_unknown_chunk unk_chunk[2];
strcpy((char *) unk_chunk[0].name, "prVt";
unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
unk_chunk[0].location = PNG_HAVE_IHDR;
strcpy((char *) unk_chunk[1].name, "miNE";
unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
unk_chunk[1].location = PNG_AFTER_IDAT;
png_set_unknown_chunks(write_ptr, write_info_ptr,
unk_chunk, 2);
/* Needed because miNE is not safe-to-copy */
png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
(png_bytep) "miNE", 1);
/* Deal with unknown chunk location bug in 1.5.x and earlier */
png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
# if PNG_LIBPNG_VER < 10500
/* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
* one before IDAT and another after IDAT, so don't use it; only use
* PNG_HAVE_IHDR location. This call resets the location previously
* set by assignment and png_set_unknown_chunk_location() for chunk 1.
*/
png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
# endif
#endif
The high-level write interface The high-level write interface
@ -4625,7 +4655,7 @@ Other rules can be inferred by inspecting the libpng source.
XIV. Y2K Compliance in libpng XIV. Y2K Compliance in libpng
April 26, 2013 April 29, 2013
Since the PNG Development group is an ad-hoc body, we can't make Since the PNG Development group is an ad-hoc body, we can't make
an official declaration. an official declaration.

64
libpng.3
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@ -1,4 +1,4 @@
.TH LIBPNG 3 "April 26, 2013" .TH LIBPNG 3 "April 29, 2013"
.SH NAME .SH NAME
libpng \- Portable Network Graphics (PNG) Reference Library 1.5.16beta04 libpng \- Portable Network Graphics (PNG) Reference Library 1.5.16beta04
.SH SYNOPSIS .SH SYNOPSIS
@ -492,7 +492,7 @@ Following is a copy of the libpng-manual.txt file that accompanies libpng.
.SH LIBPNG.TXT .SH LIBPNG.TXT
Libpng-manual.txt - A description on how to use and modify libpng Libpng-manual.txt - A description on how to use and modify libpng
libpng version 1.5.16beta04 - April 26, 2013 libpng version 1.5.16beta04 - April 29, 2013
Updated and distributed by Glenn Randers-Pehrson Updated and distributed by Glenn Randers-Pehrson
<glennrp at users.sourceforge.net> <glennrp at users.sourceforge.net>
Copyright (c) 1998-2013 Glenn Randers-Pehrson Copyright (c) 1998-2013 Glenn Randers-Pehrson
@ -503,7 +503,7 @@ Libpng-manual.txt - A description on how to use and modify libpng
Based on: Based on:
libpng versions 0.97, January 1998, through 1.5.16beta04 - April 26, 2013 libpng versions 0.97, January 1998, through 1.5.16beta04 - April 29, 2013
Updated and distributed by Glenn Randers-Pehrson Updated and distributed by Glenn Randers-Pehrson
Copyright (c) 1998-2013 Glenn Randers-Pehrson Copyright (c) 1998-2013 Glenn Randers-Pehrson
@ -523,9 +523,7 @@ Libpng-manual.txt - A description on how to use and modify libpng
.SH I. Introduction .SH I. Introduction
This file describes how to use and modify the PNG reference library This file describes how to use and modify the PNG reference library
(known as libpng) for your own use. There are five sections to this (known as libpng) for your own use. In addition to this
file: introduction, structures, reading, writing, and modification and
configuration notes for various special platforms. In addition to this
file, example.c is a good starting point for using the library, as file, example.c is a good starting point for using the library, as
it is heavily commented and should include everything most people it is heavily commented and should include everything most people
will need. We assume that libpng is already installed; see the will need. We assume that libpng is already installed; see the
@ -3529,13 +3527,45 @@ from PNG time to an RFC 1123 format string.
.SS Writing unknown chunks .SS Writing unknown chunks
You can use the png_set_unknown_chunks function to queue up chunks You can use the png_set_unknown_chunks function to queue up private chunks
for writing. You give it a chunk name, raw data, and a size; that's for writing. You give it a chunk name, location, raw data, and a size. You
all there is to it. The chunks will be written by the next following also must use png_set_keep_unknown_chunks() to ensure that libpng will
png_write_info_before_PLTE, png_write_info, or png_write_end function. handle them. That's all there is to it. The chunks will be written by the
Any chunks previously read into the info structure's unknown-chunk next following png_write_info_before_PLTE, png_write_info, or png_write_end
list will also be written out in a sequence that satisfies the PNG function, depending upon the specified location. Any chunks previously
specification's ordering rules. read into the info structure's unknown-chunk list will also be written out
in a sequence that satisfies the PNG specification's ordering rules.
Here is an example of writing two private chunks, prVt and miNE:
#ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
/* Set unknown chunk data */
png_unknown_chunk unk_chunk[2];
strcpy((char *) unk_chunk[0].name, "prVt";
unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
unk_chunk[0].location = PNG_HAVE_IHDR;
strcpy((char *) unk_chunk[1].name, "miNE";
unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
unk_chunk[1].location = PNG_AFTER_IDAT;
png_set_unknown_chunks(write_ptr, write_info_ptr,
unk_chunk, 2);
/* Needed because miNE is not safe-to-copy */
png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
(png_bytep) "miNE", 1);
/* Deal with unknown chunk location bug in 1.5.x and earlier */
png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
# if PNG_LIBPNG_VER < 10500
/* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
* one before IDAT and another after IDAT, so don't use it; only use
* PNG_HAVE_IHDR location. This call resets the location previously
* set by assignment and png_set_unknown_chunk_location() for chunk 1.
*/
png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
# endif
#endif
.SS The high-level write interface .SS The high-level write interface
@ -5118,7 +5148,7 @@ Other rules can be inferred by inspecting the libpng source.
.SH XIV. Y2K Compliance in libpng .SH XIV. Y2K Compliance in libpng
April 26, 2013 April 29, 2013
Since the PNG Development group is an ad-hoc body, we can't make Since the PNG Development group is an ad-hoc body, we can't make
an official declaration. an official declaration.
@ -5407,7 +5437,7 @@ possible without all of you.
Thanks to Frank J. T. Wojcik for helping with the documentation. Thanks to Frank J. T. Wojcik for helping with the documentation.
Libpng version 1.5.16beta04 - April 26, 2013: Libpng version 1.5.16beta04 - April 29, 2013:
Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc. Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net). Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
@ -5430,7 +5460,7 @@ this sentence.
This code is released under the libpng license. This code is released under the libpng license.
libpng versions 1.2.6, August 15, 2004, through 1.5.16beta04, April 26, 2013, are libpng versions 1.2.6, August 15, 2004, through 1.5.16beta04, April 29, 2013, are
Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are Copyright (c) 2004,2006-2007 Glenn Randers-Pehrson, and are
distributed according to the same disclaimer and license as libpng-1.2.5 distributed according to the same disclaimer and license as libpng-1.2.5
with the following individual added to the list of Contributing Authors with the following individual added to the list of Contributing Authors
@ -5529,7 +5559,7 @@ certification mark of the Open Source Initiative.
Glenn Randers-Pehrson Glenn Randers-Pehrson
glennrp at users.sourceforge.net glennrp at users.sourceforge.net
April 26, 2013 April 29, 2013
.\" end of man page .\" end of man page