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[libpng16] Expanded manual paragraph about writing private chunks, particularly

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about the need to call png_set_keep_unknown_chunks() when writing them.
This commit is contained in:
Glenn Randers-Pehrson
2013-04-27 18:03:03 -05:00
parent c62fda06a3
commit 49f9c24910
4 changed files with 71 additions and 35 deletions
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44
libpng-manual.txt
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@@ -1,6 +1,6 @@
libpng-manual.txt - A description on how to use and modify libpng
libpng version 1.6.3beta03 - April 26, 2013
libpng version 1.6.3beta03 - April 27, 2013
Updated and distributed by Glenn Randers-Pehrson
<glennrp at users.sourceforge.net>
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:
libpng versions 0.97, January 1998, through 1.6.3beta03 - April 26, 2013
libpng versions 0.97, January 1998, through 1.6.3beta03 - April 27, 2013
Updated and distributed by Glenn Randers-Pehrson
Copyright (c) 1998-2013 Glenn Randers-Pehrson
@@ -50,9 +50,7 @@ libpng-manual.txt - A description on how to use and modify libpng
I. Introduction
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
file: introduction, structures, reading, writing, and modification and
configuration notes for various special platforms. In addition to this
(known as libpng) for your own use. In addition to this
file, example.c is a good starting point for using the library, as
it is heavily commented and should include everything most people
will need. We assume that libpng is already installed; see the
@@ -3093,13 +3091,31 @@ a writeable buffer of at least 29 bytes.
Writing unknown chunks
You can use the png_set_unknown_chunks function to queue up chunks
for writing. You give it a chunk name, raw data, and a size; that's
all there is to it. The chunks will be written by the next following
png_write_info_before_PLTE, png_write_info, or png_write_end function.
Any chunks previously 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.
You can use the png_set_unknown_chunks function to queue up private chunks
for writing. You give it a chunk name, location, raw data, and a size. You
also must use png_set_keep_unknown_chunks() to ensure that libpng will
handle them. That's all there is to it. The chunks will be written by the
next following png_write_info_before_PLTE, png_write_info, or png_write_end
function, depending upon the specified location. Any chunks previously
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 unkc[2];
png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS, NULL, 0);
strcpy((char *) unkc[0].name, "prVt";
unkc[0].data = (unsigned char *) "PRIVATE CHUNK DATA";
unkc[0].size = strlen(unkc[0].data)+1;
unkc[0].location = PNG_HAVE_IHDR;
strcpy((char *) unkc[1].name, "miNE";
unkc[1].data = (unsigned char *) "MY CHUNK DATA";
unkc[1].size = strlen(unkc[0].data)+1;
unkc[1].location = PNG_AFTER_IDAT;
png_set_unknown_chunks(png, info, unkc, 2);
#endif
The high-level write interface
@@ -4947,7 +4963,7 @@ symbols, using the PNG_PREFIX macro.
We no longer include string.h in png.h. The include statement has been moved
to pngpriv.h, where it is not accessible by applications. Applications that
need access to information in string.h must add an '#include "string.h"'
need access to information in string.h must add an '#include <string.h>'
directive. It does not matter whether this is placed prior to or after
the '"#include png.h"' directive.
@@ -5165,7 +5181,7 @@ Other rules can be inferred by inspecting the libpng source.
XVI. Y2K Compliance in libpng
April 26, 2013
April 27, 2013
Since the PNG Development group is an ad-hoc body, we can't make
an official declaration.