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git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/branches/ogl-es@6172 dfc29bdd-3216-0410-991c-e03cc46cb475
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cutealien
2020-12-19 15:03:11 +00:00
parent 01920bf808
commit fa0b1cb509
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source/Irrlicht/libpng/libpng-manual.txt
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@@ -1,9 +1,7 @@
libpng-manual.txt - A description on how to use and modify libpng
libpng version 1.6.23 - June 9, 2016
Updated and distributed by Glenn Randers-Pehrson
<glennrp at users.sourceforge.net>
Copyright (c) 1998-2016 Glenn Randers-Pehrson
Copyright (c) 2018-2019 Cosmin Truta
Copyright (c) 1998-2018 Glenn Randers-Pehrson
This document is released under the libpng license.
For conditions of distribution and use, see the disclaimer
@@ -11,9 +9,13 @@ libpng-manual.txt - A description on how to use and modify libpng
Based on:
libpng versions 0.97, January 1998, through 1.6.23 - June 9, 2016
libpng version 1.6.36, December 2018, through 1.6.37 - April 2019
Updated and distributed by Cosmin Truta
Copyright (c) 2018-2019 Cosmin Truta
libpng versions 0.97, January 1998, through 1.6.35 - July 2018
Updated and distributed by Glenn Randers-Pehrson
Copyright (c) 1998-2016 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
@@ -45,7 +47,6 @@ 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
@@ -66,17 +67,17 @@ file format in application programs.
The PNG specification (second edition), November 2003, is available as
a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
<http://www.w3.org/TR/2003/REC-PNG-20031110/
<https://www.w3.org/TR/2003/REC-PNG-20031110/>.
The W3C and ISO documents have identical technical content.
The PNG-1.2 specification is available at
<http://png-mng.sourceforge.net/pub/png/spec/1.2/>.
<https://png-mng.sourceforge.io/pub/png/spec/1.2/>.
It is technically equivalent
to the PNG specification (second edition) but has some additional material.
The PNG-1.0 specification is available as RFC 2083
<http://png-mng.sourceforge.net/pub/png/spec/1.0/> and as a
W3C Recommendation <http://www.w3.org/TR/REC-png-961001>.
The PNG-1.0 specification is available as RFC 2083 at
<https://png-mng.sourceforge.io/pub/png/spec/1.0/> and as a
W3C Recommendation at <https://www.w3.org/TR/REC-png-961001>.
Some additional chunks are described in the special-purpose public chunks
documents at <http://www.libpng.org/pub/png/spec/register/>
@@ -101,7 +102,7 @@ majority of the needs of its users.
Libpng uses zlib for its compression and decompression of PNG files.
Further information about zlib, and the latest version of zlib, can
be found at the zlib home page, <http://zlib.net/>.
be found at the zlib home page, <https://zlib.net/>.
The zlib compression utility is a general purpose utility that is
useful for more than PNG files, and can be used without libpng.
See the documentation delivered with zlib for more details.
@@ -348,18 +349,18 @@ Customizing libpng.
FILE *fp = fopen(file_name, "rb");
if (!fp)
{
return (ERROR);
return ERROR;
}
if (fread(header, 1, number, fp) != number)
{
return (ERROR);
return ERROR;
}
is_png = !png_sig_cmp(header, 0, number);
if (!is_png)
{
return (NOT_PNG);
return NOT_PNG;
}
Next, png_struct and png_info need to be allocated and initialized. In
@@ -378,7 +379,7 @@ create the structure, so your application should check for that.
user_error_fn, user_warning_fn);
if (!png_ptr)
return (ERROR);
return ERROR;
png_infop info_ptr = png_create_info_struct(png_ptr);
@@ -386,7 +387,7 @@ create the structure, so your application should check for that.
{
png_destroy_read_struct(&png_ptr,
(png_infopp)NULL, (png_infopp)NULL);
return (ERROR);
return ERROR;
}
If you want to use your own memory allocation routines,
@@ -421,7 +422,7 @@ free any memory.
png_destroy_read_struct(&png_ptr, &info_ptr,
&end_info);
fclose(fp);
return (ERROR);
return ERROR;
}
Pass (png_infopp)NULL instead of &end_info if you didn't create
@@ -467,8 +468,9 @@ the default, use
The values for png_set_crc_action() say how libpng is to handle CRC errors in
ancillary and critical chunks, and whether to use the data contained
therein. Note that it is impossible to "discard" data in a critical
chunk.
therein. Starting with libpng-1.6.26, this also governs how an ADLER32 error
is handled while reading the IDAT chunk. Note that it is impossible to
"discard" data in a critical chunk.
Choices for (int) crit_action are
PNG_CRC_DEFAULT 0 error/quit
@@ -485,6 +487,9 @@ Choices for (int) ancil_action are
PNG_CRC_QUIET_USE 4 quiet/use data
PNG_CRC_NO_CHANGE 5 use the current value
When the setting for crit_action is PNG_CRC_QUIET_USE, the CRC and ADLER32
checksums are not only ignored, but they are not evaluated.
Setting up callback code
You can set up a callback function to handle any unknown chunks in the
@@ -499,7 +504,7 @@ input stream. You must supply the function
png_byte name[5];
png_byte *data;
png_size_t size;
size_t size;
/* Note that libpng has already taken care of
the CRC handling */
@@ -508,9 +513,9 @@ input stream. You must supply the function
unknown chunk structure, process it, and return one
of the following: */
return (-n); /* chunk had an error */
return (0); /* did not recognize */
return (n); /* success */
return -n; /* chunk had an error */
return 0; /* did not recognize */
return n; /* success */
}
(You can give your function another name that you like instead of
@@ -559,7 +564,7 @@ non-interlaced case the row that was just handled is simply one less than the
passed in row number, and pass will always be 0. For the interlaced case the
same applies unless the row value is 0, in which case the row just handled was
the last one from one of the preceding passes. Because interlacing may skip a
pass you cannot be sure that the preceding pass is just 'pass-1', if you really
pass you cannot be sure that the preceding pass is just 'pass-1'; if you really
need to know what the last pass is record (row,pass) from the callback and use
the last recorded value each time.
@@ -684,8 +689,9 @@ where 0x7fffffffL means unlimited. You can retrieve this limit with
chunk_cache_max = png_get_chunk_cache_max(png_ptr);
Libpng imposes a limit of 8 Megabytes (8,000,000 bytes) on the amount of
memory that a compressed chunk other than IDAT can occupy, when decompressed.
You can change this limit with
memory that any chunk other than IDAT can occupy, originally or when
decompressed (prior to libpng-1.6.32 the limit was only applied to compressed
chunks after decompression). You can change this limit with
png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
@@ -981,15 +987,24 @@ premultiplication.
png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
This is the default libpng handling of the alpha channel - it is not
pre-multiplied into the color components. In addition the call states
Choices for the alpha_mode are
PNG_ALPHA_PNG 0 /* according to the PNG standard */
PNG_ALPHA_STANDARD 1 /* according to Porter/Duff */
PNG_ALPHA_ASSOCIATED 1 /* as above; this is the normal practice */
PNG_ALPHA_PREMULTIPLIED 1 /* as above */
PNG_ALPHA_OPTIMIZED 2 /* 'PNG' for opaque pixels, else 'STANDARD' */
PNG_ALPHA_BROKEN 3 /* the alpha channel is gamma encoded */
PNG_ALPHA_PNG is the default libpng handling of the alpha channel. It is not
pre-multiplied into the color components. In addition the call states
that the output is for a sRGB system and causes all PNG files without gAMA
chunks to be assumed to be encoded using sRGB.
png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
In this case the output is assumed to be something like an sRGB conformant
display preceeded by a power-law lookup table of power 1.45. This is how
display preceded by a power-law lookup table of power 1.45. This is how
early Mac systems behaved.
png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR);
@@ -997,7 +1012,7 @@ early Mac systems behaved.
This is the classic Jim Blinn approach and will work in academic
environments where everything is done by the book. It has the shortcoming
of assuming that input PNG data with no gamma information is linear - this
is unlikely to be correct unless the PNG files where generated locally.
is unlikely to be correct unless the PNG files were generated locally.
Most of the time the output precision will be so low as to show
significant banding in dark areas of the image.
@@ -1041,7 +1056,7 @@ faster.)
When the default gamma of PNG files doesn't match the output gamma.
If you have PNG files with no gamma information png_set_alpha_mode allows
you to provide a default gamma, but it also sets the ouput gamma to the
you to provide a default gamma, but it also sets the output gamma to the
matching value. If you know your PNG files have a gamma that doesn't
match the output you can take advantage of the fact that
png_set_alpha_mode always sets the output gamma but only sets the PNG
@@ -1186,7 +1201,20 @@ row_pointers prior to calling png_read_png() with
png_set_rows(png_ptr, info_ptr, &row_pointers);
Alternatively you could allocate your image in one big block and define
row_pointers[i] to point into the proper places in your block.
row_pointers[i] to point into the proper places in your block, but first
be sure that your platform is able to allocate such a large buffer:
/* Guard against integer overflow */
if (height > PNG_SIZE_MAX/(width*pixel_size)) {
png_error(png_ptr,"image_data buffer would be too large");
}
png_bytep buffer=png_malloc(png_ptr,height*width*pixel_size);
for (int i=0; i<height, i++)
row_pointers[i]=buffer+i*width*pixel_size;
png_set_rows(png_ptr, info_ptr, &row_pointers);
If you use png_set_rows(), the application is responsible for freeing
row_pointers (and row_pointers[i], if they were separately allocated).
@@ -1313,6 +1341,11 @@ in until png_read_end() has read the chunk data following the image.
rowbytes = png_get_rowbytes(png_ptr, info_ptr);
rowbytes - number of bytes needed to hold a row
This value, the bit_depth, color_type,
and the number of channels can change
if you use transforms such as
png_set_expand(). See
png_read_update_info(), below.
signature = png_get_signature(png_ptr, info_ptr);
@@ -1431,6 +1464,11 @@ png_set_rgb_to_gray()).
the single transparent color for
non-paletted images (PNG_INFO_tRNS)
png_get_eXIf_1(png_ptr, info_ptr, &num_exif, &exif);
(PNG_INFO_eXIf)
exif - Exif profile (array of png_byte)
png_get_hIST(png_ptr, info_ptr, &hist);
(PNG_INFO_hIST)
@@ -2142,6 +2180,16 @@ are allocating one large chunk, you will need to build an
array of pointers to each row, as it will be needed for some
of the functions below.
Be sure that your platform can allocate the buffer that you'll need.
libpng internally checks for oversize width, but you'll need to
do your own check for number_of_rows*width*pixel_size if you are using
a multiple-row buffer:
/* Guard against integer overflow */
if (number_of_rows > PNG_SIZE_MAX/(width*pixel_size)) {
png_error(png_ptr,"image_data buffer would be too large");
}
Remember: Before you call png_read_update_info(), the png_get_*()
functions return the values corresponding to the original PNG image.
After you call png_read_update_info the values refer to the image
@@ -2230,7 +2278,8 @@ is exactly the same. If you are planning on displaying the image
after each pass, the "rectangle" effect is generally considered the
better looking one.
If you only want the "sparkle" effect, just call png_read_rows() as
If you only want the "sparkle" effect, just call png_read_row() or
png_read_rows() as
normal, with the third parameter NULL. Make sure you make pass over
the image number_of_passes times, and you don't change the data in the
rows between calls. You can change the locations of the data, just
@@ -2239,6 +2288,8 @@ pass, and assumes the data from previous passes is still valid.
png_read_rows(png_ptr, row_pointers, NULL,
number_of_rows);
or
png_read_row(png_ptr, row_pointers, NULL);
If you only want the first effect (the rectangles), do the same as
before except pass the row buffer in the third parameter, and leave
@@ -2246,6 +2297,8 @@ the second parameter NULL.
png_read_rows(png_ptr, NULL, row_pointers,
number_of_rows);
or
png_read_row(png_ptr, NULL, row_pointers);
If you don't want libpng to handle the interlacing details, just call
png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
@@ -2357,7 +2410,7 @@ separate.
{
png_destroy_read_struct(&png_ptr, &info_ptr,
(png_infopp)NULL);
return (ERROR);
return ERROR;
}
png_read_end(png_ptr, end_info);
@@ -2461,6 +2514,7 @@ your application instead of by libpng, you can use
PNG_INFO_gAMA, PNG_INFO_sBIT,
PNG_INFO_cHRM, PNG_INFO_PLTE,
PNG_INFO_tRNS, PNG_INFO_bKGD,
PNG_INFO_eXIf,
PNG_INFO_hIST, PNG_INFO_pHYs,
PNG_INFO_oFFs, PNG_INFO_tIME,
PNG_INFO_pCAL, PNG_INFO_sRGB,
@@ -2496,7 +2550,7 @@ png_infop info_ptr;
user_error_fn, user_warning_fn);
if (!png_ptr)
return (ERROR);
return ERROR;
info_ptr = png_create_info_struct(png_ptr);
@@ -2504,14 +2558,14 @@ png_infop info_ptr;
{
png_destroy_read_struct(&png_ptr,
(png_infopp)NULL, (png_infopp)NULL);
return (ERROR);
return ERROR;
}
if (setjmp(png_jmpbuf(png_ptr)))
{
png_destroy_read_struct(&png_ptr, &info_ptr,
(png_infopp)NULL);
return (ERROR);
return ERROR;
}
/* This one's new. You can provide functions
@@ -2545,7 +2599,7 @@ png_infop info_ptr;
{
png_destroy_read_struct(&png_ptr, &info_ptr,
(png_infopp)NULL);
return (ERROR);
return ERROR;
}
/* This one's new also. Simply give it a chunk
@@ -2689,7 +2743,7 @@ custom writing functions. See the discussion under Customizing libpng.
FILE *fp = fopen(file_name, "wb");
if (!fp)
return (ERROR);
return ERROR;
Next, png_struct and png_info need to be allocated and initialized.
As these can be both relatively large, you may not want to store these
@@ -2704,14 +2758,14 @@ both "png_ptr"; you can call them anything you like, such as
user_error_fn, user_warning_fn);
if (!png_ptr)
return (ERROR);
return ERROR;
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr)
{
png_destroy_write_struct(&png_ptr,
(png_infopp)NULL);
return (ERROR);
return ERROR;
}
If you want to use your own memory allocation routines,
@@ -2738,7 +2792,7 @@ section below for more information on the libpng error handling.
{
png_destroy_write_struct(&png_ptr, &info_ptr);
fclose(fp);
return (ERROR);
return ERROR;
}
...
return;
@@ -3060,6 +3114,11 @@ width, height, bit_depth, and color_type must be the same in each call.
single transparent color for
non-paletted images (PNG_INFO_tRNS)
png_set_eXIf_1(png_ptr, info_ptr, num_exif, exif);
exif - Exif profile (array of
png_byte) (PNG_INFO_eXIf)
png_set_hIST(png_ptr, info_ptr, hist);
hist - histogram of palette (array of
@@ -3721,7 +3780,7 @@ in-memory bitmap formats or to be written from the same formats. If these
formats do not accommodate your needs then you can, and should, use the more
sophisticated APIs above - these support a wide variety of in-memory formats
and a wide variety of sophisticated transformations to those formats as well
as a wide variety of APIs to manipulate ancilliary information.
as a wide variety of APIs to manipulate ancillary information.
To read a PNG file using the simplified API:
@@ -3815,7 +3874,7 @@ PNG_FORMAT_FLAG_LINEAR flag below.
When the simplified API needs to convert between sRGB and linear colorspaces,
the actual sRGB transfer curve defined in the sRGB specification (see the
article at http://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
approximation used elsewhere in libpng.
When an alpha channel is present it is expected to denote pixel coverage
@@ -3997,7 +4056,7 @@ Flags containing additional information about the image are held in
the 'flags' field of png_image.
PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
This indicates the the RGB values of the in-memory bitmap do not
This indicates that the RGB values of the in-memory bitmap do not
correspond to the red, green and blue end-points defined by sRGB.
PNG_IMAGE_FLAG_FAST == 0x02
@@ -4044,7 +4103,7 @@ READ APIs
The PNG header is read from the stdio FILE object.
int png_image_begin_read_from_memory(png_imagep image,
png_const_voidp memory, png_size_t size)
png_const_voidp memory, size_t size)
The PNG header is read from the given memory buffer.
@@ -4079,7 +4138,7 @@ READ APIs
When the simplified API needs to convert between sRGB and linear colorspaces,
the actual sRGB transfer curve defined in the sRGB specification (see the
article at http://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
approximation used elsewhere in libpng.
WRITE APIS
@@ -4197,10 +4256,10 @@ png_get_io_ptr(). For example:
The replacement I/O functions must have prototypes as follows:
void user_read_data(png_structp png_ptr,
png_bytep data, png_size_t length);
png_bytep data, size_t length);
void user_write_data(png_structp png_ptr,
png_bytep data, png_size_t length);
png_bytep data, size_t length);
void user_flush_data(png_structp png_ptr);
@@ -4237,8 +4296,6 @@ functions after png_create_*_struct() has been called by calling:
png_voidp error_ptr, png_error_ptr error_fn,
png_error_ptr warning_fn);
png_voidp error_ptr = png_get_error_ptr(png_ptr);
If NULL is supplied for either error_fn or warning_fn, then the libpng
default function will be used, calling fprintf() and/or longjmp() if a
problem is encountered. The replacement error functions should have
@@ -4250,6 +4307,11 @@ parameters as follows:
void user_warning_fn(png_structp png_ptr,
png_const_charp warning_msg);
Then, within your user_error_fn or user_warning_fn, you can retrieve
the error_ptr if you need it, by calling
png_voidp error_ptr = png_get_error_ptr(png_ptr);
The motivation behind using setjmp() and longjmp() is the C++ throw and
catch exception handling methods. This makes the code much easier to write,
as there is no need to check every return code of every function call.
@@ -4257,7 +4319,7 @@ However, there are some uncertainties about the status of local variables
after a longjmp, so the user may want to be careful about doing anything
after setjmp returns non-zero besides returning itself. Consult your
compiler documentation for more details. For an alternative approach, you
may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net),
may wish to use the "cexcept" facility (see https://cexcept.sourceforge.io/),
which is illustrated in pngvalid.c and in contrib/visupng.
Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
@@ -4460,7 +4522,7 @@ 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.
@@ -4485,9 +4547,9 @@ in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
and the MHDR and MEND chunks. Libpng does not provide support for these
or any other MNG chunks; your application must provide its own support for
them. You may wish to consider using libmng (available at
http://www.libmng.com) instead.
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
@@ -4542,7 +4604,7 @@ 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(),
@@ -4639,7 +4701,7 @@ 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.
@@ -4723,7 +4785,7 @@ behavior in case the application runs out of memory part-way through
the process.
We changed the prototypes of png_get_compression_buffer_size() and
png_set_compression_buffer_size() to work with png_size_t instead of
png_set_compression_buffer_size() to work with size_t instead of
png_uint_32.
Support for numbered error messages was removed by default, since we
@@ -4749,7 +4811,7 @@ 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.
@@ -4812,7 +4874,7 @@ to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
There are changes of form in png.h, including new and changed macros to
declare parts of the API. Some API functions with arguments that are
pointers to data not modified within the function have been corrected to
declare these arguments with PNG_CONST.
declare these arguments with const.
Much of the internal use of C macros to control the library build has also
changed and some of this is visible in the exported header files, in
@@ -4908,18 +4970,14 @@ PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
that it could be used to override them. Now this function will reduce or
increase the limits.
Starting in libpng-1.5.10, the user limits can be set en masse with the
configuration option PNG_SAFE_LIMITS_SUPPORTED. If this option is enabled,
a set of "safe" limits is applied in pngpriv.h. These can be overridden by
application calls to png_set_user_limits(), png_set_user_chunk_cache_max(),
and/or png_set_user_malloc_max() that increase or decrease the limits. Also,
in libpng-1.5.10 the default width and height limits were increased
from 1,000,000 to 0x7fffffff (i.e., made unlimited). Therefore, the
limits are now
default safe
Starting in libpng-1.5.22, default user limits were established. These
can be overridden by application calls to png_set_user_limits(),
png_set_user_chunk_cache_max(), and/or png_set_user_malloc_max().
The limits are now
max possible default
png_user_width_max 0x7fffffff 1,000,000
png_user_height_max 0x7fffffff 1,000,000
png_user_chunk_cache_max 0 (unlimited) 128
png_user_chunk_cache_max 0 (unlimited) 1000
png_user_chunk_malloc_max 0 (unlimited) 8,000,000
The png_set_option() function (and the "options" member of the png struct) was
@@ -5011,7 +5069,7 @@ 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
@@ -5169,7 +5227,12 @@ is an error. Previously this requirement of the PNG specification was not
enforced, and the palette was always limited to 256 entries. An over-length
PLTE chunk found in an input PNG is silently truncated.
XIII. Detecting libpng
Starting with libpng-1.6.31, the eXIf chunk is supported. Libpng does not
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
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
@@ -5185,27 +5248,32 @@ control. The git repository was built from old libpng-x.y.z.tar.gz files
going back to version 0.70. You can access the git repository (read only)
at
git://git.code.sf.net/p/libpng/code
https://github.com/glennrp/libpng or
https://git.code.sf.net/p/libpng/code.git
or you can browse it with a web browser by selecting the "code" button at
or you can browse it with a web browser at
https://sourceforge.net/projects/libpng
https://github.com/glennrp/libpng or
https://sourceforge.net/p/libpng/code/ci/libpng16/tree/
Patches can be sent to glennrp at users.sourceforge.net or to
png-mng-implement at lists.sourceforge.net or you can upload them to
the libpng bug tracker at
Patches can be sent to png-mng-implement at lists.sourceforge.net or
uploaded to the libpng bug tracker at
http://libpng.sourceforge.net
https://libpng.sourceforge.io/
or as a "pull request" to
https://github.com/glennrp/libpng/pulls
We also accept patches built from the tar or zip distributions, and
simple verbal discriptions of bug fixes, reported either to the
simple verbal descriptions of bug fixes, reported either to the
SourceForge bug tracker, to the png-mng-implement at lists.sf.net
mailing list, or directly to glennrp.
mailing list, as github issues.
XV. Coding style
Our coding style is similar to the "Allman" style
(See http://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
(See https://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
braces on separate lines:
if (condition)
@@ -5221,7 +5289,7 @@ braces on separate lines:
The braces can be omitted from simple one-line actions:
if (condition)
return (0);
return 0;
We use 3-space indentation, except for continued statements which
are usually indented the same as the first line of the statement
@@ -5306,7 +5374,7 @@ Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
though it were a function.
Control keywords if, for, while, and switch are always followed by a space
to distinguish them from function calls, which have no trailing space.
to distinguish them from function calls, which have no trailing space.
We put a space after each comma and after each semicolon
in "for" statements, and we put spaces before and after each
@@ -5330,66 +5398,12 @@ with an even number of lower-case hex digits, and to make them unsigned
We prefer to use underscores rather than camelCase in names, except
for a few type names that we inherit from zlib.h.
We prefer "if (something != 0)" and "if (something == 0)"
over "if (something)" and if "(!something)", respectively.
We prefer "if (something != 0)" and "if (something == 0)" over
"if (something)" and if "(!something)", respectively, and for pointers
we prefer "if (some_pointer != NULL)" or "if (some_pointer == NULL)".
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 1.6.23 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