Imported from libpng-0.71.tar
This commit is contained in:
commit
0d5805822f
488
ansi2knr.c
Normal file
488
ansi2knr.c
Normal file
@ -0,0 +1,488 @@
|
||||
/* Copyright (C) 1989, 1991, 1993 Aladdin Enterprises. All rights reserved. */
|
||||
|
||||
/* ansi2knr.c */
|
||||
/* Convert ANSI function declarations to K&R syntax */
|
||||
|
||||
/*
|
||||
ansi2knr is distributed in the hope that it will be useful, but
|
||||
WITHOUT ANY WARRANTY. No author or distributor accepts responsibility
|
||||
to anyone for the consequences of using it or for whether it serves any
|
||||
particular purpose or works at all, unless he says so in writing. Refer
|
||||
to the GNU General Public License for full details.
|
||||
|
||||
Everyone is granted permission to copy, modify and redistribute
|
||||
ansi2knr, but only under the conditions described in the GNU
|
||||
General Public License. A copy of this license is supposed to have been
|
||||
given to you along with ansi2knr so you can know your rights and
|
||||
responsibilities. It should be in a file named COPYING. Among other
|
||||
things, the copyright notice and this notice must be preserved on all
|
||||
copies.
|
||||
*/
|
||||
|
||||
/*
|
||||
---------- Here is the GNU GPL file COPYING, referred to above ----------
|
||||
----- These terms do NOT apply to the JPEG software itself; see README ------
|
||||
|
||||
GHOSTSCRIPT GENERAL PUBLIC LICENSE
|
||||
(Clarified 11 Feb 1988)
|
||||
|
||||
Copyright (C) 1988 Richard M. Stallman
|
||||
Everyone is permitted to copy and distribute verbatim copies of this
|
||||
license, but changing it is not allowed. You can also use this wording
|
||||
to make the terms for other programs.
|
||||
|
||||
The license agreements of most software companies keep you at the
|
||||
mercy of those companies. By contrast, our general public license is
|
||||
intended to give everyone the right to share Ghostscript. To make sure
|
||||
that you get the rights we want you to have, we need to make
|
||||
restrictions that forbid anyone to deny you these rights or to ask you
|
||||
to surrender the rights. Hence this license agreement.
|
||||
|
||||
Specifically, we want to make sure that you have the right to give
|
||||
away copies of Ghostscript, that you receive source code or else can get
|
||||
it if you want it, that you can change Ghostscript or use pieces of it
|
||||
in new free programs, and that you know you can do these things.
|
||||
|
||||
To make sure that everyone has such rights, we have to forbid you to
|
||||
deprive anyone else of these rights. For example, if you distribute
|
||||
copies of Ghostscript, you must give the recipients all the rights that
|
||||
you have. You must make sure that they, too, receive or can get the
|
||||
source code. And you must tell them their rights.
|
||||
|
||||
Also, for our own protection, we must make certain that everyone finds
|
||||
out that there is no warranty for Ghostscript. If Ghostscript is
|
||||
modified by someone else and passed on, we want its recipients to know
|
||||
that what they have is not what we distributed, so that any problems
|
||||
introduced by others will not reflect on our reputation.
|
||||
|
||||
Therefore we (Richard M. Stallman and the Free Software Foundation,
|
||||
Inc.) make the following terms which say what you must do to be allowed
|
||||
to distribute or change Ghostscript.
|
||||
|
||||
|
||||
COPYING POLICIES
|
||||
|
||||
1. You may copy and distribute verbatim copies of Ghostscript source
|
||||
code as you receive it, in any medium, provided that you conspicuously
|
||||
and appropriately publish on each copy a valid copyright and license
|
||||
notice "Copyright (C) 1989 Aladdin Enterprises. All rights reserved.
|
||||
Distributed by Free Software Foundation, Inc." (or with whatever year is
|
||||
appropriate); keep intact the notices on all files that refer to this
|
||||
License Agreement and to the absence of any warranty; and give any other
|
||||
recipients of the Ghostscript program a copy of this License Agreement
|
||||
along with the program. You may charge a distribution fee for the
|
||||
physical act of transferring a copy.
|
||||
|
||||
2. You may modify your copy or copies of Ghostscript or any portion of
|
||||
it, and copy and distribute such modifications under the terms of
|
||||
Paragraph 1 above, provided that you also do the following:
|
||||
|
||||
a) cause the modified files to carry prominent notices stating
|
||||
that you changed the files and the date of any change; and
|
||||
|
||||
b) cause the whole of any work that you distribute or publish,
|
||||
that in whole or in part contains or is a derivative of Ghostscript
|
||||
or any part thereof, to be licensed at no charge to all third
|
||||
parties on terms identical to those contained in this License
|
||||
Agreement (except that you may choose to grant more extensive
|
||||
warranty protection to some or all third parties, at your option).
|
||||
|
||||
c) You may charge a distribution fee for the physical act of
|
||||
transferring a copy, and you may at your option offer warranty
|
||||
protection in exchange for a fee.
|
||||
|
||||
Mere aggregation of another unrelated program with this program (or its
|
||||
derivative) on a volume of a storage or distribution medium does not bring
|
||||
the other program under the scope of these terms.
|
||||
|
||||
3. You may copy and distribute Ghostscript (or a portion or derivative
|
||||
of it, under Paragraph 2) in object code or executable form under the
|
||||
terms of Paragraphs 1 and 2 above provided that you also do one of the
|
||||
following:
|
||||
|
||||
a) accompany it with the complete corresponding machine-readable
|
||||
source code, which must be distributed under the terms of
|
||||
Paragraphs 1 and 2 above; or,
|
||||
|
||||
b) accompany it with a written offer, valid for at least three
|
||||
years, to give any third party free (except for a nominal
|
||||
shipping charge) a complete machine-readable copy of the
|
||||
corresponding source code, to be distributed under the terms of
|
||||
Paragraphs 1 and 2 above; or,
|
||||
|
||||
c) accompany it with the information you received as to where the
|
||||
corresponding source code may be obtained. (This alternative is
|
||||
allowed only for noncommercial distribution and only if you
|
||||
received the program in object code or executable form alone.)
|
||||
|
||||
For an executable file, complete source code means all the source code for
|
||||
all modules it contains; but, as a special exception, it need not include
|
||||
source code for modules which are standard libraries that accompany the
|
||||
operating system on which the executable file runs.
|
||||
|
||||
4. You may not copy, sublicense, distribute or transfer Ghostscript
|
||||
except as expressly provided under this License Agreement. Any attempt
|
||||
otherwise to copy, sublicense, distribute or transfer Ghostscript is
|
||||
void and your rights to use the program under this License agreement
|
||||
shall be automatically terminated. However, parties who have received
|
||||
computer software programs from you with this License Agreement will not
|
||||
have their licenses terminated so long as such parties remain in full
|
||||
compliance.
|
||||
|
||||
5. If you wish to incorporate parts of Ghostscript into other free
|
||||
programs whose distribution conditions are different, write to the Free
|
||||
Software Foundation at 675 Mass Ave, Cambridge, MA 02139. We have not
|
||||
yet worked out a simple rule that can be stated here, but we will often
|
||||
permit this. We will be guided by the two goals of preserving the free
|
||||
status of all derivatives of our free software and of promoting the
|
||||
sharing and reuse of software.
|
||||
|
||||
Your comments and suggestions about our licensing policies and our
|
||||
software are welcome! Please contact the Free Software Foundation,
|
||||
Inc., 675 Mass Ave, Cambridge, MA 02139, or call (617) 876-3296.
|
||||
|
||||
NO WARRANTY
|
||||
|
||||
BECAUSE GHOSTSCRIPT IS LICENSED FREE OF CHARGE, WE PROVIDE ABSOLUTELY
|
||||
NO WARRANTY, TO THE EXTENT PERMITTED BY APPLICABLE STATE LAW. EXCEPT
|
||||
WHEN OTHERWISE STATED IN WRITING, FREE SOFTWARE FOUNDATION, INC, RICHARD
|
||||
M. STALLMAN, ALADDIN ENTERPRISES, L. PETER DEUTSCH, AND/OR OTHER PARTIES
|
||||
PROVIDE GHOSTSCRIPT "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER
|
||||
EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
|
||||
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE
|
||||
ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF GHOSTSCRIPT IS WITH
|
||||
YOU. SHOULD GHOSTSCRIPT PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
|
||||
NECESSARY SERVICING, REPAIR OR CORRECTION.
|
||||
|
||||
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW WILL RICHARD M.
|
||||
STALLMAN, THE FREE SOFTWARE FOUNDATION, INC., L. PETER DEUTSCH, ALADDIN
|
||||
ENTERPRISES, AND/OR ANY OTHER PARTY WHO MAY MODIFY AND REDISTRIBUTE
|
||||
GHOSTSCRIPT AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING
|
||||
ANY LOST PROFITS, LOST MONIES, OR OTHER SPECIAL, INCIDENTAL OR
|
||||
CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
|
||||
(INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED
|
||||
INACCURATE OR LOSSES SUSTAINED BY THIRD PARTIES OR A FAILURE OF THE
|
||||
PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS) GHOSTSCRIPT, EVEN IF YOU
|
||||
HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, OR FOR ANY CLAIM
|
||||
BY ANY OTHER PARTY.
|
||||
|
||||
-------------------- End of file COPYING ------------------------------
|
||||
*/
|
||||
|
||||
|
||||
#include <stdio.h>
|
||||
#include <ctype.h>
|
||||
|
||||
#ifdef BSD
|
||||
#include <strings.h>
|
||||
#else
|
||||
#ifdef VMS
|
||||
extern int strlen(), strncmp();
|
||||
#else
|
||||
#include <string.h>
|
||||
#endif
|
||||
#endif
|
||||
|
||||
/* malloc and free should be declared in stdlib.h, */
|
||||
/* but if you've got a K&R compiler, they probably aren't. */
|
||||
#ifdef MSDOS
|
||||
#include <malloc.h>
|
||||
#else
|
||||
#ifdef VMS
|
||||
extern char *malloc();
|
||||
extern void free();
|
||||
#else
|
||||
extern char *malloc();
|
||||
extern int free();
|
||||
#endif
|
||||
#endif
|
||||
|
||||
/* Usage:
|
||||
ansi2knr input_file [output_file]
|
||||
* If no output_file is supplied, output goes to stdout.
|
||||
* There are no error messages.
|
||||
*
|
||||
* ansi2knr recognizes functions by seeing a non-keyword identifier
|
||||
* at the left margin, followed by a left parenthesis,
|
||||
* with a right parenthesis as the last character on the line.
|
||||
* It will recognize a multi-line header provided that the last character
|
||||
* of the last line of the header is a right parenthesis,
|
||||
* and no intervening line ends with a left brace or a semicolon.
|
||||
* These algorithms ignore whitespace and comments, except that
|
||||
* the function name must be the first thing on the line.
|
||||
* The following constructs will confuse it:
|
||||
* - Any other construct that starts at the left margin and
|
||||
* follows the above syntax (such as a macro or function call).
|
||||
* - Macros that tinker with the syntax of the function header.
|
||||
*/
|
||||
|
||||
/* Scanning macros */
|
||||
#define isidchar(ch) (isalnum(ch) || (ch) == '_')
|
||||
#define isidfirstchar(ch) (isalpha(ch) || (ch) == '_')
|
||||
|
||||
/* Forward references */
|
||||
char *skipspace();
|
||||
int writeblanks();
|
||||
int test1();
|
||||
int convert1();
|
||||
|
||||
/* The main program */
|
||||
main(argc, argv)
|
||||
int argc;
|
||||
char *argv[];
|
||||
{ FILE *in, *out;
|
||||
#define bufsize 5000 /* arbitrary size */
|
||||
char *buf;
|
||||
char *line;
|
||||
switch ( argc )
|
||||
{
|
||||
default:
|
||||
printf("Usage: ansi2knr input_file [output_file]\n");
|
||||
exit(0);
|
||||
case 2:
|
||||
out = stdout; break;
|
||||
case 3:
|
||||
out = fopen(argv[2], "w");
|
||||
if ( out == NULL )
|
||||
{ fprintf(stderr, "Cannot open %s\n", argv[2]);
|
||||
exit(1);
|
||||
}
|
||||
}
|
||||
in = fopen(argv[1], "r");
|
||||
if ( in == NULL )
|
||||
{ fprintf(stderr, "Cannot open %s\n", argv[1]);
|
||||
exit(1);
|
||||
}
|
||||
fprintf(out, "#line 1 \"%s\"\n", argv[1]);
|
||||
buf = malloc(bufsize);
|
||||
line = buf;
|
||||
while ( fgets(line, (unsigned)(buf + bufsize - line), in) != NULL )
|
||||
{ switch ( test1(buf) )
|
||||
{
|
||||
case 1: /* a function */
|
||||
convert1(buf, out);
|
||||
break;
|
||||
case -1: /* maybe the start of a function */
|
||||
line = buf + strlen(buf);
|
||||
if ( line != buf + (bufsize - 1) ) /* overflow check */
|
||||
continue;
|
||||
/* falls through */
|
||||
default: /* not a function */
|
||||
fputs(buf, out);
|
||||
break;
|
||||
}
|
||||
line = buf;
|
||||
}
|
||||
if ( line != buf ) fputs(buf, out);
|
||||
free(buf);
|
||||
fclose(out);
|
||||
fclose(in);
|
||||
return 0;
|
||||
}
|
||||
|
||||
/* Skip over space and comments, in either direction. */
|
||||
char *
|
||||
skipspace(p, dir)
|
||||
register char *p;
|
||||
register int dir; /* 1 for forward, -1 for backward */
|
||||
{ for ( ; ; )
|
||||
{ while ( isspace(*p) ) p += dir;
|
||||
if ( !(*p == '/' && p[dir] == '*') ) break;
|
||||
p += dir; p += dir;
|
||||
while ( !(*p == '*' && p[dir] == '/') )
|
||||
{ if ( *p == 0 ) return p; /* multi-line comment?? */
|
||||
p += dir;
|
||||
}
|
||||
p += dir; p += dir;
|
||||
}
|
||||
return p;
|
||||
}
|
||||
|
||||
/*
|
||||
* Write blanks over part of a string.
|
||||
*/
|
||||
int
|
||||
writeblanks(start, end)
|
||||
char *start;
|
||||
char *end;
|
||||
{ char *p;
|
||||
for ( p = start; p < end; p++ ) *p = ' ';
|
||||
return 0;
|
||||
}
|
||||
|
||||
/*
|
||||
* Test whether the string in buf is a function definition.
|
||||
* The string may contain and/or end with a newline.
|
||||
* Return as follows:
|
||||
* 0 - definitely not a function definition;
|
||||
* 1 - definitely a function definition;
|
||||
* -1 - may be the beginning of a function definition,
|
||||
* append another line and look again.
|
||||
*/
|
||||
int
|
||||
test1(buf)
|
||||
char *buf;
|
||||
{ register char *p = buf;
|
||||
char *bend;
|
||||
char *endfn;
|
||||
int contin;
|
||||
if ( !isidfirstchar(*p) )
|
||||
return 0; /* no name at left margin */
|
||||
bend = skipspace(buf + strlen(buf) - 1, -1);
|
||||
switch ( *bend )
|
||||
{
|
||||
case ')': contin = 1; break;
|
||||
case '{':
|
||||
case ';': return 0; /* not a function */
|
||||
default: contin = -1;
|
||||
}
|
||||
while ( isidchar(*p) ) p++;
|
||||
endfn = p;
|
||||
p = skipspace(p, 1);
|
||||
if ( *p++ != '(' )
|
||||
return 0; /* not a function */
|
||||
p = skipspace(p, 1);
|
||||
if ( *p == ')' )
|
||||
return 0; /* no parameters */
|
||||
/* Check that the apparent function name isn't a keyword. */
|
||||
/* We only need to check for keywords that could be followed */
|
||||
/* by a left parenthesis (which, unfortunately, is most of them). */
|
||||
{ static char *words[] =
|
||||
{ "asm", "auto", "case", "char", "const", "double",
|
||||
"extern", "float", "for", "if", "int", "long",
|
||||
"register", "return", "short", "signed", "sizeof",
|
||||
"static", "switch", "typedef", "unsigned",
|
||||
"void", "volatile", "while", 0
|
||||
};
|
||||
char **key = words;
|
||||
char *kp;
|
||||
int len = endfn - buf;
|
||||
while ( (kp = *key) != 0 )
|
||||
{ if ( strlen(kp) == len && !strncmp(kp, buf, len) )
|
||||
return 0; /* name is a keyword */
|
||||
key++;
|
||||
}
|
||||
}
|
||||
return contin;
|
||||
}
|
||||
|
||||
int
|
||||
convert1(buf, out)
|
||||
char *buf;
|
||||
FILE *out;
|
||||
{ char *endfn;
|
||||
register char *p;
|
||||
char **breaks;
|
||||
unsigned num_breaks = 2; /* for testing */
|
||||
char **btop;
|
||||
char **bp;
|
||||
char **ap;
|
||||
/* Pre-ANSI implementations don't agree on whether strchr */
|
||||
/* is called strchr or index, so we open-code it here. */
|
||||
for ( endfn = buf; *(endfn++) != '('; ) ;
|
||||
top: p = endfn;
|
||||
breaks = (char **)malloc(sizeof(char *) * num_breaks * 2);
|
||||
if ( breaks == 0 )
|
||||
{ /* Couldn't allocate break table, give up */
|
||||
fprintf(stderr, "Unable to allocate break table!\n");
|
||||
fputs(buf, out);
|
||||
return -1;
|
||||
}
|
||||
btop = breaks + num_breaks * 2 - 2;
|
||||
bp = breaks;
|
||||
/* Parse the argument list */
|
||||
do
|
||||
{ int level = 0;
|
||||
char *end = NULL;
|
||||
if ( bp >= btop )
|
||||
{ /* Filled up break table. */
|
||||
/* Allocate a bigger one and start over. */
|
||||
free((char *)breaks);
|
||||
num_breaks <<= 1;
|
||||
goto top;
|
||||
}
|
||||
*bp++ = p;
|
||||
/* Find the end of the argument */
|
||||
for ( ; end == NULL; p++ )
|
||||
{ switch(*p)
|
||||
{
|
||||
case ',': if ( !level ) end = p; break;
|
||||
case '(': level++; break;
|
||||
case ')': if ( --level < 0 ) end = p; break;
|
||||
case '/': p = skipspace(p, 1) - 1; break;
|
||||
default: ;
|
||||
}
|
||||
}
|
||||
p--; /* back up over terminator */
|
||||
/* Find the name being declared. */
|
||||
/* This is complicated because of procedure and */
|
||||
/* array modifiers. */
|
||||
for ( ; ; )
|
||||
{ p = skipspace(p - 1, -1);
|
||||
switch ( *p )
|
||||
{
|
||||
case ']': /* skip array dimension(s) */
|
||||
case ')': /* skip procedure args OR name */
|
||||
{ int level = 1;
|
||||
while ( level )
|
||||
switch ( *--p )
|
||||
{
|
||||
case ']': case ')': level++; break;
|
||||
case '[': case '(': level--; break;
|
||||
case '/': p = skipspace(p, -1) + 1; break;
|
||||
default: ;
|
||||
}
|
||||
}
|
||||
if ( *p == '(' && *skipspace(p + 1, 1) == '*' )
|
||||
{ /* We found the name being declared */
|
||||
while ( !isidfirstchar(*p) )
|
||||
p = skipspace(p, 1) + 1;
|
||||
goto found;
|
||||
}
|
||||
break;
|
||||
default: goto found;
|
||||
}
|
||||
}
|
||||
found: if ( *p == '.' && p[-1] == '.' && p[-2] == '.' )
|
||||
{ p++;
|
||||
if ( bp == breaks + 1 ) /* sole argument */
|
||||
writeblanks(breaks[0], p);
|
||||
else
|
||||
writeblanks(bp[-1] - 1, p);
|
||||
bp--;
|
||||
}
|
||||
else
|
||||
{ while ( isidchar(*p) ) p--;
|
||||
*bp++ = p+1;
|
||||
}
|
||||
p = end;
|
||||
}
|
||||
while ( *p++ == ',' );
|
||||
*bp = p;
|
||||
/* Make a special check for 'void' arglist */
|
||||
if ( bp == breaks+2 )
|
||||
{ p = skipspace(breaks[0], 1);
|
||||
if ( !strncmp(p, "void", 4) )
|
||||
{ p = skipspace(p+4, 1);
|
||||
if ( p == breaks[2] - 1 )
|
||||
{ bp = breaks; /* yup, pretend arglist is empty */
|
||||
writeblanks(breaks[0], p + 1);
|
||||
}
|
||||
}
|
||||
}
|
||||
/* Put out the function name */
|
||||
p = buf;
|
||||
while ( p != endfn ) putc(*p, out), p++;
|
||||
/* Put out the declaration */
|
||||
for ( ap = breaks+1; ap < bp; ap += 2 )
|
||||
{ p = *ap;
|
||||
while ( isidchar(*p) ) putc(*p, out), p++;
|
||||
if ( ap < bp - 1 ) fputs(", ", out);
|
||||
}
|
||||
fputs(") ", out);
|
||||
/* Put out the argument declarations */
|
||||
for ( ap = breaks+2; ap <= bp; ap += 2 ) (*ap)[-1] = ';';
|
||||
fputs(breaks[0], out);
|
||||
free((char *)breaks);
|
||||
return 0;
|
||||
}
|
360
example.c
Normal file
360
example.c
Normal file
@ -0,0 +1,360 @@
|
||||
/* example.c - an example of using libpng */
|
||||
|
||||
/* this is an example of how to use libpng to read and write
|
||||
png files. The file libpng.txt is much more verbose then
|
||||
this. If you have not read it, do so first. This was
|
||||
designed to be a starting point of an implementation.
|
||||
This is not officially part of libpng, and therefore
|
||||
does not require a copyright notice.
|
||||
*/
|
||||
|
||||
#include <png.h>
|
||||
|
||||
/* check to see if a file is a png file using png_check_sig() */
|
||||
int check_png(char *file_name)
|
||||
{
|
||||
FILE *fp;
|
||||
char buf[8];
|
||||
int ret;
|
||||
|
||||
fp = fopen(file_name, "rb");
|
||||
if (!fp)
|
||||
return 0;
|
||||
ret = fread(buf, 1, 8, fp);
|
||||
fclose(fp);
|
||||
|
||||
if (ret != 8)
|
||||
return 0;
|
||||
|
||||
ret = png_check_sig(buf, 8);
|
||||
|
||||
return (ret);
|
||||
}
|
||||
|
||||
/* read a png file. You may want to return an error code if the read
|
||||
fails (depending upon the failure). */
|
||||
void read_png(char *file_name)
|
||||
{
|
||||
FILE *fp;
|
||||
png_struct *png_ptr;
|
||||
png_info *info_ptr;
|
||||
|
||||
/* open the file */
|
||||
fp = fopen(file_name, "rb");
|
||||
if (!fp)
|
||||
return;
|
||||
|
||||
/* allocate the necessary structures */
|
||||
png_ptr = malloc(sizeof (png_struct));
|
||||
if (!png_ptr)
|
||||
{
|
||||
fclose(fp);
|
||||
return;
|
||||
}
|
||||
|
||||
info_ptr = malloc(sizeof (png_info));
|
||||
if (!info_ptr)
|
||||
{
|
||||
fclose(fp);
|
||||
free(png_ptr);
|
||||
return;
|
||||
}
|
||||
|
||||
/* set error handling */
|
||||
if (setjmp(png_ptr->jmpbuf))
|
||||
{
|
||||
png_read_destroy(png_ptr, info_ptr, (png_info *)0);
|
||||
fclose(fp);
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
/* If we get here, we had a problem reading the file */
|
||||
return;
|
||||
}
|
||||
|
||||
/* initialize the structures, info first for error handling */
|
||||
png_info_init(info_ptr);
|
||||
png_read_init(png_ptr);
|
||||
|
||||
/* set up the input control */
|
||||
png_init_io(png_ptr, fp);
|
||||
|
||||
/* read the file information */
|
||||
png_read_info(png_ptr, info_ptr);
|
||||
|
||||
/* allocate the memory to hold the image using the fields
|
||||
of png_info. */
|
||||
|
||||
/* set up the transformations you want. Note that these are
|
||||
all optional. Only call them if you want them */
|
||||
|
||||
/* expand paletted colors into true rgb */
|
||||
if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
|
||||
info_ptr->bit_depth < 8)
|
||||
png_set_expand(png_ptr);
|
||||
|
||||
/* expand grayscale images to the full 8 bits */
|
||||
if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY &&
|
||||
info_ptr->bit_depth < 8)
|
||||
png_set_expand(png_ptr);
|
||||
|
||||
/* expand images with transparency to full alpha channels */
|
||||
if (info_ptr->valid & PNG_INFO_tRNS)
|
||||
png_set_expand(png_ptr);
|
||||
|
||||
/* Set the background color to draw transparent and alpha
|
||||
images over */
|
||||
png_color_16 my_background;
|
||||
|
||||
if (info_ptr->valid & PNG_INFO_bKGD)
|
||||
png_set_background(png_ptr, &(info_ptr->background),
|
||||
PNG_GAMMA_FILE, 1, 1.0);
|
||||
else
|
||||
png_set_background(png_ptr, &my_background,
|
||||
PNG_GAMMA_SCREEN, 0, 1.0);
|
||||
|
||||
/* tell libpng to handle the gamma conversion for you */
|
||||
if (info_ptr->valid & PNG_INFO_gAMA)
|
||||
png_set_gamma(png_ptr, screen_gamma, info_ptr->gamma);
|
||||
else
|
||||
png_set_gamma(png_ptr, screen_gamma, 0.45);
|
||||
|
||||
/* tell libpng to strip 16 bit depth files down to 8 bits */
|
||||
if (info_ptr->bit_depth == 16)
|
||||
png_set_strip_16(png_ptr);
|
||||
|
||||
/* dither rgb files down to 8 bit palettes & reduce palettes
|
||||
to the number of colors available on your screen */
|
||||
if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
|
||||
{
|
||||
if (info_ptr->valid & PNG_INFO_PLTE)
|
||||
png_set_dither(png_ptr, info_ptr->palette,
|
||||
info_ptr->num_palette, max_screen_colors,
|
||||
info_ptr->histogram);
|
||||
else
|
||||
{
|
||||
png_color std_color_cube[MAX_SCREEN_COLORS] =
|
||||
{/* ... colors ... */};
|
||||
|
||||
png_set_dither(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
|
||||
MAX_SCREEN_COLORS, NULL);
|
||||
}
|
||||
}
|
||||
|
||||
/* invert monocrome files */
|
||||
if (info_ptr->bit_depth == 1 &&
|
||||
info_ptr->color_type == PNG_COLOR_GRAY)
|
||||
png_set_invert(png_ptr);
|
||||
|
||||
/* shift the pixels down to their true bit depth */
|
||||
if (info_ptr->valid & PNG_INFO_sBIT &&
|
||||
info_ptr->bit_depth > info_ptr->sig_bit)
|
||||
png_set_shift(png_ptr, &(info_ptr->sig_bit));
|
||||
|
||||
/* pack pixels into bytes */
|
||||
if (info_ptr->bit_depth < 8)
|
||||
png_set_packing(png_ptr);
|
||||
|
||||
/* flip the rgb pixels to bgr */
|
||||
if (info_ptr->color_type == PNG_COLOR_TYPE_RGB ||
|
||||
info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
||||
png_set_bgr(png_ptr);
|
||||
|
||||
/* swap bytes of 16 bit files to least significant bit first */
|
||||
if (info_ptr->bit_depth == 16)
|
||||
png_set_swap(png_ptr);
|
||||
|
||||
/* add a filler byte to store rgb files as rgbx */
|
||||
if (info_ptr->bit_depth == 8 &&
|
||||
info_ptr->color_type == PNG_COLOR_TYPE_RGB)
|
||||
png_set_rgbx(png_ptr);
|
||||
|
||||
/* optional call to update palette with transformations */
|
||||
png_start_read_image(png_ptr);
|
||||
|
||||
/* the easiest way to read the image */
|
||||
void *row_pointers[height];
|
||||
png_read_image(png_ptr, row_pointers);
|
||||
|
||||
/* the other way to read images - deal with interlacing */
|
||||
|
||||
/* turn on interlace handling */
|
||||
if (info_ptr->interlace_type)
|
||||
number_passes = png_set_interlace_handling(png_ptr);
|
||||
else
|
||||
number_passes = 1;
|
||||
|
||||
for (pass = 0; pass < number_passes; pass++)
|
||||
{
|
||||
/* Read the image using the "sparkle" effect. */
|
||||
png_read_rows(png_ptr, row_pointers, NULL, number_of_rows);
|
||||
|
||||
/* If you are only reading on row at a time, this works */
|
||||
for (y = 0; y < height; y++)
|
||||
{
|
||||
char *row_pointers = row[y];
|
||||
png_read_rows(png_ptr, &row_pointers, NULL, 1);
|
||||
}
|
||||
|
||||
/* to get the rectangle effect, use the third parameter */
|
||||
png_read_rows(png_ptr, NULL, row_pointers, number_of_rows);
|
||||
|
||||
/* if you want to display the image after every pass, do
|
||||
so here */
|
||||
}
|
||||
|
||||
/* read the rest of the file, getting any additional chunks
|
||||
in info_ptr */
|
||||
png_read_end(png_ptr, info_ptr);
|
||||
|
||||
/* clean up after the read, and free any memory allocated */
|
||||
png_read_destroy(png_ptr, info_ptr, (png_info *)0);
|
||||
|
||||
/* free the structures */
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
|
||||
/* close the file */
|
||||
fclose(fp);
|
||||
|
||||
/* that's it */
|
||||
return;
|
||||
}
|
||||
|
||||
/* write a png file */
|
||||
void write_png(char *file_name, ... other image information ...)
|
||||
{
|
||||
FILE *fp;
|
||||
png_struct *png_ptr;
|
||||
png_info *info_ptr;
|
||||
|
||||
/* open the file */
|
||||
fp = fopen(file_name, "wb");
|
||||
if (!fp)
|
||||
return;
|
||||
|
||||
/* allocate the necessary structures */
|
||||
png_ptr = malloc(sizeof (png_struct));
|
||||
if (!png_ptr)
|
||||
{
|
||||
fclose(fp);
|
||||
return;
|
||||
}
|
||||
|
||||
info_ptr = malloc(sizeof (png_info));
|
||||
if (!info_ptr)
|
||||
{
|
||||
fclose(fp);
|
||||
free(png_ptr);
|
||||
return;
|
||||
}
|
||||
|
||||
/* set error handling */
|
||||
if (setjmp(png_ptr->jmpbuf))
|
||||
{
|
||||
png_write_destroy(png_ptr);
|
||||
fclose(fp);
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
/* If we get here, we had a problem reading the file */
|
||||
return;
|
||||
}
|
||||
|
||||
/* initialize the structures */
|
||||
png_info_init(info_ptr);
|
||||
png_write_init(png_ptr);
|
||||
|
||||
/* set up the output control */
|
||||
png_init_io(png_ptr, fp);
|
||||
|
||||
/* set the file information here */
|
||||
info_ptr->width = ;
|
||||
info_ptr->height = ;
|
||||
etc.
|
||||
|
||||
/* set the palette if there is one */
|
||||
info_ptr->valid |= PNG_INFO_PLTE;
|
||||
info_ptr->palette = malloc(256 * sizeof (png_color));
|
||||
info_ptr->num_palette = 256;
|
||||
... set palette colors ...
|
||||
|
||||
/* optional significant bit chunk */
|
||||
info_ptr->valid |= PNG_INFO_sBIT;
|
||||
info_ptr->sig_bit = true_bit_depth;
|
||||
|
||||
/* optional gamma chunk */
|
||||
info_ptr->valid |= PNG_INFO_gAMA;
|
||||
info_ptr->gamma = gamma;
|
||||
|
||||
/* other optional chunks */
|
||||
|
||||
/* write the file information */
|
||||
png_write_info(png_ptr, info_ptr);
|
||||
|
||||
/* set up the transformations you want. Note that these are
|
||||
all optional. Only call them if you want them */
|
||||
|
||||
/* invert monocrome pixels */
|
||||
png_set_invert(png_ptr);
|
||||
|
||||
/* shift the pixels up to a legal bit depth and fill in
|
||||
as appropriate to correctly scale the image */
|
||||
png_set_shift(png_ptr, &(info_ptr->sig_bit));
|
||||
|
||||
/* pack pixels into bytes */
|
||||
png_set_packing(png_ptr);
|
||||
|
||||
/* flip bgr pixels to rgb */
|
||||
png_set_bgr(png_ptr);
|
||||
|
||||
/* swap bytes of 16 bit files to most significant bit first */
|
||||
png_set_swap(png_ptr);
|
||||
|
||||
/* get rid of filler bytes, pack rgb into 3 bytes */
|
||||
png_set_rgbx(png_ptr);
|
||||
|
||||
/* the easiest way to write the image */
|
||||
void *row_pointers[height];
|
||||
png_write_image(png_ptr, row_pointers);
|
||||
|
||||
/* the other way to write the image - deal with interlacing */
|
||||
|
||||
/* turn on interlace handling */
|
||||
if (interlacing)
|
||||
number_passes = png_set_interlace_handling(png_ptr);
|
||||
else
|
||||
number_passes = 1;
|
||||
|
||||
for (pass = 0; pass < number_passes; pass++)
|
||||
{
|
||||
/* Write a few rows at a time. */
|
||||
png_write_rows(png_ptr, row_pointers, number_of_rows);
|
||||
|
||||
/* If you are only writing one row at a time, this works */
|
||||
for (y = 0; y < height; y++)
|
||||
{
|
||||
char *row_pointers = row[y];
|
||||
png_write_rows(png_ptr, &row_pointers, 1);
|
||||
}
|
||||
}
|
||||
|
||||
/* write the rest of the file */
|
||||
png_write_end(png_ptr, info_ptr);
|
||||
|
||||
/* clean up after the write, and free any memory allocated */
|
||||
png_write_destroy(png_ptr);
|
||||
|
||||
/* if you malloced the palette, free it here */
|
||||
if (info_ptr->palette)
|
||||
free(info_ptr->palette);
|
||||
|
||||
/* free the structures */
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
|
||||
/* close the file */
|
||||
fclose(fp);
|
||||
|
||||
/* that's it */
|
||||
return;
|
||||
}
|
||||
|
821
libpng.txt
Normal file
821
libpng.txt
Normal file
@ -0,0 +1,821 @@
|
||||
libpng.txt - a description on how to use and modify libpng
|
||||
|
||||
libpng 1.0 beta 1 - version 0.71
|
||||
For conditions of distribution and use, see copyright notice in png.h
|
||||
Copyright (c) 1995 Guy Eric Schalnat, Group 42, Inc.
|
||||
June 26, 1995
|
||||
|
||||
This file describes how to use and modify the PNG reference library
|
||||
(known as libpng) for your own use. There are four sections to this
|
||||
file: reading, writing, modifying, and configuration notes for various
|
||||
special platforms. Other then this file, the 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.
|
||||
|
||||
Libpng was written as a companion to the PNG specification, as a
|
||||
way to reduce the amount of time and effort it takes to support
|
||||
the PNG file format in application programs. Most users will not
|
||||
have to modify the library significantly; advanced users may want
|
||||
to modify it more. The library was coded for both users. All
|
||||
attempts were made to make it as complete as possible, while
|
||||
keeping the code easy to understand. Currently, this library
|
||||
only supports C. Support for other languages is being considered.
|
||||
|
||||
Libpng has been designed to handle multiple sessions at one time,
|
||||
to be easily modifiable, to be portable to the vast majority of
|
||||
machines (ANSI, K&R, 16 bit, 32 bit) available, and to be easy to
|
||||
use. The ultimate goal of libpng is to promote the acceptance of
|
||||
the PNG file format in whatever way possible. While there is still
|
||||
work to be done (see the todo.txt file), libpng should cover the
|
||||
majority of the needs of it's users.
|
||||
|
||||
Libpng uses zlib for its compression and decompression of PNG files.
|
||||
The zlib compression utility is a general purpose utility that is
|
||||
useful for more then PNG files, and can be used without libpng for
|
||||
whatever use you want. See the documentation delivered with zlib for
|
||||
more details.
|
||||
|
||||
Those people who do not need to modify libpng should still read at
|
||||
least part of the PNG specification. The most important parts are
|
||||
the data formats and the chunk descriptions. Those who will be
|
||||
making changes to libpng should read the whole specification.
|
||||
|
||||
The structures:
|
||||
|
||||
There are two main structures that are important to libpng, png_struct
|
||||
and png_info. The first, png_struct, is an internal structure that
|
||||
will not, for the most part, be used by the general user except as
|
||||
the first variable passed to every png function call.
|
||||
|
||||
The png_info structure is designed to provide information about the
|
||||
png file. All of it's fields are intended to be examined or modified
|
||||
by the user. See png.h for a good description of the png_info fields.
|
||||
|
||||
And while I'm on the topic, make sure you include the png header file:
|
||||
|
||||
#include <png.h>
|
||||
|
||||
Checking PNG files:
|
||||
|
||||
Libpng provides a simple check to see if a file is a png file. To
|
||||
use it, pass in the first 1 to 8 bytes of the file, and it will return
|
||||
true or false (1 or 0) depending on whether the bytes could be part
|
||||
of a png file. Of course, the more bytes you pass in, the greater
|
||||
the accuracy of the prediction.
|
||||
|
||||
fread(header, 1, number, fp);
|
||||
is_png = png_check_sig(header, number);
|
||||
|
||||
Reading PNG files:
|
||||
|
||||
The first thing you need to do while reading a PNG file is to allocate
|
||||
and initialize png_struct and png_info. As these are both large, you
|
||||
may not want to store these on the stack, unless you have stack space
|
||||
to spare. Of course, you will want to check if malloc returns NULL.
|
||||
|
||||
png_struct *png_ptr = malloc(sizeof (png_struct));
|
||||
if (!png_ptr)
|
||||
return;
|
||||
png_info *info_ptr = malloc(sizeof (png_info));
|
||||
if (!info_ptr)
|
||||
{
|
||||
free(png_ptr);
|
||||
return;
|
||||
}
|
||||
|
||||
You may also want to do any i/o initialization here, before
|
||||
you get into libpng, so if it doesn't work, you don't have
|
||||
much to undo.
|
||||
|
||||
FILE *fp = fopen(file_name, "rb");
|
||||
if (!fp)
|
||||
{
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
return;
|
||||
}
|
||||
|
||||
After you have these structures, you will need to set up the
|
||||
error handling. When libpng encounters an error, it expects to
|
||||
longjmp back to your routine. Therefore, you will need to call
|
||||
setjmp and pass the jmpbuf field of your png_struct. If you
|
||||
read the file from different routines, you will need to update
|
||||
the jmpbuf field every time you enter a new routine that will
|
||||
call a png_ function. See your documentation of setjmp/longjmp
|
||||
for your compiler for more information on setjmp/longjmp. See
|
||||
the discussion on png error handling in the Customizing Libpng
|
||||
section below for more information on the png error handling.
|
||||
If an error occurs, and libpng longjmp's back to your setjmp,
|
||||
you will want to call png_read_destroy() to free any memory.
|
||||
|
||||
if (setjmp(png_ptr->jmpbuf))
|
||||
{
|
||||
png_read_destroy(png_ptr, info_ptr, (png_info *)0);
|
||||
/* free pointers before returning, if necessary */
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
fclose(fp);
|
||||
return;
|
||||
}
|
||||
|
||||
Next, you will need to call png_read_init() and png_info_init().
|
||||
These functions make sure all the fields are initialized to useful
|
||||
values, and, in the case of png_read_init(), and allocate any memory
|
||||
needed for internal uses. You must call png_info_init() first, as
|
||||
png_read_init() could do a longjmp, and if the info is not initialized,
|
||||
the png_read_destroy() could try to png_free() random addresses, which
|
||||
would be bad.
|
||||
|
||||
png_info_init(info_ptr);
|
||||
png_read_init(png_ptr);
|
||||
|
||||
Now you need to set up the input code. The default for libpng is
|
||||
to use the C function fread(). If you use this, you will need to
|
||||
pass a valid FILE * in the function png_init_io(). Be sure that
|
||||
the file is opened in binary mode. If you wish to handle reading
|
||||
data in another way, see the discussion on png i/o handling in the
|
||||
Customizing Libpng section below.
|
||||
|
||||
png_init_io(png_ptr, fp);
|
||||
|
||||
You are now ready to read all the file information up to the actual
|
||||
image data. You do this with a call to png_read_info().
|
||||
|
||||
png_read_info(png_ptr, info_ptr);
|
||||
|
||||
The png_info structure is now filled in with all the data necessary
|
||||
to read the file. Some of the more important parts of the png_info are:
|
||||
width - holds the width of the file
|
||||
height - holds the height of the file
|
||||
bit_depth - holds the bit depth of one of the image channels
|
||||
color_type - describes the channels and what they mean
|
||||
see the PNG_COLOR_TYPE_ macros for more information
|
||||
channels - number of channels of info for the color type
|
||||
pixel_depth - bits per pixel
|
||||
rowbytes - number of bytes needed to hold a row
|
||||
interlace_type - currently 0 for none, 1 for interlaced
|
||||
valid - this details which optional chunks were found in the file
|
||||
to see if a chunk was present, OR valid with the appropriate
|
||||
PNG_INFO_<chunk name> define.
|
||||
palette and num_palette - the palette for the file
|
||||
gamma - the gamma the file is written at
|
||||
sig_bit and sig_bit_number - the number of significant bits
|
||||
trans, trans_values, and number_trans - transparency info
|
||||
hist - histogram of palette
|
||||
text and num_text - text comments in the file.
|
||||
for more information, see the png_info definition in png.h and the
|
||||
PNG specification for chunk contents. Be careful with trusting
|
||||
rowbytes, as some of the transformations could increase the space
|
||||
needed to hold a row (expand, rgbx, xrgb, graph_to_rgb, etc.).
|
||||
|
||||
A quick word about text and num_text. PNG stores comments in
|
||||
keyword/text pairs, one pair per chunk. While there are
|
||||
suggested keywords, there is no requirement to restrict the use
|
||||
to these strings. There is a requirement to have at least one
|
||||
character for a keyword. It is strongly suggested that keywords
|
||||
be sensible to humans (that's the point), so don't use abbreviations.
|
||||
See the png specification for more details. There is no requirement
|
||||
to have text after the keyword on tEXt chunks. However, you must
|
||||
have text after the keyword on zTXt chunks, as only the text gets
|
||||
compressed, and compressing nothing will result in an error.
|
||||
|
||||
There is no maximum length on the keyword, and nothing
|
||||
prevents you from duplicating the keyword. The text field is an
|
||||
array of png_text structures, each holding pointer to a keyword
|
||||
and a pointer to a text string. Only the text string may be null.
|
||||
The keyword/text pairs are put into the array in the order that
|
||||
they are received. However, some or all of the text chunks may be
|
||||
after the image, so to make sure you have read all the text chunks,
|
||||
don't mess with these until after you read the stuff after the image.
|
||||
This will be mentioned again below in the discussion that goes with
|
||||
png_read_end().
|
||||
|
||||
After you've read the file information, you can set up the library to
|
||||
handle any special transformations of the image data. The various
|
||||
ways to transform the data will be described in the order that they
|
||||
occur. This is important, as some of these change the color type
|
||||
and bit depth of the data, and some others only work on certain
|
||||
color types and bit depths. Even though each transformation should
|
||||
check to see if it has data that it can do somthing with, you should
|
||||
make sure to only enable a transformation if it will be valid for
|
||||
the data. For example, don't swap red and blue on grayscale data.
|
||||
|
||||
This transforms bit depths of less then 8 to 8 bits, changes paletted
|
||||
images to rgb, and adds an alpha channel if there is transparency
|
||||
information in a tRNS chunk. This is probably most useful on grayscale
|
||||
images with bit depths of 2 or 4 and tRNS chunks.
|
||||
|
||||
if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
|
||||
info_ptr->bit_depth < 8)
|
||||
png_set_expand(png_ptr);
|
||||
|
||||
if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY &&
|
||||
info_ptr->bit_depth < 8)
|
||||
png_set_expand(png_ptr);
|
||||
|
||||
if (info_ptr->valid & PNG_INFO_tRNS)
|
||||
png_set_expand(png_ptr);
|
||||
|
||||
This handles alpha and transparency by replacing it with a background
|
||||
value. If there was a valid one in the file, you can use it if you
|
||||
want. However, you can replace it with your own if you want also. If
|
||||
there wasn't one in the file, you must supply a color. If libpng is
|
||||
doing gamma correction, you will need to tell libpng where the
|
||||
background came from so it can do the appropriate gamma correction.
|
||||
If you are modifying the color data with png_set_expand(), you must
|
||||
indicate whether the background needs to be expanded. See the
|
||||
function definition in png.h for more details.
|
||||
|
||||
png_color_16 my_background;
|
||||
|
||||
if (info_ptr->valid & PNG_INFO_bKGD)
|
||||
png_set_backgrond(png_ptr, &(info_ptr->background),
|
||||
PNG_GAMMA_FILE, 1, 1.0);
|
||||
else
|
||||
png_set_background(png_ptr, &my_background,
|
||||
PNG_GAMMA_SCREEN, 0, 1.0);
|
||||
|
||||
This handles gamma transformations of the data. Pass both the file
|
||||
gamma and the desired screen gamma. If the file does not have a
|
||||
gamma value, you can pass one anyway if you wish. Note that file
|
||||
gammas are inverted from screen gammas. See the discussions on
|
||||
gamma in the PNG specification for more information.
|
||||
|
||||
if (info_ptr->valid & PNG_INFO_gAMA)
|
||||
png_set_gamma(png_ptr, screen_gamma, info_ptr->gamma);
|
||||
else
|
||||
png_set_gamma(png_ptr, screen_gamma, 0.45);
|
||||
|
||||
PNG can have files with 16 bits per channel. If you only can handle
|
||||
8 bits per channel, this will strip the pixels down to 8 bit.
|
||||
|
||||
if (info_ptr->bit_depth == 16)
|
||||
png_set_strip_16(png_ptr);
|
||||
|
||||
If you need to reduce an rgb file to a paletted file, or if a
|
||||
paletted file has more entries then will fit on your screen, this
|
||||
function will do that. Note that this is a simple match dither, that
|
||||
merely finds the closest color available. This should work fairly
|
||||
well with optimized palettes, and fairly badly with linear color
|
||||
cubes. If you pass a palette that is larger then maximum_colors,
|
||||
the file will reduce the number of colors in the palette so it
|
||||
will fit into maximum_colors. If there is an histogram, it will
|
||||
use it to make intelligent choises when reducing the palette. If
|
||||
there is no histogram, it may not do a good job.
|
||||
|
||||
if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
|
||||
{
|
||||
if (info_ptr->valid & PNG_INFO_PLTE)
|
||||
png_set_dither(png_ptr, info_ptr->palette,
|
||||
info_ptr->num_palette, max_screen_colors,
|
||||
info_ptr->histogram);
|
||||
else
|
||||
{
|
||||
png_color std_color_cube[MAX_SCREEN_COLORS] =
|
||||
{ ... colors ... };
|
||||
|
||||
png_set_dither(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
|
||||
MAX_SCREEN_COLORS, NULL);
|
||||
}
|
||||
}
|
||||
|
||||
PNG files describe monocrome as black is zero and white is one. If you
|
||||
want this reversed (black is one and white is zero), call this:
|
||||
|
||||
if (info_ptr->bit_depth == 1 &&
|
||||
info_ptr->color_type == PNG_COLOR_GRAY)
|
||||
png_set_invert(png_ptr);
|
||||
|
||||
PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. However,
|
||||
they also provide a way to describe the true bit depth of the image.
|
||||
Then they require bits to be scaled to full range for the bit depth
|
||||
used in the file. If you want to reduce your pixels back down to
|
||||
the true bit depth, call this:
|
||||
|
||||
if (info_ptr->valid & PNG_INFO_sBIT)
|
||||
png_set_shift(png_ptr, &(info_ptr->sig_bit));
|
||||
|
||||
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
||||
they can, resulting in, for example, 8 pixels per byte for 1 bit files.
|
||||
If you would rather these were expanded to 1 pixel per byte without
|
||||
changing the values of the pixels, call this:
|
||||
|
||||
if (info_ptr->bit_depth < 8)
|
||||
png_set_packing(png_ptr);
|
||||
|
||||
PNG files store 3 color pixels in red, green, blue order. If you would
|
||||
rather have the pixels as blue, green, red, call this.
|
||||
|
||||
if (info_ptr->color_type == PNG_COLOR_TYPE_RGB ||
|
||||
info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
||||
png_set_bgr(png_ptr);
|
||||
|
||||
For some uses, you may want a grayscale image to be represented as
|
||||
rgb. If you need this, call this:
|
||||
|
||||
if (info_ptr->color_type == PNG_COLOR_TYPE_GRAY ||
|
||||
info_ptr->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
||||
png_set_gray_to_rgb(png_ptr);
|
||||
|
||||
PNG files store 16 bit pixels in network byte order (most significant
|
||||
bit first). If you would rather store them the other way, (the way
|
||||
PC's store them, for example), call this:
|
||||
|
||||
if (info_ptr->bit_depth == 16)
|
||||
png_set_swap(png_ptr);
|
||||
|
||||
PNG files store rgb pixels packed into 3 bytes. If you would rather
|
||||
pack them into 4 bytes, with the filler byte last, call this:
|
||||
|
||||
if (info_ptr->bit_depth == 8 &&
|
||||
info_ptr->color_type == PNG_COLOR_TYPE_RGB)
|
||||
png_set_rgbx(png_ptr);
|
||||
|
||||
If you need the filler byte first, call this:
|
||||
|
||||
if (info_ptr->bit_depth == 8 &&
|
||||
info_ptr->color_type == PNG_COLOR_TYPE_RGB)
|
||||
png_set_xrgb(png_ptr);
|
||||
|
||||
After setting the transformations, you can update your palette by
|
||||
calling png_start_read_image(). This function is provided for those
|
||||
who need an updated palette before they read the image data. If you
|
||||
don't call this function, the library will automatically call it
|
||||
before it reads the first row.
|
||||
|
||||
png_start_read_image(png_ptr);
|
||||
|
||||
That's it for the transformations. Now you can read the image data.
|
||||
The simplest way to do this is in one function call. If you are
|
||||
allocating enough memory to hold the whole image, you can just
|
||||
call png_read_image() and libpng will read in all the image data
|
||||
and put it in the memory area supplied. You will need to pass in
|
||||
an array of pointers to each row.
|
||||
|
||||
This function automatically handles interlacing, so you don't need
|
||||
to call png_set_interlace_handling() or call this function multiple
|
||||
times, or any of that other stuff necessary with png_read_rows().
|
||||
|
||||
png_read_image(png_ptr, row_pointers);
|
||||
|
||||
where row_pointers is:
|
||||
|
||||
void *row_pointers[height];
|
||||
|
||||
You can point to void or char or whatever you use for pixels.
|
||||
|
||||
If you don't want to read the whole image in at once, you can
|
||||
use png_read_rows() instead. If there is no interlacing (check
|
||||
info_ptr->interlace_type), this is simple:
|
||||
|
||||
png_read_rows(png_ptr, row_pointers, NULL, number_of_rows);
|
||||
|
||||
row_pointers is the same as in the png_read_image() call.
|
||||
|
||||
If you are just calling one row at a time, you can do this for
|
||||
row_pointers:
|
||||
|
||||
char *row_pointers = row;
|
||||
|
||||
png_read_rows(png_ptr, &row_pointers, NULL, 1);
|
||||
|
||||
When the file is interlaced (info_ptr->interlace_type == 1), things
|
||||
get a good deal harder. PNG files have a complicated interlace scheme
|
||||
that breaks down an image into seven smaller images of varying size.
|
||||
Libpng will fill out those images if you want, or it will give them
|
||||
to you "as is". If you want to fill them out, there is two ways
|
||||
to do that. The one mentioned in the PNG specification is to expand
|
||||
each pixel to cover those pixels that have not been read yet. This
|
||||
results in a blocky image for the first pass, which gradually smooths
|
||||
out as more pixels are read. The other method is the "sparkle" method,
|
||||
where pixels are draw only in their final locations, with the rest of
|
||||
the image remaining whatever colors they were initialized to before
|
||||
the start of the read. The first method usually looks better, but
|
||||
tends to be slower, as there are more pixels to put in the rows. Some
|
||||
examples to help clear this up:
|
||||
|
||||
If you don't want libpng to handle the interlacing details, just
|
||||
call png_read_rows() the correct number of times to read in all
|
||||
seven images. See the PNG specification for more details on the
|
||||
interlacing scheme.
|
||||
|
||||
If you want libpng to expand the images, call this:
|
||||
|
||||
if (info_ptr->interlace_type)
|
||||
number_passes = png_set_interlace_handling(png_ptr);
|
||||
|
||||
This will return the number of passes needed. Currently, this
|
||||
is seven, but may change if another interlace type is added.
|
||||
This function can be called even if the file is not interlaced,
|
||||
when it will return one.
|
||||
|
||||
If you are not going to display the image after each pass, but are
|
||||
going to wait until the entire image is read in, use the sparkle
|
||||
effect. This effect is faster and the end result of either method
|
||||
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
|
||||
normal, with the third parameter NULL. Make sure you make pass over
|
||||
the image number_passes times, and you don't change the data in the
|
||||
rows between calls. You can change the locations of the data, just
|
||||
not the data. Each pass only writes the pixels appropriate for that
|
||||
pass, and assumes the data from previous passes is still valid.
|
||||
|
||||
png_read_rows(png_ptr, row_pointers, NULL, number_of_rows);
|
||||
|
||||
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
|
||||
the second parameter NULL.
|
||||
|
||||
png_read_rows(png_ptr, NULL, row_pointers, number_of_rows);
|
||||
|
||||
After you are finished reading the image, you can finish reading
|
||||
the file. If you are interested in comments or time, you should
|
||||
pass the png_info pointer from the png_read_info() call. If you
|
||||
are not interested, you can pass NULL.
|
||||
|
||||
png_read_end(png_ptr, info_ptr);
|
||||
|
||||
When you are done, you can free all memory used by libpng like this:
|
||||
|
||||
png_read_destroy(png_ptr, info_ptr, (png_info *)0);
|
||||
|
||||
After that, you can discard the structures, or reuse them another
|
||||
read or write. For a more compact example of reading a PNG image,
|
||||
see the file example.c.
|
||||
|
||||
|
||||
Writing PNG files:
|
||||
|
||||
Much of this is very similar to reading. However, everything of
|
||||
importance is repeated here, so you don't have to constantly look
|
||||
back up in the Reading PNG files section to understand writing.
|
||||
|
||||
The first thing you need to do while writing a PNG file is to allocate
|
||||
and initialize png_struct and png_info. As these are both large, you
|
||||
may not want to store these on the stack, unless you have stack space
|
||||
to spare.
|
||||
|
||||
png_struct *png_ptr = malloc(sizeof (png_struct));
|
||||
if (!png_ptr)
|
||||
return;
|
||||
png_info *info_ptr = malloc(sizeof (png_info));
|
||||
if (!info_ptr)
|
||||
{
|
||||
free(png_ptr);
|
||||
return;
|
||||
}
|
||||
|
||||
You may also want to do any i/o initialization here, before
|
||||
you get into libpng, so if it doesn't work, you don't have
|
||||
much to undo.
|
||||
|
||||
FILE *fp = fopen(file_name, "wb");
|
||||
if (!fp)
|
||||
{
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
return;
|
||||
}
|
||||
|
||||
After you have these structures, you will need to set up the
|
||||
error handling. When libpng encounters an error, it expects to
|
||||
longjmp back to your routine. Therefore, you will need to call
|
||||
setjmp and pass the jmpbuf field of your png_struct. If you
|
||||
write the file from different routines, you will need to update
|
||||
the jmpbuf field every time you enter a new routine that will
|
||||
call a png_ function. See your documentation of setjmp/longjmp
|
||||
for your compiler for more information on setjmp/longjmp. See
|
||||
the discussion on png error handling in the Customizing Libpng
|
||||
section below for more information on the png error handling.
|
||||
|
||||
if (setjmp(png_ptr->jmpbuf))
|
||||
{
|
||||
png_write_destroy(png_ptr);
|
||||
/* free pointers before returning. Make sure you clean up
|
||||
anything else you've done. */
|
||||
free(png_ptr);
|
||||
free(info_ptr);
|
||||
fclose(fp);
|
||||
return;
|
||||
}
|
||||
|
||||
Next, you will need to call png_write_init() and png_info_init().
|
||||
These functions make sure all the fields are initialized to useful
|
||||
values, and, in the case of png_write_init(), allocate any memory
|
||||
needed for internal uses. Do png_info_init() first, so if
|
||||
png_write_init() longjmps, you know info_ptr is valid, so you
|
||||
don't free random memory pointers, which would be bad.
|
||||
|
||||
png_info_init(info_ptr);
|
||||
png_write_init(png_ptr);
|
||||
|
||||
Now you need to set up the input code. The default for libpng is
|
||||
to use the C function fwrite(). If you use this, you will need to
|
||||
pass a valid FILE * in the function png_init_io(). Be sure that
|
||||
the file is opened in binary mode. If you wish to handle writing
|
||||
data in another way, see the discussion on png i/o handling in the
|
||||
Customizing Libpng section below.
|
||||
|
||||
png_init_io(png_ptr, fp);
|
||||
|
||||
You now need to fill in the png_info structure with all the data
|
||||
you wish to write before the actual image. Note that the only thing
|
||||
you are allowed to write after the image is the text chunks and the
|
||||
time chunk. See png_write_end() for more information on that. If you
|
||||
wish to write them before the image, fill them in now. If you want to
|
||||
wait until after the data, don't fill them until png_write_end(). For
|
||||
all the fields in png_info, see png.h. For explinations of what the
|
||||
fields contain, see the PNG specification. Some of the more important
|
||||
parts of the png_info are:
|
||||
width - holds the width of the file
|
||||
height - holds the height of the file
|
||||
bit_depth - holds the bit depth of one of the image channels
|
||||
color_type - describes the channels and what they mean
|
||||
see the PNG_COLOR_TYPE_ defines for more information
|
||||
interlace_type - currently 0 for none, 1 for interlaced
|
||||
valid - this describes which optional chunks to write to the
|
||||
file. Note that if you are writing a PNG_COLOR_TYPE_PALETTE
|
||||
file, the PLTE chunk is not optional, but must still be marked
|
||||
for writing. To mark chunks for writing, OR valid with the
|
||||
appropriate PNG_INFO_<chunk name> define.
|
||||
palette and num_palette - the palette for the file
|
||||
gamma - the gamma the file is written at
|
||||
sig_bit and sig_bit_number - the number of significant bits
|
||||
trans, trans_values, and number_trans - transparency info
|
||||
hist - histogram of palette
|
||||
text and num_text - text comments in the file.
|
||||
|
||||
A quick word about text and num_text. text is an array of png_text
|
||||
structures. num_text is the number of valid structures in the array.
|
||||
If you want, you can use max_text to hold the size of the array, but
|
||||
libpng ignores it for writing (it does use it for reading). Each
|
||||
png_text structure holds a keyword-text value, and a compression type.
|
||||
The compression types have the same valid numbers as the compression
|
||||
types of the image data. Currently, the only valid number is zero.
|
||||
However, you can store text either compressed or uncompressed, unlike
|
||||
images which always have to be compressed. So if you don't want the
|
||||
text compressed, set the compression type to -1. Until text gets
|
||||
arount 1000 bytes, it is not worth compressing it.
|
||||
|
||||
The keyword-text pairs work like this. Keywords should be short
|
||||
simple descriptions of what the comment is about. Some typical
|
||||
keywords are found in the PNG specification, as is some recomendations
|
||||
on keywords. You can repeat keywords in a file. You can even write
|
||||
some text before the image and some after. For example, you may want
|
||||
to put a description of the image before the image, but leave the
|
||||
disclaimer until after, so viewers working over modem connections
|
||||
don't have to wait for the disclaimer to go over the modem before
|
||||
they start seeing the image. Finally, keywords should be full
|
||||
words, not abbreviations. Keywords can not contain NUL characters,
|
||||
and should not contain control characters. Text in general should
|
||||
not contain control characters. The keyword must be present, but
|
||||
you can leave off the text string on non-compressed pairs.
|
||||
Compressed pairs must have a text string, as only the text string
|
||||
is compressed anyway, so the compression would be meaningless.
|
||||
|
||||
PNG supports modification time via the png_time structure. Two
|
||||
conversion routines are proved, png_convert_from_time_t() for
|
||||
time_t and png_convert_from_struct_tm() for struct tm. The
|
||||
time_t routine uses gmtime(). You don't have to use either of
|
||||
these, but if you wish to fill in the png_time structure directly,
|
||||
you should provide the time in universal time (GMT) if possible
|
||||
instead of your local time.
|
||||
|
||||
You are now ready to write all the file information up to the actual
|
||||
image data. You do this with a call to png_write_info().
|
||||
|
||||
png_write_info(png_ptr, info_ptr);
|
||||
|
||||
After you've read the file information, you can set up the library to
|
||||
handle any special transformations of the image data. The various
|
||||
ways to transform the data will be described in the order that they
|
||||
occur. This is important, as some of these change the color type
|
||||
and bit depth of the data, and some others only work on certain
|
||||
color types and bit depths. Even though each transformation should
|
||||
check to see if it has data that it can do somthing with, you should
|
||||
make sure to only enable a transformation if it will be valid for
|
||||
the data. For example, don't swap red and blue on grayscale data.
|
||||
|
||||
PNG files store rgb pixels packed into 3 bytes. If you would rather
|
||||
supply the pixels as 4 bytes per pixel, with the filler byte last,
|
||||
call this:
|
||||
|
||||
png_set_rgbx(png_ptr);
|
||||
|
||||
If your filler byte goes first, call this:
|
||||
|
||||
png_set_xrgb(png_ptr);
|
||||
|
||||
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
||||
they can, resulting in, for example, 8 pixels per byte for 1 bit files.
|
||||
If you would rather supply the data 1 pixel per byte, but with the
|
||||
values limited to the correct number of bits, call this:
|
||||
|
||||
png_set_packing(png_ptr);
|
||||
|
||||
PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
|
||||
data is of another bit depth, but is packed into the bytes correctly,
|
||||
this will scale the values to appear to be the correct bit depth.
|
||||
Make sure you write a sBIT chunk when you do this, so others, if
|
||||
they want, can reduce the values down to their true depth.
|
||||
|
||||
/* do this before png_write_info() */
|
||||
info_ptr->valid |= PNG_INFO_sBIT;
|
||||
|
||||
/* note that you can cheat and set all the values of
|
||||
sig_bit to true_bit_depth if you want */
|
||||
if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
|
||||
{
|
||||
info_ptr->sig_bit.red = true_bit_depth;
|
||||
info_ptr->sig_bit.green = true_bit_depth;
|
||||
info_ptr->sig_bit.blue = true_bit_depth;
|
||||
}
|
||||
else
|
||||
{
|
||||
info_ptr->sig_bit.gray = true_bit_depth;
|
||||
}
|
||||
|
||||
if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
|
||||
{
|
||||
info_ptr->sig_bit.alpha = true_bit_depth;
|
||||
}
|
||||
|
||||
png_set_shift(png_ptr, &(info_ptr->sig_bit));
|
||||
|
||||
PNG files store 16 bit pixels in network byte order (most significant
|
||||
bit first). If you would rather supply them the other way, (the way
|
||||
PC's store them, for example), call this:
|
||||
|
||||
png_set_swap(png_ptr);
|
||||
|
||||
PNG files store 3 color pixels in red, green, blue order. If you would
|
||||
rather supply the pixels as blue, green, red, call this.
|
||||
|
||||
png_set_bgr(png_ptr);
|
||||
|
||||
PNG files describe moncrome as black is zero and white is one. If you
|
||||
would rather supply the pixels with this reversed (black is one and
|
||||
white is zero), call this:
|
||||
|
||||
png_set_invert(png_ptr);
|
||||
|
||||
That's it for the transformations. Now you can write the image data.
|
||||
The simplest way to do this is in one function call. If have the
|
||||
whole image in memory, you can just call png_write_image() and libpng
|
||||
will write the image. You will need to pass in an array of pointers to
|
||||
each row. This function automatically handles interlacing, so you don't
|
||||
need to call png_set_interlace_handling() or call this function multiple
|
||||
times, or any of that other stuff necessary with png_write_rows().
|
||||
|
||||
png_write_image(png_ptr, row_pointers);
|
||||
|
||||
where row_pointers is:
|
||||
|
||||
void *row_pointers[height];
|
||||
|
||||
You can point to void or char or whatever you use for pixels.
|
||||
|
||||
If you can't want to write the whole image at once, you can
|
||||
use png_write_rows() instead. If the file is not interlaced,
|
||||
this is simple:
|
||||
|
||||
png_write_rows(png_ptr, row_pointers, number_of_rows);
|
||||
|
||||
row_pointers is the same as in the png_write_image() call.
|
||||
|
||||
If you are just calling one row at a time, you can do this for
|
||||
row_pointers:
|
||||
|
||||
char *row_pointers = row;
|
||||
|
||||
png_write_rows(png_ptr, &row_pointers, 1);
|
||||
|
||||
When the file is interlaced, things can get a good deal harder.
|
||||
PNG files have a complicated interlace scheme that breaks down an
|
||||
image into seven smaller images of varying size. Libpng will
|
||||
build these images if you want, or you can do them yourself. If
|
||||
you want to build them yourself, see the PNG specification for
|
||||
details of which pixels to write when.
|
||||
|
||||
If you don't want libpng to handle the interlacing details, just
|
||||
call png_write_rows() the correct number of times to write all
|
||||
seven sub-images.
|
||||
|
||||
If you want libpng to build the sub-images, call this:
|
||||
|
||||
number_passes = png_set_interlace_handling(png_ptr);
|
||||
|
||||
This will return the number of passes needed. Currently, this
|
||||
is seven, but may change if another interlace type is added.
|
||||
|
||||
Then write the image number_passes times.
|
||||
|
||||
png_write_rows(png_ptr, row_pointers, number_of_rows);
|
||||
|
||||
As some of these rows are not used, and thus return immediately,
|
||||
you may want to read about interlacing in the PNG specification,
|
||||
and only update the rows that are actually used.
|
||||
|
||||
After you are finished writing the image, you should finish writing
|
||||
the file. If you are interested in writing comments or time, you should
|
||||
pass the an appropriately filled png_info pointer. If you
|
||||
are not interested, you can pass NULL. Be careful that you don't
|
||||
write the same text or time chunks here as you did in png_write_info().
|
||||
|
||||
png_write_end(png_ptr, info_ptr);
|
||||
|
||||
When you are done, you can free all memory used by libpng like this:
|
||||
|
||||
png_write_destroy(png_ptr);
|
||||
|
||||
Any data you allocated for png_info, you must free yourself.
|
||||
|
||||
After that, you can discard the structures, or reuse them another
|
||||
read or write. For a more compact example of writing a PNG image,
|
||||
see the file example.c.
|
||||
|
||||
|
||||
Customizing libpng:
|
||||
|
||||
There are two issues here. The first is changing how libpng does
|
||||
standard things like memory allocation, input/output, and error handling.
|
||||
The second deals with more complicated things like adding new chunks,
|
||||
adding new transformations, and generally changing how libpng works.
|
||||
|
||||
All of the memory allocation, input/output, and error handling in libpng
|
||||
goes through the routines in pngstub.c. The file as plenty of comments
|
||||
describing each function and how it expects to work, so I will just
|
||||
summarize here. See pngstub.c for more details.
|
||||
|
||||
Memory allocation is done through the functions png_large_malloc(),
|
||||
png_malloc(), png_realloc(), png_large_free(), and png_free().
|
||||
These currently just call the standard C functions. The large
|
||||
functions must handle exactly 64K, but they don't have to handle
|
||||
more then that. If your pointers can't access more then 64K at a
|
||||
time, you will want to set MAXSEG_64K in zlib.h.
|
||||
|
||||
Input/Output in libpng is done throught png_read() and png_write(), which
|
||||
currently just call fread() and fwrite(). The FILE * is stored in
|
||||
png_struct, and is initialized via png_init_io(). If you wish to change
|
||||
this, make the appropriate changes in pngstub.c and png.h. Make sure you
|
||||
change the function prototype for png_init_io() if you are no longer
|
||||
using a FILE *.
|
||||
|
||||
Error handling in libpng is done through png_error() and png_warning().
|
||||
Errors handled through png_error() are fatal, meaning that png_error()
|
||||
should never return to it's caller. Currently, this is handled via
|
||||
setjmp() and longjmp(), but you could change this to do things like
|
||||
exit() if you should wish. Similarly, both png_error() and png_warning()
|
||||
print a message on stderr, but that can also be changed. 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. 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.
|
||||
|
||||
If you need to read or write custom chunks, you will need to get deeper
|
||||
into the libpng code. First, read t |