This program decodes and displays PNG images, with gamma correction and
optionally with a user-specified background color (in case the image has
transparency). It is very nearly the most basic PNG viewer possible.
This version is for the X Window System (tested by author under Unix and
by Martin Zinser under OpenVMS; may work under OS/2 with some tweaking).
to do:
- 8-bit support
- use %.1023s to simplify truncation of title-bar string?
Changelog:
- 1.01: initial public release
- 1.02: modified to allow abbreviated options; fixed long/ulong mis-
match; switched to png_jmpbuf() macro
- 1.10: added support for non-default visuals; fixed X pixel-conversion
- 1.11: added extra set of parentheses to png_jmpbuf() macro; fixed
command-line parsing bug
- 1.12: fixed small X memory leak (thanks to Francois Petitjean)
Copyright (c) 1998-2001 Greg Roelofs. All rights reserved.
This software is provided "as is," without warranty of any kind,
express or implied. In no event shall the author or contributors
be held liable for any damages arising in any way from the use of
this software.
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute
it freely, subject to the following restrictions:
1. Redistributions of source code must retain the above copyright
notice, disclaimer, and this list of conditions.
2. Redistributions in binary form must reproduce the above copyright
notice, disclaimer, and this list of conditions in the documenta-
tion and/or other materials provided with the distribution.
3. All advertising materials mentioning features or use of this
software must display the following acknowledgment:
This product includes software developed by Greg Roelofs
and contributors for the book, "PNG: The Definitive Guide,"
published by O'Reilly and Associates.
/* #define DEBUG : this enables the Trace() macros */
#include "readpng.h" /* typedefs, common macros, readpng prototypes */
/* could just include png.h, but this macro is the only thing we need
* (name and typedefs changed to local versions); note that side effects
* only happen with alpha (which could easily be avoided with
* "ush acopy = (alpha);") */
/* local prototypes */
static int rpng_x_create_window(void);
static int rpng_x_display_image(void);
static void rpng_x_cleanup(void);
static int rpng_x_msb(ulg u32val);
/* First set the default value for our display-system exponent, i.e.,
* the product of the CRT exponent and the exponent corresponding to
* the frame-buffer's lookup table (LUT), if any. This is not an
* exhaustive list of LUT values (e.g., OpenStep has a lot of weird
* ones), but it should cover 99% of the current possibilities. */
#if defined(NeXT)
LUT_exponent = 1.0 / 2.2;
/*
if (some_next_function_that_returns_gamma(&next_gamma))
LUT_exponent = 1.0 / next_gamma;
*/
#elif defined(sgi)
LUT_exponent = 1.0 / 1.7;
/* there doesn't seem to be any documented function to get the
* "gamma" value, so we do it the hard way */
infile = fopen("/etc/config/system.glGammaVal", "r");
if (infile) {
double sgi_gamma;
/* the defaults above give 1.0, 1.3, 1.5 and 2.2, respectively: */
default_display_exponent = LUT_exponent * CRT_exponent;
/* If the user has set the SCREEN_GAMMA environment variable as suggested
* (somewhat imprecisely) in the libpng documentation, use that; otherwise
* use the default value we just calculated. Either way, the user may
* override this via a command-line option. */
/* Now parse the command line for options and the PNG filename. */
while (*++argv && !error) {
if (!strncmp(*argv, "-display", 2)) {
if (!*++argv)
++error;
else
displayname = *argv;
} else if (!strncmp(*argv, "-gamma", 2)) {
if (!*++argv)
++error;
else {
display_exponent = atof(*argv);
if (display_exponent <= 0.0)
++error;
}
} else if (!strncmp(*argv, "-bgcolor", 2)) {
if (!*++argv)
++error;
else {
bgstr = *argv;
if (strlen(bgstr) != 7 || bgstr[0] != '#')
++error;
else
have_bg = TRUE;
}
} else {
if (**argv != '-') {
filename = *argv;
if (argv[1]) /* shouldn't be any more args after filename */
++error;
} else
++error; /* not expecting any other options */
}
}
if (!filename) {
++error;
} else if (!(infile = fopen(filename, "rb"))) {
fprintf(stderr, PROGNAME ": can't open PNG file [%s]\n", filename);
++error;
} else {
if ((rc = readpng_init(infile, &image_width, &image_height)) != 0) {
switch (rc) {
case 1:
fprintf(stderr, PROGNAME
": [%s] is not a PNG file: incorrect signature\n",
filename);
break;
case 2:
fprintf(stderr, PROGNAME
": [%s] has bad IHDR (libpng longjmp)\n",
filename);
break;
case 4:
fprintf(stderr, PROGNAME ": insufficient memory\n");
break;
default:
fprintf(stderr, PROGNAME
": unknown readpng_init() error\n");
break;
}
++error;
} else {
display = XOpenDisplay(displayname);
if (!display) {
readpng_cleanup(TRUE);
fprintf(stderr, PROGNAME ": can't open X display [%s]\n",
displayname? displayname : "default");
++error;
}
}
if (error)
fclose(infile);
}
/* usage screen */
if (error) {
fprintf(stderr, "\n%s %s: %s\n", PROGNAME, VERSION, appname);
readpng_version_info();
fprintf(stderr, "\n"
"Usage: %s [-display xdpy] [-gamma exp] [-bgcolor bg] file.png\n"
" xdpy\tname of the target X display (e.g., ``hostname:0'')\n"
" exp \ttransfer-function exponent (``gamma'') of the display\n"
"\t\t system in floating-point format (e.g., ``%.1f''); equal\n"
"\t\t to the product of the lookup-table exponent (varies)\n"
"\t\t and the CRT exponent (usually 2.2); must be positive\n"
" bg \tdesired background color in 7-character hex RGB format\n"
"\t\t (e.g., ``#ff7700'' for orange: same as HTML colors);\n"
"\t\t used with transparent images\n"
"\nPress Q, Esc or mouse button 1 (within image window, after image\n"
"is displayed) to quit.\n"
"\n", PROGNAME, default_display_exponent);
exit(1);
}
/* set the title-bar string, but make sure buffer doesn't overflow */
/* if the user didn't specify a background color on the command line,
* check for one in the PNG file--if not, the initialized values of 0
* (black) will be used */
if (have_bg) {
unsigned r, g, b; /* this approach quiets compiler warnings */
/* various properties and hints no longer needed; free memory */
if (pWindowName)
XFree(pWindowName->value);
if (pIconName)
XFree(pIconName->value);
if (size_hints)
XFree(size_hints);
if (wm_hints)
XFree(wm_hints);
XMapWindow(display, window);
gc = XCreateGC(display, window, 0, &gcvalues);
/*---------------------------------------------------------------------------
Fill window with the specified background color.
---------------------------------------------------------------------------*/
/*---------------------------------------------------------------------------
Wait for first Expose event to do any drawing, then flush.
---------------------------------------------------------------------------*/
do
XNextEvent(display, &e);
while (e.type != Expose || e.xexpose.count);
XFlush(display);
/*---------------------------------------------------------------------------
Allocate memory for the X- and display-specific version of the image.
---------------------------------------------------------------------------*/
if (depth == 24 || depth == 32) {
xdata = (uch *)malloc(4*image_width*image_height);
pad = 32;
} else if (depth == 16) {
xdata = (uch *)malloc(2*image_width*image_height);
pad = 16;
} else /* depth == 8 */ {
xdata = (uch *)malloc(image_width*image_height);
pad = 8;
}
if (!xdata) {
fprintf(stderr, PROGNAME ": unable to allocate image memory\n");
return 4;
}
/* to avoid testing the byte order every pixel (or doubling the size of
* the drawing routine with a giant if-test), we arbitrarily set the byte
* order to MSBFirst and let Xlib worry about inverting things on little-
* endian machines (like Linux/x86, old VAXen, etc.)--this is not the most
* efficient approach (the giant if-test would be better), but in the
* interest of clarity, we take the easy way out... */
ximage->byte_order = MSBFirst;
return 0;
} /* end function rpng_x_create_window() */
static int rpng_x_display_image(void)
{
uch *src;
char *dest;
uch r, g, b, a;
ulg i, row, lastrow = 0;
ulg pixel;
int ximage_rowbytes = ximage->bytes_per_line;
/* int bpp = ximage->bits_per_pixel; */
if (ximage) {
if (ximage->data) {
free(ximage->data); /* we allocated it, so we free it */
ximage->data = (char *)NULL; /* instead of XDestroyImage() */
}
XDestroyImage(ximage);
ximage = NULL;
}
XFreeGC(display, gc);
if (have_window)
XDestroyWindow(display, window);
if (have_colormap)
XFreeColormap(display, colormap);
if (have_nondefault_visual)
XFree(visual_list);
}
static int rpng_x_msb(ulg u32val)
{
int i;
for (i = 31; i >= 0; --i) {
if (u32val & 0x80000000L)
break;
u32val <<= 1;
}
return i;
}
