1/*---------------------------------------------------------------------------
2
3   rpng - simple PNG display program                              readpng.c
4
5  ---------------------------------------------------------------------------
6
7      Copyright (c) 1998-2007 Greg Roelofs.  All rights reserved.
8
9      This software is provided "as is," without warranty of any kind,
10      express or implied.  In no event shall the author or contributors
11      be held liable for any damages arising in any way from the use of
12      this software.
13
14      The contents of this file are DUAL-LICENSED.  You may modify and/or
15      redistribute this software according to the terms of one of the
16      following two licenses (at your option):
17
18
19      LICENSE 1 ("BSD-like with advertising clause"):
20
21      Permission is granted to anyone to use this software for any purpose,
22      including commercial applications, and to alter it and redistribute
23      it freely, subject to the following restrictions:
24
25      1. Redistributions of source code must retain the above copyright
26         notice, disclaimer, and this list of conditions.
27      2. Redistributions in binary form must reproduce the above copyright
28         notice, disclaimer, and this list of conditions in the documenta-
29         tion and/or other materials provided with the distribution.
30      3. All advertising materials mentioning features or use of this
31         software must display the following acknowledgment:
32
33            This product includes software developed by Greg Roelofs
34            and contributors for the book, "PNG: The Definitive Guide,"
35            published by O'Reilly and Associates.
36
37
38      LICENSE 2 (GNU GPL v2 or later):
39
40      This program is free software; you can redistribute it and/or modify
41      it under the terms of the GNU General Public License as published by
42      the Free Software Foundation; either version 2 of the License, or
43      (at your option) any later version.
44
45      This program is distributed in the hope that it will be useful,
46      but WITHOUT ANY WARRANTY; without even the implied warranty of
47      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
48      GNU General Public License for more details.
49
50      You should have received a copy of the GNU General Public License
51      along with this program; if not, write to the Free Software Foundation,
52      Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
53
54  ---------------------------------------------------------------------------*/
55
56#include <stdio.h>
57#include <stdlib.h>
58
59#include "png.h"        /* libpng header; includes zlib.h */
60#include "readpng.h"    /* typedefs, common macros, public prototypes */
61
62/* future versions of libpng will provide this macro: */
63#ifndef png_jmpbuf
64#  define png_jmpbuf(png_ptr)   ((png_ptr)->jmpbuf)
65#endif
66
67
68static png_structp png_ptr = NULL;
69static png_infop info_ptr = NULL;
70
71png_uint_32  width, height;
72int  bit_depth, color_type;
73uch  *image_data = NULL;
74
75
76void readpng_version_info(void)
77{
78    fprintf(stderr, "   Compiled with libpng %s; using libpng %s.\n",
79      PNG_LIBPNG_VER_STRING, png_libpng_ver);
80    fprintf(stderr, "   Compiled with zlib %s; using zlib %s.\n",
81      ZLIB_VERSION, zlib_version);
82}
83
84
85/* return value = 0 for success, 1 for bad sig, 2 for bad IHDR, 4 for no mem */
86
87int readpng_init(FILE *infile, ulg *pWidth, ulg *pHeight)
88{
89    uch sig[8];
90
91
92    /* first do a quick check that the file really is a PNG image; could
93     * have used slightly more general png_sig_cmp() function instead */
94
95    fread(sig, 1, 8, infile);
96    if (png_sig_cmp(sig, 0, 8))
97        return 1;   /* bad signature */
98
99
100    /* could pass pointers to user-defined error handlers instead of NULLs: */
101
102    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
103    if (!png_ptr)
104        return 4;   /* out of memory */
105
106    info_ptr = png_create_info_struct(png_ptr);
107    if (!info_ptr) {
108        png_destroy_read_struct(&png_ptr, NULL, NULL);
109        return 4;   /* out of memory */
110    }
111
112
113    /* we could create a second info struct here (end_info), but it's only
114     * useful if we want to keep pre- and post-IDAT chunk info separated
115     * (mainly for PNG-aware image editors and converters) */
116
117
118    /* setjmp() must be called in every function that calls a PNG-reading
119     * libpng function */
120
121    if (setjmp(png_jmpbuf(png_ptr))) {
122        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
123        return 2;
124    }
125
126
127    png_init_io(png_ptr, infile);
128    png_set_sig_bytes(png_ptr, 8);  /* we already read the 8 signature bytes */
129
130    png_read_info(png_ptr, info_ptr);  /* read all PNG info up to image data */
131
132
133    /* alternatively, could make separate calls to png_get_image_width(),
134     * etc., but want bit_depth and color_type for later [don't care about
135     * compression_type and filter_type => NULLs] */
136
137    png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
138      NULL, NULL, NULL);
139    *pWidth = width;
140    *pHeight = height;
141
142
143    /* OK, that's all we need for now; return happy */
144
145    return 0;
146}
147
148
149
150
151/* returns 0 if succeeds, 1 if fails due to no bKGD chunk, 2 if libpng error;
152 * scales values to 8-bit if necessary */
153
154int readpng_get_bgcolor(uch *red, uch *green, uch *blue)
155{
156    png_color_16p pBackground;
157
158
159    /* setjmp() must be called in every function that calls a PNG-reading
160     * libpng function */
161
162    if (setjmp(png_jmpbuf(png_ptr))) {
163        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
164        return 2;
165    }
166
167
168    if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_bKGD))
169        return 1;
170
171    /* it is not obvious from the libpng documentation, but this function
172     * takes a pointer to a pointer, and it always returns valid red, green
173     * and blue values, regardless of color_type: */
174
175    png_get_bKGD(png_ptr, info_ptr, &pBackground);
176
177
178    /* however, it always returns the raw bKGD data, regardless of any
179     * bit-depth transformations, so check depth and adjust if necessary */
180
181    if (bit_depth == 16) {
182        *red   = pBackground->red   >> 8;
183        *green = pBackground->green >> 8;
184        *blue  = pBackground->blue  >> 8;
185    } else if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) {
186        if (bit_depth == 1)
187            *red = *green = *blue = pBackground->gray? 255 : 0;
188        else if (bit_depth == 2)
189            *red = *green = *blue = (255/3) * pBackground->gray;
190        else /* bit_depth == 4 */
191            *red = *green = *blue = (255/15) * pBackground->gray;
192    } else {
193        *red   = (uch)pBackground->red;
194        *green = (uch)pBackground->green;
195        *blue  = (uch)pBackground->blue;
196    }
197
198    return 0;
199}
200
201
202
203
204/* display_exponent == LUT_exponent * CRT_exponent */
205
206uch *readpng_get_image(double display_exponent, int *pChannels, ulg *pRowbytes)
207{
208    double  gamma;
209    png_uint_32  i, rowbytes;
210    png_bytepp  row_pointers = NULL;
211
212
213    /* setjmp() must be called in every function that calls a PNG-reading
214     * libpng function */
215
216    if (setjmp(png_jmpbuf(png_ptr))) {
217        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
218        return NULL;
219    }
220
221
222    /* expand palette images to RGB, low-bit-depth grayscale images to 8 bits,
223     * transparency chunks to full alpha channel; strip 16-bit-per-sample
224     * images to 8 bits per sample; and convert grayscale to RGB[A] */
225
226    if (color_type == PNG_COLOR_TYPE_PALETTE)
227        png_set_expand(png_ptr);
228    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
229        png_set_expand(png_ptr);
230    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
231        png_set_expand(png_ptr);
232    if (bit_depth == 16)
233        png_set_strip_16(png_ptr);
234    if (color_type == PNG_COLOR_TYPE_GRAY ||
235        color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
236        png_set_gray_to_rgb(png_ptr);
237
238
239    /* unlike the example in the libpng documentation, we have *no* idea where
240     * this file may have come from--so if it doesn't have a file gamma, don't
241     * do any correction ("do no harm") */
242
243    if (png_get_gAMA(png_ptr, info_ptr, &gamma))
244        png_set_gamma(png_ptr, display_exponent, gamma);
245
246
247    /* all transformations have been registered; now update info_ptr data,
248     * get rowbytes and channels, and allocate image memory */
249
250    png_read_update_info(png_ptr, info_ptr);
251
252    *pRowbytes = rowbytes = png_get_rowbytes(png_ptr, info_ptr);
253    *pChannels = (int)png_get_channels(png_ptr, info_ptr);
254
255    if ((image_data = (uch *)malloc(rowbytes*height)) == NULL) {
256        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
257        return NULL;
258    }
259    if ((row_pointers = (png_bytepp)malloc(height*sizeof(png_bytep))) == NULL) {
260        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
261        free(image_data);
262        image_data = NULL;
263        return NULL;
264    }
265
266    Trace((stderr, "readpng_get_image:  channels = %d, rowbytes = %ld, height = %ld\n", *pChannels, rowbytes, height));
267
268
269    /* set the individual row_pointers to point at the correct offsets */
270
271    for (i = 0;  i < height;  ++i)
272        row_pointers[i] = image_data + i*rowbytes;
273
274
275    /* now we can go ahead and just read the whole image */
276
277    png_read_image(png_ptr, row_pointers);
278
279
280    /* and we're done!  (png_read_end() can be omitted if no processing of
281     * post-IDAT text/time/etc. is desired) */
282
283    free(row_pointers);
284    row_pointers = NULL;
285
286    png_read_end(png_ptr, NULL);
287
288    return image_data;
289}
290
291
292void readpng_cleanup(int free_image_data)
293{
294    if (free_image_data && image_data) {
295        free(image_data);
296        image_data = NULL;
297    }
298
299    if (png_ptr && info_ptr) {
300        png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
301        png_ptr = NULL;
302        info_ptr = NULL;
303    }
304}
305