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      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 #include <zlib.h>
     59 
     60 #include "png.h"        /* libpng header */
     61 #include "readpng.h"    /* typedefs, common macros, public prototypes */
     62 
     63 /* future versions of libpng will provide this macro: */
     64 #ifndef png_jmpbuf
     65 #  define png_jmpbuf(png_ptr)   ((png_ptr)->jmpbuf)
     66 #endif
     67 
     68 
     69 static png_structp png_ptr = NULL;
     70 static png_infop info_ptr = NULL;
     71 
     72 png_uint_32  width, height;
     73 int  bit_depth, color_type;
     74 uch  *image_data = NULL;
     75 
     76 
     77 void readpng_version_info(void)
     78 {
     79     fprintf(stderr, "   Compiled with libpng %s; using libpng %s.\n",
     80       PNG_LIBPNG_VER_STRING, png_libpng_ver);
     81     fprintf(stderr, "   Compiled with zlib %s; using zlib %s.\n",
     82       ZLIB_VERSION, zlib_version);
     83 }
     84 
     85 
     86 /* return value = 0 for success, 1 for bad sig, 2 for bad IHDR, 4 for no mem */
     87 
     88 int readpng_init(FILE *infile, ulg *pWidth, ulg *pHeight)
     89 {
     90     uch sig[8];
     91 
     92 
     93     /* first do a quick check that the file really is a PNG image; could
     94      * have used slightly more general png_sig_cmp() function instead */
     95 
     96     fread(sig, 1, 8, infile);
     97     if (png_sig_cmp(sig, 0, 8))
     98         return 1;   /* bad signature */
     99 
    100 
    101     /* could pass pointers to user-defined error handlers instead of NULLs: */
    102 
    103     png_ptr = png_create_read_struct(png_get_libpng_ver(NULL), NULL, NULL,
    104         NULL);
    105     if (!png_ptr)
    106         return 4;   /* out of memory */
    107 
    108     info_ptr = png_create_info_struct(png_ptr);
    109     if (!info_ptr) {
    110         png_destroy_read_struct(&png_ptr, NULL, NULL);
    111         return 4;   /* out of memory */
    112     }
    113 
    114 
    115     /* we could create a second info struct here (end_info), but it's only
    116      * useful if we want to keep pre- and post-IDAT chunk info separated
    117      * (mainly for PNG-aware image editors and converters) */
    118 
    119 
    120     /* setjmp() must be called in every function that calls a PNG-reading
    121      * libpng function */
    122 
    123     if (setjmp(png_jmpbuf(png_ptr))) {
    124         png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    125         return 2;
    126     }
    127 
    128 
    129     png_init_io(png_ptr, infile);
    130     png_set_sig_bytes(png_ptr, 8);  /* we already read the 8 signature bytes */
    131 
    132     png_read_info(png_ptr, info_ptr);  /* read all PNG info up to image data */
    133 
    134 
    135     /* alternatively, could make separate calls to png_get_image_width(),
    136      * etc., but want bit_depth and color_type for later [don't care about
    137      * compression_type and filter_type => NULLs] */
    138 
    139     png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
    140       NULL, NULL, NULL);
    141     *pWidth = width;
    142     *pHeight = height;
    143 
    144 
    145     /* OK, that's all we need for now; return happy */
    146 
    147     return 0;
    148 }
    149 
    150 
    151 
    152 
    153 /* returns 0 if succeeds, 1 if fails due to no bKGD chunk, 2 if libpng error;
    154  * scales values to 8-bit if necessary */
    155 
    156 int readpng_get_bgcolor(uch *red, uch *green, uch *blue)
    157 {
    158     png_color_16p pBackground;
    159 
    160 
    161     /* setjmp() must be called in every function that calls a PNG-reading
    162      * libpng function */
    163 
    164     if (setjmp(png_jmpbuf(png_ptr))) {
    165         png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    166         return 2;
    167     }
    168 
    169 
    170     if (!png_get_valid(png_ptr, info_ptr, PNG_INFO_bKGD))
    171         return 1;
    172 
    173     /* it is not obvious from the libpng documentation, but this function
    174      * takes a pointer to a pointer, and it always returns valid red, green
    175      * and blue values, regardless of color_type: */
    176 
    177     png_get_bKGD(png_ptr, info_ptr, &pBackground);
    178 
    179 
    180     /* however, it always returns the raw bKGD data, regardless of any
    181      * bit-depth transformations, so check depth and adjust if necessary */
    182 
    183     if (bit_depth == 16) {
    184         *red   = pBackground->red   >> 8;
    185         *green = pBackground->green >> 8;
    186         *blue  = pBackground->blue  >> 8;
    187     } else if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8) {
    188         if (bit_depth == 1)
    189             *red = *green = *blue = pBackground->gray? 255 : 0;
    190         else if (bit_depth == 2)
    191             *red = *green = *blue = (255/3) * pBackground->gray;
    192         else /* bit_depth == 4 */
    193             *red = *green = *blue = (255/15) * pBackground->gray;
    194     } else {
    195         *red   = (uch)pBackground->red;
    196         *green = (uch)pBackground->green;
    197         *blue  = (uch)pBackground->blue;
    198     }
    199 
    200     return 0;
    201 }
    202 
    203 
    204 
    205 
    206 /* display_exponent == LUT_exponent * CRT_exponent */
    207 
    208 uch *readpng_get_image(double display_exponent, int *pChannels, ulg *pRowbytes)
    209 {
    210     double  gamma;
    211     png_uint_32  i, rowbytes;
    212     png_bytepp  row_pointers = NULL;
    213 
    214 
    215     /* setjmp() must be called in every function that calls a PNG-reading
    216      * libpng function */
    217 
    218     if (setjmp(png_jmpbuf(png_ptr))) {
    219         free(image_data);
    220         image_data = NULL;
    221         free(row_pointers);
    222         row_pointers = NULL;
    223         png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    224         return NULL;
    225     }
    226 
    227 
    228     /* expand palette images to RGB, low-bit-depth grayscale images to 8 bits,
    229      * transparency chunks to full alpha channel; strip 16-bit-per-sample
    230      * images to 8 bits per sample; and convert grayscale to RGB[A] */
    231 
    232     if (color_type == PNG_COLOR_TYPE_PALETTE)
    233         png_set_expand(png_ptr);
    234     if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
    235         png_set_expand(png_ptr);
    236     if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
    237         png_set_expand(png_ptr);
    238 #ifdef PNG_READ_16_TO_8_SUPPORTED
    239     if (bit_depth == 16)
    240 #  ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
    241         png_set_scale_16(png_ptr);
    242 #  else
    243         png_set_strip_16(png_ptr);
    244 #  endif
    245 #endif
    246     if (color_type == PNG_COLOR_TYPE_GRAY ||
    247         color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
    248         png_set_gray_to_rgb(png_ptr);
    249 
    250 
    251     /* unlike the example in the libpng documentation, we have *no* idea where
    252      * this file may have come from--so if it doesn't have a file gamma, don't
    253      * do any correction ("do no harm") */
    254 
    255     if (png_get_gAMA(png_ptr, info_ptr, &gamma))
    256         png_set_gamma(png_ptr, display_exponent, gamma);
    257 
    258 
    259     /* all transformations have been registered; now update info_ptr data,
    260      * get rowbytes and channels, and allocate image memory */
    261 
    262     png_read_update_info(png_ptr, info_ptr);
    263 
    264     *pRowbytes = rowbytes = png_get_rowbytes(png_ptr, info_ptr);
    265     *pChannels = (int)png_get_channels(png_ptr, info_ptr);
    266 
    267     if ((image_data = (uch *)malloc(rowbytes*height)) == NULL) {
    268         png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    269         return NULL;
    270     }
    271     if ((row_pointers = (png_bytepp)malloc(height*sizeof(png_bytep))) == NULL) {
    272         png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    273         free(image_data);
    274         image_data = NULL;
    275         return NULL;
    276     }
    277 
    278     Trace((stderr, "readpng_get_image:  channels = %d, rowbytes = %ld, height = %ld\n",
    279         *pChannels, rowbytes, height));
    280 
    281 
    282     /* set the individual row_pointers to point at the correct offsets */
    283 
    284     for (i = 0;  i < height;  ++i)
    285         row_pointers[i] = image_data + i*rowbytes;
    286 
    287 
    288     /* now we can go ahead and just read the whole image */
    289 
    290     png_read_image(png_ptr, row_pointers);
    291 
    292 
    293     /* and we're done!  (png_read_end() can be omitted if no processing of
    294      * post-IDAT text/time/etc. is desired) */
    295 
    296     free(row_pointers);
    297     row_pointers = NULL;
    298 
    299     png_read_end(png_ptr, NULL);
    300 
    301     return image_data;
    302 }
    303 
    304 
    305 void readpng_cleanup(int free_image_data)
    306 {
    307     if (free_image_data && image_data) {
    308         free(image_data);
    309         image_data = NULL;
    310     }
    311 
    312     if (png_ptr && info_ptr) {
    313         png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    314         png_ptr = NULL;
    315         info_ptr = NULL;
    316     }
    317 }
    318