1
2 #if 0 /* in case someone actually tries to compile this */
3
4 /* example.c - an example of using libpng
5 *
6 * Maintained 2018 Cosmin Truta
7 * Maintained 1998-2016 Glenn Randers-Pehrson
8 * Maintained 1996-1997 Andreas Dilger
9 * Written 1995-1996 Guy Eric Schalnat, Group 42, Inc.
10 *
11 * To the extent possible under law, the authors have waived
12 * all copyright and related or neighboring rights to this file.
13 * This work is published from: United States, Canada.
14 */
15
16 /* This is an example of how to use libpng to read and write PNG files.
17 * The file libpng-manual.txt is much more verbose then this. If you have
18 * not read it, do so first. This was designed to be a starting point of an
19 * implementation. This is not officially part of libpng, is hereby placed
20 * in the public domain, and therefore does not require a copyright notice.
21 *
22 * This file does not currently compile, because it is missing certain
23 * parts, like allocating memory to hold an image. You will have to
24 * supply these parts to get it to compile. For an example of a minimal
25 * working PNG reader/writer, see pngtest.c, included in this distribution;
26 * see also the programs in the contrib directory.
27 */
28
29 /* The simple, but restricted approach to reading a PNG file or data stream
30 * requires just two function calls, as in the following complete program.
31 * Writing a file needs just one function call, so long as the data has an
32 * appropriate layout.
33 *
34 * The following code reads PNG image data from a file and writes it, in a
35 * potentially new format, to a new file. While this code will compile, there
36 * is minimal (insufficient) error checking. For a more realistic version,
37 * see contrib/examples/pngtopng.c
38 */
39
40 #include <stddef.h>
41 #include <stdlib.h>
42 #include <string.h>
43 #include <stdio.h>
44 #include <png.h>
45 #include <zlib.h>
46
47 int main(int argc, const char **argv)
48 {
49 if (argc == 3)
50 {
51 png_image image; /* The control structure used by libpng */
52
53 /* Initialize the 'png_image' structure. */
54 memset(&image, 0, (sizeof image));
55 image.version = PNG_IMAGE_VERSION;
56
57 /* The first argument is the file to read: */
58 if (png_image_begin_read_from_file(&image, argv[1]) != 0)
59 {
60 png_bytep buffer;
61
62 /* Set the format in which to read the PNG file; this code chooses a
63 * simple sRGB format with a non-associated alpha channel, adequate to
64 * store most images.
65 */
66 image.format = PNG_FORMAT_RGBA;
67
68 /* Now allocate enough memory to hold the image in this format; the
69 * PNG_IMAGE_SIZE macro uses the information about the image (width,
70 * height and format) stored in 'image'.
71 */
72 buffer = malloc(PNG_IMAGE_SIZE(image));
73
74 /* If enough memory was available, read the image in the desired
75 * format, then write the result out to the new file. 'background' is
76 * not necessary when reading the image, because the alpha channel is
77 * preserved; if it were to be removed, for example if we requested
78 * PNG_FORMAT_RGB, then either a solid background color would have to
79 * be supplied, or the output buffer would have to be initialized to
80 * the actual background of the image.
81 *
82 * The fourth argument to png_image_finish_read is the 'row_stride' -
83 * this is the number of components allocated for the image in each
84 * row. It has to be at least as big as the value returned by
85 * PNG_IMAGE_ROW_STRIDE, but if you just allocate space for the
86 * default, minimum size, using PNG_IMAGE_SIZE as above, you can pass
87 * zero.
88 *
89 * The final argument is a pointer to a buffer for the colormap;
90 * colormaps have exactly the same format as a row of image pixels
91 * (so you choose what format to make the colormap by setting
92 * image.format). A colormap is only returned if
93 * PNG_FORMAT_FLAG_COLORMAP is also set in image.format, so in this
94 * case NULL is passed as the final argument. If you do want to force
95 * all images into an index/color-mapped format, then you can use:
96 *
97 * PNG_IMAGE_COLORMAP_SIZE(image)
98 *
99 * to find the maximum size of the colormap in bytes.
100 */
101 if (buffer != NULL &&
102 png_image_finish_read(&image, NULL/*background*/, buffer,
103 0/*row_stride*/, NULL/*colormap*/) != 0)
104 {
105 /* Now write the image out to the second argument. In the write
106 * call 'convert_to_8bit' allows 16-bit data to be squashed down to
107 * 8 bits; this isn't necessary here because the original read was
108 * to the 8-bit format.
109 */
110 if (png_image_write_to_file(&image, argv[2], 0/*convert_to_8bit*/,
111 buffer, 0/*row_stride*/, NULL/*colormap*/) != 0)
112 {
113 /* The image has been written successfully. */
114 exit(0);
115 }
116 }
117 else
118 {
119 /* Calling png_image_free is optional unless the simplified API was
120 * not run to completion. In this case, if there wasn't enough
121 * memory for 'buffer', we didn't complete the read, so we must
122 * free the image:
123 */
124 if (buffer == NULL)
125 png_image_free(&image);
126 else
127 free(buffer);
128 }
129 }
130
131 /* Something went wrong reading or writing the image. libpng stores a
132 * textual message in the 'png_image' structure:
133 */
134 fprintf(stderr, "pngtopng: error: %s\n", image.message);
135 exit(1);
136 }
137
138 fprintf(stderr, "pngtopng: usage: pngtopng input-file output-file\n");
139 exit(2);
140 }
141
142 /* That's it ;-) Of course you probably want to do more with PNG files than
143 * just converting them all to 32-bit RGBA PNG files; you can do that between
144 * the call to png_image_finish_read and png_image_write_to_file. You can also
145 * ask for the image data to be presented in a number of different formats.
146 * You do this by simply changing the 'format' parameter set before allocating
147 * the buffer.
148 *
149 * The format parameter consists of five flags that define various aspects of
150 * the image. You can simply add these together to get the format, or you can
151 * use one of the predefined macros from png.h (as above):
152 *
153 * PNG_FORMAT_FLAG_COLOR: if set, the image will have three color components
154 * per pixel (red, green and blue); if not set, the image will just have one
155 * luminance (grayscale) component.
156 *
157 * PNG_FORMAT_FLAG_ALPHA: if set, each pixel in the image will have an
158 * additional alpha value; a linear value that describes the degree the
159 * image pixel covers (overwrites) the contents of the existing pixel on the
160 * display.
161 *
162 * PNG_FORMAT_FLAG_LINEAR: if set, the components of each pixel will be
163 * returned as a series of 16-bit linear values; if not set, the components
164 * will be returned as a series of 8-bit values encoded according to the
165 * sRGB standard. The 8-bit format is the normal format for images intended
166 * for direct display, because almost all display devices do the inverse of
167 * the sRGB transformation to the data they receive. The 16-bit format is
168 * more common for scientific data and image data that must be further
169 * processed; because it is linear, simple math can be done on the component
170 * values. Regardless of the setting of this flag, the alpha channel is
171 * always linear, although it will be 8 bits or 16 bits wide as specified by
172 * the flag.
173 *
174 * PNG_FORMAT_FLAG_BGR: if set, the components of a color pixel will be
175 * returned in the order blue, then green, then red. If not set, the pixel
176 * components are in the order red, then green, then blue.
177 *
178 * PNG_FORMAT_FLAG_AFIRST: if set, the alpha channel (if present) precedes the
179 * color or grayscale components. If not set, the alpha channel follows the
180 * components.
181 *
182 * You do not have to read directly from a file. You can read from memory or,
183 * on systems that support it, from a <stdio.h> FILE*. This is controlled by
184 * the particular png_image_read_from_ function you call at the start.
185 * Likewise, on write, you can write to a FILE* if your system supports it.
186 * Check the macro PNG_STDIO_SUPPORTED to see if stdio support has been
187 * included in your libpng build.
188 *
189 * If you read 16-bit (PNG_FORMAT_FLAG_LINEAR) data, you may need to write it
190 * in the 8-bit format for display. You do this by setting the convert_to_8bit
191 * flag to 'true'.
192 *
193 * Don't repeatedly convert between the 8-bit and 16-bit forms. There is
194 * significant data loss when 16-bit data is converted to the 8-bit encoding,
195 * and the current libpng implementation of conversion to 16-bit is also
196 * significantly lossy. The latter will be fixed in the future, but the former
197 * is unavoidable - the 8-bit format just doesn't have enough resolution.
198 */
199
200 /* If your program needs more information from the PNG data it reads, or if you
201 * need to do more complex transformations, or minimize transformations, on the
202 * data you read, then you must use one of the several lower level libpng
203 * interfaces.
204 *
205 * All these interfaces require that you do your own error handling - your
206 * program must be able to arrange for control to return to your own code, any
207 * time libpng encounters a problem. There are several ways to do this, but
208 * the standard way is to use the <setjmp.h> interface to establish a return
209 * point within your own code. You must do this if you do not use the
210 * simplified interface (above).
211 *
212 * The first step is to include the header files you need, including the libpng
213 * header file. Include any standard headers and feature test macros your
214 * program requires before including png.h:
215 */
216 #include <png.h>
217
218 /* The png_jmpbuf() macro, used in error handling, became available in
219 * libpng version 1.0.6. If you want to be able to run your code with older
220 * versions of libpng, you must define the macro yourself (but only if it
221 * is not already defined by libpng!)
222 */
223
224 #ifndef png_jmpbuf
225 # define png_jmpbuf(png_ptr) ((png_ptr)->png_jmpbuf)
226 #endif
227
228 /* Check to see if a file is a PNG file using png_sig_cmp(). png_sig_cmp()
229 * returns zero if the image is a PNG, and nonzero otherwise.
230 *
231 * The function check_if_png() shown here, but not used, returns nonzero (true)
232 * if the file can be opened and is a PNG, and 0 (false) otherwise.
233 *
234 * If this call is successful, and you are going to keep the file open,
235 * you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once
236 * you have created the png_ptr, so that libpng knows your application
237 * has read that many bytes from the start of the file. Make sure you
238 * don't call png_set_sig_bytes() with more than 8 bytes read or give it
239 * an incorrect number of bytes read, or you will either have read too
240 * many bytes (your fault), or you are telling libpng to read the wrong
241 * number of magic bytes (also your fault).
242 *
243 * Many applications already read the first 2 or 4 bytes from the start
244 * of the image to determine the file type, so it would be easiest just
245 * to pass the bytes to png_sig_cmp(), or even skip that if you know
246 * you have a PNG file, and call png_set_sig_bytes().
247 */
248 #define PNG_BYTES_TO_CHECK 4
249 int check_if_png(char *file_name, FILE **fp)
250 {
251 char buf[PNG_BYTES_TO_CHECK];
252
253 /* Open the prospective PNG file. */
254 if ((*fp = fopen(file_name, "rb")) == NULL)
255 return 0;
256
257 /* Read in some of the signature bytes. */
258 if (fread(buf, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK)
259 return 0;
260
261 /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.
262 * Return nonzero (true) if they match.
263 */
264 return(!png_sig_cmp(buf, 0, PNG_BYTES_TO_CHECK));
265 }
266
267 /* Read a PNG file. You may want to return an error code if the read
268 * fails (depending upon the failure). There are two "prototypes" given
269 * here - one where we are given the filename, and we need to open the
270 * file, and the other where we are given an open file (possibly with
271 * some or all of the magic bytes read - see comments above).
272 */
273 #ifdef open_file /* prototype 1 */
274 void read_png(char *file_name) /* We need to open the file */
275 {
276 png_structp png_ptr;
277 png_infop info_ptr;
278 int sig_read = 0;
279 png_uint_32 width, height;
280 int bit_depth, color_type, interlace_type;
281 FILE *fp;
282
283 if ((fp = fopen(file_name, "rb")) == NULL)
284 return (ERROR);
285
286 #else no_open_file /* prototype 2 */
287 void read_png(FILE *fp, int sig_read) /* File is already open */
288 {
289 png_structp png_ptr;
290 png_infop info_ptr;
291 png_uint_32 width, height;
292 int bit_depth, color_type, interlace_type;
293 #endif no_open_file /* Only use one prototype! */
294
295 /* Create and initialize the png_struct with the desired error handler
296 * functions. If you want to use the default stderr and longjump method,
297 * you can supply NULL for the last three parameters. We also supply the
298 * the compiler header file version, so that we know if the application
299 * was compiled with a compatible version of the library. REQUIRED.
300 */
301 png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
302 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
303
304 if (png_ptr == NULL)
305 {
306 fclose(fp);
307 return (ERROR);
308 }
309
310 /* Allocate/initialize the memory for image information. REQUIRED. */
311 info_ptr = png_create_info_struct(png_ptr);
312 if (info_ptr == NULL)
313 {
314 fclose(fp);
315 png_destroy_read_struct(&png_ptr, NULL, NULL);
316 return (ERROR);
317 }
318
319 /* Set error handling if you are using the setjmp/longjmp method (this is
320 * the normal method of doing things with libpng). REQUIRED unless you
321 * set up your own error handlers in the png_create_read_struct() earlier.
322 */
323 if (setjmp(png_jmpbuf(png_ptr)))
324 {
325 /* Free all of the memory associated with the png_ptr and info_ptr. */
326 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
327 fclose(fp);
328 /* If we get here, we had a problem reading the file. */
329 return (ERROR);
330 }
331
332 /* One of the following I/O initialization methods is REQUIRED. */
333 #ifdef streams /* PNG file I/O method 1 */
334 /* Set up the input control if you are using standard C streams. */
335 png_init_io(png_ptr, fp);
336
337 #else no_streams /* PNG file I/O method 2 */
338 /* If you are using replacement read functions, instead of calling
339 * png_init_io(), you would call:
340 */
341 png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn);
342 /* where user_io_ptr is a structure you want available to the callbacks. */
343 #endif no_streams /* Use only one I/O method! */
344
345 /* If we have already read some of the signature */
346 png_set_sig_bytes(png_ptr, sig_read);
347
348 #ifdef hilevel
349 /* If you have enough memory to read in the entire image at once,
350 * and you need to specify only transforms that can be controlled
351 * with one of the PNG_TRANSFORM_* bits (this presently excludes
352 * quantizing, filling, setting background, and doing gamma
353 * adjustment), then you can read the entire image (including
354 * pixels) into the info structure with this call:
355 */
356 png_read_png(png_ptr, info_ptr, png_transforms, NULL);
357
358 #else
359 /* OK, you're doing it the hard way, with the lower-level functions. */
360
361 /* The call to png_read_info() gives us all of the information from the
362 * PNG file before the first IDAT (image data chunk). REQUIRED.
363 */
364 png_read_info(png_ptr, info_ptr);
365
366 png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
367 &interlace_type, NULL, NULL);
368
369 /* Set up the data transformations you want. Note that these are all
370 * optional. Only call them if you want/need them. Many of the
371 * transformations only work on specific types of images, and many
372 * are mutually exclusive.
373 */
374
375 /* Tell libpng to strip 16 bits/color files down to 8 bits/color.
376 * Use accurate scaling if it's available, otherwise just chop off the
377 * low byte.
378 */
379 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
380 png_set_scale_16(png_ptr);
381 #else
382 png_set_strip_16(png_ptr);
383 #endif
384
385 /* Strip alpha bytes from the input data without combining with the
386 * background (not recommended).
387 */
388 png_set_strip_alpha(png_ptr);
389
390 /* Extract multiple pixels with bit depths of 1, 2 or 4 from a single
391 * byte into separate bytes (useful for paletted and grayscale images).
392 */
393 png_set_packing(png_ptr);
394
395 /* Change the order of packed pixels to least significant bit first
396 * (not useful if you are using png_set_packing).
397 */
398 png_set_packswap(png_ptr);
399
400 /* Expand paletted colors into true RGB triplets. */
401 if (color_type == PNG_COLOR_TYPE_PALETTE)
402 png_set_palette_to_rgb(png_ptr);
403
404 /* Expand grayscale images to the full 8 bits from 1, 2 or 4 bits/pixel. */
405 if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
406 png_set_expand_gray_1_2_4_to_8(png_ptr);
407
408 /* Expand paletted or RGB images with transparency to full alpha channels
409 * so the data will be available as RGBA quartets.
410 */
411 if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) != 0)
412 png_set_tRNS_to_alpha(png_ptr);
413
414 /* Set the background color to draw transparent and alpha images over.
415 * It is possible to set the red, green and blue components directly
416 * for paletted images, instead of supplying a palette index. Note that,
417 * even if the PNG file supplies a background, you are not required to
418 * use it - you should use the (solid) application background if it has one.
419 */
420 png_color_16 my_background, *image_background;
421
422 if (png_get_bKGD(png_ptr, info_ptr, &image_background) != 0)
423 png_set_background(png_ptr, image_background,
424 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
425 else
426 png_set_background(png_ptr, &my_background,
427 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
428
429 /* Some suggestions as to how to get a screen gamma value.
430 *
431 * Note that screen gamma is the display_exponent, which includes
432 * the CRT_exponent and any correction for viewing conditions.
433 */
434 if (/* We have a user-defined screen gamma value */)
435 screen_gamma = user-defined screen_gamma;
436 /* This is one way that applications share the same screen gamma value. */
437 else if ((gamma_str = getenv("SCREEN_GAMMA")) != NULL)
438 screen_gamma = atof(gamma_str);
439 /* If we don't have another value */
440 else
441 {
442 screen_gamma = PNG_DEFAULT_sRGB; /* A good guess for a PC monitor
443 in a dimly lit room */
444 screen_gamma = PNG_GAMMA_MAC_18 or 1.0; /* Good guesses for Mac
445 systems */
446 }
447
448 /* Tell libpng to handle the gamma conversion for you. The final call
449 * is a good guess for PC generated images, but it should be configurable
450 * by the user at run time. Gamma correction support in your application
451 * is strongly recommended.
452 */
453
454 int intent;
455
456 if (png_get_sRGB(png_ptr, info_ptr, &intent) != 0)
457 png_set_gamma(png_ptr, screen_gamma, PNG_DEFAULT_sRGB);
458 else
459 {
460 double image_gamma;
461 if (png_get_gAMA(png_ptr, info_ptr, &image_gamma) != 0)
462 png_set_gamma(png_ptr, screen_gamma, image_gamma);
463 else
464 png_set_gamma(png_ptr, screen_gamma, 0.45455);
465 }
466
467 #ifdef PNG_READ_QUANTIZE_SUPPORTED
468 /* Quantize RGB files down to 8-bit palette, or reduce palettes
469 * to the number of colors available on your screen.
470 */
471 if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
472 {
473 int num_palette;
474 png_colorp palette;
475
476 /* This reduces the image to the application-supplied palette. */
477 if (/* We have our own palette */)
478 {
479 /* An array of colors to which the image should be quantized. */
480 png_color std_color_cube[MAX_SCREEN_COLORS];
481 png_set_quantize(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
482 MAX_SCREEN_COLORS, NULL, 0);
483 }
484 /* This reduces the image to the palette supplied in the file. */
485 else if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette) != 0)
486 {
487 png_uint_16p histogram = NULL;
488 png_get_hIST(png_ptr, info_ptr, &histogram);
489 png_set_quantize(png_ptr, palette, num_palette,
490 max_screen_colors, histogram, 0);
491 }
492 }
493 #endif /* READ_QUANTIZE */
494
495 /* Invert monochrome files to have 0 as white and 1 as black. */
496 png_set_invert_mono(png_ptr);
497
498 /* If you want to shift the pixel values from the range [0,255] or
499 * [0,65535] to the original [0,7] or [0,31], or whatever range the
500 * colors were originally in:
501 */
502 if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT) != 0)
503 {
504 png_color_8p sig_bit_p;
505 png_get_sBIT(png_ptr, info_ptr, &sig_bit_p);
506 png_set_shift(png_ptr, sig_bit_p);
507 }
508
509 /* Flip the RGB pixels to BGR (or RGBA to BGRA). */
510 if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
511 png_set_bgr(png_ptr);
512
513 /* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR). */
514 png_set_swap_alpha(png_ptr);
515
516 /* Swap bytes of 16-bit files to least significant byte first. */
517 png_set_swap(png_ptr);
518
519 /* Add filler (or alpha) byte (before/after each RGB triplet). */
520 png_set_filler(png_ptr, 0xffff, PNG_FILLER_AFTER);
521
522 #ifdef PNG_READ_INTERLACING_SUPPORTED
523 /* Turn on interlace handling. REQUIRED if you are not using
524 * png_read_image(). To see how to handle interlacing passes,
525 * see the png_read_row() method below:
526 */
527 number_passes = png_set_interlace_handling(png_ptr);
528 #else /* !READ_INTERLACING */
529 number_passes = 1;
530 #endif /* READ_INTERLACING */
531
532 /* Optional call to gamma correct and add the background to the palette
533 * and update info structure. REQUIRED if you are expecting libpng to
534 * update the palette for you (i.e. you selected such a transform above).
535 */
536 png_read_update_info(png_ptr, info_ptr);
537
538 /* Allocate the memory to hold the image using the fields of info_ptr. */
539 png_bytep row_pointers[height];
540 for (row = 0; row < height; row++)
541 row_pointers[row] = NULL; /* Clear the pointer array */
542 for (row = 0; row < height; row++)
543 row_pointers[row] = png_malloc(png_ptr, png_get_rowbytes(png_ptr,
544 info_ptr));
545
546 /* Now it's time to read the image. One of these methods is REQUIRED. */
547 #ifdef entire /* Read the entire image in one go */
548 png_read_image(png_ptr, row_pointers);
549
550 #else no_entire /* Read the image one or more scanlines at a time */
551 /* The other way to read images - deal with interlacing: */
552 for (pass = 0; pass < number_passes; pass++)
553 {
554 #ifdef single /* Read the image a single row at a time */
555 for (y = 0; y < height; y++)
556 png_read_rows(png_ptr, &row_pointers[y], NULL, 1);
557
558 #else no_single /* Read the image several rows at a time */
559 for (y = 0; y < height; y += number_of_rows)
560 {
561 #ifdef sparkle /* Read the image using the "sparkle" effect. */
562 png_read_rows(png_ptr, &row_pointers[y], NULL,
563 number_of_rows);
564 #else no_sparkle /* Read the image using the "rectangle" effect */
565 png_read_rows(png_ptr, NULL, &row_pointers[y],
566 number_of_rows);
567 #endif no_sparkle /* Use only one of these two methods */
568 }
569
570 /* If you want to display the image after every pass, do so here. */
571 #endif no_single /* Use only one of these two methods */
572 }
573 #endif no_entire /* Use only one of these two methods */
574
575 /* Read rest of file, and get additional chunks in info_ptr. REQUIRED. */
576 png_read_end(png_ptr, info_ptr);
577 #endif hilevel
578
579 /* At this point you have read the entire image. */
580
581 /* Clean up after the read, and free any memory allocated. REQUIRED. */
582 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
583
584 /* Close the file. */
585 fclose(fp);
586
587 /* That's it! */
588 return (OK);
589 }
590
591 /* Progressively read a file */
592
593 int
594 initialize_png_reader(png_structp *png_ptr, png_infop *info_ptr)
595 {
596 /* Create and initialize the png_struct with the desired error handler
597 * functions. If you want to use the default stderr and longjump method,
598 * you can supply NULL for the last three parameters. We also check that
599 * the library version is compatible, in case we are using dynamically
600 * linked libraries.
601 */
602 *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
603 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
604 if (*png_ptr == NULL)
605 {
606 *info_ptr = NULL;
607 return (ERROR);
608 }
609 *info_ptr = png_create_info_struct(png_ptr);
610 if (*info_ptr == NULL)
611 {
612 png_destroy_read_struct(png_ptr, info_ptr, NULL);
613 return (ERROR);
614 }
615 if (setjmp(png_jmpbuf((*png_ptr))))
616 {
617 png_destroy_read_struct(png_ptr, info_ptr, NULL);
618 return (ERROR);
619 }
620
621 /* You will need to provide all three function callbacks,
622 * even if you aren't using all of them.
623 * If you aren't using all functions, you can specify NULL
624 * parameters. Even when all three functions are NULL,
625 * you need to call png_set_progressive_read_fn().
626 * These functions shouldn't be dependent on global or
627 * static variables if you are decoding several images
628 * simultaneously. You should store stream specific data
629 * in a separate struct, given as the second parameter,
630 * and retrieve the pointer from inside the callbacks using
631 * the function png_get_progressive_ptr(png_ptr).
632 */
633 png_set_progressive_read_fn(*png_ptr, (void *)stream_data,
634 info_callback, row_callback, end_callback);
635 return (OK);
636 }
637
638 int
639 process_data(png_structp *png_ptr, png_infop *info_ptr,
640 png_bytep buffer, png_uint_32 length)
641 {
642 if (setjmp(png_jmpbuf((*png_ptr))))
643 {
644 /* Free the png_ptr and info_ptr memory on error. */
645 png_destroy_read_struct(png_ptr, info_ptr, NULL);
646 return (ERROR);
647 }
648
649 /* Give chunks of data as they arrive from the data stream
650 * (in order, of course).
651 * On segmented machines, don't give it any more than 64K.
652 * The library seems to run fine with sizes of 4K, although
653 * you can give it much less if necessary. (I assume you can
654 * give it chunks of 1 byte, but I haven't tried with less
655 * than 256 bytes yet.) When this function returns, you may
656 * want to display any rows that were generated in the row
657 * callback, if you aren't already displaying them there.
658 */
659 png_process_data(*png_ptr, *info_ptr, buffer, length);
660 return (OK);
661 }
662
663 info_callback(png_structp png_ptr, png_infop info)
664 {
665 /* Do any setup here, including setting any of the transformations
666 * mentioned in the Reading PNG files section. For now, you _must_
667 * call either png_start_read_image() or png_read_update_info()
668 * after all the transformations are set (even if you don't set
669 * any). You may start getting rows before png_process_data()
670 * returns, so this is your last chance to prepare for that.
671 */
672 }
673
674 row_callback(png_structp png_ptr, png_bytep new_row,
675 png_uint_32 row_num, int pass)
676 {
677 /* This function is called for every row in the image. If the
678 * image is interlaced, and you turned on the interlace handler,
679 * this function will be called for every row in every pass.
680 *
681 * In this function you will receive a pointer to new row data from
682 * libpng called new_row that is to replace a corresponding row (of
683 * the same data format) in a buffer allocated by your application.
684 *
685 * The new row data pointer "new_row" may be NULL, indicating there is
686 * no new data to be replaced (in cases of interlace loading).
687 *
688 * If new_row is not NULL, then you need to call
689 * png_progressive_combine_row(), to replace the corresponding row as
690 * shown below:
691 */
692
693 /* Get pointer to corresponding row in our PNG read buffer. */
694 png_bytep old_row = ((png_bytep *)our_data)[row_num];
695
696 #ifdef PNG_READ_INTERLACING_SUPPORTED
697 /* If both rows are allocated, then copy the new row
698 * data to the corresponding row data.
699 */
700 if (old_row != NULL && new_row != NULL)
701 png_progressive_combine_row(png_ptr, old_row, new_row);
702
703 /* The rows and passes are called in order, so you don't really
704 * need the row_num and pass, but I'm supplying them because it
705 * may make your life easier.
706 *
707 * For the non-NULL rows of interlaced images, you must call
708 * png_progressive_combine_row() passing in the new row and the
709 * old row, as demonstrated above. You can call this function for
710 * NULL rows (it will just return) and for non-interlaced images
711 * (it just does the memcpy for you) if it will make the code
712 * easier. Thus, you can just do this for all cases:
713 */
714 png_progressive_combine_row(png_ptr, old_row, new_row);
715
716 /* where old_row is what was displayed for previous rows. Note
717 * that the first pass (pass == 0 really) will completely cover
718 * the old row, so the rows do not have to be initialized. After
719 * the first pass (and only for interlaced images), you will have
720 * to pass the current row as new_row, and the function will combine
721 * the old row and the new row.
722 */
723 #endif /* READ_INTERLACING */
724 }
725
726 end_callback(png_structp png_ptr, png_infop info)
727 {
728 /* This function is called when the whole image has been read,
729 * including any chunks after the image (up to and including
730 * the IEND). You will usually have the same info chunk as you
731 * had in the header, although some data may have been added
732 * to the comments and time fields.
733 *
734 * Most people won't do much here, perhaps setting a flag that
735 * marks the image as finished.
736 */
737 }
738
739 /* Write a png file */
740 void write_png(char *file_name /* , ... other image information ... */)
741 {
742 FILE *fp;
743 png_structp png_ptr;
744 png_infop info_ptr;
745 png_colorp palette;
746
747 /* Open the file */
748 fp = fopen(file_name, "wb");
749 if (fp == NULL)
750 return (ERROR);
751
752 /* Create and initialize the png_struct with the desired error handler
753 * functions. If you want to use the default stderr and longjump method,
754 * you can supply NULL for the last three parameters. We also check that
755 * the library version is compatible with the one used at compile time,
756 * in case we are using dynamically linked libraries. REQUIRED.
757 */
758 png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
759 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
760 if (png_ptr == NULL)
761 {
762 fclose(fp);
763 return (ERROR);
764 }
765
766 /* Allocate/initialize the image information data. REQUIRED. */
767 info_ptr = png_create_info_struct(png_ptr);
768 if (info_ptr == NULL)
769 {
770 fclose(fp);
771 png_destroy_write_struct(&png_ptr, NULL);
772 return (ERROR);
773 }
774
775 /* Set up error handling. REQUIRED if you aren't supplying your own
776 * error handling functions in the png_create_write_struct() call.
777 */
778 if (setjmp(png_jmpbuf(png_ptr)))
779 {
780 /* If we get here, we had a problem writing the file. */
781 fclose(fp);
782 png_destroy_write_struct(&png_ptr, &info_ptr);
783 return (ERROR);
784 }
785
786 /* One of the following I/O initialization functions is REQUIRED. */
787
788 #ifdef streams /* I/O initialization method 1 */
789 /* Set up the output control if you are using standard C streams. */
790 png_init_io(png_ptr, fp);
791
792 #else no_streams /* I/O initialization method 2 */
793 /* If you are using replacement write functions, instead of calling
794 * png_init_io(), you would call:
795 */
796 png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,
797 user_IO_flush_function);
798 /* where user_io_ptr is a structure you want available to the callbacks. */
799 #endif no_streams /* Only use one initialization method */
800
801 #ifdef hilevel
802 /* This is the easy way. Use it if you already have all the
803 * image info living in the structure. You could "|" many
804 * PNG_TRANSFORM flags into the png_transforms integer here.
805 */
806 png_write_png(png_ptr, info_ptr, png_transforms, NULL);
807
808 #else
809 /* This is the hard way. */
810
811 /* Set the image information here. Width and height are up to 2^31,
812 * bit_depth is one of 1, 2, 4, 8 or 16, but valid values also depend on
813 * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
814 * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
815 * or PNG_COLOR_TYPE_RGB_ALPHA. interlace is either PNG_INTERLACE_NONE or
816 * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
817 * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE.
818 * REQUIRED.
819 */
820 png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth,
821 PNG_COLOR_TYPE_???, PNG_INTERLACE_????,
822 PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
823
824 /* Set the palette if there is one. REQUIRED for indexed-color images. */
825 palette = (png_colorp)png_malloc(png_ptr,
826 PNG_MAX_PALETTE_LENGTH * (sizeof (png_color)));
827 /* ... Set palette colors ... */
828 png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
829 /* You must not free palette here, because png_set_PLTE only makes a link
830 * to the palette that you allocated. Wait until you are about to destroy
831 * the png structure.
832 */
833
834 /* Optional significant bit (sBIT) chunk. */
835 png_color_8 sig_bit;
836
837 /* If we are dealing with a grayscale image then */
838 sig_bit.gray = true_bit_depth;
839
840 /* Otherwise, if we are dealing with a color image then */
841 sig_bit.red = true_red_bit_depth;
842 sig_bit.green = true_green_bit_depth;
843 sig_bit.blue = true_blue_bit_depth;
844
845 /* If the image has an alpha channel then */
846 sig_bit.alpha = true_alpha_bit_depth;
847
848 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
849
850 /* Optional gamma chunk is strongly suggested if you have any guess
851 * as to the correct gamma of the image.
852 */
853 png_set_gAMA(png_ptr, info_ptr, gamma);
854
855 /* Optionally write comments into the image. */
856 {
857 png_text text_ptr[3];
858
859 char key0[] = "Title";
860 char text0[] = "Mona Lisa";
861 text_ptr[0].key = key0;
862 text_ptr[0].text = text0;
863 text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
864 text_ptr[0].itxt_length = 0;
865 text_ptr[0].lang = NULL;
866 text_ptr[0].lang_key = NULL;
867
868 char key1[] = "Author";
869 char text1[] = "Leonardo DaVinci";
870 text_ptr[1].key = key1;
871 text_ptr[1].text = text1;
872 text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;
873 text_ptr[1].itxt_length = 0;
874 text_ptr[1].lang = NULL;
875 text_ptr[1].lang_key = NULL;
876
877 char key2[] = "Description";
878 char text2[] = "<long text>";
879 text_ptr[2].key = key2;
880 text_ptr[2].text = text2;
881 text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;
882 text_ptr[2].itxt_length = 0;
883 text_ptr[2].lang = NULL;
884 text_ptr[2].lang_key = NULL;
885
886 png_set_text(write_ptr, write_info_ptr, text_ptr, 3);
887 }
888
889 /* Other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs. */
890
891 /* Note that if sRGB is present, the gAMA and cHRM chunks must be ignored
892 * on read and, if your application chooses to write them, they must
893 * be written in accordance with the sRGB profile.
894 */
895
896 /* Write the file header information. REQUIRED. */
897 png_write_info(png_ptr, info_ptr);
898
899 /* If you want, you can write the info in two steps, in case you need to
900 * write your private chunk ahead of PLTE:
901 *
902 * png_write_info_before_PLTE(write_ptr, write_info_ptr);
903 * write_my_chunk();
904 * png_write_info(png_ptr, info_ptr);
905 *
906 * However, given the level of known- and unknown-chunk support in 1.2.0
907 * and up, this should no longer be necessary.
908 */
909
910 /* Once we write out the header, the compression type on the text
911 * chunk gets changed to PNG_TEXT_COMPRESSION_NONE_WR or
912 * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again
913 * at the end.
914 */
915
916 /* Set up the transformations you want. Note that these are
917 * all optional. Only call them if you want them.
918 */
919
920 /* Invert monochrome pixels. */
921 png_set_invert_mono(png_ptr);
922
923 /* Shift the pixels up to a legal bit depth and fill in
924 * as appropriate to correctly scale the image.
925 */
926 png_set_shift(png_ptr, &sig_bit);
927
928 /* Pack pixels into bytes. */
929 png_set_packing(png_ptr);
930
931 /* Swap location of alpha bytes from ARGB to RGBA. */
932 png_set_swap_alpha(png_ptr);
933
934 /* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into
935 * RGB (4 channels -> 3 channels). The second parameter is not used.
936 */
937 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
938
939 /* Flip BGR pixels to RGB. */
940 png_set_bgr(png_ptr);
941
942 /* Swap bytes of 16-bit files to most significant byte first. */
943 png_set_swap(png_ptr);
944
945 /* Swap bits of 1-bit, 2-bit, 4-bit packed pixel formats. */
946 png_set_packswap(png_ptr);
947
948 /* Turn on interlace handling if you are not using png_write_image(). */
949 if (interlacing != 0)
950 number_passes = png_set_interlace_handling(png_ptr);
951 else
952 number_passes = 1;
953
954 /* The easiest way to write the image (you may have a different memory
955 * layout, however, so choose what fits your needs best). You need to
956 * use the first method if you aren't handling interlacing yourself.
957 */
958 png_uint_32 k, height, width;
959
960 /* In this example, "image" is a one-dimensional array of bytes. */
961
962 /* Guard against integer overflow. */
963 if (height > PNG_SIZE_MAX / (width * bytes_per_pixel))
964 png_error(png_ptr, "Image data buffer would be too large");
965
966 png_byte image[height * width * bytes_per_pixel];
967 png_bytep row_pointers[height];
968
969 if (height > PNG_UINT_32_MAX / (sizeof (png_bytep)))
970 png_error(png_ptr, "Image is too tall to process in memory");
971
972 /* Set up pointers into your "image" byte array. */
973 for (k = 0; k < height; k++)
974 row_pointers[k] = image + k * width * bytes_per_pixel;
975
976 /* One of the following output methods is REQUIRED. */
977
978 #ifdef entire /* Write out the entire image data in one call */
979 png_write_image(png_ptr, row_pointers);
980
981 /* The other way to write the image - deal with interlacing. */
982
983 #else no_entire /* Write out the image data by one or more scanlines */
984
985 /* The number of passes is either 1 for non-interlaced images,
986 * or 7 for interlaced images.
987 */
988 for (pass = 0; pass < number_passes; pass++)
989 {
990 /* Write a few rows at a time. */
991 png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);
992
993 /* If you are only writing one row at a time, this works. */
994 for (y = 0; y < height; y++)
995 png_write_rows(png_ptr, &row_pointers[y], 1);
996 }
997 #endif no_entire /* Use only one output method */
998
999 /* You can write optional chunks like tEXt, zTXt, and tIME at the end
1000 * as well. Shouldn't be necessary in 1.2.0 and up, as all the public
1001 * chunks are supported, and you can use png_set_unknown_chunks() to
1002 * register unknown chunks into the info structure to be written out.
1003 */
1004
1005 /* It is REQUIRED to call this to finish writing the rest of the file. */
1006 png_write_end(png_ptr, info_ptr);
1007 #endif hilevel
1008
1009 /* If you png_malloced a palette, free it here.
1010 * (Don't free info_ptr->palette, as shown in versions 1.0.5m and earlier of
1011 * this example; if libpng mallocs info_ptr->palette, libpng will free it).
1012 * If you allocated it with malloc() instead of png_malloc(), use free()
1013 * instead of png_free().
1014 */
1015 png_free(png_ptr, palette);
1016 palette = NULL;
1017
1018 /* Similarly, if you png_malloced any data that you passed in with
1019 * png_set_something(), such as a hist or trans array, free it here,
1020 * when you can be sure that libpng is through with it.
1021 */
1022 png_free(png_ptr, trans);
1023 trans = NULL;
1024
1025 /* Whenever you use png_free(), it is a good idea to set the pointer to
1026 * NULL in case your application inadvertently tries to png_free() it
1027 * again. When png_free() sees a NULL it returns without action, avoiding
1028 * the double-free problem.
1029 */
1030
1031 /* Clean up after the write, and free any allocated memory. */
1032 png_destroy_write_struct(&png_ptr, &info_ptr);
1033
1034 /* Close the file. */
1035 fclose(fp);
1036
1037 /* That's it! */
1038 return (OK);
1039 }
1040
1041 #endif /* if 0 */