f8591e668af8a6449d51cc4900c19926c504f24c
[reactos.git] / reactos / dll / 3rdparty / libpng / docs / example.c
1
2 #if 0 /* in case someone actually tries to compile this */
3
4 /* example.c - an example of using libpng
5 * Last changed in libpng 1.6.15 [November 20, 2014]
6 * Maintained 1998-2014 Glenn Randers-Pehrson
7 * Maintained 1996, 1997 Andreas Dilger)
8 * Written 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
9 * To the extent possible under law, the authors have waived
10 * all copyright and related or neighboring rights to this file.
11 * This work is published from: United States.
12 */
13
14 /* This is an example of how to use libpng to read and write PNG files.
15 * The file libpng-manual.txt is much more verbose then this. If you have not
16 * read it, do so first. This was designed to be a starting point of an
17 * implementation. This is not officially part of libpng, is hereby placed
18 * in the public domain, and therefore does not require a copyright notice.
19 *
20 * This file does not currently compile, because it is missing certain
21 * parts, like allocating memory to hold an image. You will have to
22 * supply these parts to get it to compile. For an example of a minimal
23 * working PNG reader/writer, see pngtest.c, included in this distribution;
24 * see also the programs in the contrib directory.
25 */
26
27 /* The simple, but restricted, approach to reading a PNG file or data stream
28 * just requires two function calls, as in the following complete program.
29 * Writing a file just needs one function call, so long as the data has an
30 * appropriate layout.
31 *
32 * The following code reads PNG image data from a file and writes it, in a
33 * potentially new format, to a new file. While this code will compile there is
34 * minimal (insufficient) error checking; for a more realistic version look at
35 * contrib/examples/pngtopng.c
36 */
37 #include <stddef.h>
38 #include <stdlib.h>
39 #include <string.h>
40 #include <stdio.h>
41 #include <png.h>
42 #include <zlib.h>
43
44 int main(int argc, const char **argv)
45 {
46 if (argc == 3)
47 {
48 png_image image; /* The control structure used by libpng */
49
50 /* Initialize the 'png_image' structure. */
51 memset(&image, 0, (sizeof image));
52 image.version = PNG_IMAGE_VERSION;
53
54 /* The first argument is the file to read: */
55 if (png_image_begin_read_from_file(&image, argv[1]) != 0)
56 {
57 png_bytep buffer;
58
59 /* Set the format in which to read the PNG file; this code chooses a
60 * simple sRGB format with a non-associated alpha channel, adequate to
61 * store most images.
62 */
63 image.format = PNG_FORMAT_RGBA;
64
65 /* Now allocate enough memory to hold the image in this format; the
66 * PNG_IMAGE_SIZE macro uses the information about the image (width,
67 * height and format) stored in 'image'.
68 */
69 buffer = malloc(PNG_IMAGE_SIZE(image));
70
71 /* If enough memory was available read the image in the desired format
72 * then write the result out to the new file. 'background' is not
73 * necessary when reading the image because the alpha channel is
74 * preserved; if it were to be removed, for example if we requested
75 * PNG_FORMAT_RGB, then either a solid background color would have to
76 * be supplied or the output buffer would have to be initialized to the
77 * actual background of the image.
78 *
79 * The fourth argument to png_image_finish_read is the 'row_stride' -
80 * this is the number of components allocated for the image in each
81 * row. It has to be at least as big as the value returned by
82 * PNG_IMAGE_ROW_STRIDE, but if you just allocate space for the
83 * default, minimum, size using PNG_IMAGE_SIZE as above you can pass
84 * zero.
85 *
86 * The final argument is a pointer to a buffer for the colormap;
87 * colormaps have exactly the same format as a row of image pixels (so
88 * you choose what format to make the colormap by setting
89 * image.format). A colormap is only returned if
90 * PNG_FORMAT_FLAG_COLORMAP is also set in image.format, so in this
91 * case NULL is passed as the final argument. If you do want to force
92 * all images into an index/color-mapped format then you can use:
93 *
94 * PNG_IMAGE_COLORMAP_SIZE(image)
95 *
96 * to find the maximum size of the colormap in bytes.
97 */
98 if (buffer != NULL &&
99 png_image_finish_read(&image, NULL/*background*/, buffer,
100 0/*row_stride*/, NULL/*colormap*/) != 0)
101 {
102 /* Now write the image out to the second argument. In the write
103 * call 'convert_to_8bit' allows 16-bit data to be squashed down to
104 * 8 bits; this isn't necessary here because the original read was
105 * to the 8-bit format.
106 */
107 if (png_image_write_to_file(&image, argv[2], 0/*convert_to_8bit*/,
108 buffer, 0/*row_stride*/, NULL/*colormap*/) != 0)
109 {
110 /* The image has been written successfully. */
111 exit(0);
112 }
113 }
114
115 else
116 {
117 /* Calling png_free_image is optional unless the simplified API was
118 * not run to completion. In this case if there wasn't enough
119 * memory for 'buffer' we didn't complete the read, so we must free
120 * the image:
121 */
122 if (buffer == NULL)
123 png_free_image(&image);
124
125 else
126 free(buffer);
127 }
128
129 /* Something went wrong reading or writing the image. libpng stores a
130 * textual message in the 'png_image' structure:
131 */
132 fprintf(stderr, "pngtopng: error: %s\n", image.message);
133 exit (1);
134 }
135
136 fprintf(stderr, "pngtopng: usage: pngtopng input-file output-file\n");
137 exit(1);
138 }
139
140 /* That's it ;-) Of course you probably want to do more with PNG files than
141 * just converting them all to 32-bit RGBA PNG files; you can do that between
142 * the call to png_image_finish_read and png_image_write_to_file. You can also
143 * ask for the image data to be presented in a number of different formats. You
144 * do this by simply changing the 'format' parameter set before allocating the
145 * buffer.
146 *
147 * The format parameter consists of five flags that define various aspects of
148 * the image, you can simply add these together to get the format or you can use
149 * one of the predefined macros from png.h (as above):
150 *
151 * PNG_FORMAT_FLAG_COLOR: if set the image will have three color components per
152 * pixel (red, green and blue), if not set the image will just have one
153 * luminance (grayscale) component.
154 *
155 * PNG_FORMAT_FLAG_ALPHA: if set each pixel in the image will have an additional
156 * alpha value; a linear value that describes the degree the image pixel
157 * covers (overwrites) the contents of the existing pixel on the display.
158 *
159 * PNG_FORMAT_FLAG_LINEAR: if set the components of each pixel will be returned
160 * as a series of 16-bit linear values, if not set the components will be
161 * returned as a series of 8-bit values encoded according to the 'sRGB'
162 * standard. The 8-bit format is the normal format for images intended for
163 * direct display, because almost all display devices do the inverse of the
164 * sRGB transformation to the data they receive. The 16-bit format is more
165 * common for scientific data and image data that must be further processed;
166 * because it is linear simple math can be done on the component values.
167 * Regardless of the setting of this flag the alpha channel is always linear,
168 * although it will be 8 bits or 16 bits wide as specified by the flag.
169 *
170 * PNG_FORMAT_FLAG_BGR: if set the components of a color pixel will be returned
171 * in the order blue, then green, then red. If not set the pixel components
172 * are in the order red, then green, then blue.
173 *
174 * PNG_FORMAT_FLAG_AFIRST: if set the alpha channel (if present) precedes the
175 * color or grayscale components. If not set the alpha channel follows the
176 * components.
177 *
178 * You do not have to read directly from a file. You can read from memory or,
179 * on systems that support it, from a <stdio.h> FILE*. This is controlled by
180 * the particular png_image_read_from_ function you call at the start. Likewise
181 * on write you can write to a FILE* if your system supports it. Check the
182 * macro PNG_STDIO_SUPPORTED to see if stdio support has been included in your
183 * libpng build.
184 *
185 * If you read 16-bit (PNG_FORMAT_FLAG_LINEAR) data you may need to write it in
186 * the 8-bit format for display. You do this by setting the convert_to_8bit
187 * flag to 'true'.
188 *
189 * Don't repeatedly convert between the 8-bit and 16-bit forms. There is
190 * significant data loss when 16-bit data is converted to the 8-bit encoding and
191 * the current libpng implementation of conversion to 16-bit is also
192 * significantly lossy. The latter will be fixed in the future, but the former
193 * is unavoidable - the 8-bit format just doesn't have enough resolution.
194 */
195
196 /* If your program needs more information from the PNG data it reads, or if you
197 * need to do more complex transformations, or minimize transformations, on the
198 * data you read, then you must use one of the several lower level libpng
199 * interfaces.
200 *
201 * All these interfaces require that you do your own error handling - your
202 * program must be able to arrange for control to return to your own code any
203 * time libpng encounters a problem. There are several ways to do this, but the
204 * standard way is to use the ANSI-C (C90) <setjmp.h> interface to establish a
205 * return point within your own code. You must do this if you do not use the
206 * simplified interface (above).
207 *
208 * The first step is to include the header files you need, including the libpng
209 * header file. Include any standard headers and feature test macros your
210 * program requires before including png.h:
211 */
212 #include <png.h>
213
214 /* The png_jmpbuf() macro, used in error handling, became available in
215 * libpng version 1.0.6. If you want to be able to run your code with older
216 * versions of libpng, you must define the macro yourself (but only if it
217 * is not already defined by libpng!).
218 */
219
220 #ifndef png_jmpbuf
221 # define png_jmpbuf(png_ptr) ((png_ptr)->png_jmpbuf)
222 #endif
223
224 /* Check to see if a file is a PNG file using png_sig_cmp(). png_sig_cmp()
225 * returns zero if the image is a PNG and nonzero if it isn't a PNG.
226 *
227 * The function check_if_png() shown here, but not used, returns nonzero (true)
228 * if the file can be opened and is a PNG, 0 (false) otherwise.
229 *
230 * If this call is successful, and you are going to keep the file open,
231 * you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once
232 * you have created the png_ptr, so that libpng knows your application
233 * has read that many bytes from the start of the file. Make sure you
234 * don't call png_set_sig_bytes() with more than 8 bytes read or give it
235 * an incorrect number of bytes read, or you will either have read too
236 * many bytes (your fault), or you are telling libpng to read the wrong
237 * number of magic bytes (also your fault).
238 *
239 * Many applications already read the first 2 or 4 bytes from the start
240 * of the image to determine the file type, so it would be easiest just
241 * to pass the bytes to png_sig_cmp() or even skip that if you know
242 * you have a PNG file, and call png_set_sig_bytes().
243 */
244 #define PNG_BYTES_TO_CHECK 4
245 int check_if_png(char *file_name, FILE **fp)
246 {
247 char buf[PNG_BYTES_TO_CHECK];
248
249 /* Open the prospective PNG file. */
250 if ((*fp = fopen(file_name, "rb")) == NULL)
251 return 0;
252
253 /* Read in some of the signature bytes */
254 if (fread(buf, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK)
255 return 0;
256
257 /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.
258 Return nonzero (true) if they match */
259
260 return(!png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK));
261 }
262
263 /* Read a PNG file. You may want to return an error code if the read
264 * fails (depending upon the failure). There are two "prototypes" given
265 * here - one where we are given the filename, and we need to open the
266 * file, and the other where we are given an open file (possibly with
267 * some or all of the magic bytes read - see comments above).
268 */
269 #ifdef open_file /* prototype 1 */
270 void read_png(char *file_name) /* We need to open the file */
271 {
272 png_structp png_ptr;
273 png_infop info_ptr;
274 int sig_read = 0;
275 png_uint_32 width, height;
276 int bit_depth, color_type, interlace_type;
277 FILE *fp;
278
279 if ((fp = fopen(file_name, "rb")) == NULL)
280 return (ERROR);
281
282 #else no_open_file /* prototype 2 */
283 void read_png(FILE *fp, int sig_read) /* File is already open */
284 {
285 png_structp png_ptr;
286 png_infop info_ptr;
287 png_uint_32 width, height;
288 int bit_depth, color_type, interlace_type;
289 #endif no_open_file /* Only use one prototype! */
290
291 /* Create and initialize the png_struct with the desired error handler
292 * functions. If you want to use the default stderr and longjump method,
293 * you can supply NULL for the last three parameters. We also supply the
294 * the compiler header file version, so that we know if the application
295 * was compiled with a compatible version of the library. REQUIRED
296 */
297 png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
298 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
299
300 if (png_ptr == NULL)
301 {
302 fclose(fp);
303 return (ERROR);
304 }
305
306 /* Allocate/initialize the memory for image information. REQUIRED. */
307 info_ptr = png_create_info_struct(png_ptr);
308 if (info_ptr == NULL)
309 {
310 fclose(fp);
311 png_destroy_read_struct(&png_ptr, NULL, NULL);
312 return (ERROR);
313 }
314
315 /* Set error handling if you are using the setjmp/longjmp method (this is
316 * the normal method of doing things with libpng). REQUIRED unless you
317 * set up your own error handlers in the png_create_read_struct() earlier.
318 */
319
320 if (setjmp(png_jmpbuf(png_ptr)))
321 {
322 /* Free all of the memory associated with the png_ptr and info_ptr */
323 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
324 fclose(fp);
325 /* If we get here, we had a problem reading the file */
326 return (ERROR);
327 }
328
329 /* One of the following I/O initialization methods is REQUIRED */
330 #ifdef streams /* PNG file I/O method 1 */
331 /* Set up the input control if you are using standard C streams */
332 png_init_io(png_ptr, fp);
333
334 #else no_streams /* PNG file I/O method 2 */
335 /* If you are using replacement read functions, instead of calling
336 * png_init_io() here you would call:
337 */
338 png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn);
339 /* where user_io_ptr is a structure you want available to the callbacks */
340 #endif no_streams /* Use only one I/O method! */
341
342 /* If we have already read some of the signature */
343 png_set_sig_bytes(png_ptr, sig_read);
344
345 #ifdef hilevel
346 /*
347 * If you have enough memory to read in the entire image at once,
348 * and you need to specify only transforms that can be controlled
349 * with one of the PNG_TRANSFORM_* bits (this presently excludes
350 * quantizing, filling, setting background, and doing gamma
351 * adjustment), then you can read the entire image (including
352 * pixels) into the info structure with this call:
353 */
354 png_read_png(png_ptr, info_ptr, png_transforms, NULL);
355
356 #else
357 /* OK, you're doing it the hard way, with the lower-level functions */
358
359 /* The call to png_read_info() gives us all of the information from the
360 * PNG file before the first IDAT (image data chunk). REQUIRED
361 */
362 png_read_info(png_ptr, info_ptr);
363
364 png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
365 &interlace_type, NULL, NULL);
366
367 /* Set up the data transformations you want. Note that these are all
368 * optional. Only call them if you want/need them. Many of the
369 * transformations only work on specific types of images, and many
370 * are mutually exclusive.
371 */
372
373 /* Tell libpng to strip 16 bits/color files down to 8 bits/color.
374 * Use accurate scaling if it's available, otherwise just chop off the
375 * low byte.
376 */
377 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
378 png_set_scale_16(png_ptr);
379 #else
380 png_set_strip_16(png_ptr);
381 #endif
382
383 /* Strip alpha bytes from the input data without combining with the
384 * background (not recommended).
385 */
386 png_set_strip_alpha(png_ptr);
387
388 /* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
389 * byte into separate bytes (useful for paletted and grayscale images).
390 */
391 png_set_packing(png_ptr);
392
393 /* Change the order of packed pixels to least significant bit first
394 * (not useful if you are using png_set_packing). */
395 png_set_packswap(png_ptr);
396
397 /* Expand paletted colors into true RGB triplets */
398 if (color_type == PNG_COLOR_TYPE_PALETTE)
399 png_set_palette_to_rgb(png_ptr);
400
401 /* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
402 if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
403 png_set_expand_gray_1_2_4_to_8(png_ptr);
404
405 /* Expand paletted or RGB images with transparency to full alpha channels
406 * so the data will be available as RGBA quartets.
407 */
408 if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS) != 0)
409 png_set_tRNS_to_alpha(png_ptr);
410
411 /* Set the background color to draw transparent and alpha images over.
412 * It is possible to set the red, green, and blue components directly
413 * for paletted images instead of supplying a palette index. Note that
414 * even if the PNG file supplies a background, you are not required to
415 * use it - you should use the (solid) application background if it has one.
416 */
417
418 png_color_16 my_background, *image_background;
419
420 if (png_get_bKGD(png_ptr, info_ptr, &image_background) != 0)
421 png_set_background(png_ptr, image_background,
422 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
423 else
424 png_set_background(png_ptr, &my_background,
425 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
426
427 /* Some suggestions as to how to get a screen gamma value
428 *
429 * Note that screen gamma is the display_exponent, which includes
430 * the CRT_exponent and any correction for viewing conditions
431 */
432 if (/* We have a user-defined screen gamma value */)
433 {
434 screen_gamma = user-defined screen_gamma;
435 }
436 /* This is one way that applications share the same screen gamma value */
437 else if ((gamma_str = getenv("SCREEN_GAMMA")) != NULL)
438 {
439 screen_gamma = atof(gamma_str);
440 }
441 /* If we don't have another value */
442 else
443 {
444 screen_gamma = PNG_DEFAULT_sRGB; /* A good guess for a PC monitor
445 in a dimly lit room */
446 screen_gamma = PNG_GAMMA_MAC_18 or 1.0; /* Good guesses for Mac systems */
447 }
448
449 /* Tell libpng to handle the gamma conversion for you. The final call
450 * is a good guess for PC generated images, but it should be configurable
451 * by the user at run time by the user. It is strongly suggested that
452 * your application support gamma correction.
453 */
454
455 int intent;
456
457 if (png_get_sRGB(png_ptr, info_ptr, &intent) != 0)
458 png_set_gamma(png_ptr, screen_gamma, PNG_DEFAULT_sRGB);
459 else
460 {
461 double image_gamma;
462 if (png_get_gAMA(png_ptr, info_ptr, &image_gamma) != 0)
463 png_set_gamma(png_ptr, screen_gamma, image_gamma);
464 else
465 png_set_gamma(png_ptr, screen_gamma, 0.45455);
466 }
467
468 #ifdef PNG_READ_QUANTIZE_SUPPORTED
469 /* Quantize RGB files down to 8-bit palette or reduce palettes
470 * to the number of colors available on your screen.
471 */
472 if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
473 {
474 int num_palette;
475 png_colorp palette;
476
477 /* This reduces the image to the application supplied palette */
478 if (/* We have our own palette */)
479 {
480 /* An array of colors to which the image should be quantized */
481 png_color std_color_cube[MAX_SCREEN_COLORS];
482
483 png_set_quantize(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
484 MAX_SCREEN_COLORS, NULL, 0);
485 }
486 /* This reduces the image to the palette supplied in the file */
487 else if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette) != 0)
488 {
489 png_uint_16p histogram = NULL;
490
491 png_get_hIST(png_ptr, info_ptr, &histogram);
492
493 png_set_quantize(png_ptr, palette, num_palette,
494 max_screen_colors, histogram, 0);
495 }
496 }
497 #endif /* READ_QUANTIZE */
498
499 /* Invert monochrome files to have 0 as white and 1 as black */
500 png_set_invert_mono(png_ptr);
501
502 /* If you want to shift the pixel values from the range [0,255] or
503 * [0,65535] to the original [0,7] or [0,31], or whatever range the
504 * colors were originally in:
505 */
506 if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT) != 0)
507 {
508 png_color_8p sig_bit_p;
509
510 png_get_sBIT(png_ptr, info_ptr, &sig_bit_p);
511 png_set_shift(png_ptr, sig_bit_p);
512 }
513
514 /* Flip the RGB pixels to BGR (or RGBA to BGRA) */
515 if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
516 png_set_bgr(png_ptr);
517
518 /* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
519 png_set_swap_alpha(png_ptr);
520
521 /* Swap bytes of 16-bit files to least significant byte first */
522 png_set_swap(png_ptr);
523
524 /* Add filler (or alpha) byte (before/after each RGB triplet) */
525 png_set_filler(png_ptr, 0xffff, PNG_FILLER_AFTER);
526
527 #ifdef PNG_READ_INTERLACING_SUPPORTED
528 /* Turn on interlace handling. REQUIRED if you are not using
529 * png_read_image(). To see how to handle interlacing passes,
530 * see the png_read_row() method below:
531 */
532 number_passes = png_set_interlace_handling(png_ptr);
533 #else
534 number_passes = 1;
535 #endif /* READ_INTERLACING */
536
537
538 /* Optional call to gamma correct and add the background to the palette
539 * and update info structure. REQUIRED if you are expecting libpng to
540 * update the palette for you (ie you selected such a transform above).
541 */
542 png_read_update_info(png_ptr, info_ptr);
543
544 /* Allocate the memory to hold the image using the fields of info_ptr. */
545
546 /* The easiest way to read the image: */
547 png_bytep row_pointers[height];
548
549 /* Clear the pointer array */
550 for (row = 0; row < height; row++)
551 row_pointers[row] = NULL;
552
553 for (row = 0; row < height; row++)
554 row_pointers[row] = png_malloc(png_ptr, png_get_rowbytes(png_ptr,
555 info_ptr));
556
557 /* Now it's time to read the image. One of these methods is REQUIRED */
558 #ifdef entire /* Read the entire image in one go */
559 png_read_image(png_ptr, row_pointers);
560
561 #else no_entire /* Read the image one or more scanlines at a time */
562 /* The other way to read images - deal with interlacing: */
563
564 for (pass = 0; pass < number_passes; pass++)
565 {
566 #ifdef single /* Read the image a single row at a time */
567 for (y = 0; y < height; y++)
568 {
569 png_read_rows(png_ptr, &row_pointers[y], NULL, 1);
570 }
571
572 #else no_single /* Read the image several rows at a time */
573 for (y = 0; y < height; y += number_of_rows)
574 {
575 #ifdef sparkle /* Read the image using the "sparkle" effect. */
576 png_read_rows(png_ptr, &row_pointers[y], NULL,
577 number_of_rows);
578 #else no_sparkle /* Read the image using the "rectangle" effect */
579 png_read_rows(png_ptr, NULL, &row_pointers[y],
580 number_of_rows);
581 #endif no_sparkle /* Use only one of these two methods */
582 }
583
584 /* If you want to display the image after every pass, do so here */
585 #endif no_single /* Use only one of these two methods */
586 }
587 #endif no_entire /* Use only one of these two methods */
588
589 /* Read rest of file, and get additional chunks in info_ptr - REQUIRED */
590 png_read_end(png_ptr, info_ptr);
591 #endif hilevel
592
593 /* At this point you have read the entire image */
594
595 /* Clean up after the read, and free any memory allocated - REQUIRED */
596 png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
597
598 /* Close the file */
599 fclose(fp);
600
601 /* That's it */
602 return (OK);
603 }
604
605 /* Progressively read a file */
606
607 int
608 initialize_png_reader(png_structp *png_ptr, png_infop *info_ptr)
609 {
610 /* Create and initialize the png_struct with the desired error handler
611 * functions. If you want to use the default stderr and longjump method,
612 * you can supply NULL for the last three parameters. We also check that
613 * the library version is compatible in case we are using dynamically
614 * linked libraries.
615 */
616 *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
617 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
618
619 if (*png_ptr == NULL)
620 {
621 *info_ptr = NULL;
622 return (ERROR);
623 }
624
625 *info_ptr = png_create_info_struct(png_ptr);
626
627 if (*info_ptr == NULL)
628 {
629 png_destroy_read_struct(png_ptr, info_ptr, NULL);
630 return (ERROR);
631 }
632
633 if (setjmp(png_jmpbuf((*png_ptr))))
634 {
635 png_destroy_read_struct(png_ptr, info_ptr, NULL);
636 return (ERROR);
637 }
638
639 /* This one's new. You will need to provide all three
640 * function callbacks, even if you aren't using them all.
641 * If you aren't using all functions, you can specify NULL
642 * parameters. Even when all three functions are NULL,
643 * you need to call png_set_progressive_read_fn().
644 * These functions shouldn't be dependent on global or
645 * static variables if you are decoding several images
646 * simultaneously. You should store stream specific data
647 * in a separate struct, given as the second parameter,
648 * and retrieve the pointer from inside the callbacks using
649 * the function png_get_progressive_ptr(png_ptr).
650 */
651 png_set_progressive_read_fn(*png_ptr, (void *)stream_data,
652 info_callback, row_callback, end_callback);
653
654 return (OK);
655 }
656
657 int
658 process_data(png_structp *png_ptr, png_infop *info_ptr,
659 png_bytep buffer, png_uint_32 length)
660 {
661 if (setjmp(png_jmpbuf((*png_ptr))))
662 {
663 /* Free the png_ptr and info_ptr memory on error */
664 png_destroy_read_struct(png_ptr, info_ptr, NULL);
665 return (ERROR);
666 }
667
668 /* This one's new also. Simply give it chunks of data as
669 * they arrive from the data stream (in order, of course).
670 * On segmented machines, don't give it any more than 64K.
671 * The library seems to run fine with sizes of 4K, although
672 * you can give it much less if necessary (I assume you can
673 * give it chunks of 1 byte, but I haven't tried with less
674 * than 256 bytes yet). When this function returns, you may
675 * want to display any rows that were generated in the row
676 * callback, if you aren't already displaying them there.
677 */
678 png_process_data(*png_ptr, *info_ptr, buffer, length);
679 return (OK);
680 }
681
682 info_callback(png_structp png_ptr, png_infop info)
683 {
684 /* Do any setup here, including setting any of the transformations
685 * mentioned in the Reading PNG files section. For now, you _must_
686 * call either png_start_read_image() or png_read_update_info()
687 * after all the transformations are set (even if you don't set
688 * any). You may start getting rows before png_process_data()
689 * returns, so this is your last chance to prepare for that.
690 */
691 }
692
693 row_callback(png_structp png_ptr, png_bytep new_row,
694 png_uint_32 row_num, int pass)
695 {
696 /*
697 * This function is called for every row in the image. If the
698 * image is interlaced, and you turned on the interlace handler,
699 * this function will be called for every row in every pass.
700 *
701 * In this function you will receive a pointer to new row data from
702 * libpng called new_row that is to replace a corresponding row (of
703 * the same data format) in a buffer allocated by your application.
704 *
705 * The new row data pointer "new_row" may be NULL, indicating there is
706 * no new data to be replaced (in cases of interlace loading).
707 *
708 * If new_row is not NULL then you need to call
709 * png_progressive_combine_row() to replace the corresponding row as
710 * shown below:
711 */
712
713 /* Get pointer to corresponding row in our
714 * PNG read buffer.
715 */
716 png_bytep old_row = ((png_bytep *)our_data)[row_num];
717
718 #ifdef PNG_READ_INTERLACING_SUPPORTED
719 /* If both rows are allocated then copy the new row
720 * data to the corresponding row data.
721 */
722 if ((old_row != NULL) && (new_row != NULL))
723 png_progressive_combine_row(png_ptr, old_row, new_row);
724
725 /*
726 * The rows and passes are called in order, so you don't really
727 * need the row_num and pass, but I'm supplying them because it
728 * may make your life easier.
729 *
730 * For the non-NULL rows of interlaced images, you must call
731 * png_progressive_combine_row() passing in the new row and the
732 * old row, as demonstrated above. You can call this function for
733 * NULL rows (it will just return) and for non-interlaced images
734 * (it just does the memcpy for you) if it will make the code
735 * easier. Thus, you can just do this for all cases:
736 */
737
738 png_progressive_combine_row(png_ptr, old_row, new_row);
739
740 /* where old_row is what was displayed for previous rows. Note
741 * that the first pass (pass == 0 really) will completely cover
742 * the old row, so the rows do not have to be initialized. After
743 * the first pass (and only for interlaced images), you will have
744 * to pass the current row as new_row, and the function will combine
745 * the old row and the new row.
746 */
747 #endif /* READ_INTERLACING */
748 }
749
750 end_callback(png_structp png_ptr, png_infop info)
751 {
752 /* This function is called when the whole image has been read,
753 * including any chunks after the image (up to and including
754 * the IEND). You will usually have the same info chunk as you
755 * had in the header, although some data may have been added
756 * to the comments and time fields.
757 *
758 * Most people won't do much here, perhaps setting a flag that
759 * marks the image as finished.
760 */
761 }
762
763 /* Write a png file */
764 void write_png(char *file_name /* , ... other image information ... */)
765 {
766 FILE *fp;
767 png_structp png_ptr;
768 png_infop info_ptr;
769 png_colorp palette;
770
771 /* Open the file */
772 fp = fopen(file_name, "wb");
773 if (fp == NULL)
774 return (ERROR);
775
776 /* Create and initialize the png_struct with the desired error handler
777 * functions. If you want to use the default stderr and longjump method,
778 * you can supply NULL for the last three parameters. We also check that
779 * the library version is compatible with the one used at compile time,
780 * in case we are using dynamically linked libraries. REQUIRED.
781 */
782 png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
783 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
784
785 if (png_ptr == NULL)
786 {
787 fclose(fp);
788 return (ERROR);
789 }
790
791 /* Allocate/initialize the image information data. REQUIRED */
792 info_ptr = png_create_info_struct(png_ptr);
793 if (info_ptr == NULL)
794 {
795 fclose(fp);
796 png_destroy_write_struct(&png_ptr, NULL);
797 return (ERROR);
798 }
799
800 /* Set error handling. REQUIRED if you aren't supplying your own
801 * error handling functions in the png_create_write_struct() call.
802 */
803 if (setjmp(png_jmpbuf(png_ptr)))
804 {
805 /* If we get here, we had a problem writing the file */
806 fclose(fp);
807 png_destroy_write_struct(&png_ptr, &info_ptr);
808 return (ERROR);
809 }
810
811 /* One of the following I/O initialization functions is REQUIRED */
812
813 #ifdef streams /* I/O initialization method 1 */
814 /* Set up the output control if you are using standard C streams */
815 png_init_io(png_ptr, fp);
816
817 #else no_streams /* I/O initialization method 2 */
818 /* If you are using replacement write functions, instead of calling
819 * png_init_io() here you would call
820 */
821 png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,
822 user_IO_flush_function);
823 /* where user_io_ptr is a structure you want available to the callbacks */
824 #endif no_streams /* Only use one initialization method */
825
826 #ifdef hilevel
827 /* This is the easy way. Use it if you already have all the
828 * image info living in the structure. You could "|" many
829 * PNG_TRANSFORM flags into the png_transforms integer here.
830 */
831 png_write_png(png_ptr, info_ptr, png_transforms, NULL);
832
833 #else
834 /* This is the hard way */
835
836 /* Set the image information here. Width and height are up to 2^31,
837 * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
838 * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
839 * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
840 * or PNG_COLOR_TYPE_RGB_ALPHA. interlace is either PNG_INTERLACE_NONE or
841 * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
842 * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
843 */
844 png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,
845 PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
846
847 /* Set the palette if there is one. REQUIRED for indexed-color images */
848 palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH
849 * (sizeof (png_color)));
850 /* ... Set palette colors ... */
851 png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
852 /* You must not free palette here, because png_set_PLTE only makes a link to
853 * the palette that you malloced. Wait until you are about to destroy
854 * the png structure.
855 */
856
857 /* Optional significant bit (sBIT) chunk */
858 png_color_8 sig_bit;
859
860 /* If we are dealing with a grayscale image then */
861 sig_bit.gray = true_bit_depth;
862
863 /* Otherwise, if we are dealing with a color image then */
864 sig_bit.red = true_red_bit_depth;
865 sig_bit.green = true_green_bit_depth;
866 sig_bit.blue = true_blue_bit_depth;
867
868 /* If the image has an alpha channel then */
869 sig_bit.alpha = true_alpha_bit_depth;
870
871 png_set_sBIT(png_ptr, info_ptr, &sig_bit);
872
873
874 /* Optional gamma chunk is strongly suggested if you have any guess
875 * as to the correct gamma of the image.
876 */
877 png_set_gAMA(png_ptr, info_ptr, gamma);
878
879 /* Optionally write comments into the image */
880 {
881 png_text text_ptr[3];
882
883 char key0[]="Title";
884 char text0[]="Mona Lisa";
885 text_ptr[0].key = key0;
886 text_ptr[0].text = text0;
887 text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
888 text_ptr[0].itxt_length = 0;
889 text_ptr[0].lang = NULL;
890 text_ptr[0].lang_key = NULL;
891
892 char key1[]="Author";
893 char text1[]="Leonardo DaVinci";
894 text_ptr[1].key = key1;
895 text_ptr[1].text = text1;
896 text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;
897 text_ptr[1].itxt_length = 0;
898 text_ptr[1].lang = NULL;
899 text_ptr[1].lang_key = NULL;
900
901 char key2[]="Description";
902 char text2[]="<long text>";
903 text_ptr[2].key = key2;
904 text_ptr[2].text = text2;
905 text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;
906 text_ptr[2].itxt_length = 0;
907 text_ptr[2].lang = NULL;
908 text_ptr[2].lang_key = NULL;
909
910 png_set_text(write_ptr, write_info_ptr, text_ptr, 3);
911 }
912
913 /* Other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs */
914
915 /* Note that if sRGB is present the gAMA and cHRM chunks must be ignored
916 * on read and, if your application chooses to write them, they must
917 * be written in accordance with the sRGB profile
918 */
919
920 /* Write the file header information. REQUIRED */
921 png_write_info(png_ptr, info_ptr);
922
923 /* If you want, you can write the info in two steps, in case you need to
924 * write your private chunk ahead of PLTE:
925 *
926 * png_write_info_before_PLTE(write_ptr, write_info_ptr);
927 * write_my_chunk();
928 * png_write_info(png_ptr, info_ptr);
929 *
930 * However, given the level of known- and unknown-chunk support in 1.2.0
931 * and up, this should no longer be necessary.
932 */
933
934 /* Once we write out the header, the compression type on the text
935 * chunk gets changed to PNG_TEXT_COMPRESSION_NONE_WR or
936 * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again
937 * at the end.
938 */
939
940 /* Set up the transformations you want. Note that these are
941 * all optional. Only call them if you want them.
942 */
943
944 /* Invert monochrome pixels */
945 png_set_invert_mono(png_ptr);
946
947 /* Shift the pixels up to a legal bit depth and fill in
948 * as appropriate to correctly scale the image.
949 */
950 png_set_shift(png_ptr, &sig_bit);
951
952 /* Pack pixels into bytes */
953 png_set_packing(png_ptr);
954
955 /* Swap location of alpha bytes from ARGB to RGBA */
956 png_set_swap_alpha(png_ptr);
957
958 /* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into
959 * RGB (4 channels -> 3 channels). The second parameter is not used.
960 */
961 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
962
963 /* Flip BGR pixels to RGB */
964 png_set_bgr(png_ptr);
965
966 /* Swap bytes of 16-bit files to most significant byte first */
967 png_set_swap(png_ptr);
968
969 /* Swap bits of 1-bit, 2-bit, 4-bit packed pixel formats */
970 png_set_packswap(png_ptr);
971
972 /* Turn on interlace handling if you are not using png_write_image() */
973 if (interlacing != 0)
974 number_passes = png_set_interlace_handling(png_ptr);
975
976 else
977 number_passes = 1;
978
979 /* The easiest way to write the image (you may have a different memory
980 * layout, however, so choose what fits your needs best). You need to
981 * use the first method if you aren't handling interlacing yourself.
982 */
983 png_uint_32 k, height, width;
984
985 /* In this example, "image" is a one-dimensional array of bytes */
986 png_byte image[height*width*bytes_per_pixel];
987
988 png_bytep row_pointers[height];
989
990 if (height > PNG_UINT_32_MAX/(sizeof (png_bytep)))
991 png_error (png_ptr, "Image is too tall to process in memory");
992
993 /* Set up pointers into your "image" byte array */
994 for (k = 0; k < height; k++)
995 row_pointers[k] = image + k*width*bytes_per_pixel;
996
997 /* One of the following output methods is REQUIRED */
998
999 #ifdef entire /* Write out the entire image data in one call */
1000 png_write_image(png_ptr, row_pointers);
1001
1002 /* The other way to write the image - deal with interlacing */
1003
1004 #else no_entire /* Write out the image data by one or more scanlines */
1005
1006 /* The number of passes is either 1 for non-interlaced images,
1007 * or 7 for interlaced images.
1008 */
1009 for (pass = 0; pass < number_passes; pass++)
1010 {
1011 /* Write a few rows at a time. */
1012 png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);
1013
1014 /* If you are only writing one row at a time, this works */
1015 for (y = 0; y < height; y++)
1016 png_write_rows(png_ptr, &row_pointers[y], 1);
1017 }
1018 #endif no_entire /* Use only one output method */
1019
1020 /* You can write optional chunks like tEXt, zTXt, and tIME at the end
1021 * as well. Shouldn't be necessary in 1.2.0 and up as all the public
1022 * chunks are supported and you can use png_set_unknown_chunks() to
1023 * register unknown chunks into the info structure to be written out.
1024 */
1025
1026 /* It is REQUIRED to call this to finish writing the rest of the file */
1027 png_write_end(png_ptr, info_ptr);
1028 #endif hilevel
1029
1030 /* If you png_malloced a palette, free it here (don't free info_ptr->palette,
1031 * as recommended in versions 1.0.5m and earlier of this example; if
1032 * libpng mallocs info_ptr->palette, libpng will free it). If you
1033 * allocated it with malloc() instead of png_malloc(), use free() instead
1034 * of png_free().
1035 */
1036 png_free(png_ptr, palette);
1037 palette = NULL;
1038
1039 /* Similarly, if you png_malloced any data that you passed in with
1040 * png_set_something(), such as a hist or trans array, free it here,
1041 * when you can be sure that libpng is through with it.
1042 */
1043 png_free(png_ptr, trans);
1044 trans = NULL;
1045 /* Whenever you use png_free() it is a good idea to set the pointer to
1046 * NULL in case your application inadvertently tries to png_free() it
1047 * again. When png_free() sees a NULL it returns without action, thus
1048 * avoiding the double-free security problem.
1049 */
1050
1051 /* Clean up after the write, and free any memory allocated */
1052 png_destroy_write_struct(&png_ptr, &info_ptr);
1053
1054 /* Close the file */
1055 fclose(fp);
1056
1057 /* That's it */
1058 return (OK);
1059 }
1060
1061 #endif /* if 0 */