example.c 39 KB

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