2 #if 0 /* in case someone actually tries to compile this */
4 /* example.c - an example of using libpng */
6 /* This is an example of how to use libpng to read and write PNG files.
7 * The file libpng.txt is much more verbose then this. If you have not
8 * read it, do so first. This was designed to be a starting point of an
9 * implementation. This is not officially part of libpng, is hereby placed
10 * in the public domain, and therefore does not require a copyright notice.
12 * This file does not currently compile, because it is missing certain
13 * parts, like allocating memory to hold an image. You will have to
14 * supply these parts to get it to compile. For an example of a minimal
15 * working PNG reader/writer, see pngtest.c, included in this distribution;
16 * see also the programs in the contrib directory.
21 /* The png_jmpbuf() macro, used in error handling, became available in
22 * libpng version 1.0.6. If you want to be able to run your code with older
23 * versions of libpng, you must define the macro yourself (but only if it
24 * is not already defined by libpng!).
28 # define png_jmpbuf(png_ptr) ((png_ptr)->jmpbuf)
31 /* Check to see if a file is a PNG file using png_sig_cmp(). png_sig_cmp()
32 * returns zero if the image is a PNG and nonzero if it isn't a PNG.
34 * The function check_if_png() shown here, but not used, returns nonzero (true)
35 * if the file can be opened and is a PNG, 0 (false) otherwise.
37 * If this call is successful, and you are going to keep the file open,
38 * you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once
39 * you have created the png_ptr, so that libpng knows your application
40 * has read that many bytes from the start of the file. Make sure you
41 * don't call png_set_sig_bytes() with more than 8 bytes read or give it
42 * an incorrect number of bytes read, or you will either have read too
43 * many bytes (your fault), or you are telling libpng to read the wrong
44 * number of magic bytes (also your fault).
46 * Many applications already read the first 2 or 4 bytes from the start
47 * of the image to determine the file type, so it would be easiest just
48 * to pass the bytes to png_sig_cmp() or even skip that if you know
49 * you have a PNG file, and call png_set_sig_bytes().
51 #define PNG_BYTES_TO_CHECK 4
52 int check_if_png(char *file_name, FILE **fp)
54 char buf[PNG_BYTES_TO_CHECK];
56 /* Open the prospective PNG file. */
57 if ((*fp = fopen(file_name, "rb")) == NULL)
60 /* Read in some of the signature bytes */
61 if (fread(buf, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK)
64 /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.
65 Return nonzero (true) if they match */
67 return(!png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK));
70 /* Read a PNG file. You may want to return an error code if the read
71 * fails (depending upon the failure). There are two "prototypes" given
72 * here - one where we are given the filename, and we need to open the
73 * file, and the other where we are given an open file (possibly with
74 * some or all of the magic bytes read - see comments above).
76 #ifdef open_file /* prototype 1 */
77 void read_png(char *file_name) /* We need to open the file */
81 unsigned int sig_read = 0;
82 png_uint_32 width, height;
83 int bit_depth, color_type, interlace_type;
86 if ((fp = fopen(file_name, "rb")) == NULL)
88 #else no_open_file /* prototype 2 */
89 void read_png(FILE *fp, unsigned int sig_read) /* file is already open */
93 png_uint_32 width, height;
94 int bit_depth, color_type, interlace_type;
95 #endif no_open_file /* only use one prototype! */
97 /* Create and initialize the png_struct with the desired error handler
98 * functions. If you want to use the default stderr and longjump method,
99 * you can supply NULL for the last three parameters. We also supply the
100 * the compiler header file version, so that we know if the application
101 * was compiled with a compatible version of the library. REQUIRED
103 png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
104 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
112 /* Allocate/initialize the memory for image information. REQUIRED. */
113 info_ptr = png_create_info_struct(png_ptr);
114 if (info_ptr == NULL)
117 png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
121 /* Set error handling if you are using the setjmp/longjmp method (this is
122 * the normal method of doing things with libpng). REQUIRED unless you
123 * set up your own error handlers in the png_create_read_struct() earlier.
126 if (setjmp(png_jmpbuf(png_ptr)))
128 /* Free all of the memory associated with the png_ptr and info_ptr */
129 png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
131 /* If we get here, we had a problem reading the file */
135 /* One of the following I/O initialization methods is REQUIRED */
136 #ifdef streams /* PNG file I/O method 1 */
137 /* Set up the input control if you are using standard C streams */
138 png_init_io(png_ptr, fp);
140 #else no_streams /* PNG file I/O method 2 */
141 /* If you are using replacement read functions, instead of calling
142 * png_init_io() here you would call:
144 png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn);
145 /* where user_io_ptr is a structure you want available to the callbacks */
146 #endif no_streams /* Use only one I/O method! */
148 /* If we have already read some of the signature */
149 png_set_sig_bytes(png_ptr, sig_read);
153 * If you have enough memory to read in the entire image at once,
154 * and you need to specify only transforms that can be controlled
155 * with one of the PNG_TRANSFORM_* bits (this presently excludes
156 * dithering, filling, setting background, and doing gamma
157 * adjustment), then you can read the entire image (including
158 * pixels) into the info structure with this call:
160 png_read_png(png_ptr, info_ptr, png_transforms, NULL);
162 /* OK, you're doing it the hard way, with the lower-level functions */
164 /* The call to png_read_info() gives us all of the information from the
165 * PNG file before the first IDAT (image data chunk). REQUIRED
167 png_read_info(png_ptr, info_ptr);
169 png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
170 &interlace_type, NULL, NULL);
172 /**** Set up the data transformations you want. Note that these are all
173 **** optional. Only call them if you want/need them. Many of the
174 **** transformations only work on specific types of images, and many
175 **** are mutually exclusive.
178 /* tell libpng to strip 16 bit/color files down to 8 bits/color */
179 png_set_strip_16(png_ptr);
181 /* Strip alpha bytes from the input data without combining with the
182 * background (not recommended).
184 png_set_strip_alpha(png_ptr);
186 /* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
187 * byte into separate bytes (useful for paletted and grayscale images).
189 png_set_packing(png_ptr);
191 /* Change the order of packed pixels to least significant bit first
192 * (not useful if you are using png_set_packing). */
193 png_set_packswap(png_ptr);
195 /* Expand paletted colors into true RGB triplets */
196 if (color_type == PNG_COLOR_TYPE_PALETTE)
197 png_set_palette_rgb(png_ptr);
199 /* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
200 if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
201 png_set_gray_1_2_4_to_8(png_ptr);
203 /* Expand paletted or RGB images with transparency to full alpha channels
204 * so the data will be available as RGBA quartets.
206 if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
207 png_set_tRNS_to_alpha(png_ptr);
209 /* Set the background color to draw transparent and alpha images over.
210 * It is possible to set the red, green, and blue components directly
211 * for paletted images instead of supplying a palette index. Note that
212 * even if the PNG file supplies a background, you are not required to
213 * use it - you should use the (solid) application background if it has one.
216 png_color_16 my_background, *image_background;
218 if (png_get_bKGD(png_ptr, info_ptr, &image_background))
219 png_set_background(png_ptr, image_background,
220 PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
222 png_set_background(png_ptr, &my_background,
223 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
225 /* Some suggestions as to how to get a screen gamma value */
227 /* Note that screen gamma is the display_exponent, which includes
228 * the CRT_exponent and any correction for viewing conditions */
229 if (/* We have a user-defined screen gamma value */)
231 screen_gamma = user-defined screen_gamma;
233 /* This is one way that applications share the same screen gamma value */
234 else if ((gamma_str = getenv("SCREEN_GAMMA")) != NULL)
236 screen_gamma = atof(gamma_str);
238 /* If we don't have another value */
241 screen_gamma = 2.2; /* A good guess for a PC monitors in a dimly
243 screen_gamma = 1.7 or 1.0; /* A good guess for Mac systems */
246 /* Tell libpng to handle the gamma conversion for you. The final call
247 * is a good guess for PC generated images, but it should be configurable
248 * by the user at run time by the user. It is strongly suggested that
249 * your application support gamma correction.
254 if (png_get_sRGB(png_ptr, info_ptr, &intent))
255 png_set_gamma(png_ptr, screen_gamma, 0.45455);
259 if (png_get_gAMA(png_ptr, info_ptr, &image_gamma))
260 png_set_gamma(png_ptr, screen_gamma, image_gamma);
262 png_set_gamma(png_ptr, screen_gamma, 0.45455);
265 /* Dither RGB files down to 8 bit palette or reduce palettes
266 * to the number of colors available on your screen.
268 if (color_type & PNG_COLOR_MASK_COLOR)
273 /* This reduces the image to the application supplied palette */
274 if (/* we have our own palette */)
276 /* An array of colors to which the image should be dithered */
277 png_color std_color_cube[MAX_SCREEN_COLORS];
279 png_set_dither(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
280 MAX_SCREEN_COLORS, NULL, 0);
282 /* This reduces the image to the palette supplied in the file */
283 else if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette))
285 png_uint_16p histogram;
287 png_get_hIST(png_ptr, info_ptr, &histogram);
289 png_set_dither(png_ptr, palette, num_palette,
290 max_screen_colors, histogram, 0);
294 /* invert monochrome files to have 0 as white and 1 as black */
295 png_set_invert_mono(png_ptr);
297 /* If you want to shift the pixel values from the range [0,255] or
298 * [0,65535] to the original [0,7] or [0,31], or whatever range the
299 * colors were originally in:
301 if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT))
303 png_color_8p sig_bit;
305 png_get_sBIT(png_ptr, info_ptr, &sig_bit);
306 png_set_shift(png_ptr, sig_bit);
309 /* flip the RGB pixels to BGR (or RGBA to BGRA) */
310 if (color_type & PNG_COLOR_MASK_COLOR)
311 png_set_bgr(png_ptr);
313 /* swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
314 png_set_swap_alpha(png_ptr);
316 /* swap bytes of 16 bit files to least significant byte first */
317 png_set_swap(png_ptr);
319 /* Add filler (or alpha) byte (before/after each RGB triplet) */
320 png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
322 /* Turn on interlace handling. REQUIRED if you are not using
323 * png_read_image(). To see how to handle interlacing passes,
324 * see the png_read_row() method below:
326 number_passes = png_set_interlace_handling(png_ptr);
328 /* Optional call to gamma correct and add the background to the palette
329 * and update info structure. REQUIRED if you are expecting libpng to
330 * update the palette for you (ie you selected such a transform above).
332 png_read_update_info(png_ptr, info_ptr);
334 /* Allocate the memory to hold the image using the fields of info_ptr. */
336 /* The easiest way to read the image: */
337 png_bytep row_pointers[height];
339 for (row = 0; row < height; row++)
341 row_pointers[row] = png_malloc(png_ptr, png_get_rowbytes(png_ptr,
345 /* Now it's time to read the image. One of these methods is REQUIRED */
346 #ifdef entire /* Read the entire image in one go */
347 png_read_image(png_ptr, row_pointers);
349 #else no_entire /* Read the image one or more scanlines at a time */
350 /* The other way to read images - deal with interlacing: */
352 for (pass = 0; pass < number_passes; pass++)
354 #ifdef single /* Read the image a single row at a time */
355 for (y = 0; y < height; y++)
357 png_read_rows(png_ptr, &row_pointers[y], NULL, 1);
360 #else no_single /* Read the image several rows at a time */
361 for (y = 0; y < height; y += number_of_rows)
363 #ifdef sparkle /* Read the image using the "sparkle" effect. */
364 png_read_rows(png_ptr, &row_pointers[y], NULL, number_of_rows);
365 #else no_sparkle /* Read the image using the "rectangle" effect */
366 png_read_rows(png_ptr, NULL, &row_pointers[y], number_of_rows);
367 #endif no_sparkle /* use only one of these two methods */
370 /* if you want to display the image after every pass, do
372 #endif no_single /* use only one of these two methods */
374 #endif no_entire /* use only one of these two methods */
376 /* read rest of file, and get additional chunks in info_ptr - REQUIRED */
377 png_read_end(png_ptr, info_ptr);
380 /* At this point you have read the entire image */
382 /* clean up after the read, and free any memory allocated - REQUIRED */
383 png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
392 /* progressively read a file */
395 initialize_png_reader(png_structp *png_ptr, png_infop *info_ptr)
397 /* Create and initialize the png_struct with the desired error handler
398 * functions. If you want to use the default stderr and longjump method,
399 * you can supply NULL for the last three parameters. We also check that
400 * the library version is compatible in case we are using dynamically
403 *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
404 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
406 if (*png_ptr == NULL)
412 *info_ptr = png_create_info_struct(png_ptr);
414 if (*info_ptr == NULL)
416 png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL);
420 if (setjmp(png_jmpbuf((*png_ptr))))
422 png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL);
426 /* This one's new. You will need to provide all three
427 * function callbacks, even if you aren't using them all.
428 * If you aren't using all functions, you can specify NULL
429 * parameters. Even when all three functions are NULL,
430 * you need to call png_set_progressive_read_fn().
431 * These functions shouldn't be dependent on global or
432 * static variables if you are decoding several images
433 * simultaneously. You should store stream specific data
434 * in a separate struct, given as the second parameter,
435 * and retrieve the pointer from inside the callbacks using
436 * the function png_get_progressive_ptr(png_ptr).
438 png_set_progressive_read_fn(*png_ptr, (void *)stream_data,
439 info_callback, row_callback, end_callback);
445 process_data(png_structp *png_ptr, png_infop *info_ptr,
446 png_bytep buffer, png_uint_32 length)
448 if (setjmp(png_jmpbuf((*png_ptr))))
450 /* Free the png_ptr and info_ptr memory on error */
451 png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL);
455 /* This one's new also. Simply give it chunks of data as
456 * they arrive from the data stream (in order, of course).
457 * On Segmented machines, don't give it any more than 64K.
458 * The library seems to run fine with sizes of 4K, although
459 * you can give it much less if necessary (I assume you can
460 * give it chunks of 1 byte, but I haven't tried with less
461 * than 256 bytes yet). When this function returns, you may
462 * want to display any rows that were generated in the row
463 * callback, if you aren't already displaying them there.
465 png_process_data(*png_ptr, *info_ptr, buffer, length);
469 info_callback(png_structp png_ptr, png_infop info)
471 /* do any setup here, including setting any of the transformations
472 * mentioned in the Reading PNG files section. For now, you _must_
473 * call either png_start_read_image() or png_read_update_info()
474 * after all the transformations are set (even if you don't set
475 * any). You may start getting rows before png_process_data()
476 * returns, so this is your last chance to prepare for that.
480 row_callback(png_structp png_ptr, png_bytep new_row,
481 png_uint_32 row_num, int pass)
483 /* this function is called for every row in the image. If the
484 * image is interlacing, and you turned on the interlace handler,
485 * this function will be called for every row in every pass.
486 * Some of these rows will not be changed from the previous pass.
487 * When the row is not changed, the new_row variable will be NULL.
488 * The rows and passes are called in order, so you don't really
489 * need the row_num and pass, but I'm supplying them because it
490 * may make your life easier.
492 * For the non-NULL rows of interlaced images, you must call
493 * png_progressive_combine_row() passing in the row and the
494 * old row. You can call this function for NULL rows (it will
495 * just return) and for non-interlaced images (it just does the
496 * png_memcpy for you) if it will make the code easier. Thus, you
497 * can just do this for all cases:
500 png_progressive_combine_row(png_ptr, old_row, new_row);
502 /* where old_row is what was displayed for previous rows. Note
503 * that the first pass (pass == 0 really) will completely cover
504 * the old row, so the rows do not have to be initialized. After
505 * the first pass (and only for interlaced images), you will have
506 * to pass the current row, and the function will combine the
507 * old row and the new row.
511 end_callback(png_structp png_ptr, png_infop info)
513 /* this function is called when the whole image has been read,
514 * including any chunks after the image (up to and including
515 * the IEND). You will usually have the same info chunk as you
516 * had in the header, although some data may have been added
517 * to the comments and time fields.
519 * Most people won't do much here, perhaps setting a flag that
520 * marks the image as finished.
524 /* write a png file */
525 void write_png(char *file_name /* , ... other image information ... */)
533 fp = fopen(file_name, "wb");
537 /* Create and initialize the png_struct with the desired error handler
538 * functions. If you want to use the default stderr and longjump method,
539 * you can supply NULL for the last three parameters. We also check that
540 * the library version is compatible with the one used at compile time,
541 * in case we are using dynamically linked libraries. REQUIRED.
543 png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
544 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
552 /* Allocate/initialize the image information data. REQUIRED */
553 info_ptr = png_create_info_struct(png_ptr);
554 if (info_ptr == NULL)
557 png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
561 /* Set error handling. REQUIRED if you aren't supplying your own
562 * error handling functions in the png_create_write_struct() call.
564 if (setjmp(png_jmpbuf(png_ptr)))
566 /* If we get here, we had a problem reading the file */
568 png_destroy_write_struct(&png_ptr, &info_ptr);
572 /* One of the following I/O initialization functions is REQUIRED */
573 #ifdef streams /* I/O initialization method 1 */
574 /* set up the output control if you are using standard C streams */
575 png_init_io(png_ptr, fp);
576 #else no_streams /* I/O initialization method 2 */
577 /* If you are using replacement read functions, instead of calling
578 * png_init_io() here you would call */
579 png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,
580 user_IO_flush_function);
581 /* where user_io_ptr is a structure you want available to the callbacks */
582 #endif no_streams /* only use one initialization method */
585 /* This is the easy way. Use it if you already have all the
586 * image info living info in the structure. You could "|" many
587 * PNG_TRANSFORM flags into the png_transforms integer here.
589 png_write_png(png_ptr, info_ptr, png_transforms, NULL);
591 /* This is the hard way */
593 /* Set the image information here. Width and height are up to 2^31,
594 * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
595 * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
596 * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
597 * or PNG_COLOR_TYPE_RGB_ALPHA. interlace is either PNG_INTERLACE_NONE or
598 * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
599 * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
601 png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,
602 PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
604 /* set the palette if there is one. REQUIRED for indexed-color images */
605 palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH
606 * sizeof (png_color));
607 /* ... set palette colors ... */
608 png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
609 /* You must not free palette here, because png_set_PLTE only makes a link to
610 the palette that you malloced. Wait until you are about to destroy
611 the png structure. */
613 /* optional significant bit chunk */
614 /* if we are dealing with a grayscale image then */
615 sig_bit.gray = true_bit_depth;
616 /* otherwise, if we are dealing with a color image then */
617 sig_bit.red = true_red_bit_depth;
618 sig_bit.green = true_green_bit_depth;
619 sig_bit.blue = true_blue_bit_depth;
620 /* if the image has an alpha channel then */
621 sig_bit.alpha = true_alpha_bit_depth;
622 png_set_sBIT(png_ptr, info_ptr, sig_bit);
625 /* Optional gamma chunk is strongly suggested if you have any guess
626 * as to the correct gamma of the image.
628 png_set_gAMA(png_ptr, info_ptr, gamma);
630 /* Optionally write comments into the image */
631 text_ptr[0].key = "Title";
632 text_ptr[0].text = "Mona Lisa";
633 text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
634 text_ptr[1].key = "Author";
635 text_ptr[1].text = "Leonardo DaVinci";
636 text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;
637 text_ptr[2].key = "Description";
638 text_ptr[2].text = "<long text>";
639 text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;
640 #ifdef PNG_iTXt_SUPPORTED
641 text_ptr[0].lang = NULL;
642 text_ptr[1].lang = NULL;
643 text_ptr[2].lang = NULL;
645 png_set_text(png_ptr, info_ptr, text_ptr, 3);
647 /* other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs, */
648 /* note that if sRGB is present the gAMA and cHRM chunks must be ignored
649 * on read and must be written in accordance with the sRGB profile */
651 /* Write the file header information. REQUIRED */
652 png_write_info(png_ptr, info_ptr);
654 /* If you want, you can write the info in two steps, in case you need to
655 * write your private chunk ahead of PLTE:
657 * png_write_info_before_PLTE(write_ptr, write_info_ptr);
659 * png_write_info(png_ptr, info_ptr);
661 * However, given the level of known- and unknown-chunk support in 1.1.0
662 * and up, this should no longer be necessary.
665 /* Once we write out the header, the compression type on the text
666 * chunks gets changed to PNG_TEXT_COMPRESSION_NONE_WR or
667 * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again
671 /* set up the transformations you want. Note that these are
672 * all optional. Only call them if you want them.
675 /* invert monochrome pixels */
676 png_set_invert_mono(png_ptr);
678 /* Shift the pixels up to a legal bit depth and fill in
679 * as appropriate to correctly scale the image.
681 png_set_shift(png_ptr, &sig_bit);
683 /* pack pixels into bytes */
684 png_set_packing(png_ptr);
686 /* swap location of alpha bytes from ARGB to RGBA */
687 png_set_swap_alpha(png_ptr);
689 /* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into
690 * RGB (4 channels -> 3 channels). The second parameter is not used.
692 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
694 /* flip BGR pixels to RGB */
695 png_set_bgr(png_ptr);
697 /* swap bytes of 16-bit files to most significant byte first */
698 png_set_swap(png_ptr);
700 /* swap bits of 1, 2, 4 bit packed pixel formats */
701 png_set_packswap(png_ptr);
703 /* turn on interlace handling if you are not using png_write_image() */
705 number_passes = png_set_interlace_handling(png_ptr);
709 /* The easiest way to write the image (you may have a different memory
710 * layout, however, so choose what fits your needs best). You need to
711 * use the first method if you aren't handling interlacing yourself.
713 png_uint_32 k, height, width;
714 png_byte image[height][width*bytes_per_pixel];
715 png_bytep row_pointers[height];
716 for (k = 0; k < height; k++)
717 row_pointers[k] = image + k*width*bytes_per_pixel;
719 /* One of the following output methods is REQUIRED */
720 #ifdef entire /* write out the entire image data in one call */
721 png_write_image(png_ptr, row_pointers);
723 /* the other way to write the image - deal with interlacing */
725 #else no_entire /* write out the image data by one or more scanlines */
726 /* The number of passes is either 1 for non-interlaced images,
727 * or 7 for interlaced images.
729 for (pass = 0; pass < number_passes; pass++)
731 /* Write a few rows at a time. */
732 png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);
734 /* If you are only writing one row at a time, this works */
735 for (y = 0; y < height; y++)
737 png_write_rows(png_ptr, &row_pointers[y], 1);
740 #endif no_entire /* use only one output method */
742 /* You can write optional chunks like tEXt, zTXt, and tIME at the end
743 * as well. Shouldn't be necessary in 1.1.0 and up as all the public
744 * chunks are supported and you can use png_set_unknown_chunks() to
745 * register unknown chunks into the info structure to be written out.
748 /* It is REQUIRED to call this to finish writing the rest of the file */
749 png_write_end(png_ptr, info_ptr);
752 /* If you png_malloced a palette, free it here (don't free info_ptr->palette,
753 as recommended in versions 1.0.5m and earlier of this example; if
754 libpng mallocs info_ptr->palette, libpng will free it). If you
755 allocated it with malloc() instead of png_malloc(), use free() instead
757 png_free(png_ptr, palette);
760 /* Similarly, if you png_malloced any data that you passed in with
761 png_set_something(), such as a hist or trans array, free it here,
762 when you can be sure that libpng is through with it. */
763 png_free(png_ptr, trans);
766 /* clean up after the write, and free any memory allocated */
767 png_destroy_write_struct(&png_ptr, &info_ptr);