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, png_voidp_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, int_p_NULL, int_p_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, png_uint_16p_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 = NULL;
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], png_bytepp_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], png_bytepp_NULL,
366 #else no_sparkle /* Read the image using the "rectangle" effect */
367 png_read_rows(png_ptr, png_bytepp_NULL, &row_pointers[y],
369 #endif no_sparkle /* use only one of these two methods */
372 /* if you want to display the image after every pass, do
374 #endif no_single /* use only one of these two methods */
376 #endif no_entire /* use only one of these two methods */
378 /* read rest of file, and get additional chunks in info_ptr - REQUIRED */
379 png_read_end(png_ptr, info_ptr);
382 /* At this point you have read the entire image */
384 /* clean up after the read, and free any memory allocated - REQUIRED */
385 png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);
394 /* progressively read a file */
397 initialize_png_reader(png_structp *png_ptr, png_infop *info_ptr)
399 /* Create and initialize the png_struct with the desired error handler
400 * functions. If you want to use the default stderr and longjump method,
401 * you can supply NULL for the last three parameters. We also check that
402 * the library version is compatible in case we are using dynamically
405 *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
406 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
408 if (*png_ptr == NULL)
414 *info_ptr = png_create_info_struct(png_ptr);
416 if (*info_ptr == NULL)
418 png_destroy_read_struct(png_ptr, info_ptr, png_infopp_NULL);
422 if (setjmp(png_jmpbuf((*png_ptr))))
424 png_destroy_read_struct(png_ptr, info_ptr, png_infopp_NULL);
428 /* This one's new. You will need to provide all three
429 * function callbacks, even if you aren't using them all.
430 * If you aren't using all functions, you can specify NULL
431 * parameters. Even when all three functions are NULL,
432 * you need to call png_set_progressive_read_fn().
433 * These functions shouldn't be dependent on global or
434 * static variables if you are decoding several images
435 * simultaneously. You should store stream specific data
436 * in a separate struct, given as the second parameter,
437 * and retrieve the pointer from inside the callbacks using
438 * the function png_get_progressive_ptr(png_ptr).
440 png_set_progressive_read_fn(*png_ptr, (void *)stream_data,
441 info_callback, row_callback, end_callback);
447 process_data(png_structp *png_ptr, png_infop *info_ptr,
448 png_bytep buffer, png_uint_32 length)
450 if (setjmp(png_jmpbuf((*png_ptr))))
452 /* Free the png_ptr and info_ptr memory on error */
453 png_destroy_read_struct(png_ptr, info_ptr, png_infopp_NULL);
457 /* This one's new also. Simply give it chunks of data as
458 * they arrive from the data stream (in order, of course).
459 * On Segmented machines, don't give it any more than 64K.
460 * The library seems to run fine with sizes of 4K, although
461 * you can give it much less if necessary (I assume you can
462 * give it chunks of 1 byte, but I haven't tried with less
463 * than 256 bytes yet). When this function returns, you may
464 * want to display any rows that were generated in the row
465 * callback, if you aren't already displaying them there.
467 png_process_data(*png_ptr, *info_ptr, buffer, length);
471 info_callback(png_structp png_ptr, png_infop info)
473 /* do any setup here, including setting any of the transformations
474 * mentioned in the Reading PNG files section. For now, you _must_
475 * call either png_start_read_image() or png_read_update_info()
476 * after all the transformations are set (even if you don't set
477 * any). You may start getting rows before png_process_data()
478 * returns, so this is your last chance to prepare for that.
482 row_callback(png_structp png_ptr, png_bytep new_row,
483 png_uint_32 row_num, int pass)
486 * This function is called for every row in the image. If the
487 * image is interlaced, and you turned on the interlace handler,
488 * this function will be called for every row in every pass.
490 * In this function you will receive a pointer to new row data from
491 * libpng called new_row that is to replace a corresponding row (of
492 * the same data format) in a buffer allocated by your application.
494 * The new row data pointer new_row may be NULL, indicating there is
495 * no new data to be replaced (in cases of interlace loading).
497 * If new_row is not NULL then you need to call
498 * png_progressive_combine_row() to replace the corresponding row as
501 /* Check if row_num is in bounds. */
502 if((row_num >= 0) && (row_num < height))
504 /* Get pointer to corresponding row in our
507 png_bytep old_row = ((png_bytep *)our_data)[row_num];
509 /* If both rows are allocated then copy the new row
510 * data to the corresponding row data.
512 if((old_row != NULL) && (new_row != NULL))
513 png_progressive_combine_row(png_ptr, old_row, new_row);
516 * The rows and passes are called in order, so you don't really
517 * need the row_num and pass, but I'm supplying them because it
518 * may make your life easier.
520 * For the non-NULL rows of interlaced images, you must call
521 * png_progressive_combine_row() passing in the new row and the
522 * old row, as demonstrated above. You can call this function for
523 * NULL rows (it will just return) and for non-interlaced images
524 * (it just does the png_memcpy for you) if it will make the code
525 * easier. Thus, you can just do this for all cases:
528 png_progressive_combine_row(png_ptr, old_row, new_row);
530 /* where old_row is what was displayed for previous rows. Note
531 * that the first pass (pass == 0 really) will completely cover
532 * the old row, so the rows do not have to be initialized. After
533 * the first pass (and only for interlaced images), you will have
534 * to pass the current row as new_row, and the function will combine
535 * the old row and the new row.
539 end_callback(png_structp png_ptr, png_infop info)
541 /* this function is called when the whole image has been read,
542 * including any chunks after the image (up to and including
543 * the IEND). You will usually have the same info chunk as you
544 * had in the header, although some data may have been added
545 * to the comments and time fields.
547 * Most people won't do much here, perhaps setting a flag that
548 * marks the image as finished.
552 /* write a png file */
553 void write_png(char *file_name /* , ... other image information ... */)
561 fp = fopen(file_name, "wb");
565 /* Create and initialize the png_struct with the desired error handler
566 * functions. If you want to use the default stderr and longjump method,
567 * you can supply NULL for the last three parameters. We also check that
568 * the library version is compatible with the one used at compile time,
569 * in case we are using dynamically linked libraries. REQUIRED.
571 png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
572 png_voidp user_error_ptr, user_error_fn, user_warning_fn);
580 /* Allocate/initialize the image information data. REQUIRED */
581 info_ptr = png_create_info_struct(png_ptr);
582 if (info_ptr == NULL)
585 png_destroy_write_struct(&png_ptr, png_infopp_NULL);
589 /* Set error handling. REQUIRED if you aren't supplying your own
590 * error handling functions in the png_create_write_struct() call.
592 if (setjmp(png_jmpbuf(png_ptr)))
594 /* If we get here, we had a problem reading the file */
596 png_destroy_write_struct(&png_ptr, &info_ptr);
600 /* One of the following I/O initialization functions is REQUIRED */
601 #ifdef streams /* I/O initialization method 1 */
602 /* set up the output control if you are using standard C streams */
603 png_init_io(png_ptr, fp);
604 #else no_streams /* I/O initialization method 2 */
605 /* If you are using replacement read functions, instead of calling
606 * png_init_io() here you would call */
607 png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,
608 user_IO_flush_function);
609 /* where user_io_ptr is a structure you want available to the callbacks */
610 #endif no_streams /* only use one initialization method */
613 /* This is the easy way. Use it if you already have all the
614 * image info living info in the structure. You could "|" many
615 * PNG_TRANSFORM flags into the png_transforms integer here.
617 png_write_png(png_ptr, info_ptr, png_transforms, png_voidp_NULL);
619 /* This is the hard way */
621 /* Set the image information here. Width and height are up to 2^31,
622 * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
623 * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
624 * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
625 * or PNG_COLOR_TYPE_RGB_ALPHA. interlace is either PNG_INTERLACE_NONE or
626 * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
627 * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
629 png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,
630 PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
632 /* set the palette if there is one. REQUIRED for indexed-color images */
633 palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH
634 * sizeof (png_color));
635 /* ... set palette colors ... */
636 png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
637 /* You must not free palette here, because png_set_PLTE only makes a link to
638 the palette that you malloced. Wait until you are about to destroy
639 the png structure. */
641 /* optional significant bit chunk */
642 /* if we are dealing with a grayscale image then */
643 sig_bit.gray = true_bit_depth;
644 /* otherwise, if we are dealing with a color image then */
645 sig_bit.red = true_red_bit_depth;
646 sig_bit.green = true_green_bit_depth;
647 sig_bit.blue = true_blue_bit_depth;
648 /* if the image has an alpha channel then */
649 sig_bit.alpha = true_alpha_bit_depth;
650 png_set_sBIT(png_ptr, info_ptr, sig_bit);
653 /* Optional gamma chunk is strongly suggested if you have any guess
654 * as to the correct gamma of the image.
656 png_set_gAMA(png_ptr, info_ptr, gamma);
658 /* Optionally write comments into the image */
659 text_ptr[0].key = "Title";
660 text_ptr[0].text = "Mona Lisa";
661 text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
662 text_ptr[1].key = "Author";
663 text_ptr[1].text = "Leonardo DaVinci";
664 text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;
665 text_ptr[2].key = "Description";
666 text_ptr[2].text = "<long text>";
667 text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;
668 #ifdef PNG_iTXt_SUPPORTED
669 text_ptr[0].lang = NULL;
670 text_ptr[1].lang = NULL;
671 text_ptr[2].lang = NULL;
673 png_set_text(png_ptr, info_ptr, text_ptr, 3);
675 /* other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs, */
676 /* note that if sRGB is present the gAMA and cHRM chunks must be ignored
677 * on read and must be written in accordance with the sRGB profile */
679 /* Write the file header information. REQUIRED */
680 png_write_info(png_ptr, info_ptr);
682 /* If you want, you can write the info in two steps, in case you need to
683 * write your private chunk ahead of PLTE:
685 * png_write_info_before_PLTE(write_ptr, write_info_ptr);
687 * png_write_info(png_ptr, info_ptr);
689 * However, given the level of known- and unknown-chunk support in 1.1.0
690 * and up, this should no longer be necessary.
693 /* Once we write out the header, the compression type on the text
694 * chunks gets changed to PNG_TEXT_COMPRESSION_NONE_WR or
695 * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again
699 /* set up the transformations you want. Note that these are
700 * all optional. Only call them if you want them.
703 /* invert monochrome pixels */
704 png_set_invert_mono(png_ptr);
706 /* Shift the pixels up to a legal bit depth and fill in
707 * as appropriate to correctly scale the image.
709 png_set_shift(png_ptr, &sig_bit);
711 /* pack pixels into bytes */
712 png_set_packing(png_ptr);
714 /* swap location of alpha bytes from ARGB to RGBA */
715 png_set_swap_alpha(png_ptr);
717 /* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into
718 * RGB (4 channels -> 3 channels). The second parameter is not used.
720 png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
722 /* flip BGR pixels to RGB */
723 png_set_bgr(png_ptr);
725 /* swap bytes of 16-bit files to most significant byte first */
726 png_set_swap(png_ptr);
728 /* swap bits of 1, 2, 4 bit packed pixel formats */
729 png_set_packswap(png_ptr);
731 /* turn on interlace handling if you are not using png_write_image() */
733 number_passes = png_set_interlace_handling(png_ptr);
737 /* The easiest way to write the image (you may have a different memory
738 * layout, however, so choose what fits your needs best). You need to
739 * use the first method if you aren't handling interlacing yourself.
741 png_uint_32 k, height, width;
742 png_byte image[height][width*bytes_per_pixel];
743 png_bytep row_pointers[height];
744 for (k = 0; k < height; k++)
745 row_pointers[k] = image + k*width*bytes_per_pixel;
747 /* One of the following output methods is REQUIRED */
748 #ifdef entire /* write out the entire image data in one call */
749 png_write_image(png_ptr, row_pointers);
751 /* the other way to write the image - deal with interlacing */
753 #else no_entire /* write out the image data by one or more scanlines */
754 /* The number of passes is either 1 for non-interlaced images,
755 * or 7 for interlaced images.
757 for (pass = 0; pass < number_passes; pass++)
759 /* Write a few rows at a time. */
760 png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);
762 /* If you are only writing one row at a time, this works */
763 for (y = 0; y < height; y++)
765 png_write_rows(png_ptr, &row_pointers[y], 1);
768 #endif no_entire /* use only one output method */
770 /* You can write optional chunks like tEXt, zTXt, and tIME at the end
771 * as well. Shouldn't be necessary in 1.1.0 and up as all the public
772 * chunks are supported and you can use png_set_unknown_chunks() to
773 * register unknown chunks into the info structure to be written out.
776 /* It is REQUIRED to call this to finish writing the rest of the file */
777 png_write_end(png_ptr, info_ptr);
780 /* If you png_malloced a palette, free it here (don't free info_ptr->palette,
781 as recommended in versions 1.0.5m and earlier of this example; if
782 libpng mallocs info_ptr->palette, libpng will free it). If you
783 allocated it with malloc() instead of png_malloc(), use free() instead
785 png_free(png_ptr, palette);
788 /* Similarly, if you png_malloced any data that you passed in with
789 png_set_something(), such as a hist or trans array, free it here,
790 when you can be sure that libpng is through with it. */
791 png_free(png_ptr, trans);
794 /* clean up after the write, and free any memory allocated */
795 png_destroy_write_struct(&png_ptr, &info_ptr);