1 

     2 #if 0 /* in case someone actually tries to compile this */

     3 

     4 /* example.c - an example of using libpng

     5  * Last changed in libpng 1.2.37 [June 4, 2009]

     6  * This file has been placed in the public domain by the authors.

     7  * Maintained 1998-2009 Glenn Randers-Pehrson

     8  * Maintained 1996, 1997 Andreas Dilger)

     9  * Written 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)

    10  */

    11 

    12 /* This is an example of how to use libpng to read and write PNG files.

    13  * The file libpng.txt is much more verbose then this.  If you have not

    14  * read it, do so first.  This was designed to be a starting point of an

    15  * implementation.  This is not officially part of libpng, is hereby placed

    16  * in the public domain, and therefore does not require a copyright notice.

    17  *

    18  * This file does not currently compile, because it is missing certain

    19  * parts, like allocating memory to hold an image.  You will have to

    20  * supply these parts to get it to compile.  For an example of a minimal

    21  * working PNG reader/writer, see pngtest.c, included in this distribution;

    22  * see also the programs in the contrib directory.

    23  */

    24 

    25 #include "png.h"

    26 

    27  /* The png_jmpbuf() macro, used in error handling, became available in

    28   * libpng version 1.0.6.  If you want to be able to run your code with older

    29   * versions of libpng, you must define the macro yourself (but only if it

    30   * is not already defined by libpng!).

    31   */

    32 

    33 #ifndef png_jmpbuf

    34 #  define png_jmpbuf(png_ptr) ((png_ptr)->jmpbuf)

    35 #endif

    36 

    37 /* Check to see if a file is a PNG file using png_sig_cmp().  png_sig_cmp()

    38  * returns zero if the image is a PNG and nonzero if it isn't a PNG.

    39  *

    40  * The function check_if_png() shown here, but not used, returns nonzero (true)

    41  * if the file can be opened and is a PNG, 0 (false) otherwise.

    42  *

    43  * If this call is successful, and you are going to keep the file open,

    44  * you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once

    45  * you have created the png_ptr, so that libpng knows your application

    46  * has read that many bytes from the start of the file.  Make sure you

    47  * don't call png_set_sig_bytes() with more than 8 bytes read or give it

    48  * an incorrect number of bytes read, or you will either have read too

    49  * many bytes (your fault), or you are telling libpng to read the wrong

    50  * number of magic bytes (also your fault).

    51  *

    52  * Many applications already read the first 2 or 4 bytes from the start

    53  * of the image to determine the file type, so it would be easiest just

    54  * to pass the bytes to png_sig_cmp() or even skip that if you know

    55  * you have a PNG file, and call png_set_sig_bytes().

    56  */

    57 #define PNG_BYTES_TO_CHECK 4

    58 int check_if_png(char *file_name, FILE **fp)

    59 {

    60    char buf[PNG_BYTES_TO_CHECK];

    61 

    62    /* Open the prospective PNG file. */

    63    if ((*fp = fopen(file_name, "rb")) == NULL)

    64       return 0;

    65 

    66    /* Read in some of the signature bytes */

    67    if (fread(buf, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK)

    68       return 0;

    69 

    70    /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.

    71       Return nonzero (true) if they match */

    72 

    73    return(!png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK));

    74 }

    75 

    76 /* Read a PNG file.  You may want to return an error code if the read

    77  * fails (depending upon the failure).  There are two "prototypes" given

    78  * here - one where we are given the filename, and we need to open the

    79  * file, and the other where we are given an open file (possibly with

    80  * some or all of the magic bytes read - see comments above).

    81  */

    82 #ifdef open_file /* prototype 1 */

    83 void read_png(char *file_name)  /* We need to open the file */

    84 {

    85    png_structp png_ptr;

    86    png_infop info_ptr;

    87    unsigned int sig_read = 0;

    88    png_uint_32 width, height;

    89    int bit_depth, color_type, interlace_type;

    90    FILE *fp;

    91 

    92    if ((fp = fopen(file_name, "rb")) == NULL)

    93       return (ERROR);

    94 

    95 #else no_open_file /* prototype 2 */

    96 void read_png(FILE *fp, unsigned int sig_read)  /* File is already open */

    97 {

    98    png_structp png_ptr;

    99    png_infop info_ptr;

   100    png_uint_32 width, height;

   101    int bit_depth, color_type, interlace_type;

   102 #endif no_open_file /* Only use one prototype! */

   103 

   104    /* Create and initialize the png_struct with the desired error handler

   105     * functions.  If you want to use the default stderr and longjump method,

   106     * you can supply NULL for the last three parameters.  We also supply the

   107     * the compiler header file version, so that we know if the application

   108     * was compiled with a compatible version of the library.  REQUIRED

   109     */

   110    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,

   111       png_voidp user_error_ptr, user_error_fn, user_warning_fn);

   112 

   113    if (png_ptr == NULL)

   114    {

   115       fclose(fp);

   116       return (ERROR);

   117    }

   118 

   119    /* Allocate/initialize the memory for image information.  REQUIRED. */

   120    info_ptr = png_create_info_struct(png_ptr);

   121    if (info_ptr == NULL)

   122    {

   123       fclose(fp);

   124       png_destroy_read_struct(&png_ptr, png_infopp_NULL, png_infopp_NULL);

   125       return (ERROR);

   126    }

   127 

   128    /* Set error handling if you are using the setjmp/longjmp method (this is

   129     * the normal method of doing things with libpng).  REQUIRED unless you

   130     * set up your own error handlers in the png_create_read_struct() earlier.

   131     */

   132 

   133    if (setjmp(png_jmpbuf(png_ptr)))

   134    {

   135       /* Free all of the memory associated with the png_ptr and info_ptr */

   136       png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);

   137       fclose(fp);

   138       /* If we get here, we had a problem reading the file */

   139       return (ERROR);

   140    }

   141 

   142    /* One of the following I/O initialization methods is REQUIRED */

   143 #ifdef streams /* PNG file I/O method 1 */

   144    /* Set up the input control if you are using standard C streams */

   145    png_init_io(png_ptr, fp);

   146 

   147 #else no_streams /* PNG file I/O method 2 */

   148    /* If you are using replacement read functions, instead of calling

   149     * png_init_io() here you would call:

   150     */

   151    png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn);

   152    /* where user_io_ptr is a structure you want available to the callbacks */

   153 #endif no_streams /* Use only one I/O method! */

   154 

   155    /* If we have already read some of the signature */

   156    png_set_sig_bytes(png_ptr, sig_read);

   157 

   158 #ifdef hilevel

   159    /*

   160     * If you have enough memory to read in the entire image at once,

   161     * and you need to specify only transforms that can be controlled

   162     * with one of the PNG_TRANSFORM_* bits (this presently excludes

   163     * dithering, filling, setting background, and doing gamma

   164     * adjustment), then you can read the entire image (including

   165     * pixels) into the info structure with this call:

   166     */

   167    png_read_png(png_ptr, info_ptr, png_transforms, png_voidp_NULL);

   168 

   169 #else

   170    /* OK, you're doing it the hard way, with the lower-level functions */

   171 

   172    /* The call to png_read_info() gives us all of the information from the

   173     * PNG file before the first IDAT (image data chunk).  REQUIRED

   174     */

   175    png_read_info(png_ptr, info_ptr);

   176 

   177    png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,

   178        &interlace_type, int_p_NULL, int_p_NULL);

   179 

   180    /* Set up the data transformations you want.  Note that these are all

   181     * optional.  Only call them if you want/need them.  Many of the

   182     * transformations only work on specific types of images, and many

   183     * are mutually exclusive.

   184     */

   185 

   186    /* Tell libpng to strip 16 bit/color files down to 8 bits/color */

   187    png_set_strip_16(png_ptr);

   188 

   189    /* Strip alpha bytes from the input data without combining with the

   190     * background (not recommended).

   191     */

   192    png_set_strip_alpha(png_ptr);

   193 

   194    /* Extract multiple pixels with bit depths of 1, 2, and 4 from a single

   195     * byte into separate bytes (useful for paletted and grayscale images).

   196     */

   197    png_set_packing(png_ptr);

   198 

   199    /* Change the order of packed pixels to least significant bit first

   200     * (not useful if you are using png_set_packing). */

   201    png_set_packswap(png_ptr);

   202 

   203    /* Expand paletted colors into true RGB triplets */

   204    if (color_type == PNG_COLOR_TYPE_PALETTE)

   205       png_set_palette_to_rgb(png_ptr);

   206 

   207    /* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */

   208    if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)

   209       png_set_expand_gray_1_2_4_to_8(png_ptr);

   210 

   211    /* Expand paletted or RGB images with transparency to full alpha channels

   212     * so the data will be available as RGBA quartets.

   213     */

   214    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))

   215       png_set_tRNS_to_alpha(png_ptr);

   216 

   217    /* Set the background color to draw transparent and alpha images over.

   218     * It is possible to set the red, green, and blue components directly

   219     * for paletted images instead of supplying a palette index.  Note that

   220     * even if the PNG file supplies a background, you are not required to

   221     * use it - you should use the (solid) application background if it has one.

   222     */

   223 

   224    png_color_16 my_background, *image_background;

   225 

   226    if (png_get_bKGD(png_ptr, info_ptr, &image_background))

   227       png_set_background(png_ptr, image_background,

   228                          PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);

   229    else

   230       png_set_background(png_ptr, &my_background,

   231                          PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);

   232 

   233    /* Some suggestions as to how to get a screen gamma value

   234     *

   235     * Note that screen gamma is the display_exponent, which includes

   236     * the CRT_exponent and any correction for viewing conditions

   237     */

   238    if (/* We have a user-defined screen gamma value */)

   239    {

   240       screen_gamma = user-defined screen_gamma;

   241    }

   242    /* This is one way that applications share the same screen gamma value */

   243    else if ((gamma_str = getenv("SCREEN_GAMMA")) != NULL)

   244    {

   245       screen_gamma = atof(gamma_str);

   246    }

   247    /* If we don't have another value */

   248    else

   249    {

   250       screen_gamma = 2.2;  /* A good guess for a PC monitor in a dimly

   251                               lit room */

   252       screen_gamma = 1.7 or 1.0;  /* A good guess for Mac systems */

   253    }

   254 

   255    /* Tell libpng to handle the gamma conversion for you.  The final call

   256     * is a good guess for PC generated images, but it should be configurable

   257     * by the user at run time by the user.  It is strongly suggested that

   258     * your application support gamma correction.

   259     */

   260 

   261    int intent;

   262 

   263    if (png_get_sRGB(png_ptr, info_ptr, &intent))

   264       png_set_gamma(png_ptr, screen_gamma, 0.45455);

   265    else

   266    {

   267       double image_gamma;

   268       if (png_get_gAMA(png_ptr, info_ptr, &image_gamma))

   269          png_set_gamma(png_ptr, screen_gamma, image_gamma);

   270       else

   271          png_set_gamma(png_ptr, screen_gamma, 0.45455);

   272    }

   273 

   274    /* Dither RGB files down to 8 bit palette or reduce palettes

   275     * to the number of colors available on your screen.

   276     */

   277    if (color_type & PNG_COLOR_MASK_COLOR)

   278    {

   279       int num_palette;

   280       png_colorp palette;

   281 

   282       /* This reduces the image to the application supplied palette */

   283       if (/* We have our own palette */)

   284       {

   285          /* An array of colors to which the image should be dithered */

   286          png_color std_color_cube[MAX_SCREEN_COLORS];

   287 

   288          png_set_dither(png_ptr, std_color_cube, MAX_SCREEN_COLORS,

   289             MAX_SCREEN_COLORS, png_uint_16p_NULL, 0);

   290       }

   291       /* This reduces the image to the palette supplied in the file */

   292       else if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette))

   293       {

   294          png_uint_16p histogram = NULL;

   295 

   296          png_get_hIST(png_ptr, info_ptr, &histogram);

   297 

   298          png_set_dither(png_ptr, palette, num_palette,

   299                         max_screen_colors, histogram, 0);

   300       }

   301    }

   302 

   303    /* Invert monochrome files to have 0 as white and 1 as black */

   304    png_set_invert_mono(png_ptr);

   305 

   306    /* If you want to shift the pixel values from the range [0,255] or

   307     * [0,65535] to the original [0,7] or [0,31], or whatever range the

   308     * colors were originally in:

   309     */

   310    if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT))

   311    {

   312       png_color_8p sig_bit_p;

   313 

   314       png_get_sBIT(png_ptr, info_ptr, &sig_bit_p);

   315       png_set_shift(png_ptr, sig_bit_p);

   316    }

   317 

   318    /* Flip the RGB pixels to BGR (or RGBA to BGRA) */

   319    if (color_type & PNG_COLOR_MASK_COLOR)

   320       png_set_bgr(png_ptr);

   321 

   322    /* Swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */

   323    png_set_swap_alpha(png_ptr);

   324 

   325    /* Swap bytes of 16 bit files to least significant byte first */

   326    png_set_swap(png_ptr);

   327 

   328    /* Add filler (or alpha) byte (before/after each RGB triplet) */

   329    png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);

   330 

   331    /* Turn on interlace handling.  REQUIRED if you are not using

   332     * png_read_image().  To see how to handle interlacing passes,

   333     * see the png_read_row() method below:

   334     */

   335    number_passes = png_set_interlace_handling(png_ptr);

   336 

   337    /* Optional call to gamma correct and add the background to the palette

   338     * and update info structure.  REQUIRED if you are expecting libpng to

   339     * update the palette for you (ie you selected such a transform above).

   340     */

   341    png_read_update_info(png_ptr, info_ptr);

   342 

   343    /* Allocate the memory to hold the image using the fields of info_ptr. */

   344 

   345    /* The easiest way to read the image: */

   346    png_bytep row_pointers[height];

   347 

   348    /* Clear the pointer array */

   349    for (row = 0; row < height; row++)

   350       row_pointers[row] = NULL;

   351 

   352    for (row = 0; row < height; row++)

   353       row_pointers[row] = png_malloc(png_ptr, png_get_rowbytes(png_ptr,

   354          info_ptr));

   355 

   356    /* Now it's time to read the image.  One of these methods is REQUIRED */

   357 #ifdef entire /* Read the entire image in one go */

   358    png_read_image(png_ptr, row_pointers);

   359 

   360 #else no_entire /* Read the image one or more scanlines at a time */

   361    /* The other way to read images - deal with interlacing: */

   362 

   363    for (pass = 0; pass < number_passes; pass++)

   364    {

   365 #ifdef single /* Read the image a single row at a time */

   366       for (y = 0; y < height; y++)

   367       {

   368          png_read_rows(png_ptr, &row_pointers[y], png_bytepp_NULL, 1);

   369       }

   370 

   371 #else no_single /* Read the image several rows at a time */

   372       for (y = 0; y < height; y += number_of_rows)

   373       {

   374 #ifdef sparkle /* Read the image using the "sparkle" effect. */

   375          png_read_rows(png_ptr, &row_pointers[y], png_bytepp_NULL,

   376             number_of_rows);

   377 #else no_sparkle /* Read the image using the "rectangle" effect */

   378          png_read_rows(png_ptr, png_bytepp_NULL, &row_pointers[y],

   379             number_of_rows);

   380 #endif no_sparkle /* Use only one of these two methods */

   381       }

   382 

   383       /* If you want to display the image after every pass, do so here */

   384 #endif no_single /* Use only one of these two methods */

   385    }

   386 #endif no_entire /* Use only one of these two methods */

   387 

   388    /* Read rest of file, and get additional chunks in info_ptr - REQUIRED */

   389    png_read_end(png_ptr, info_ptr);

   390 #endif hilevel

   391 

   392    /* At this point you have read the entire image */

   393 

   394    /* Clean up after the read, and free any memory allocated - REQUIRED */

   395    png_destroy_read_struct(&png_ptr, &info_ptr, png_infopp_NULL);

   396 

   397    /* Close the file */

   398    fclose(fp);

   399 

   400    /* That's it */

   401    return (OK);

   402 }

   403 

   404 /* Progressively read a file */

   405 

   406 int

   407 initialize_png_reader(png_structp *png_ptr, png_infop *info_ptr)

   408 {

   409    /* Create and initialize the png_struct with the desired error handler

   410     * functions.  If you want to use the default stderr and longjump method,

   411     * you can supply NULL for the last three parameters.  We also check that

   412     * the library version is compatible in case we are using dynamically

   413     * linked libraries.

   414     */

   415    *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,

   416        png_voidp user_error_ptr, user_error_fn, user_warning_fn);

   417 

   418    if (*png_ptr == NULL)

   419    {

   420       *info_ptr = NULL;

   421       return (ERROR);

   422    }

   423 

   424    *info_ptr = png_create_info_struct(png_ptr);

   425 

   426    if (*info_ptr == NULL)

   427    {

   428       png_destroy_read_struct(png_ptr, info_ptr, png_infopp_NULL);

   429       return (ERROR);

   430    }

   431 

   432    if (setjmp(png_jmpbuf((*png_ptr))))

   433    {

   434       png_destroy_read_struct(png_ptr, info_ptr, png_infopp_NULL);

   435       return (ERROR);

   436    }

   437 

   438    /* This one's new.  You will need to provide all three

   439     * function callbacks, even if you aren't using them all.

   440     * If you aren't using all functions, you can specify NULL

   441     * parameters.  Even when all three functions are NULL,

   442     * you need to call png_set_progressive_read_fn().

   443     * These functions shouldn't be dependent on global or

   444     * static variables if you are decoding several images

   445     * simultaneously.  You should store stream specific data

   446     * in a separate struct, given as the second parameter,

   447     * and retrieve the pointer from inside the callbacks using

   448     * the function png_get_progressive_ptr(png_ptr).

   449     */

   450    png_set_progressive_read_fn(*png_ptr, (void *)stream_data,

   451       info_callback, row_callback, end_callback);

   452 

   453    return (OK);

   454 }

   455 

   456 int

   457 process_data(png_structp *png_ptr, png_infop *info_ptr,

   458    png_bytep buffer, png_uint_32 length)

   459 {

   460    if (setjmp(png_jmpbuf((*png_ptr))))

   461    {

   462       /* Free the png_ptr and info_ptr memory on error */

   463       png_destroy_read_struct(png_ptr, info_ptr, png_infopp_NULL);

   464       return (ERROR);

   465    }

   466 

   467    /* This one's new also.  Simply give it chunks of data as

   468     * they arrive from the data stream (in order, of course).

   469     * On segmented machines, don't give it any more than 64K.

   470     * The library seems to run fine with sizes of 4K, although

   471     * you can give it much less if necessary (I assume you can

   472     * give it chunks of 1 byte, but I haven't tried with less

   473     * than 256 bytes yet).  When this function returns, you may

   474     * want to display any rows that were generated in the row

   475     * callback, if you aren't already displaying them there.

   476     */

   477    png_process_data(*png_ptr, *info_ptr, buffer, length);

   478    return (OK);

   479 }

   480 

   481 info_callback(png_structp png_ptr, png_infop info)

   482 {

   483    /* Do any setup here, including setting any of the transformations

   484     * mentioned in the Reading PNG files section.  For now, you _must_

   485     * call either png_start_read_image() or png_read_update_info()

   486     * after all the transformations are set (even if you don't set

   487     * any).  You may start getting rows before png_process_data()

   488     * returns, so this is your last chance to prepare for that.

   489     */

   490 }

   491 

   492 row_callback(png_structp png_ptr, png_bytep new_row,

   493    png_uint_32 row_num, int pass)

   494 {

   495    /*

   496     * This function is called for every row in the image.  If the

   497     * image is interlaced, and you turned on the interlace handler,

   498     * this function will be called for every row in every pass.

   499     *

   500     * In this function you will receive a pointer to new row data from

   501     * libpng called new_row that is to replace a corresponding row (of

   502     * the same data format) in a buffer allocated by your application.

   503     *

   504     * The new row data pointer "new_row" may be NULL, indicating there is

   505     * no new data to be replaced (in cases of interlace loading).

   506     *

   507     * If new_row is not NULL then you need to call

   508     * png_progressive_combine_row() to replace the corresponding row as

   509     * shown below:

   510     */

   511 

   512    /* Check if row_num is in bounds. */

   513    if ((row_num >= 0) && (row_num < height))

   514    {

   515      /* Get pointer to corresponding row in our

   516       * PNG read buffer.

   517       */

   518      png_bytep old_row = ((png_bytep *)our_data)[row_num];

   519 

   520      /* If both rows are allocated then copy the new row

   521       * data to the corresponding row data.

   522       */

   523      if ((old_row != NULL) && (new_row != NULL))

   524      png_progressive_combine_row(png_ptr, old_row, new_row);

   525    }

   526    /*

   527     * The rows and passes are called in order, so you don't really

   528     * need the row_num and pass, but I'm supplying them because it

   529     * may make your life easier.

   530     *

   531     * For the non-NULL rows of interlaced images, you must call

   532     * png_progressive_combine_row() passing in the new row and the

   533     * old row, as demonstrated above.  You can call this function for

   534     * NULL rows (it will just return) and for non-interlaced images

   535     * (it just does the png_memcpy for you) if it will make the code

   536     * easier.  Thus, you can just do this for all cases:

   537     */

   538 

   539    png_progressive_combine_row(png_ptr, old_row, new_row);

   540 

   541    /* where old_row is what was displayed for previous rows.  Note

   542     * that the first pass (pass == 0 really) will completely cover

   543     * the old row, so the rows do not have to be initialized.  After

   544     * the first pass (and only for interlaced images), you will have

   545     * to pass the current row as new_row, and the function will combine

   546     * the old row and the new row.

   547     */

   548 }

   549 

   550 end_callback(png_structp png_ptr, png_infop info)

   551 {

   552    /* This function is called when the whole image has been read,

   553     * including any chunks after the image (up to and including

   554     * the IEND).  You will usually have the same info chunk as you

   555     * had in the header, although some data may have been added

   556     * to the comments and time fields.

   557     *

   558     * Most people won't do much here, perhaps setting a flag that

   559     * marks the image as finished.

   560     */

   561 }

   562 

   563 /* Write a png file */

   564 void write_png(char *file_name /* , ... other image information ... */)

   565 {

   566    FILE *fp;

   567    png_structp png_ptr;

   568    png_infop info_ptr;

   569    png_colorp palette;

   570 

   571    /* Open the file */

   572    fp = fopen(file_name, "wb");

   573    if (fp == NULL)

   574       return (ERROR);

   575 

   576    /* Create and initialize the png_struct with the desired error handler

   577     * functions.  If you want to use the default stderr and longjump method,

   578     * you can supply NULL for the last three parameters.  We also check that

   579     * the library version is compatible with the one used at compile time,

   580     * in case we are using dynamically linked libraries.  REQUIRED.

   581     */

   582    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,

   583       png_voidp user_error_ptr, user_error_fn, user_warning_fn);

   584 

   585    if (png_ptr == NULL)

   586    {

   587       fclose(fp);

   588       return (ERROR);

   589    }

   590 

   591    /* Allocate/initialize the image information data.  REQUIRED */

   592    info_ptr = png_create_info_struct(png_ptr);

   593    if (info_ptr == NULL)

   594    {

   595       fclose(fp);

   596       png_destroy_write_struct(&png_ptr,  png_infopp_NULL);

   597       return (ERROR);

   598    }

   599 

   600    /* Set error handling.  REQUIRED if you aren't supplying your own

   601     * error handling functions in the png_create_write_struct() call.

   602     */

   603    if (setjmp(png_jmpbuf(png_ptr)))

   604    {

   605       /* If we get here, we had a problem writing the file */

   606       fclose(fp);

   607       png_destroy_write_struct(&png_ptr, &info_ptr);

   608       return (ERROR);

   609    }

   610 

   611    /* One of the following I/O initialization functions is REQUIRED */

   612 

   613 #ifdef streams /* I/O initialization method 1 */

   614    /* Set up the output control if you are using standard C streams */

   615    png_init_io(png_ptr, fp);

   616 

   617 #else no_streams /* I/O initialization method 2 */

   618    /* If you are using replacement write functions, instead of calling

   619     * png_init_io() here you would call

   620     */

   621    png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,

   622       user_IO_flush_function);

   623    /* where user_io_ptr is a structure you want available to the callbacks */

   624 #endif no_streams /* Only use one initialization method */

   625 

   626 #ifdef hilevel

   627    /* This is the easy way.  Use it if you already have all the

   628     * image info living in the structure.  You could "|" many

   629     * PNG_TRANSFORM flags into the png_transforms integer here.

   630     */

   631    png_write_png(png_ptr, info_ptr, png_transforms, png_voidp_NULL);

   632 

   633 #else

   634    /* This is the hard way */

   635 

   636    /* Set the image information here.  Width and height are up to 2^31,

   637     * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on

   638     * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,

   639     * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,

   640     * or PNG_COLOR_TYPE_RGB_ALPHA.  interlace is either PNG_INTERLACE_NONE or

   641     * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST

   642     * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED

   643     */

   644    png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,

   645       PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);

   646 

   647    /* Set the palette if there is one.  REQUIRED for indexed-color images */

   648    palette = (png_colorp)png_malloc(png_ptr, PNG_MAX_PALETTE_LENGTH

   649              * png_sizeof(png_color));

   650    /* ... Set palette colors ... */

   651    png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);

   652    /* You must not free palette here, because png_set_PLTE only makes a link to

   653     * the palette that you malloced.  Wait until you are about to destroy

   654     * the png structure.

   655     */

   656 

   657    /* Optional significant bit (sBIT) chunk */

   658    png_color_8 sig_bit;

   659    /* If we are dealing with a grayscale image then */

   660    sig_bit.gray = true_bit_depth;

   661    /* Otherwise, if we are dealing with a color image then */

   662    sig_bit.red = true_red_bit_depth;

   663    sig_bit.green = true_green_bit_depth;

   664    sig_bit.blue = true_blue_bit_depth;

   665    /* If the image has an alpha channel then */

   666    sig_bit.alpha = true_alpha_bit_depth;

   667    png_set_sBIT(png_ptr, info_ptr, &sig_bit);

   668 

   669 

   670    /* Optional gamma chunk is strongly suggested if you have any guess

   671     * as to the correct gamma of the image.

   672     */

   673    png_set_gAMA(png_ptr, info_ptr, gamma);

   674 

   675    /* Optionally write comments into the image */

   676    text_ptr[0].key = "Title";

   677    text_ptr[0].text = "Mona Lisa";

   678    text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;

   679    text_ptr[1].key = "Author";

   680    text_ptr[1].text = "Leonardo DaVinci";

   681    text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;

   682    text_ptr[2].key = "Description";

   683    text_ptr[2].text = "<long text>";

   684    text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;

   685 #ifdef PNG_iTXt_SUPPORTED

   686    text_ptr[0].lang = NULL;

   687    text_ptr[1].lang = NULL;

   688    text_ptr[2].lang = NULL;

   689 #endif

   690    png_set_text(png_ptr, info_ptr, text_ptr, 3);

   691 

   692    /* Other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs */

   693 

   694    /* Note that if sRGB is present the gAMA and cHRM chunks must be ignored

   695     * on read and, if your application chooses to write them, they must

   696     * be written in accordance with the sRGB profile

   697     */

   698 

   699    /* Write the file header information.  REQUIRED */

   700    png_write_info(png_ptr, info_ptr);

   701 

   702    /* If you want, you can write the info in two steps, in case you need to

   703     * write your private chunk ahead of PLTE:

   704     *

   705     *   png_write_info_before_PLTE(write_ptr, write_info_ptr);

   706     *   write_my_chunk();

   707     *   png_write_info(png_ptr, info_ptr);

   708     *

   709     * However, given the level of known- and unknown-chunk support in 1.2.0

   710     * and up, this should no longer be necessary.

   711     */

   712 

   713    /* Once we write out the header, the compression type on the text

   714     * chunks gets changed to PNG_TEXT_COMPRESSION_NONE_WR or

   715     * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again

   716     * at the end.

   717     */

   718 

   719    /* Set up the transformations you want.  Note that these are

   720     * all optional.  Only call them if you want them.

   721     */

   722 

   723    /* Invert monochrome pixels */

   724    png_set_invert_mono(png_ptr);

   725 

   726    /* Shift the pixels up to a legal bit depth and fill in

   727     * as appropriate to correctly scale the image.

   728     */

   729    png_set_shift(png_ptr, &sig_bit);

   730 

   731    /* Pack pixels into bytes */

   732    png_set_packing(png_ptr);

   733 

   734    /* Swap location of alpha bytes from ARGB to RGBA */

   735    png_set_swap_alpha(png_ptr);

   736 

   737    /* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into

   738     * RGB (4 channels -> 3 channels). The second parameter is not used.

   739     */

   740    png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);

   741 

   742    /* Flip BGR pixels to RGB */

   743    png_set_bgr(png_ptr);

   744 

   745    /* Swap bytes of 16-bit files to most significant byte first */

   746    png_set_swap(png_ptr);

   747 

   748    /* Swap bits of 1, 2, 4 bit packed pixel formats */

   749    png_set_packswap(png_ptr);

   750 

   751    /* Turn on interlace handling if you are not using png_write_image() */

   752    if (interlacing)

   753       number_passes = png_set_interlace_handling(png_ptr);

   754    else

   755       number_passes = 1;

   756 

   757    /* The easiest way to write the image (you may have a different memory

   758     * layout, however, so choose what fits your needs best).  You need to

   759     * use the first method if you aren't handling interlacing yourself.

   760     */

   761    png_uint_32 k, height, width;

   762    png_byte image[height][width*bytes_per_pixel];

   763    png_bytep row_pointers[height];

   764 

   765    if (height > PNG_UINT_32_MAX/png_sizeof(png_bytep))

   766      png_error (png_ptr, "Image is too tall to process in memory");

   767 

   768    for (k = 0; k < height; k++)

   769      row_pointers[k] = image + k*width*bytes_per_pixel;

   770 

   771    /* One of the following output methods is REQUIRED */

   772 

   773 #ifdef entire /* Write out the entire image data in one call */

   774    png_write_image(png_ptr, row_pointers);

   775 

   776    /* The other way to write the image - deal with interlacing */

   777 

   778 #else no_entire /* Write out the image data by one or more scanlines */

   779 

   780    /* The number of passes is either 1 for non-interlaced images,

   781     * or 7 for interlaced images.

   782     */

   783    for (pass = 0; pass < number_passes; pass++)

   784    {

   785       /* Write a few rows at a time. */

   786       png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);

   787 

   788       /* If you are only writing one row at a time, this works */

   789       for (y = 0; y < height; y++)

   790          png_write_rows(png_ptr, &row_pointers[y], 1);

   791    }

   792 #endif no_entire /* Use only one output method */

   793 

   794    /* You can write optional chunks like tEXt, zTXt, and tIME at the end

   795     * as well.  Shouldn't be necessary in 1.2.0 and up as all the public

   796     * chunks are supported and you can use png_set_unknown_chunks() to

   797     * register unknown chunks into the info structure to be written out.

   798     */

   799 

   800    /* It is REQUIRED to call this to finish writing the rest of the file */

   801    png_write_end(png_ptr, info_ptr);

   802 #endif hilevel

   803 

   804    /* If you png_malloced a palette, free it here (don't free info_ptr->palette,

   805     * as recommended in versions 1.0.5m and earlier of this example; if

   806     * libpng mallocs info_ptr->palette, libpng will free it).  If you

   807     * allocated it with malloc() instead of png_malloc(), use free() instead

   808     * of png_free().

   809     */

   810    png_free(png_ptr, palette);

   811    palette = NULL;

   812 

   813    /* Similarly, if you png_malloced any data that you passed in with

   814     * png_set_something(), such as a hist or trans array, free it here,

   815     * when you can be sure that libpng is through with it.

   816     */

   817    png_free(png_ptr, trans);

   818    trans = NULL;

   819    /* Whenever you use png_free() it is a good idea to set the pointer to

   820     * NULL in case your application inadvertently tries to png_free() it

   821     * again.  When png_free() sees a NULL it returns without action, thus

   822     * avoiding the double-free security problem.

   823     */

   824 

   825    /* Clean up after the write, and free any memory allocated */

   826    png_destroy_write_struct(&png_ptr, &info_ptr);

   827 

   828    /* Close the file */

   829    fclose(fp);

   830 

   831    /* That's it */

   832    return (OK);

   833 }

   834 

   835 #endif /* if 0 */