text: 
  #if 0 /* in case someone actually tries to compile this */
  
  /* example.c - an example of using libpng */
  
  /* This is an example of how to use libpng to read and write PNG files.
   * The file libpng.txt is much more verbose then this.  If you have not
   * read it, do so first.  This was designed to be a starting point of an
   * implementation.  This is not officially part of libpng, and therefore
   * does not require a copyright notice.
   *
   * This file does not currently compile, because it is missing certain
   * parts, like allocating memory to hold an image.  You will have to
   * supply these parts to get it to compile.  For an example of a minimal
   * working PNG reader/writer, see pngtest.c, included in this distribution.
   */
  
  #include "png.h"
  
  /* Check to see if a file is a PNG file using png_sig_cmp().  png_sig_cmp()
   * returns zero if the image is a PNG and nonzero if it isn't a PNG.
   *
   * The function check_if_png() shown here, but not used, returns nonzero (true)
   * if the file can be opened and is a PNG, 0 (false) otherwise.
   *
   * If this call is successful, and you are going to keep the file open,
   * you should call png_set_sig_bytes(png_ptr, PNG_BYTES_TO_CHECK); once
   * you have created the png_ptr, so that libpng knows your application
   * has read that many bytes from the start of the file.  Make sure you
   * don't call png_set_sig_bytes() with more than 8 bytes read or give it
   * an incorrect number of bytes read, or you will either have read too
   * many bytes (your fault), or you are telling libpng to read the wrong
   * number of magic bytes (also your fault).
   *
   * Many applications already read the first 2 or 4 bytes from the start
   * of the image to determine the file type, so it would be easiest just
   * to pass the bytes to png_sig_cmp() or even skip that if you know
   * you have a PNG file, and call png_set_sig_bytes().
   */
  #define PNG_BYTES_TO_CHECK 4
  int check_if_png(char *file_name, FILE **fp)
  {
     char buf[PNG_BYTES_TO_CHECK];
  
     /* Open the prospective PNG file. */
     if ((*fp = fopen(file_name, "rb")) != NULL);
        return 0;
  
     /* Read in some of the signature bytes */
     if (fread(buf, 1, PNG_BYTES_TO_CHECK, *fp) != PNG_BYTES_TO_CHECK)
        return 0;
  
     /* Compare the first PNG_BYTES_TO_CHECK bytes of the signature.
        Return nonzero (true) if they match */
  
     return(!png_sig_cmp(buf, (png_size_t)0, PNG_BYTES_TO_CHECK));
  }
  
  /* Read a PNG file.  You may want to return an error code if the read
   * fails (depending upon the failure).  There are two "prototypes" given
   * here - one where we are given the filename, and we need to open the
   * file, and the other where we are given an open file (possibly with
   * some or all of the magic bytes read - see comments above).
   */
  #ifdef open_file /* prototype 1 */
  void read_png(char *file_name)  /* We need to open the file */
  {
     png_structp png_ptr;
     png_infop info_ptr;
     unsigned int sig_read = 0;
     png_uint_32 width, height;
     int bit_depth, color_type, interlace_type;
     FILE *fp;
  
     if ((fp = fopen(file_name, "rb")) == NULL)
        return;
  #else no_open_file /* prototype 2 */
  void read_png(FILE *fp, unsigned int sig_read)  /* file is already open */
  {
     png_structp png_ptr;
     png_infop info_ptr;
     png_uint_32 width, height;
     int bit_depth, color_type, interlace_type;
  #endif no_open_file /* only use one prototype! */
  
     /* Create and initialize the png_struct with the desired error handler
      * functions.  If you want to use the default stderr and longjump method,
      * you can supply NULL for the last three parameters.  We also supply the
      * the compiler header file version, so that we know if the application
      * was compiled with a compatible version of the library.  REQUIRED
      */
     png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
        png_voidp user_error_ptr, user_error_fn, user_warning_fn);
  
     if (png_ptr == NULL)
     {
        fclose(fp);
        return;
     }
  
     /* Allocate/initialize the memory for image information.  REQUIRED. */
     info_ptr = png_create_info_struct(png_ptr);
     if (info_ptr == NULL)
     {
        fclose(fp);
        png_destroy_read_struct(&png_ptr, (png_infopp)NULL, (png_infopp)NULL);
        return;
     }
  
     /* Set error handling if you are using the setjmp/longjmp method (this is
      * the normal method of doing things with libpng).  REQUIRED unless you
      * set up your own error handlers in the png_create_read_struct() earlier.
      */
     if (setjmp(png_ptr->jmpbuf))
     {
        /* Free all of the memory associated with the png_ptr and info_ptr */
        png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
        fclose(fp);
        /* If we get here, we had a problem reading the file */
        return;
     }
  
     /* One of the following I/O initialization methods is REQUIRED */
  #ifdef streams /* PNG file I/O method 1 */
     /* Set up the input control if you are using standard C streams */
     png_init_io(png_ptr, fp);
  
  #else no_streams /* PNG file I/O method 2 */
     /* If you are using replacement read functions, instead of calling
      * png_init_io() here you would call:
      */
     png_set_read_fn(png_ptr, (void *)user_io_ptr, user_read_fn);
     /* where user_io_ptr is a structure you want available to the callbacks */
  #endif no_streams /* Use only one I/O method! */
  
     /* If we have already read some of the signature */
     png_set_sig_bytes(png_ptr, sig_read);
  
     /* The call to png_read_info() gives us all of the information from the
      * PNG file before the first IDAT (image data chunk).  REQUIRED
      */
     png_read_info(png_ptr, info_ptr);
  
     png_get_IHDR(png_ptr, info_ptr, &width, &height, &bit_depth, &color_type,
         &interlace_type, NULL, NULL);
  
  /**** Set up the data transformations you want.  Note that these are all
   **** optional.  Only call them if you want/need them.  Many of the
   **** transformations only work on specific types of images, and many
   **** are mutually exclusive.
   ****/
  
     /* tell libpng to strip 16 bit/color files down to 8 bits/color */
     png_set_strip_16(png_ptr);
  
     /* Strip alpha bytes from the input data without combining with the
      * background (not recommended).
      */
     png_set_strip_alpha(png_ptr);
  
     /* Extract multiple pixels with bit depths of 1, 2, and 4 from a single
      * byte into separate bytes (useful for paletted and grayscale images).
      */
     png_set_packing(png_ptr);
  
     /* Change the order of packed pixels to least significant bit first
      * (not useful if you are using png_set_packing). */
     png_set_packswap(png_ptr);
  
     /* Expand paletted colors into true RGB triplets */
     if (color_type == PNG_COLOR_TYPE_PALETTE)
        png_set_expand(png_ptr);
  
     /* Expand grayscale images to the full 8 bits from 1, 2, or 4 bits/pixel */
     if (color_type == PNG_COLOR_TYPE_GRAY && bit_depth < 8)
        png_set_expand(png_ptr);
  
     /* Expand paletted or RGB images with transparency to full alpha channels
      * so the data will be available as RGBA quartets.
      */
     if (png_get_valid(png_ptr, info_ptr, PNG_INFO_tRNS))
        png_set_expand(png_ptr);
  
     /* Set the background color to draw transparent and alpha images over.
      * It is possible to set the red, green, and blue components directly
      * for paletted images instead of supplying a palette index.  Note that
      * even if the PNG file supplies a background, you are not required to
      * use it - you should use the (solid) application background if it has one.
      */
  
     png_color_16 my_background, *image_background;
  
     if (png_get_bKGD(png_ptr, info_ptr, &image_background))
        png_set_background(png_ptr, image_background,
                           PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
     else
        png_set_background(png_ptr, &my_background,
                           PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
  
     /* Some suggestions as to how to get a screen gamma value */
  
     /* Note that screen gamma is the display_exponent, which includes
      * the CRT_exponent and any correction for viewing conditions */
     if (/* We have a user-defined screen gamma value */)
     {
        screen_gamma = user-defined screen_gamma;
     }
     /* This is one way that applications share the same screen gamma value */
     else if ((gamma_str = getenv("SCREEN_GAMMA")) != NULL)
     {
        screen_gamma = atof(gamma_str);
     }
     /* If we don't have another value */
     else
     {
        screen_gamma = 2.2;  /* A good guess for a PC monitors in a dimly
                                lit room */
        screen_gamma = 1.7 or 1.0;  /* A good guess for Mac systems */
     }
  
     /* Tell libpng to handle the gamma conversion for you.  The second call
      * is a good guess for PC generated images, but it should be configurable
      * by the user at run time by the user.  It is strongly suggested that
      * your application support gamma correction.
      */
  
     int intent;
  
     if (png_get_sRGB(png_ptr, info_ptr, &intent))
        png_set_sRGB(png_ptr, intent, 0);
     else
     {
        double image_gamma;
        if (png_get_gAMA(png_ptr, info_ptr, &image_gamma))
           png_set_gamma(png_ptr, screen_gamma, image_gamma);
        else
           png_set_gamma(png_ptr, screen_gamma, 0.45455);
     }
  
     /* Dither RGB files down to 8 bit palette or reduce palettes
      * to the number of colors available on your screen.
      */
     if (color_type & PNG_COLOR_MASK_COLOR)
     {
        png_uint_32 num_palette;
        png_colorp palette;
  
        /* This reduces the image to the application supplied palette */
        if (/* we have our own palette */)
        {
           /* An array of colors to which the image should be dithered */
           png_color std_color_cube[MAX_SCREEN_COLORS];
  
           png_set_dither(png_ptr, std_color_cube, MAX_SCREEN_COLORS,
              MAX_SCREEN_COLORS, NULL, 0);
        }
        /* This reduces the image to the palette supplied in the file */
        else if (png_get_PLTE(png_ptr, info_ptr, &palette, &num_palette))
        {
           png_color16p histogram;
  
           png_get_hIST(png_ptr, info_ptr, &histogram);
  
           png_set_dither(png_ptr, palette, num_palette,
                          max_screen_colors, histogram, 0);
        }
     }
  
     /* invert monocrome files to have 0 as white and 1 as black */
     png_set_invert_mono(png_ptr);
  
     /* If you want to shift the pixel values from the range [0,255] or
      * [0,65535] to the original [0,7] or [0,31], or whatever range the
      * colors were originally in:
      */
     if (png_get_valid(png_ptr, info_ptr, PNG_INFO_sBIT))
     {
        png_color8p sig_bit;
  
        png_get_sBIT(png_ptr, info_ptr, &sig_bit);
        png_set_shift(png_ptr, sig_bit);
     }
  
     /* flip the RGB pixels to BGR (or RGBA to BGRA) */
     png_set_bgr(png_ptr);
  
     /* swap the RGBA or GA data to ARGB or AG (or BGRA to ABGR) */
     png_set_swap_alpha(png_ptr);
  
     /* swap bytes of 16 bit files to least significant byte first */
     png_set_swap(png_ptr);
  
     /* Add filler (or alpha) byte (before/after each RGB triplet) */
     png_set_filler(png_ptr, 0xff, PNG_FILLER_AFTER);
  
     /* Turn on interlace handling.  REQUIRED if you are not using
      * png_read_image().  To see how to handle interlacing passes,
      * see the png_read_row() method below:
      */
     number_passes = png_set_interlace_handling(png_ptr);
  
     /* Optional call to gamma correct and add the background to the palette
      * and update info structure.  REQUIRED if you are expecting libpng to
      * update the palette for you (ie you selected such a transform above).
      */
     png_read_update_info(png_ptr, info_ptr);
  
     /* Allocate the memory to hold the image using the fields of info_ptr. */
  
     /* The easiest way to read the image: */
     png_bytep row_pointers[height];
  
     for (row = 0; row < height; row++)
     {
        row_pointers[row] = malloc(png_get_rowbytes(png_ptr, info_ptr));
     }
  
     /* Now it's time to read the image.  One of these methods is REQUIRED */
  #ifdef entire /* Read the entire image in one go */
     png_read_image(png_ptr, row_pointers);
  
  #else no_entire /* Read the image one or more scanlines at a time */
     /* The other way to read images - deal with interlacing: */
  
     for (pass = 0; pass < number_passes; pass++)
     {
  #ifdef single /* Read the image a single row at a time */
        for (y = 0; y < height; y++)
        {
           png_read_rows(png_ptr, &row_pointers[y], NULL, 1);
        }
  
  #else no_single /* Read the image several rows at a time */
        for (y = 0; y < height; y += number_of_rows)
        {
  #ifdef sparkle /* Read the image using the "sparkle" effect. */
           png_read_rows(png_ptr, &row_pointers[y], NULL, number_of_rows);
  
           png_read_rows(png_ptr, NULL, row_pointers[y], number_of_rows);
  #else no_sparkle /* Read the image using the "rectangle" effect */
           png_read_rows(png_ptr, NULL, &row_pointers[y], number_of_rows);
  #endif no_sparkle /* use only one of these two methods */
        }
  
        /* if you want to display the image after every pass, do
           so here */
  #endif no_single /* use only one of these two methods */
     }
  #endif no_entire /* use only one of these two methods */
  
     /* read rest of file, and get additional chunks in info_ptr - REQUIRED */
     png_read_end(png_ptr, info_ptr);
  
     /* clean up after the read, and free any memory allocated - REQUIRED */
     png_destroy_read_struct(&png_ptr, &info_ptr, (png_infopp)NULL);
  
     /* close the file */
     fclose(fp);
  
     /* that's it */
     return;
  }
  
  /* progressively read a file */
  
  int
  initialize_png_reader(png_structp *png_ptr, png_infop *info_ptr)
  {
     /* Create and initialize the png_struct with the desired error handler
      * functions.  If you want to use the default stderr and longjump method,
      * you can supply NULL for the last three parameters.  We also check that
      * the library version is compatible in case we are using dynamically
      * linked libraries.
      */
     *png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING,
         png_voidp user_error_ptr, user_error_fn, user_warning_fn);
  
     if (*png_ptr == NULL)
     {
        *info_ptr = NULL;
        return ERROR;
     }
  
     *info_ptr = png_create_info_struct(png_ptr);
  
     if (*info_ptr == NULL)
     {
        png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL);
        return ERROR;
     }
  
     if (setjmp((*png_ptr)->jmpbuf))
     {
        png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL);
        return ERROR;
     }
  
     /* This one's new.  You will need to provide all three
      * function callbacks, even if you aren't using them all.
      * If you aren't using all functions, you can specify NULL
      * parameters.  Even when all three functions are NULL,
      * you need to call png_set_progressive_read_fn().
      * These functions shouldn't be dependent on global or
      * static variables if you are decoding several images
      * simultaneously.  You should store stream specific data
      * in a separate struct, given as the second parameter,
      * and retrieve the pointer from inside the callbacks using
      * the function png_get_progressive_ptr(png_ptr).
      */
     png_set_progressive_read_fn(*png_ptr, (void *)stream_data,
        info_callback, row_callback, end_callback);
  
     return OK;
  }
  
  int
  process_data(png_structp *png_ptr, png_infop *info_ptr,
     png_bytep buffer, png_uint_32 length)
  {
     if (setjmp((*png_ptr)->jmpbuf))
     {
        /* Free the png_ptr and info_ptr memory on error */
        png_destroy_read_struct(png_ptr, info_ptr, (png_infopp)NULL);
        return ERROR;
     }
  
     /* This one's new also.  Simply give it chunks of data as
      * they arrive from the data stream (in order, of course).
      * On Segmented machines, don't give it any more than 64K.
      * The library seems to run fine with sizes of 4K, although
      * you can give it much less if necessary (I assume you can
      * give it chunks of 1 byte, but I haven't tried with less
      * than 256 bytes yet).  When this function returns, you may
      * want to display any rows that were generated in the row
      * callback, if you aren't already displaying them there.
      */
     png_process_data(*png_ptr, *info_ptr, buffer, length);
     return OK;
  }
  
  info_callback(png_structp png_ptr, png_infop info)
  {
  /* do any setup here, including setting any of the transformations
   * mentioned in the Reading PNG files section.  For now, you _must_
   * call either png_start_read_image() or png_read_update_info()
   * after all the transformations are set (even if you don't set
   * any).  You may start getting rows before png_process_data()
   * returns, so this is your last chance to prepare for that.
   */
  }
  
  row_callback(png_structp png_ptr, png_bytep new_row,
     png_uint_32 row_num, int pass)
  {
  /* this function is called for every row in the image.  If the
   * image is interlacing, and you turned on the interlace handler,
   * this function will be called for every row in every pass.
   * Some of these rows will not be changed from the previous pass.
   * When the row is not changed, the new_row variable will be NULL.
   * The rows and passes are called in order, so you don't really
   * need the row_num and pass, but I'm supplying them because it
   * may make your life easier.
   *
   * For the non-NULL rows of interlaced images, you must call
   * png_progressive_combine_row() passing in the row and the
   * old row.  You can call this function for NULL rows (it will
   * just return) and for non-interlaced images (it just does the
   * memcpy for you) if it will make the code easier.  Thus, you
   * can just do this for all cases:
   */
  
     png_progressive_combine_row(png_ptr, old_row, new_row);
  
  /* where old_row is what was displayed for previous rows.  Note
   * that the first pass (pass == 0 really) will completely cover
   * the old row, so the rows do not have to be initialized.  After
   * the first pass (and only for interlaced images), you will have
   * to pass the current row, and the function will combine the
   * old row and the new row.
   */
  }
  
  end_callback(png_structp png_ptr, png_infop info)
  {
  /* this function is called when the whole image has been read,
   * including any chunks after the image (up to and including
   * the IEND).  You will usually have the same info chunk as you
   * had in the header, although some data may have been added
   * to the comments and time fields.
   *
   * Most people won't do much here, perhaps setting a flag that
   * marks the image as finished.
   */
  }
  
  /* write a png file */
  void write_png(char *file_name /* , ... other image information ... */)
  {
     FILE *fp;
     png_structp png_ptr;
     png_infop info_ptr;
  
     /* open the file */
     fp = fopen(file_name, "wb");
     if (fp == NULL)
        return;
  
     /* Create and initialize the png_struct with the desired error handler
      * functions.  If you want to use the default stderr and longjump method,
      * you can supply NULL for the last three parameters.  We also check that
      * the library version is compatible with the one used at compile time,
      * in case we are using dynamically linked libraries.  REQUIRED.
      */
     png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING,
        png_voidp user_error_ptr, user_error_fn, user_warning_fn);
  
     if (png_ptr == NULL)
     {
        fclose(fp);
        return;
     }
  
     /* Allocate/initialize the image information data.  REQUIRED */
     info_ptr = png_create_info_struct(png_ptr);
     if (info_ptr == NULL)
     {
        fclose(fp);
        png_destroy_write_struct(&png_ptr,  (png_infopp)NULL);
        return;
     }
  
     /* Set error handling.  REQUIRED if you aren't supplying your own
      * error hadnling functions in the png_create_write_struct() call.
      */
     if (setjmp(png_ptr->jmpbuf))
     {
        /* If we get here, we had a problem reading the file */
        fclose(fp);
        png_destroy_write_struct(&png_ptr,  (png_infopp)NULL);
        return;
     }
  
     /* One of the following I/O initialization functions is REQUIRED */
  #ifdef streams /* I/O initialization method 1 */
     /* set up the output control if you are using standard C streams */
     png_init_io(png_ptr, fp);
  #else no_streams /* I/O initialization method 2 */
     /* If you are using replacement read functions, instead of calling
      * png_init_io() here you would call */
     png_set_write_fn(png_ptr, (void *)user_io_ptr, user_write_fn,
        user_IO_flush_function);
     /* where user_io_ptr is a structure you want available to the callbacks */
  #endif no_streams /* only use one initialization method */
  
     /* Set the image information here.  Width and height are up to 2^31,
      * bit_depth is one of 1, 2, 4, 8, or 16, but valid values also depend on
      * the color_type selected. color_type is one of PNG_COLOR_TYPE_GRAY,
      * PNG_COLOR_TYPE_GRAY_ALPHA, PNG_COLOR_TYPE_PALETTE, PNG_COLOR_TYPE_RGB,
      * or PNG_COLOR_TYPE_RGB_ALPHA.  interlace is either PNG_INTERLACE_NONE or
      * PNG_INTERLACE_ADAM7, and the compression_type and filter_type MUST
      * currently be PNG_COMPRESSION_TYPE_BASE and PNG_FILTER_TYPE_BASE. REQUIRED
      */
     png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth, PNG_COLOR_TYPE_???,
        PNG_INTERLACE_????, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
  
     /* set the palette if there is one.  REQUIRED for indexed-color images */
     palette = (png_colorp)png_malloc(png_ptr, 256 * sizeof (png_color));
     /* ... set palette colors ... */
     png_set_PLTE(png_ptr, info_ptr, palette, 256);
  
     /* optional significant bit chunk */
     /* if we are dealing with a grayscale image then */
     sig_bit.gray = true_bit_depth;
     /* otherwise, if we are dealing with a color image then */
     sig_bit.red = true_red_bit_depth;
     sig_bit.green = true_green_bit_depth;
     sig_bit.blue = true_blue_bit_depth;
     /* if the image has an alpha channel then */
     sig_bit.alpha = true_alpha_bit_depth;
     png_set_sBIT(png_ptr, info_ptr, sig_bit);
  
  
     /* Optional gamma chunk is strongly suggested if you have any guess
      * as to the correct gamma of the image.
      */
     png_set_gAMA(png_ptr, info_ptr, gamma);
  
     /* Optionally write comments into the image */
     text_ptr[0].key = "Title";
     text_ptr[0].text = "Mona Lisa";
     text_ptr[0].compression = PNG_TEXT_COMPRESSION_NONE;
     text_ptr[1].key = "Author";
     text_ptr[1].text = "Leonardo DaVinci";
     text_ptr[1].compression = PNG_TEXT_COMPRESSION_NONE;
     text_ptr[2].key = "Description";
     text_ptr[2].text = "<long text>";
     text_ptr[2].compression = PNG_TEXT_COMPRESSION_zTXt;
     png_set_text(png_ptr, info_ptr, text_ptr, 3);
  
     /* other optional chunks like cHRM, bKGD, tRNS, tIME, oFFs, pHYs, */
     /* note that if sRGB is present the cHRM chunk must be ignored
      * on read and must be written in accordance with the sRGB profile */
  
     /* Write the file header information.  REQUIRED */
     png_write_info(png_ptr, info_ptr);
  
     /* Once we write out the header, the compression type on the text
      * chunks gets changed to PNG_TEXT_COMPRESSION_NONE_WR or
      * PNG_TEXT_COMPRESSION_zTXt_WR, so it doesn't get written out again
      * at the end.
      */
  
     /* set up the transformations you want.  Note that these are
      * all optional.  Only call them if you want them.
      */
  
     /* invert monocrome pixels */
     png_set_invert_mono(png_ptr);
  
     /* Shift the pixels up to a legal bit depth and fill in
      * as appropriate to correctly scale the image.
      */
     png_set_shift(png_ptr, &sig_bit);
  
     /* pack pixels into bytes */
     png_set_packing(png_ptr);
  
     /* swap location of alpha bytes from ARGB to RGBA */
     png_set_swap_alpha(png_ptr);
  
     /* Get rid of filler (OR ALPHA) bytes, pack XRGB/RGBX/ARGB/RGBA into
      * RGB (4 channels -> 3 channels). The second parameter is not used.
      */
     png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
  
     /* flip BGR pixels to RGB */
     png_set_bgr(png_ptr);
  
     /* swap bytes of 16-bit files to most significant byte first */
     png_set_swap(png_ptr);
  
     /* swap bits of 1, 2, 4 bit packed pixel formats */
     png_set_packswap(png_ptr);
  
     /* turn on interlace handling if you are not using png_write_image() */
     if (interlacing)
        number_passes = png_set_interlace_handling(png_ptr);
     else
        number_passes = 1;
  
     /* The easiest way to write the image (you may have a different memory
      * layout, however, so choose what fits your needs best).  You need to
      * use the first method if you aren't handling interlacing yourself.
      */
     png_uint_32 k, height, width;
     png_byte image[height][width];
     png_bytep row_pointers[height];
     for (k = 0; k < height; k++)
       row_pointers[k] = image + k*width;
  
     /* One of the following output methods is REQUIRED */
  #ifdef entire /* write out the entire image data in one call */
     png_write_image(png_ptr, row_pointers);
  
     /* the other way to write the image - deal with interlacing */
  
  #else no_entire /* write out the image data by one or more scanlines */
     /* The number of passes is either 1 for non-interlaced images,
      * or 7 for interlaced images.
      */
     for (pass = 0; pass < number_passes; pass++)
     {
        /* Write a few rows at a time. */
        png_write_rows(png_ptr, &row_pointers[first_row], number_of_rows);
  
        /* If you are only writing one row at a time, this works */
        for (y = 0; y < height; y++)
        {
           png_write_rows(png_ptr, &row_pointers[y], 1);
        }
     }
  #endif no_entire /* use only one output method */
  
     /* You can write optional chunks like tEXt, zTXt, and tIME at the end
      * as well.
      */
  
     /* It is REQUIRED to call this to finish writing the rest of the file */
     png_write_end(png_ptr, info_ptr);
  
     /* if you malloced the palette, free it here */
     free(info_ptr->palette);
  
     /* if you allocated any text comments, free them here */
  
     /* clean up after the write, and free any memory allocated */
     png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
  
     /* close the file */
     fclose(fp);
  
     /* that's it */
     return;
  }
  
  #endif /* if 0 */
  