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

/* example.c - an example of using libpng
 * Last changed in libpng 1.2.33 [December 18, 2008]
 * This file has been placed in the public domain by the authors.
 * Maintained 1998-2008 Glenn Randers-Pehrson
 * Maintained 1996, 1997 Andreas Dilger)
 * Written 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 */

/* 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, is hereby placed
 * in the public domain, 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;
 * see also the programs in the contrib directory.
 */

#include "png.h"

 /* The png_jmpbuf() macro, used in error handling, became available in
  * libpng version 1.0.6.  If you want to be able to run your code with older
  * versions of libpng, you must define the macro yourself (but only if it
  * is not already defined by libpng!).
  */

#ifndef png_jmpbuf
#  define png_jmpbuf(png_ptr) ((png_ptr)->jmpbuf)
#endif

/* 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 (ERROR);
#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 (ERROR);
   }

   /* 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 (ERROR);
   }

   /* 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_jmpbuf(png_ptr)))
   {
      /* 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 (ERROR);
   }

   /* 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);

#ifdef hilevel
   /*
    * If you have enough memory to read in the entire image at once,
    * and you need to specify only transforms that can be controlled
    * with one of the PNG_TRANSFORM_* bits (this presently excludes
    * dithering, filling, setting background, and doing gamma
    * adjustment), then you can read the entire image (including
    * pixels) into the info structure with this call:
    */
   png_read_png(png_ptr, info_ptr, png_transforms, png_voidp_NULL);
#else
   /* OK, you're doing it the hard way, with the lower-level functions */

   /* 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, int_p_NULL, int_p_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_palette_to_rgb(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_gray_1_2_4_to_8(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_tRNS_to_alpha(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 final 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_gamma(png_ptr, screen_gamma, 0.45455);
   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)
   {
      int 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, png_uint_16p_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_uint_16p histogram = NULL;

         png_get_hIST(png_ptr, info_ptr, &histogram);

         png_set_dither(png_ptr, palette, num_palette,
                        max_screen_colors, histogram, 0);
      }
   }

   /* invert monochrome 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_color_8p 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) */
   if (color_type & PNG_COLOR_MASK_COLOR)
      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] = png_malloc(png_ptr, 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], png_bytepp_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], png_bytepp_NULL,
            number_of_rows);
#else no_sparkle /* Read the image using the "rectangle" effect */
         png_read_rows(png_ptr, png_bytepp_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);
#endif hilevel

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

   /* 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 (OK);
}

/* 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_jmpbuf((*png_ptr))))
   {
      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_jmpbuf((*png_ptr))))
   {
      /* 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 interlaced, and you turned on the interlace handler,
 * this function will be called for every row in every pass.
 *
 * In this function you will receive a pointer to new row data from
 * libpng called new_row that is to replace a corresponding row (of
 * the same data format) in a buffer allocated by your application.
 *
 * The new row data pointer new_row may be NULL, indicating there is
 * no new data to be replaced (in cases of interlace loading).
 *
 * If new_row is not NULL then you need to call
 * png_progressive_combine_row() to replace the corresponding row as
 * shown below:
 */
   /* Check if row_num is in bounds. */
   if ((row_num >= 0) && (row_num < height))
   {
     /* Get pointer to corresponding row in our
      * PNG read buffer.
      */
     png_bytep old_row = ((png_bytep *)our_data)[row_num];

     /* If both rows are allocated then copy the new row
      * data to the corresponding row data.
      */
     if ((old_row != NULL) && (new_row != NULL))
     png_progressive_combine_row(png_ptr, old_row, new_row);
   }
/*
 * 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 new row and the
 * old row, as demonstrated above.  You can call this function for
 * NULL rows (it will just return) and for non-interlaced images
 * (it just does the png_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 as new_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;
   png_colorp palette;

   /* open the file */
   fp = fopen(file_name, "wb");
   if (fp == NULL)
      return (ERROR);

   /* 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 (ERROR);
   }

   /* 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 (ERROR);
   }

   /* Set error handling.  REQUIRED if you aren't supplying your own
    * error handling functions in the png_create_write_struct() call.
    */
   if (setjmp(png_jmpbuf(png_ptr)))
   {
      /* If we get here, we had a problem reading the file */
      fclose(fp);
      png_destroy_write_struct(&png_ptr, &info_ptr);
      return (ERROR);
   }

   /* 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 write 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 */

#ifdef hilevel
   /* This is the easy way.  Use it if you already have all the
    * image info living info in the structure.  You could "|" many
    * PNG_TRANSFORM flags into the png_transforms integer here.
    */
   png_write_png(png_ptr, info_ptr, png_transforms, png_voidp_NULL);
#else
   /* This is the hard way */

   /* 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, PNG_MAX_PALETTE_LENGTH
             * png_sizeof(png_color));
   /* ... set palette colors ... */
   png_set_PLTE(png_ptr, info_ptr, palette, PNG_MAX_PALETTE_LENGTH);
   /* You must not free palette here, because png_set_PLTE only makes a link to
      the palette that you malloced.  Wait until you are about to destroy
      the png structure. */

   /* 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;
#ifdef PNG_iTXt_SUPPORTED
   text_ptr[0].lang = NULL;
   text_ptr[1].lang = NULL;
   text_ptr[2].lang = NULL;
#endif
   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 gAMA and cHRM chunks 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);

   /* If you want, you can write the info in two steps, in case you need to
    * write your private chunk ahead of PLTE:
    *
    *   png_write_info_before_PLTE(write_ptr, write_info_ptr);
    *   write_my_chunk();
    *   png_write_info(png_ptr, info_ptr);
    *
    * However, given the level of known- and unknown-chunk support in 1.1.0
    * and up, this should no longer be necessary.
    */

   /* 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 monochrome 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*bytes_per_pixel];
   png_bytep row_pointers[height];

   if (height > PNG_UINT_32_MAX/png_sizeof(png_bytep))
     png_error (png_ptr, "Image is too tall to process in memory");

   for (k = 0; k < height; k++)
     row_pointers[k] = image + k*width*bytes_per_pixel;

   /* 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.  Shouldn't be necessary in 1.1.0 and up as all the public
    * chunks are supported and you can use png_set_unknown_chunks() to
    * register unknown chunks into the info structure to be written out.
    */

   /* It is REQUIRED to call this to finish writing the rest of the file */
   png_write_end(png_ptr, info_ptr);
#endif hilevel

   /* If you png_malloced a palette, free it here (don't free info_ptr->palette,
      as recommended in versions 1.0.5m and earlier of this example; if
      libpng mallocs info_ptr->palette, libpng will free it).  If you
      allocated it with malloc() instead of png_malloc(), use free() instead
      of png_free(). */
   png_free(png_ptr, palette);
   palette = NULL;

   /* Similarly, if you png_malloced any data that you passed in with
      png_set_something(), such as a hist or trans array, free it here,
      when you can be sure that libpng is through with it. */
   png_free(png_ptr, trans);
   trans = NULL;

   /* clean up after the write, and free any memory allocated */
   png_destroy_write_struct(&png_ptr, &info_ptr);

   /* close the file */
   fclose(fp);

   /* that's it */
   return (OK);
}

#endif /* if 0 */


code:
/* png.c - location for general purpose libpng functions
 *
 * Last changed in libpng 1.2.34 [December 18, 2008]
 * For conditions of distribution and use, see copyright notice in png.h
 * Copyright (c) 1998-2008 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 */

#define PNG_INTERNAL
#define PNG_NO_EXTERN
#include "png.h"

/* Generate a compiler error if there is an old png.h in the search path. */
typedef version_1_2_34 Your_png_h_is_not_version_1_2_34;

/* Version information for C files.  This had better match the version
 * string defined in png.h.  */

#ifdef PNG_USE_GLOBAL_ARRAYS
/* png_libpng_ver was changed to a function in version 1.0.5c */
PNG_CONST char png_libpng_ver[18] = PNG_LIBPNG_VER_STRING;

#ifdef PNG_READ_SUPPORTED

/* png_sig was changed to a function in version 1.0.5c */
/* Place to hold the signature string for a PNG file. */
PNG_CONST png_byte FARDATA png_sig[8] = {137, 80, 78, 71, 13, 10, 26, 10};
#endif /* PNG_READ_SUPPORTED */

/* Invoke global declarations for constant strings for known chunk types */
PNG_IHDR;
PNG_IDAT;
PNG_IEND;
PNG_PLTE;
PNG_bKGD;
PNG_cHRM;
PNG_gAMA;
PNG_hIST;
PNG_iCCP;
PNG_iTXt;
PNG_oFFs;
PNG_pCAL;
PNG_sCAL;
PNG_pHYs;
PNG_sBIT;
PNG_sPLT;
PNG_sRGB;
PNG_tEXt;
PNG_tIME;
PNG_tRNS;
PNG_zTXt;

#ifdef PNG_READ_SUPPORTED
/* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

/* start of interlace block */
PNG_CONST int FARDATA png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};

/* offset to next interlace block */
PNG_CONST int FARDATA png_pass_inc[] = {8, 8, 4, 4, 2, 2, 1};

/* start of interlace block in the y direction */
PNG_CONST int FARDATA png_pass_ystart[] = {0, 0, 4, 0, 2, 0, 1};

/* offset to next interlace block in the y direction */
PNG_CONST int FARDATA png_pass_yinc[] = {8, 8, 8, 4, 4, 2, 2};

/* Height of interlace block.  This is not currently used - if you need
 * it, uncomment it here and in png.h
PNG_CONST int FARDATA png_pass_height[] = {8, 8, 4, 4, 2, 2, 1};
*/

/* Mask to determine which pixels are valid in a pass */
PNG_CONST int FARDATA png_pass_mask[] = {0x80, 0x08, 0x88, 0x22, 0xaa, 0x55, 0xff};

/* Mask to determine which pixels to overwrite while displaying */
PNG_CONST int FARDATA png_pass_dsp_mask[]
   = {0xff, 0x0f, 0xff, 0x33, 0xff, 0x55, 0xff};

#endif /* PNG_READ_SUPPORTED */
#endif /* PNG_USE_GLOBAL_ARRAYS */

/* Tells libpng that we have already handled the first "num_bytes" bytes
 * of the PNG file signature.  If the PNG data is embedded into another
 * stream we can set num_bytes = 8 so that libpng will not attempt to read
 * or write any of the magic bytes before it starts on the IHDR.
 */

#ifdef PNG_READ_SUPPORTED
void PNGAPI
png_set_sig_bytes(png_structp png_ptr, int num_bytes)
{
   if (png_ptr == NULL) return;
   png_debug(1, "in png_set_sig_bytes");
   if (num_bytes > 8)
      png_error(png_ptr, "Too many bytes for PNG signature.");

   png_ptr->sig_bytes = (png_byte)(num_bytes < 0 ? 0 : num_bytes);
}

/* Checks whether the supplied bytes match the PNG signature.  We allow
 * checking less than the full 8-byte signature so that those apps that
 * already read the first few bytes of a file to determine the file type
 * can simply check the remaining bytes for extra assurance.  Returns
 * an integer less than, equal to, or greater than zero if sig is found,
 * respectively, to be less than, to match, or be greater than the correct
 * PNG signature (this is the same behaviour as strcmp, memcmp, etc).
 */
int PNGAPI
png_sig_cmp(png_bytep sig, png_size_t start, png_size_t num_to_check)
{
   png_byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
   if (num_to_check > 8)
      num_to_check = 8;
   else if (num_to_check < 1)
      return (-1);

   if (start > 7)
      return (-1);

   if (start + num_to_check > 8)
      num_to_check = 8 - start;

   return ((int)(png_memcmp(&sig[start], &png_signature[start], num_to_check)));
}

#if defined(PNG_1_0_X) || defined(PNG_1_2_X)
/* (Obsolete) function to check signature bytes.  It does not allow one
 * to check a partial signature.  This function might be removed in the
 * future - use png_sig_cmp().  Returns true (nonzero) if the file is PNG.
 */
int PNGAPI
png_check_sig(png_bytep sig, int num)
{
  return ((int)!png_sig_cmp(sig, (png_size_t)0, (png_size_t)num));
}
#endif
#endif /* PNG_READ_SUPPORTED */

#if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
/* Function to allocate memory for zlib and clear it to 0. */
#ifdef PNG_1_0_X
voidpf PNGAPI
#else
voidpf /* private */
#endif
png_zalloc(voidpf png_ptr, uInt items, uInt size)
{
   png_voidp ptr;
   png_structp p=(png_structp)png_ptr;
   png_uint_32 save_flags=p->flags;
   png_uint_32 num_bytes;

   if (png_ptr == NULL) return (NULL);
   if (items > PNG_UINT_32_MAX/size)
   {
     png_warning (p, "Potential overflow in png_zalloc()");
     return (NULL);
   }
   num_bytes = (png_uint_32)items * size;

   p->flags|=PNG_FLAG_MALLOC_NULL_MEM_OK;
   ptr = (png_voidp)png_malloc((png_structp)png_ptr, num_bytes);
   p->flags=save_flags;

#if defined(PNG_1_0_X) && !defined(PNG_NO_ZALLOC_ZERO)
   if (ptr == NULL)
       return ((voidpf)ptr);

   if (num_bytes > (png_uint_32)0x8000L)
   {
      png_memset(ptr, 0, (png_size_t)0x8000L);
      png_memset((png_bytep)ptr + (png_size_t)0x8000L, 0,
         (png_size_t)(num_bytes - (png_uint_32)0x8000L));
   }
   else
   {
      png_memset(ptr, 0, (png_size_t)num_bytes);
   }
#endif
   return ((voidpf)ptr);
}

/* function to free memory for zlib */
#ifdef PNG_1_0_X
void PNGAPI
#else
void /* private */
#endif
png_zfree(voidpf png_ptr, voidpf ptr)
{
   png_free((png_structp)png_ptr, (png_voidp)ptr);
}

/* Reset the CRC variable to 32 bits of 1's.  Care must be taken
 * in case CRC is > 32 bits to leave the top bits 0.
 */
void /* PRIVATE */
png_reset_crc(png_structp png_ptr)
{
   png_ptr->crc = crc32(0, Z_NULL, 0);
}

/* Calculate the CRC over a section of data.  We can only pass as
 * much data to this routine as the largest single buffer size.  We
 * also check that this data will actually be used before going to the
 * trouble of calculating it.
 */
void /* PRIVATE */
png_calculate_crc(png_structp png_ptr, png_bytep ptr, png_size_t length)
{
   int need_crc = 1;

   if (png_ptr->chunk_name[0] & 0x20)                     /* ancillary */
   {
      if ((png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_MASK) ==
          (PNG_FLAG_CRC_ANCILLARY_USE | PNG_FLAG_CRC_ANCILLARY_NOWARN))
         need_crc = 0;
   }
   else                                                    /* critical */
   {
      if (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_IGNORE)
         need_crc = 0;
   }

   if (need_crc)
      png_ptr->crc = crc32(png_ptr->crc, ptr, (uInt)length);
}

/* Allocate the memory for an info_struct for the application.  We don't
 * really need the png_ptr, but it could potentially be useful in the
 * future.  This should be used in favour of malloc(png_sizeof(png_info))
 * and png_info_init() so that applications that want to use a shared
 * libpng don't have to be recompiled if png_info changes size.
 */
png_infop PNGAPI
png_create_info_struct(png_structp png_ptr)
{
   png_infop info_ptr;

   png_debug(1, "in png_create_info_struct");
   if (png_ptr == NULL) return (NULL);
#ifdef PNG_USER_MEM_SUPPORTED
   info_ptr = (png_infop)png_create_struct_2(PNG_STRUCT_INFO,
      png_ptr->malloc_fn, png_ptr->mem_ptr);
#else
   info_ptr = (png_infop)png_create_struct(PNG_STRUCT_INFO);
#endif
   if (info_ptr != NULL)
      png_info_init_3(&info_ptr, png_sizeof(png_info));

   return (info_ptr);
}

/* This function frees the memory associated with a single info struct.
 * Normally, one would use either png_destroy_read_struct() or
 * png_destroy_write_struct() to free an info struct, but this may be
 * useful for some applications.
 */
void PNGAPI
png_destroy_info_struct(png_structp png_ptr, png_infopp info_ptr_ptr)
{
   png_infop info_ptr = NULL;
   if (png_ptr == NULL) return;

   png_debug(1, "in png_destroy_info_struct");
   if (info_ptr_ptr != NULL)
      info_ptr = *info_ptr_ptr;

   if (info_ptr != NULL)
   {
      png_info_destroy(png_ptr, info_ptr);

#ifdef PNG_USER_MEM_SUPPORTED
      png_destroy_struct_2((png_voidp)info_ptr, png_ptr->free_fn,
          png_ptr->mem_ptr);
#else
      png_destroy_struct((png_voidp)info_ptr);
#endif
      *info_ptr_ptr = NULL;
   }
}

/* Initialize the info structure.  This is now an internal function (0.89)
 * and applications using it are urged to use png_create_info_struct()
 * instead.
 */
#if defined(PNG_1_0_X) || defined(PNG_1_2_X)
#undef png_info_init
void PNGAPI
png_info_init(png_infop info_ptr)
{
   /* We only come here via pre-1.0.12-compiled applications */
   png_info_init_3(&info_ptr, 0);
}
#endif

void PNGAPI
png_info_init_3(png_infopp ptr_ptr, png_size_t png_info_struct_size)
{
   png_infop info_ptr = *ptr_ptr;

   if (info_ptr == NULL) return;

   png_debug(1, "in png_info_init_3");

   if (png_sizeof(png_info) > png_info_struct_size)
     {
       png_destroy_struct(info_ptr);
       info_ptr = (png_infop)png_create_struct(PNG_STRUCT_INFO);
       *ptr_ptr = info_ptr;
     }

   /* set everything to 0 */
   png_memset(info_ptr, 0, png_sizeof(png_info));
}

#ifdef PNG_FREE_ME_SUPPORTED
void PNGAPI
png_data_freer(png_structp png_ptr, png_infop info_ptr,
   int freer, png_uint_32 mask)
{
   png_debug(1, "in png_data_freer");
   if (png_ptr == NULL || info_ptr == NULL)
      return;
   if (freer == PNG_DESTROY_WILL_FREE_DATA)
      info_ptr->free_me |= mask;
   else if (freer == PNG_USER_WILL_FREE_DATA)
      info_ptr->free_me &= ~mask;
   else
      png_warning(png_ptr,
         "Unknown freer parameter in png_data_freer.");
}
#endif

void PNGAPI
png_free_data(png_structp png_ptr, png_infop info_ptr, png_uint_32 mask,
   int num)
{
   png_debug(1, "in png_free_data");
   if (png_ptr == NULL || info_ptr == NULL)
      return;

#if defined(PNG_TEXT_SUPPORTED)
/* free text item num or (if num == -1) all text items */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_TEXT) & info_ptr->free_me)
#else
if (mask & PNG_FREE_TEXT)
#endif
{
   if (num != -1)
   {
     if (info_ptr->text && info_ptr->text[num].key)
     {
         png_free(png_ptr, info_ptr->text[num].key);
         info_ptr->text[num].key = NULL;
     }
   }
   else
   {
       int i;
       for (i = 0; i < info_ptr->num_text; i++)
           png_free_data(png_ptr, info_ptr, PNG_FREE_TEXT, i);
       png_free(png_ptr, info_ptr->text);
       info_ptr->text = NULL;
       info_ptr->num_text=0;
   }
}
#endif

#if defined(PNG_tRNS_SUPPORTED)
/* free any tRNS entry */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_TRNS) & info_ptr->free_me)
#else
if ((mask & PNG_FREE_TRNS) && (png_ptr->flags & PNG_FLAG_FREE_TRNS))
#endif
{
    png_free(png_ptr, info_ptr->trans);
    info_ptr->trans = NULL;
    info_ptr->valid &= ~PNG_INFO_tRNS;
#ifndef PNG_FREE_ME_SUPPORTED
    png_ptr->flags &= ~PNG_FLAG_FREE_TRNS;
#endif
}
#endif

#if defined(PNG_sCAL_SUPPORTED)
/* free any sCAL entry */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_SCAL) & info_ptr->free_me)
#else
if (mask & PNG_FREE_SCAL)
#endif
{
#if defined(PNG_FIXED_POINT_SUPPORTED) && !defined(PNG_FLOATING_POINT_SUPPORTED)
    png_free(png_ptr, info_ptr->scal_s_width);
    png_free(png_ptr, info_ptr->scal_s_height);
    info_ptr->scal_s_width = NULL;
    info_ptr->scal_s_height = NULL;
#endif
    info_ptr->valid &= ~PNG_INFO_sCAL;
}
#endif

#if defined(PNG_pCAL_SUPPORTED)
/* free any pCAL entry */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_PCAL) & info_ptr->free_me)
#else
if (mask & PNG_FREE_PCAL)
#endif
{
    png_free(png_ptr, info_ptr->pcal_purpose);
    png_free(png_ptr, info_ptr->pcal_units);
    info_ptr->pcal_purpose = NULL;
    info_ptr->pcal_units = NULL;
    if (info_ptr->pcal_params != NULL)
    {
        int i;
        for (i = 0; i < (int)info_ptr->pcal_nparams; i++)
        {
          png_free(png_ptr, info_ptr->pcal_params[i]);
          info_ptr->pcal_params[i]=NULL;
        }
        png_free(png_ptr, info_ptr->pcal_params);
        info_ptr->pcal_params = NULL;
    }
    info_ptr->valid &= ~PNG_INFO_pCAL;
}
#endif

#if defined(PNG_iCCP_SUPPORTED)
/* free any iCCP entry */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_ICCP) & info_ptr->free_me)
#else
if (mask & PNG_FREE_ICCP)
#endif
{
    png_free(png_ptr, info_ptr->iccp_name);
    png_free(png_ptr, info_ptr->iccp_profile);
    info_ptr->iccp_name = NULL;
    info_ptr->iccp_profile = NULL;
    info_ptr->valid &= ~PNG_INFO_iCCP;
}
#endif

#if defined(PNG_sPLT_SUPPORTED)
/* free a given sPLT entry, or (if num == -1) all sPLT entries */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_SPLT) & info_ptr->free_me)
#else
if (mask & PNG_FREE_SPLT)
#endif
{
   if (num != -1)
   {
      if (info_ptr->splt_palettes)
      {
          png_free(png_ptr, info_ptr->splt_palettes[num].name);
          png_free(png_ptr, info_ptr->splt_palettes[num].entries);
          info_ptr->splt_palettes[num].name = NULL;
          info_ptr->splt_palettes[num].entries = NULL;
      }
   }
   else
   {
       if (info_ptr->splt_palettes_num)
       {
         int i;
         for (i = 0; i < (int)info_ptr->splt_palettes_num; i++)
            png_free_data(png_ptr, info_ptr, PNG_FREE_SPLT, i);

         png_free(png_ptr, info_ptr->splt_palettes);
         info_ptr->splt_palettes = NULL;
         info_ptr->splt_palettes_num = 0;
       }
       info_ptr->valid &= ~PNG_INFO_sPLT;
   }
}
#endif

#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
  if (png_ptr->unknown_chunk.data)
  {
    png_free(png_ptr, png_ptr->unknown_chunk.data);
    png_ptr->unknown_chunk.data = NULL;
  }

#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_UNKN) & info_ptr->free_me)
#else
if (mask & PNG_FREE_UNKN)
#endif
{
   if (num != -1)
   {
       if (info_ptr->unknown_chunks)
       {
          png_free(png_ptr, info_ptr->unknown_chunks[num].data);
          info_ptr->unknown_chunks[num].data = NULL;
       }
   }
   else
   {
       int i;

       if (info_ptr->unknown_chunks_num)
       {
         for (i = 0; i < (int)info_ptr->unknown_chunks_num; i++)
            png_free_data(png_ptr, info_ptr, PNG_FREE_UNKN, i);

         png_free(png_ptr, info_ptr->unknown_chunks);
         info_ptr->unknown_chunks = NULL;
         info_ptr->unknown_chunks_num = 0;
       }
   }
}
#endif

#if defined(PNG_hIST_SUPPORTED)
/* free any hIST entry */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_HIST)  & info_ptr->free_me)
#else
if ((mask & PNG_FREE_HIST) && (png_ptr->flags & PNG_FLAG_FREE_HIST))
#endif
{
    png_free(png_ptr, info_ptr->hist);
    info_ptr->hist = NULL;
    info_ptr->valid &= ~PNG_INFO_hIST;
#ifndef PNG_FREE_ME_SUPPORTED
    png_ptr->flags &= ~PNG_FLAG_FREE_HIST;
#endif
}
#endif

/* free any PLTE entry that was internally allocated */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_PLTE) & info_ptr->free_me)
#else
if ((mask & PNG_FREE_PLTE) && (png_ptr->flags & PNG_FLAG_FREE_PLTE))
#endif
{
    png_zfree(png_ptr, info_ptr->palette);
    info_ptr->palette = NULL;
    info_ptr->valid &= ~PNG_INFO_PLTE;
#ifndef PNG_FREE_ME_SUPPORTED
    png_ptr->flags &= ~PNG_FLAG_FREE_PLTE;
#endif
    info_ptr->num_palette = 0;
}

#if defined(PNG_INFO_IMAGE_SUPPORTED)
/* free any image bits attached to the info structure */
#ifdef PNG_FREE_ME_SUPPORTED
if ((mask & PNG_FREE_ROWS) & info_ptr->free_me)
#else
if (mask & PNG_FREE_ROWS)
#endif
{
    if (info_ptr->row_pointers)
    {
       int row;
       for (row = 0; row < (int)info_ptr->height; row++)
       {
          png_free(png_ptr, info_ptr->row_pointers[row]);
          info_ptr->row_pointers[row]=NULL;
       }
       png_free(png_ptr, info_ptr->row_pointers);
       info_ptr->row_pointers=NULL;
    }
    info_ptr->valid &= ~PNG_INFO_IDAT;
}
#endif

#ifdef PNG_FREE_ME_SUPPORTED
   if (num == -1)
     info_ptr->free_me &= ~mask;
   else
     info_ptr->free_me &= ~(mask & ~PNG_FREE_MUL);
#endif
}

/* This is an internal routine to free any memory that the info struct is
 * pointing to before re-using it or freeing the struct itself.  Recall
 * that png_free() checks for NULL pointers for us.
 */
void /* PRIVATE */
png_info_destroy(png_structp png_ptr, png_infop info_ptr)
{
   png_debug(1, "in png_info_destroy");

   png_free_data(png_ptr, info_ptr, PNG_FREE_ALL, -1);

#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
   if (png_ptr->num_chunk_list)
   {
       png_free(png_ptr, png_ptr->chunk_list);
       png_ptr->chunk_list=NULL;
       png_ptr->num_chunk_list = 0;
   }
#endif

   png_info_init_3(&info_ptr, png_sizeof(png_info));
}
#endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */

/* This function returns a pointer to the io_ptr associated with the user
 * functions.  The application should free any memory associated with this
 * pointer before png_write_destroy() or png_read_destroy() are called.
 */
png_voidp PNGAPI
png_get_io_ptr(png_structp png_ptr)
{
   if (png_ptr == NULL) return (NULL);
   return (png_ptr->io_ptr);
}

#if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
#if !defined(PNG_NO_STDIO)
/* Initialize the default input/output functions for the PNG file.  If you
 * use your own read or write routines, you can call either png_set_read_fn()
 * or png_set_write_fn() instead of png_init_io().  If you have defined
 * PNG_NO_STDIO, you must use a function of your own because "FILE *" isn't
 * necessarily available.
 */
void PNGAPI
png_init_io(png_structp png_ptr, png_FILE_p fp)
{
   png_debug(1, "in png_init_io");
   if (png_ptr == NULL) return;
   png_ptr->io_ptr = (png_voidp)fp;
}
#endif

#if defined(PNG_TIME_RFC1123_SUPPORTED)
/* Convert the supplied time into an RFC 1123 string suitable for use in
 * a "Creation Time" or other text-based time string.
 */
png_charp PNGAPI
png_convert_to_rfc1123(png_structp png_ptr, png_timep ptime)
{
   static PNG_CONST char short_months[12][4] =
        {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
         "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};

   if (png_ptr == NULL) return (NULL);
   if (png_ptr->time_buffer == NULL)
   {
      png_ptr->time_buffer = (png_charp)png_malloc(png_ptr, (png_uint_32)(29*
         png_sizeof(char)));
   }

#if defined(_WIN32_WCE)
   {
      wchar_t time_buf[29];
      wsprintf(time_buf, TEXT("%d %S %d %02d:%02d:%02d +0000"),
          ptime->day % 32, short_months[(ptime->month - 1) % 12],
        ptime->year, ptime->hour % 24, ptime->minute % 60,
          ptime->second % 61);
      WideCharToMultiByte(CP_ACP, 0, time_buf, -1, png_ptr->time_buffer, 29,
          NULL, NULL);
   }
#else
#ifdef USE_FAR_KEYWORD
   {
      char near_time_buf[29];
      png_snprintf6(near_time_buf, 29, "%d %s %d %02d:%02d:%02d +0000",
          ptime->day % 32, short_months[(ptime->month - 1) % 12],
          ptime->year, ptime->hour % 24, ptime->minute % 60,
          ptime->second % 61);
      png_memcpy(png_ptr->time_buffer, near_time_buf,
          29*png_sizeof(char));
   }
#else
   png_snprintf6(png_ptr->time_buffer, 29, "%d %s %d %02d:%02d:%02d +0000",
       ptime->day % 32, short_months[(ptime->month - 1) % 12],
       ptime->year, ptime->hour % 24, ptime->minute % 60,
       ptime->second % 61);
#endif
#endif /* _WIN32_WCE */
   return ((png_charp)png_ptr->time_buffer);
}
#endif /* PNG_TIME_RFC1123_SUPPORTED */

#endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */

png_charp PNGAPI
png_get_copyright(png_structp png_ptr)
{
   png_ptr = png_ptr;  /* silence compiler warning about unused png_ptr */
   return ((png_charp) "\n libpng version 1.2.34 - December 18, 2008\n\
   Copyright (c) 1998-2008 Glenn Randers-Pehrson\n\
   Copyright (c) 1996-1997 Andreas Dilger\n\
   Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.\n");
}

/* The following return the library version as a short string in the
 * format 1.0.0 through 99.99.99zz.  To get the version of *.h files
 * used with your application, print out PNG_LIBPNG_VER_STRING, which
 * is defined in png.h.
 * Note: now there is no difference between png_get_libpng_ver() and
 * png_get_header_ver().  Due to the version_nn_nn_nn typedef guard,
 * it is guaranteed that png.c uses the correct version of png.h.
 */
png_charp PNGAPI
png_get_libpng_ver(png_structp png_ptr)
{
   /* Version of *.c files used when building libpng */
   png_ptr = png_ptr;  /* silence compiler warning about unused png_ptr */
   return ((png_charp) PNG_LIBPNG_VER_STRING);
}

png_charp PNGAPI
png_get_header_ver(png_structp png_ptr)
{
   /* Version of *.h files used when building libpng */
   png_ptr = png_ptr;  /* silence compiler warning about unused png_ptr */
   return ((png_charp) PNG_LIBPNG_VER_STRING);
}

png_charp PNGAPI
png_get_header_version(png_structp png_ptr)
{
   /* Returns longer string containing both version and date */
   png_ptr = png_ptr;  /* silence compiler warning about unused png_ptr */
   return ((png_charp) PNG_HEADER_VERSION_STRING
#ifndef PNG_READ_SUPPORTED
   "     (NO READ SUPPORT)"
#endif
   "\n");
}

#if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
#ifdef PNG_HANDLE_AS_UNKNOWN_SUPPORTED
int PNGAPI
png_handle_as_unknown(png_structp png_ptr, png_bytep chunk_name)
{
   /* check chunk_name and return "keep" value if it's on the list, else 0 */
   int i;
   png_bytep p;
   if (png_ptr == NULL || chunk_name == NULL || png_ptr->num_chunk_list<=0)
      return 0;
   p = png_ptr->chunk_list + png_ptr->num_chunk_list*5 - 5;
   for (i = png_ptr->num_chunk_list; i; i--, p -= 5)
      if (!png_memcmp(chunk_name, p, 4))
        return ((int)*(p + 4));
   return 0;
}
#endif

/* This function, added to libpng-1.0.6g, is untested. */
int PNGAPI
png_reset_zstream(png_structp png_ptr)
{
   if (png_ptr == NULL) return Z_STREAM_ERROR;
   return (inflateReset(&png_ptr->zstream));
}
#endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */

/* This function was added to libpng-1.0.7 */
png_uint_32 PNGAPI
png_access_version_number(void)
{
   /* Version of *.c files used when building libpng */
   return((png_uint_32) PNG_LIBPNG_VER);
}

#if defined(PNG_READ_SUPPORTED) && defined(PNG_ASSEMBLER_CODE_SUPPORTED)
#if !defined(PNG_1_0_X)
/* this function was added to libpng 1.2.0 */
int PNGAPI
png_mmx_support(void)
{
   /* obsolete, to be removed from libpng-1.4.0 */
    return -1;
}
#endif /* PNG_1_0_X */
#endif /* PNG_READ_SUPPORTED && PNG_ASSEMBLER_CODE_SUPPORTED */

#if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)
#ifdef PNG_SIZE_T
/* Added at libpng version 1.2.6 */
   PNG_EXTERN png_size_t PNGAPI png_convert_size PNGARG((size_t size));
png_size_t PNGAPI
png_convert_size(size_t size)
{
  if (size > (png_size_t)-1)
     PNG_ABORT();  /* We haven't got access to png_ptr, so no png_error() */
  return ((png_size_t)size);
}
#endif /* PNG_SIZE_T */

/* Added at libpng version 1.2.34 and 1.4.0 (moved from pngset.c) */
#if defined(PNG_cHRM_SUPPORTED)
#if !defined(PNG_NO_CHECK_cHRM)
/*
 Multiply two 32-bit numbers, V1 and V2, using 32-bit
 arithmetic, to produce a 64 bit result in the HI/LO words.

          A B
        x C D
       ------
      AD || BD
AC || CB || 0

 where A and B are the high and low 16-bit words of V1,
 C and D are the 16-bit words of V2, AD is the product of
 A and D, and X || Y is (X << 16) + Y.
*/

void png_64bit_product (long v1, long v2, unsigned long *hi_product,
   unsigned long *lo_product)
{
 int a, b, c, d;
 long lo, hi, x, y;

 a = (v1 >> 16) & 0xffff;
 b = v1 & 0xffff;
 c = (v2 >> 16) & 0xffff;
 d = v2 & 0xffff;

 lo = b * d;                   /* BD */
 x = a * d + c * b;            /* AD + CB */
 y = ((lo >> 16) & 0xffff) + x;

 lo = (lo & 0xffff) | ((y & 0xffff) << 16);
 hi = (y >> 16) & 0xffff;

 hi += a * c;                  /* AC */

 *hi_product = (unsigned long)hi;
 *lo_product = (unsigned long)lo;
}
int /* private */
png_check_cHRM_fixed(png_structp png_ptr,
   png_fixed_point white_x, png_fixed_point white_y, png_fixed_point red_x,
   png_fixed_point red_y, png_fixed_point green_x, png_fixed_point green_y,
   png_fixed_point blue_x, png_fixed_point blue_y)
{
   int ret = 1;
   unsigned long xy_hi,xy_lo,yx_hi,yx_lo;

   png_debug(1, "in function png_check_cHRM_fixed");
   if (png_ptr == NULL)
      return 0;

   if (white_x < 0 || white_y <= 0 ||
         red_x < 0 ||   red_y <  0 ||
       green_x < 0 || green_y <  0 ||
        blue_x < 0 ||  blue_y <  0)
   {
      png_warning(png_ptr,
        "Ignoring attempt to set negative chromaticity value");
      ret = 0;
   }
   if (white_x > (png_fixed_point) PNG_UINT_31_MAX ||
       white_y > (png_fixed_point) PNG_UINT_31_MAX ||
         red_x > (png_fixed_point) PNG_UINT_31_MAX ||
         red_y > (png_fixed_point) PNG_UINT_31_MAX ||
       green_x > (png_fixed_point) PNG_UINT_31_MAX ||
       green_y > (png_fixed_point) PNG_UINT_31_MAX ||
        blue_x > (png_fixed_point) PNG_UINT_31_MAX ||
        blue_y > (png_fixed_point) PNG_UINT_31_MAX )
   {
      png_warning(png_ptr,
        "Ignoring attempt to set chromaticity value exceeding 21474.83");
      ret = 0;
   }
   if (white_x > 100000L - white_y)
   {
      png_warning(png_ptr, "Invalid cHRM white point");
      ret = 0;
   }
   if (red_x > 100000L - red_y)
   {
      png_warning(png_ptr, "Invalid cHRM red point");
      ret = 0;
   }
   if (green_x > 100000L - green_y)
   {
      png_warning(png_ptr, "Invalid cHRM green point");
      ret = 0;
   }
   if (blue_x > 100000L - blue_y)
   {
      png_warning(png_ptr, "Invalid cHRM blue point");
      ret = 0;
   }

   png_64bit_product(green_x - red_x, blue_y - red_y, &xy_hi, &xy_lo);
   png_64bit_product(green_y - red_y, blue_x - red_x, &yx_hi, &yx_lo);

   if (xy_hi == yx_hi && xy_lo == yx_lo)
   {
      png_warning(png_ptr,
         "Ignoring attempt to set cHRM RGB triangle with zero area");
      ret = 0;
   }

   return ret;
}
#endif /* NO_PNG_CHECK_cHRM */
#endif /* PNG_cHRM_SUPPORTED */
#endif /* defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED) */

license: mit