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src/Source/LibPNG/example.c  view on Meta::CPAN

   /* 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 1.2.0
    * and up, this should no longer be necessary.
    */

   /* Once we write out the header, the compression type on the text
    * chunk 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 != 0)
      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;

   /* In this example, "image" is a one-dimensional array of bytes */
   png_byte image[height*width*bytes_per_pixel];

   png_bytep row_pointers[height];

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

   /* Set up pointers into your "image" byte array */
   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 1.2.0 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,