text: 
  /* pngwrite.c - general routines to write a PNG file
   *
   * Last changed in libpng 1.6.32 [August 24, 2017]
   * Copyright (c) 1998-2002,2004,2006-2017 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.)
   *
   * This code is released under the libpng license.
   * For conditions of distribution and use, see the disclaimer
   * and license in png.h
   */
  
  #include "pngpriv.h"
  #ifdef PNG_SIMPLIFIED_WRITE_STDIO_SUPPORTED
  #  include <errno.h>
  #endif /* SIMPLIFIED_WRITE_STDIO */
  
  #ifdef PNG_WRITE_SUPPORTED
  
  #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
  /* Write out all the unknown chunks for the current given location */
  static void
  write_unknown_chunks(png_structrp png_ptr, png_const_inforp info_ptr,
      unsigned int where)
  {
     if (info_ptr->unknown_chunks_num != 0)
     {
        png_const_unknown_chunkp up;
  
        png_debug(5, "writing extra chunks");
  
        for (up = info_ptr->unknown_chunks;
             up < info_ptr->unknown_chunks + info_ptr->unknown_chunks_num;
             ++up)
           if ((up->location & where) != 0)
        {
           /* If per-chunk unknown chunk handling is enabled use it, otherwise
            * just write the chunks the application has set.
            */
  #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
           int keep = png_handle_as_unknown(png_ptr, up->name);
  
           /* NOTE: this code is radically different from the read side in the
            * matter of handling an ancillary unknown chunk.  In the read side
            * the default behavior is to discard it, in the code below the default
            * behavior is to write it.  Critical chunks are, however, only
            * written if explicitly listed or if the default is set to write all
            * unknown chunks.
            *
            * The default handling is also slightly weird - it is not possible to
            * stop the writing of all unsafe-to-copy chunks!
            *
            * TODO: REVIEW: this would seem to be a bug.
            */
           if (keep != PNG_HANDLE_CHUNK_NEVER &&
               ((up->name[3] & 0x20) /* safe-to-copy overrides everything */ ||
                keep == PNG_HANDLE_CHUNK_ALWAYS ||
                (keep == PNG_HANDLE_CHUNK_AS_DEFAULT &&
                 png_ptr->unknown_default == PNG_HANDLE_CHUNK_ALWAYS)))
  #endif
           {
              /* TODO: review, what is wrong with a zero length unknown chunk? */
              if (up->size == 0)
                 png_warning(png_ptr, "Writing zero-length unknown chunk");
  
              png_write_chunk(png_ptr, up->name, up->data, up->size);
           }
        }
     }
  }
  #endif /* WRITE_UNKNOWN_CHUNKS */
  
  /* Writes all the PNG information.  This is the suggested way to use the
   * library.  If you have a new chunk to add, make a function to write it,
   * and put it in the correct location here.  If you want the chunk written
   * after the image data, put it in png_write_end().  I strongly encourage
   * you to supply a PNG_INFO_ flag, and check info_ptr->valid before writing
   * the chunk, as that will keep the code from breaking if you want to just
   * write a plain PNG file.  If you have long comments, I suggest writing
   * them in png_write_end(), and compressing them.
   */
  void PNGAPI
  png_write_info_before_PLTE(png_structrp png_ptr, png_const_inforp info_ptr)
  {
     png_debug(1, "in png_write_info_before_PLTE");
  
     if (png_ptr == NULL || info_ptr == NULL)
        return;
  
     if ((png_ptr->mode & PNG_WROTE_INFO_BEFORE_PLTE) == 0)
     {
        /* Write PNG signature */
        png_write_sig(png_ptr);
  
  #ifdef PNG_MNG_FEATURES_SUPPORTED
        if ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) != 0 && \
            png_ptr->mng_features_permitted != 0)
        {
           png_warning(png_ptr,
               "MNG features are not allowed in a PNG datastream");
           png_ptr->mng_features_permitted = 0;
        }
  #endif
  
        /* Write IHDR information. */
        png_write_IHDR(png_ptr, info_ptr->width, info_ptr->height,
            info_ptr->bit_depth, info_ptr->color_type, info_ptr->compression_type,
            info_ptr->filter_type,
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
            info_ptr->interlace_type
  #else
            0
  #endif
           );
  
        /* The rest of these check to see if the valid field has the appropriate
         * flag set, and if it does, writes the chunk.
         *
         * 1.6.0: COLORSPACE support controls the writing of these chunks too, and
         * the chunks will be written if the WRITE routine is there and
         * information * is available in the COLORSPACE. (See
         * png_colorspace_sync_info in png.c for where the valid flags get set.)
         *
         * Under certain circumstances the colorspace can be invalidated without
         * syncing the info_struct 'valid' flags; this happens if libpng detects
         * an error and calls png_error while the color space is being set, yet
         * the application continues writing the PNG.  So check the 'invalid'
         * flag here too.
         */
  #ifdef PNG_WRITE_APNG_SUPPORTED
        if (info_ptr->valid & PNG_INFO_acTL)
           png_write_acTL(png_ptr, info_ptr->num_frames, info_ptr->num_plays);
  #endif
  #ifdef PNG_GAMMA_SUPPORTED
  #  ifdef PNG_WRITE_gAMA_SUPPORTED
        if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) == 0 &&
            (info_ptr->colorspace.flags & PNG_COLORSPACE_FROM_gAMA) != 0 &&
            (info_ptr->valid & PNG_INFO_gAMA) != 0)
           png_write_gAMA_fixed(png_ptr, info_ptr->colorspace.gamma);
  #  endif
  #endif
  
  #ifdef PNG_COLORSPACE_SUPPORTED
        /* Write only one of sRGB or an ICC profile.  If a profile was supplied
         * and it matches one of the known sRGB ones issue a warning.
         */
  #  ifdef PNG_WRITE_iCCP_SUPPORTED
           if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) == 0 &&
               (info_ptr->valid & PNG_INFO_iCCP) != 0)
           {
  #    ifdef PNG_WRITE_sRGB_SUPPORTED
                 if ((info_ptr->valid & PNG_INFO_sRGB) != 0)
                    png_app_warning(png_ptr,
                        "profile matches sRGB but writing iCCP instead");
  #     endif
  
              png_write_iCCP(png_ptr, info_ptr->iccp_name,
                  info_ptr->iccp_profile);
           }
  #     ifdef PNG_WRITE_sRGB_SUPPORTED
           else
  #     endif
  #  endif
  
  #  ifdef PNG_WRITE_sRGB_SUPPORTED
           if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) == 0 &&
               (info_ptr->valid & PNG_INFO_sRGB) != 0)
              png_write_sRGB(png_ptr, info_ptr->colorspace.rendering_intent);
  #  endif /* WRITE_sRGB */
  #endif /* COLORSPACE */
  
  #ifdef PNG_WRITE_sBIT_SUPPORTED
           if ((info_ptr->valid & PNG_INFO_sBIT) != 0)
              png_write_sBIT(png_ptr, &(info_ptr->sig_bit), info_ptr->color_type);
  #endif
  
  #ifdef PNG_COLORSPACE_SUPPORTED
  #  ifdef PNG_WRITE_cHRM_SUPPORTED
           if ((info_ptr->colorspace.flags & PNG_COLORSPACE_INVALID) == 0 &&
               (info_ptr->colorspace.flags & PNG_COLORSPACE_FROM_cHRM) != 0 &&
               (info_ptr->valid & PNG_INFO_cHRM) != 0)
              png_write_cHRM_fixed(png_ptr, &info_ptr->colorspace.end_points_xy);
  #  endif
  #endif
  
  #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
           write_unknown_chunks(png_ptr, info_ptr, PNG_HAVE_IHDR);
  #endif
  
        png_ptr->mode |= PNG_WROTE_INFO_BEFORE_PLTE;
     }
  }
  
  void PNGAPI
  png_write_info(png_structrp png_ptr, png_const_inforp info_ptr)
  {
  #if defined(PNG_WRITE_TEXT_SUPPORTED) || defined(PNG_WRITE_sPLT_SUPPORTED)
     int i;
  #endif
  
     png_debug(1, "in png_write_info");
  
     if (png_ptr == NULL || info_ptr == NULL)
        return;
  
     png_write_info_before_PLTE(png_ptr, info_ptr);
  
     if ((info_ptr->valid & PNG_INFO_PLTE) != 0)
        png_write_PLTE(png_ptr, info_ptr->palette,
            (png_uint_32)info_ptr->num_palette);
  
     else if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        png_error(png_ptr, "Valid palette required for paletted images");
  
  #ifdef PNG_WRITE_tRNS_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_tRNS) !=0)
     {
  #ifdef PNG_WRITE_INVERT_ALPHA_SUPPORTED
        /* Invert the alpha channel (in tRNS) */
        if ((png_ptr->transformations & PNG_INVERT_ALPHA) != 0 &&
            info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        {
           int j, jend;
  
           jend = info_ptr->num_trans;
           if (jend > PNG_MAX_PALETTE_LENGTH)
              jend = PNG_MAX_PALETTE_LENGTH;
  
           for (j = 0; j<jend; ++j)
              info_ptr->trans_alpha[j] =
                 (png_byte)(255 - info_ptr->trans_alpha[j]);
        }
  #endif
        png_write_tRNS(png_ptr, info_ptr->trans_alpha, &(info_ptr->trans_color),
            info_ptr->num_trans, info_ptr->color_type);
     }
  #endif
  #ifdef PNG_WRITE_bKGD_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_bKGD) != 0)
        png_write_bKGD(png_ptr, &(info_ptr->background), info_ptr->color_type);
  #endif
  
  #ifdef PNG_WRITE_eXIf_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_eXIf) != 0)
        png_write_eXIf(png_ptr, info_ptr->exif, info_ptr->num_exif);
  #endif
  
  #ifdef PNG_WRITE_hIST_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_hIST) != 0)
        png_write_hIST(png_ptr, info_ptr->hist, info_ptr->num_palette);
  #endif
  
  #ifdef PNG_WRITE_oFFs_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_oFFs) != 0)
        png_write_oFFs(png_ptr, info_ptr->x_offset, info_ptr->y_offset,
            info_ptr->offset_unit_type);
  #endif
  
  #ifdef PNG_WRITE_pCAL_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_pCAL) != 0)
        png_write_pCAL(png_ptr, info_ptr->pcal_purpose, info_ptr->pcal_X0,
            info_ptr->pcal_X1, info_ptr->pcal_type, info_ptr->pcal_nparams,
            info_ptr->pcal_units, info_ptr->pcal_params);
  #endif
  
  #ifdef PNG_WRITE_sCAL_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_sCAL) != 0)
        png_write_sCAL_s(png_ptr, (int)info_ptr->scal_unit,
            info_ptr->scal_s_width, info_ptr->scal_s_height);
  #endif /* sCAL */
  
  #ifdef PNG_WRITE_pHYs_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_pHYs) != 0)
        png_write_pHYs(png_ptr, info_ptr->x_pixels_per_unit,
            info_ptr->y_pixels_per_unit, info_ptr->phys_unit_type);
  #endif /* pHYs */
  
  #ifdef PNG_WRITE_tIME_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_tIME) != 0)
     {
        png_write_tIME(png_ptr, &(info_ptr->mod_time));
        png_ptr->mode |= PNG_WROTE_tIME;
     }
  #endif /* tIME */
  
  #ifdef PNG_WRITE_sPLT_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_sPLT) != 0)
        for (i = 0; i < (int)info_ptr->splt_palettes_num; i++)
           png_write_sPLT(png_ptr, info_ptr->splt_palettes + i);
  #endif /* sPLT */
  
  #ifdef PNG_WRITE_TEXT_SUPPORTED
     /* Check to see if we need to write text chunks */
     for (i = 0; i < info_ptr->num_text; i++)
     {
        png_debug2(2, "Writing header text chunk %d, type %d", i,
            info_ptr->text[i].compression);
        /* An internationalized chunk? */
        if (info_ptr->text[i].compression > 0)
        {
  #ifdef PNG_WRITE_iTXt_SUPPORTED
           /* Write international chunk */
           png_write_iTXt(png_ptr,
               info_ptr->text[i].compression,
               info_ptr->text[i].key,
               info_ptr->text[i].lang,
               info_ptr->text[i].lang_key,
               info_ptr->text[i].text);
           /* Mark this chunk as written */
           if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
              info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
           else
              info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
  #else
           png_warning(png_ptr, "Unable to write international text");
  #endif
        }
  
        /* If we want a compressed text chunk */
        else if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_zTXt)
        {
  #ifdef PNG_WRITE_zTXt_SUPPORTED
           /* Write compressed chunk */
           png_write_zTXt(png_ptr, info_ptr->text[i].key,
               info_ptr->text[i].text, info_ptr->text[i].compression);
           /* Mark this chunk as written */
           info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
  #else
           png_warning(png_ptr, "Unable to write compressed text");
  #endif
        }
  
        else if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
        {
  #ifdef PNG_WRITE_tEXt_SUPPORTED
           /* Write uncompressed chunk */
           png_write_tEXt(png_ptr, info_ptr->text[i].key,
               info_ptr->text[i].text,
               0);
           /* Mark this chunk as written */
           info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
  #else
           /* Can't get here */
           png_warning(png_ptr, "Unable to write uncompressed text");
  #endif
        }
     }
  #endif /* tEXt */
  
  #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
     write_unknown_chunks(png_ptr, info_ptr, PNG_HAVE_PLTE);
  #endif
  }
  
  /* Writes the end of the PNG file.  If you don't want to write comments or
   * time information, you can pass NULL for info.  If you already wrote these
   * in png_write_info(), do not write them again here.  If you have long
   * comments, I suggest writing them here, and compressing them.
   */
  void PNGAPI
  png_write_end(png_structrp png_ptr, png_inforp info_ptr)
  {
     png_debug(1, "in png_write_end");
  
     if (png_ptr == NULL)
        return;
  
     if ((png_ptr->mode & PNG_HAVE_IDAT) == 0)
        png_error(png_ptr, "No IDATs written into file");
  
  #ifdef PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED
     if (png_ptr->num_palette_max > png_ptr->num_palette)
        png_benign_error(png_ptr, "Wrote palette index exceeding num_palette");
  #endif
  
  #ifdef PNG_WRITE_APNG_SUPPORTED
     if (png_ptr->num_frames_written != png_ptr->num_frames_to_write)
        png_error(png_ptr, "Not enough frames written");
  #endif
  
     /* See if user wants us to write information chunks */
     if (info_ptr != NULL)
     {
  #ifdef PNG_WRITE_TEXT_SUPPORTED
        int i; /* local index variable */
  #endif
  #ifdef PNG_WRITE_tIME_SUPPORTED
        /* Check to see if user has supplied a time chunk */
        if ((info_ptr->valid & PNG_INFO_tIME) != 0 &&
            (png_ptr->mode & PNG_WROTE_tIME) == 0)
           png_write_tIME(png_ptr, &(info_ptr->mod_time));
  
  #endif
  #ifdef PNG_WRITE_TEXT_SUPPORTED
        /* Loop through comment chunks */
        for (i = 0; i < info_ptr->num_text; i++)
        {
           png_debug2(2, "Writing trailer text chunk %d, type %d", i,
               info_ptr->text[i].compression);
           /* An internationalized chunk? */
           if (info_ptr->text[i].compression > 0)
           {
  #ifdef PNG_WRITE_iTXt_SUPPORTED
              /* Write international chunk */
              png_write_iTXt(png_ptr,
                  info_ptr->text[i].compression,
                  info_ptr->text[i].key,
                  info_ptr->text[i].lang,
                  info_ptr->text[i].lang_key,
                  info_ptr->text[i].text);
              /* Mark this chunk as written */
              if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
                 info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
              else
                 info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
  #else
              png_warning(png_ptr, "Unable to write international text");
  #endif
           }
  
           else if (info_ptr->text[i].compression >= PNG_TEXT_COMPRESSION_zTXt)
           {
  #ifdef PNG_WRITE_zTXt_SUPPORTED
              /* Write compressed chunk */
              png_write_zTXt(png_ptr, info_ptr->text[i].key,
                  info_ptr->text[i].text, info_ptr->text[i].compression);
              /* Mark this chunk as written */
              info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
  #else
              png_warning(png_ptr, "Unable to write compressed text");
  #endif
           }
  
           else if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
           {
  #ifdef PNG_WRITE_tEXt_SUPPORTED
              /* Write uncompressed chunk */
              png_write_tEXt(png_ptr, info_ptr->text[i].key,
                  info_ptr->text[i].text, 0);
              /* Mark this chunk as written */
              info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
  #else
              png_warning(png_ptr, "Unable to write uncompressed text");
  #endif
           }
        }
  #endif
  
  #ifdef PNG_WRITE_eXIf_SUPPORTED
     if ((info_ptr->valid & PNG_INFO_eXIf) != 0)
        png_write_eXIf(png_ptr, info_ptr->exif, info_ptr->num_exif);
  #endif
  
  #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
        write_unknown_chunks(png_ptr, info_ptr, PNG_AFTER_IDAT);
  #endif
     }
  
     png_ptr->mode |= PNG_AFTER_IDAT;
  
     /* Write end of PNG file */
     png_write_IEND(png_ptr);
  
     /* This flush, added in libpng-1.0.8, removed from libpng-1.0.9beta03,
      * and restored again in libpng-1.2.30, may cause some applications that
      * do not set png_ptr->output_flush_fn to crash.  If your application
      * experiences a problem, please try building libpng with
      * PNG_WRITE_FLUSH_AFTER_IEND_SUPPORTED defined, and report the event to
      * png-mng-implement at lists.sf.net .
      */
  #ifdef PNG_WRITE_FLUSH_SUPPORTED
  #  ifdef PNG_WRITE_FLUSH_AFTER_IEND_SUPPORTED
     png_flush(png_ptr);
  #  endif
  #endif
  }
  
  #ifdef PNG_CONVERT_tIME_SUPPORTED
  void PNGAPI
  png_convert_from_struct_tm(png_timep ptime, PNG_CONST struct tm * ttime)
  {
     png_debug(1, "in png_convert_from_struct_tm");
  
     ptime->year = (png_uint_16)(1900 + ttime->tm_year);
     ptime->month = (png_byte)(ttime->tm_mon + 1);
     ptime->day = (png_byte)ttime->tm_mday;
     ptime->hour = (png_byte)ttime->tm_hour;
     ptime->minute = (png_byte)ttime->tm_min;
     ptime->second = (png_byte)ttime->tm_sec;
  }
  
  void PNGAPI
  png_convert_from_time_t(png_timep ptime, time_t ttime)
  {
     struct tm *tbuf;
  
     png_debug(1, "in png_convert_from_time_t");
  
     tbuf = gmtime(&ttime);
     png_convert_from_struct_tm(ptime, tbuf);
  }
  #endif
  
  /* Initialize png_ptr structure, and allocate any memory needed */
  PNG_FUNCTION(png_structp,PNGAPI
  png_create_write_struct,(png_const_charp user_png_ver, png_voidp error_ptr,
      png_error_ptr error_fn, png_error_ptr warn_fn),PNG_ALLOCATED)
  {
  #ifndef PNG_USER_MEM_SUPPORTED
     png_structrp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
         error_fn, warn_fn, NULL, NULL, NULL);
  #else
     return png_create_write_struct_2(user_png_ver, error_ptr, error_fn,
         warn_fn, NULL, NULL, NULL);
  }
  
  /* Alternate initialize png_ptr structure, and allocate any memory needed */
  PNG_FUNCTION(png_structp,PNGAPI
  png_create_write_struct_2,(png_const_charp user_png_ver, png_voidp error_ptr,
      png_error_ptr error_fn, png_error_ptr warn_fn, png_voidp mem_ptr,
      png_malloc_ptr malloc_fn, png_free_ptr free_fn),PNG_ALLOCATED)
  {
     png_structrp png_ptr = png_create_png_struct(user_png_ver, error_ptr,
         error_fn, warn_fn, mem_ptr, malloc_fn, free_fn);
  #endif /* USER_MEM */
     if (png_ptr != NULL)
     {
        /* Set the zlib control values to defaults; they can be overridden by the
         * application after the struct has been created.
         */
        png_ptr->zbuffer_size = PNG_ZBUF_SIZE;
  
        /* The 'zlib_strategy' setting is irrelevant because png_default_claim in
         * pngwutil.c defaults it according to whether or not filters will be
         * used, and ignores this setting.
         */
        png_ptr->zlib_strategy = PNG_Z_DEFAULT_STRATEGY;
        png_ptr->zlib_level = PNG_Z_DEFAULT_COMPRESSION;
        png_ptr->zlib_mem_level = 8;
        png_ptr->zlib_window_bits = 15;
        png_ptr->zlib_method = 8;
  
  #ifdef PNG_WRITE_COMPRESSED_TEXT_SUPPORTED
        png_ptr->zlib_text_strategy = PNG_TEXT_Z_DEFAULT_STRATEGY;
        png_ptr->zlib_text_level = PNG_TEXT_Z_DEFAULT_COMPRESSION;
        png_ptr->zlib_text_mem_level = 8;
        png_ptr->zlib_text_window_bits = 15;
        png_ptr->zlib_text_method = 8;
  #endif /* WRITE_COMPRESSED_TEXT */
  
        /* This is a highly dubious configuration option; by default it is off,
         * but it may be appropriate for private builds that are testing
         * extensions not conformant to the current specification, or of
         * applications that must not fail to write at all costs!
         */
  #ifdef PNG_BENIGN_WRITE_ERRORS_SUPPORTED
        /* In stable builds only warn if an application error can be completely
         * handled.
         */
        png_ptr->flags |= PNG_FLAG_BENIGN_ERRORS_WARN;
  #endif
  
        /* App warnings are warnings in release (or release candidate) builds but
         * are errors during development.
         */
  #if PNG_RELEASE_BUILD
        png_ptr->flags |= PNG_FLAG_APP_WARNINGS_WARN;
  #endif
  
        /* TODO: delay this, it can be done in png_init_io() (if the app doesn't
         * do it itself) avoiding setting the default function if it is not
         * required.
         */
        png_set_write_fn(png_ptr, NULL, NULL, NULL);
     }
  
     return png_ptr;
  }
  
  
  /* Write a few rows of image data.  If the image is interlaced,
   * either you will have to write the 7 sub images, or, if you
   * have called png_set_interlace_handling(), you will have to
   * "write" the image seven times.
   */
  void PNGAPI
  png_write_rows(png_structrp png_ptr, png_bytepp row,
      png_uint_32 num_rows)
  {
     png_uint_32 i; /* row counter */
     png_bytepp rp; /* row pointer */
  
     png_debug(1, "in png_write_rows");
  
     if (png_ptr == NULL)
        return;
  
     /* Loop through the rows */
     for (i = 0, rp = row; i < num_rows; i++, rp++)
     {
        png_write_row(png_ptr, *rp);
     }
  }
  
  /* Write the image.  You only need to call this function once, even
   * if you are writing an interlaced image.
   */
  void PNGAPI
  png_write_image(png_structrp png_ptr, png_bytepp image)
  {
     png_uint_32 i; /* row index */
     int pass, num_pass; /* pass variables */
     png_bytepp rp; /* points to current row */
  
     if (png_ptr == NULL)
        return;
  
     png_debug(1, "in png_write_image");
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* Initialize interlace handling.  If image is not interlaced,
      * this will set pass to 1
      */
     num_pass = png_set_interlace_handling(png_ptr);
  #else
     num_pass = 1;
  #endif
     /* Loop through passes */
     for (pass = 0; pass < num_pass; pass++)
     {
        /* Loop through image */
        for (i = 0, rp = image; i < png_ptr->height; i++, rp++)
        {
           png_write_row(png_ptr, *rp);
        }
     }
  }
  
  #ifdef PNG_MNG_FEATURES_SUPPORTED
  /* Performs intrapixel differencing  */
  static void
  png_do_write_intrapixel(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_write_intrapixel");
  
     if ((row_info->color_type & PNG_COLOR_MASK_COLOR) != 0)
     {
        int bytes_per_pixel;
        png_uint_32 row_width = row_info->width;
        if (row_info->bit_depth == 8)
        {
           png_bytep rp;
           png_uint_32 i;
  
           if (row_info->color_type == PNG_COLOR_TYPE_RGB)
              bytes_per_pixel = 3;
  
           else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
              bytes_per_pixel = 4;
  
           else
              return;
  
           for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
           {
              *(rp)     = (png_byte)(*rp       - *(rp + 1));
              *(rp + 2) = (png_byte)(*(rp + 2) - *(rp + 1));
           }
        }
  
  #ifdef PNG_WRITE_16BIT_SUPPORTED
        else if (row_info->bit_depth == 16)
        {
           png_bytep rp;
           png_uint_32 i;
  
           if (row_info->color_type == PNG_COLOR_TYPE_RGB)
              bytes_per_pixel = 6;
  
           else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
              bytes_per_pixel = 8;
  
           else
              return;
  
           for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
           {
              png_uint_32 s0   = (png_uint_32)(*(rp    ) << 8) | *(rp + 1);
              png_uint_32 s1   = (png_uint_32)(*(rp + 2) << 8) | *(rp + 3);
              png_uint_32 s2   = (png_uint_32)(*(rp + 4) << 8) | *(rp + 5);
              png_uint_32 red  = (png_uint_32)((s0 - s1) & 0xffffL);
              png_uint_32 blue = (png_uint_32)((s2 - s1) & 0xffffL);
              *(rp    ) = (png_byte)(red >> 8);
              *(rp + 1) = (png_byte)red;
              *(rp + 4) = (png_byte)(blue >> 8);
              *(rp + 5) = (png_byte)blue;
           }
        }
  #endif /* WRITE_16BIT */
     }
  }
  #endif /* MNG_FEATURES */
  
  /* Called by user to write a row of image data */
  void PNGAPI
  png_write_row(png_structrp png_ptr, png_const_bytep row)
  {
     /* 1.5.6: moved from png_struct to be a local structure: */
     png_row_info row_info;
  
     if (png_ptr == NULL)
        return;
  
     png_debug2(1, "in png_write_row (row %u, pass %d)",
         png_ptr->row_number, png_ptr->pass);
  
     /* Initialize transformations and other stuff if first time */
     if (png_ptr->row_number == 0 && png_ptr->pass == 0)
     {
        /* Make sure we wrote the header info */
        if ((png_ptr->mode & PNG_WROTE_INFO_BEFORE_PLTE) == 0)
           png_error(png_ptr,
               "png_write_info was never called before png_write_row");
  
        /* Check for transforms that have been set but were defined out */
  #if !defined(PNG_WRITE_INVERT_SUPPORTED) && defined(PNG_READ_INVERT_SUPPORTED)
        if ((png_ptr->transformations & PNG_INVERT_MONO) != 0)
           png_warning(png_ptr, "PNG_WRITE_INVERT_SUPPORTED is not defined");
  #endif
  
  #if !defined(PNG_WRITE_FILLER_SUPPORTED) && defined(PNG_READ_FILLER_SUPPORTED)
        if ((png_ptr->transformations & PNG_FILLER) != 0)
           png_warning(png_ptr, "PNG_WRITE_FILLER_SUPPORTED is not defined");
  #endif
  #if !defined(PNG_WRITE_PACKSWAP_SUPPORTED) && \
      defined(PNG_READ_PACKSWAP_SUPPORTED)
        if ((png_ptr->transformations & PNG_PACKSWAP) != 0)
           png_warning(png_ptr,
               "PNG_WRITE_PACKSWAP_SUPPORTED is not defined");
  #endif
  
  #if !defined(PNG_WRITE_PACK_SUPPORTED) && defined(PNG_READ_PACK_SUPPORTED)
        if ((png_ptr->transformations & PNG_PACK) != 0)
           png_warning(png_ptr, "PNG_WRITE_PACK_SUPPORTED is not defined");
  #endif
  
  #if !defined(PNG_WRITE_SHIFT_SUPPORTED) && defined(PNG_READ_SHIFT_SUPPORTED)
        if ((png_ptr->transformations & PNG_SHIFT) != 0)
           png_warning(png_ptr, "PNG_WRITE_SHIFT_SUPPORTED is not defined");
  #endif
  
  #if !defined(PNG_WRITE_BGR_SUPPORTED) && defined(PNG_READ_BGR_SUPPORTED)
        if ((png_ptr->transformations & PNG_BGR) != 0)
           png_warning(png_ptr, "PNG_WRITE_BGR_SUPPORTED is not defined");
  #endif
  
  #if !defined(PNG_WRITE_SWAP_SUPPORTED) && defined(PNG_READ_SWAP_SUPPORTED)
        if ((png_ptr->transformations & PNG_SWAP_BYTES) != 0)
           png_warning(png_ptr, "PNG_WRITE_SWAP_SUPPORTED is not defined");
  #endif
  
        png_write_start_row(png_ptr);
     }
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* If interlaced and not interested in row, return */
     if (png_ptr->interlaced != 0 &&
         (png_ptr->transformations & PNG_INTERLACE) != 0)
     {
        switch (png_ptr->pass)
        {
           case 0:
              if ((png_ptr->row_number & 0x07) != 0)
              {
                 png_write_finish_row(png_ptr);
                 return;
              }
              break;
  
           case 1:
              if ((png_ptr->row_number & 0x07) != 0 || png_ptr->width < 5)
              {
                 png_write_finish_row(png_ptr);
                 return;
              }
              break;
  
           case 2:
              if ((png_ptr->row_number & 0x07) != 4)
              {
                 png_write_finish_row(png_ptr);
                 return;
              }
              break;
  
           case 3:
              if ((png_ptr->row_number & 0x03) != 0 || png_ptr->width < 3)
              {
                 png_write_finish_row(png_ptr);
                 return;
              }
              break;
  
           case 4:
              if ((png_ptr->row_number & 0x03) != 2)
              {
                 png_write_finish_row(png_ptr);
                 return;
              }
              break;
  
           case 5:
              if ((png_ptr->row_number & 0x01) != 0 || png_ptr->width < 2)
              {
                 png_write_finish_row(png_ptr);
                 return;
              }
              break;
  
           case 6:
              if ((png_ptr->row_number & 0x01) == 0)
              {
                 png_write_finish_row(png_ptr);
                 return;
              }
              break;
  
           default: /* error: ignore it */
              break;
        }
     }
  #endif
  
     /* Set up row info for transformations */
     row_info.color_type = png_ptr->color_type;
     row_info.width = png_ptr->usr_width;
     row_info.channels = png_ptr->usr_channels;
     row_info.bit_depth = png_ptr->usr_bit_depth;
     row_info.pixel_depth = (png_byte)(row_info.bit_depth * row_info.channels);
     row_info.rowbytes = PNG_ROWBYTES(row_info.pixel_depth, row_info.width);
  
     png_debug1(3, "row_info->color_type = %d", row_info.color_type);
     png_debug1(3, "row_info->width = %u", row_info.width);
     png_debug1(3, "row_info->channels = %d", row_info.channels);
     png_debug1(3, "row_info->bit_depth = %d", row_info.bit_depth);
     png_debug1(3, "row_info->pixel_depth = %d", row_info.pixel_depth);
     png_debug1(3, "row_info->rowbytes = %lu", (unsigned long)row_info.rowbytes);
  
     /* Copy user's row into buffer, leaving room for filter byte. */
     memcpy(png_ptr->row_buf + 1, row, row_info.rowbytes);
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* Handle interlacing */
     if (png_ptr->interlaced && png_ptr->pass < 6 &&
         (png_ptr->transformations & PNG_INTERLACE) != 0)
     {
        png_do_write_interlace(&row_info, png_ptr->row_buf + 1, png_ptr->pass);
        /* This should always get caught above, but still ... */
        if (row_info.width == 0)
        {
           png_write_finish_row(png_ptr);
           return;
        }
     }
  #endif
  
  #ifdef PNG_WRITE_TRANSFORMS_SUPPORTED
     /* Handle other transformations */
     if (png_ptr->transformations != 0)
        png_do_write_transformations(png_ptr, &row_info);
  #endif
  
     /* At this point the row_info pixel depth must match the 'transformed' depth,
      * which is also the output depth.
      */
     if (row_info.pixel_depth != png_ptr->pixel_depth ||
         row_info.pixel_depth != png_ptr->transformed_pixel_depth)
        png_error(png_ptr, "internal write transform logic error");
  
  #ifdef PNG_MNG_FEATURES_SUPPORTED
     /* Write filter_method 64 (intrapixel differencing) only if
      * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
      * 2. Libpng did not write a PNG signature (this filter_method is only
      *    used in PNG datastreams that are embedded in MNG datastreams) and
      * 3. The application called png_permit_mng_features with a mask that
      *    included PNG_FLAG_MNG_FILTER_64 and
      * 4. The filter_method is 64 and
      * 5. The color_type is RGB or RGBA
      */
     if ((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) != 0 &&
         (png_ptr->filter_type == PNG_INTRAPIXEL_DIFFERENCING))
     {
        /* Intrapixel differencing */
        png_do_write_intrapixel(&row_info, png_ptr->row_buf + 1);
     }
  #endif
  
  /* Added at libpng-1.5.10 */
  #ifdef PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED
     /* Check for out-of-range palette index */
     if (row_info.color_type == PNG_COLOR_TYPE_PALETTE &&
         png_ptr->num_palette_max >= 0)
        png_do_check_palette_indexes(png_ptr, &row_info);
  #endif
  
     /* Find a filter if necessary, filter the row and write it out. */
     png_write_find_filter(png_ptr, &row_info);
  
     if (png_ptr->write_row_fn != NULL)
        (*(png_ptr->write_row_fn))(png_ptr, png_ptr->row_number, png_ptr->pass);
  }
  
  #ifdef PNG_WRITE_FLUSH_SUPPORTED
  /* Set the automatic flush interval or 0 to turn flushing off */
  void PNGAPI
  png_set_flush(png_structrp png_ptr, int nrows)
  {
     png_debug(1, "in png_set_flush");
  
     if (png_ptr == NULL)
        return;
  
     png_ptr->flush_dist = (nrows < 0 ? 0 : (png_uint_32)nrows);
  }
  
  /* Flush the current output buffers now */
  void PNGAPI
  png_write_flush(png_structrp png_ptr)
  {
     png_debug(1, "in png_write_flush");
  
     if (png_ptr == NULL)
        return;
  
     /* We have already written out all of the data */
     if (png_ptr->row_number >= png_ptr->num_rows)
        return;
  
     png_compress_IDAT(png_ptr, NULL, 0, Z_SYNC_FLUSH);
     png_ptr->flush_rows = 0;
     png_flush(png_ptr);
  }
  #endif /* WRITE_FLUSH */
  
  /* Free any memory used in png_ptr struct without freeing the struct itself. */
  static void
  png_write_destroy(png_structrp png_ptr)
  {
     png_debug(1, "in png_write_destroy");
  
     /* Free any memory zlib uses */
     if ((png_ptr->flags & PNG_FLAG_ZSTREAM_INITIALIZED) != 0)
        deflateEnd(&png_ptr->zstream);
  
     /* Free our memory.  png_free checks NULL for us. */
     png_free_buffer_list(png_ptr, &png_ptr->zbuffer_list);
     png_free(png_ptr, png_ptr->row_buf);
     png_ptr->row_buf = NULL;
  #ifdef PNG_WRITE_FILTER_SUPPORTED
     png_free(png_ptr, png_ptr->prev_row);
     png_free(png_ptr, png_ptr->try_row);
     png_free(png_ptr, png_ptr->tst_row);
     png_ptr->prev_row = NULL;
     png_ptr->try_row = NULL;
     png_ptr->tst_row = NULL;
  #endif
  
  #ifdef PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
     png_free(png_ptr, png_ptr->chunk_list);
     png_ptr->chunk_list = NULL;
  #endif
  
     /* The error handling and memory handling information is left intact at this
      * point: the jmp_buf may still have to be freed.  See png_destroy_png_struct
      * for how this happens.
      */
  }
  
  /* Free all memory used by the write.
   * In libpng 1.6.0 this API changed quietly to no longer accept a NULL value for
   * *png_ptr_ptr.  Prior to 1.6.0 it would accept such a value and it would free
   * the passed in info_structs but it would quietly fail to free any of the data
   * inside them.  In 1.6.0 it quietly does nothing (it has to be quiet because it
   * has no png_ptr.)
   */
  void PNGAPI
  png_destroy_write_struct(png_structpp png_ptr_ptr, png_infopp info_ptr_ptr)
  {
     png_debug(1, "in png_destroy_write_struct");
  
     if (png_ptr_ptr != NULL)
     {
        png_structrp png_ptr = *png_ptr_ptr;
  
        if (png_ptr != NULL) /* added in libpng 1.6.0 */
        {
           png_destroy_info_struct(png_ptr, info_ptr_ptr);
  
           *png_ptr_ptr = NULL;
           png_write_destroy(png_ptr);
           png_destroy_png_struct(png_ptr);
        }
     }
  }
  
  /* Allow the application to select one or more row filters to use. */
  void PNGAPI
  png_set_filter(png_structrp png_ptr, int method, int filters)
  {
     png_debug(1, "in png_set_filter");
  
     if (png_ptr == NULL)
        return;
  
  #ifdef PNG_MNG_FEATURES_SUPPORTED
     if ((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) != 0 &&
         (method == PNG_INTRAPIXEL_DIFFERENCING))
        method = PNG_FILTER_TYPE_BASE;
  
  #endif
     if (method == PNG_FILTER_TYPE_BASE)
     {
        switch (filters & (PNG_ALL_FILTERS | 0x07))
        {
  #ifdef PNG_WRITE_FILTER_SUPPORTED
           case 5:
           case 6:
           case 7: png_app_error(png_ptr, "Unknown row filter for method 0");
  #endif /* WRITE_FILTER */
              /* FALLTHROUGH */
           case PNG_FILTER_VALUE_NONE:
              png_ptr->do_filter = PNG_FILTER_NONE; break;
  
  #ifdef PNG_WRITE_FILTER_SUPPORTED
           case PNG_FILTER_VALUE_SUB:
              png_ptr->do_filter = PNG_FILTER_SUB; break;
  
           case PNG_FILTER_VALUE_UP:
              png_ptr->do_filter = PNG_FILTER_UP; break;
  
           case PNG_FILTER_VALUE_AVG:
              png_ptr->do_filter = PNG_FILTER_AVG; break;
  
           case PNG_FILTER_VALUE_PAETH:
              png_ptr->do_filter = PNG_FILTER_PAETH; break;
  
           default:
              png_ptr->do_filter = (png_byte)filters; break;
  #else
           default:
              png_app_error(png_ptr, "Unknown row filter for method 0");
  #endif /* WRITE_FILTER */
        }
  
  #ifdef PNG_WRITE_FILTER_SUPPORTED
        /* If we have allocated the row_buf, this means we have already started
         * with the image and we should have allocated all of the filter buffers
         * that have been selected.  If prev_row isn't already allocated, then
         * it is too late to start using the filters that need it, since we
         * will be missing the data in the previous row.  If an application
         * wants to start and stop using particular filters during compression,
         * it should start out with all of the filters, and then remove them
         * or add them back after the start of compression.
         *
         * NOTE: this is a nasty constraint on the code, because it means that the
         * prev_row buffer must be maintained even if there are currently no
         * 'prev_row' requiring filters active.
         */
        if (png_ptr->row_buf != NULL)
        {
           int num_filters;
           png_alloc_size_t buf_size;
  
           /* Repeat the checks in png_write_start_row; 1 pixel high or wide
            * images cannot benefit from certain filters.  If this isn't done here
            * the check below will fire on 1 pixel high images.
            */
           if (png_ptr->height == 1)
              filters &= ~(PNG_FILTER_UP|PNG_FILTER_AVG|PNG_FILTER_PAETH);
  
           if (png_ptr->width == 1)
              filters &= ~(PNG_FILTER_SUB|PNG_FILTER_AVG|PNG_FILTER_PAETH);
  
           if ((filters & (PNG_FILTER_UP|PNG_FILTER_AVG|PNG_FILTER_PAETH)) != 0
              && png_ptr->prev_row == NULL)
           {
              /* This is the error case, however it is benign - the previous row
               * is not available so the filter can't be used.  Just warn here.
               */
              png_app_warning(png_ptr,
                  "png_set_filter: UP/AVG/PAETH cannot be added after start");
              filters &= ~(PNG_FILTER_UP|PNG_FILTER_AVG|PNG_FILTER_PAETH);
           }
  
           num_filters = 0;
  
           if (filters & PNG_FILTER_SUB)
              num_filters++;
  
           if (filters & PNG_FILTER_UP)
              num_filters++;
  
           if (filters & PNG_FILTER_AVG)
              num_filters++;
  
           if (filters & PNG_FILTER_PAETH)
              num_filters++;
  
           /* Allocate needed row buffers if they have not already been
            * allocated.
            */
           buf_size = PNG_ROWBYTES(png_ptr->usr_channels * png_ptr->usr_bit_depth,
               png_ptr->width) + 1;
  
           if (png_ptr->try_row == NULL)
              png_ptr->try_row = png_voidcast(png_bytep,
                  png_malloc(png_ptr, buf_size));
  
           if (num_filters > 1)
           {
              if (png_ptr->tst_row == NULL)
                 png_ptr->tst_row = png_voidcast(png_bytep,
                     png_malloc(png_ptr, buf_size));
           }
        }
        png_ptr->do_filter = (png_byte)filters;
  #endif
     }
     else
        png_error(png_ptr, "Unknown custom filter method");
  }
  
  #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED /* DEPRECATED */
  /* Provide floating and fixed point APIs */
  #ifdef PNG_FLOATING_POINT_SUPPORTED
  void PNGAPI
  png_set_filter_heuristics(png_structrp png_ptr, int heuristic_method,
      int num_weights, png_const_doublep filter_weights,
      png_const_doublep filter_costs)
  {
     PNG_UNUSED(png_ptr)
     PNG_UNUSED(heuristic_method)
     PNG_UNUSED(num_weights)
     PNG_UNUSED(filter_weights)
     PNG_UNUSED(filter_costs)
  }
  #endif /* FLOATING_POINT */
  
  #ifdef PNG_FIXED_POINT_SUPPORTED
  void PNGAPI
  png_set_filter_heuristics_fixed(png_structrp png_ptr, int heuristic_method,
      int num_weights, png_const_fixed_point_p filter_weights,
      png_const_fixed_point_p filter_costs)
  {
     PNG_UNUSED(png_ptr)
     PNG_UNUSED(heuristic_method)
     PNG_UNUSED(num_weights)
     PNG_UNUSED(filter_weights)
     PNG_UNUSED(filter_costs)
  }
  #endif /* FIXED_POINT */
  #endif /* WRITE_WEIGHTED_FILTER */
  
  #ifdef PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED
  void PNGAPI
  png_set_compression_level(png_structrp png_ptr, int level)
  {
     png_debug(1, "in png_set_compression_level");
  
     if (png_ptr == NULL)
        return;
  
     png_ptr->zlib_level = level;
  }
  
  void PNGAPI
  png_set_compression_mem_level(png_structrp png_ptr, int mem_level)
  {
     png_debug(1, "in png_set_compression_mem_level");
  
     if (png_ptr == NULL)
        return;
  
     png_ptr->zlib_mem_level = mem_level;
  }
  
  void PNGAPI
  png_set_compression_strategy(png_structrp png_ptr, int strategy)
  {
     png_debug(1, "in png_set_compression_strategy");
  
     if (png_ptr == NULL)
        return;
  
     /* The flag setting here prevents the libpng dynamic selection of strategy.
      */
     png_ptr->flags |= PNG_FLAG_ZLIB_CUSTOM_STRATEGY;
     png_ptr->zlib_strategy = strategy;
  }
  
  /* If PNG_WRITE_OPTIMIZE_CMF_SUPPORTED is defined, libpng will use a
   * smaller value of window_bits if it can do so safely.
   */
  void PNGAPI
  png_set_compression_window_bits(png_structrp png_ptr, int window_bits)
  {
     if (png_ptr == NULL)
        return;
  
     /* Prior to 1.6.0 this would warn but then set the window_bits value. This
      * meant that negative window bits values could be selected that would cause
      * libpng to write a non-standard PNG file with raw deflate or gzip
      * compressed IDAT or ancillary chunks.  Such files can be read and there is
      * no warning on read, so this seems like a very bad idea.
      */
     if (window_bits > 15)
     {
        png_warning(png_ptr, "Only compression windows <= 32k supported by PNG");
        window_bits = 15;
     }
  
     else if (window_bits < 8)
     {
        png_warning(png_ptr, "Only compression windows >= 256 supported by PNG");
        window_bits = 8;
     }
  
     png_ptr->zlib_window_bits = window_bits;
  }
  
  void PNGAPI
  png_set_compression_method(png_structrp png_ptr, int method)
  {
     png_debug(1, "in png_set_compression_method");
  
     if (png_ptr == NULL)
        return;
  
     /* This would produce an invalid PNG file if it worked, but it doesn't and
      * deflate will fault it, so it is harmless to just warn here.
      */
     if (method != 8)
        png_warning(png_ptr, "Only compression method 8 is supported by PNG");
  
     png_ptr->zlib_method = method;
  }
  #endif /* WRITE_CUSTOMIZE_COMPRESSION */
  
  /* The following were added to libpng-1.5.4 */
  #ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED
  void PNGAPI
  png_set_text_compression_level(png_structrp png_ptr, int level)
  {
     png_debug(1, "in png_set_text_compression_level");
  
     if (png_ptr == NULL)
        return;
  
     png_ptr->zlib_text_level = level;
  }
  
  void PNGAPI
  png_set_text_compression_mem_level(png_structrp png_ptr, int mem_level)
  {
     png_debug(1, "in png_set_text_compression_mem_level");
  
     if (png_ptr == NULL)
        return;
  
     png_ptr->zlib_text_mem_level = mem_level;
  }
  
  void PNGAPI
  png_set_text_compression_strategy(png_structrp png_ptr, int strategy)
  {
     png_debug(1, "in png_set_text_compression_strategy");
  
     if (png_ptr == NULL)
        return;
  
     png_ptr->zlib_text_strategy = strategy;
  }
  
  /* If PNG_WRITE_OPTIMIZE_CMF_SUPPORTED is defined, libpng will use a
   * smaller value of window_bits if it can do so safely.
   */
  void PNGAPI
  png_set_text_compression_window_bits(png_structrp png_ptr, int window_bits)
  {
     if (png_ptr == NULL)
        return;
  
     if (window_bits > 15)
     {
        png_warning(png_ptr, "Only compression windows <= 32k supported by PNG");
        window_bits = 15;
     }
  
     else if (window_bits < 8)
     {
        png_warning(png_ptr, "Only compression windows >= 256 supported by PNG");
        window_bits = 8;
     }
  
     png_ptr->zlib_text_window_bits = window_bits;
  }
  
  void PNGAPI
  png_set_text_compression_method(png_structrp png_ptr, int method)
  {
     png_debug(1, "in png_set_text_compression_method");
  
     if (png_ptr == NULL)
        return;
  
     if (method != 8)
        png_warning(png_ptr, "Only compression method 8 is supported by PNG");
  
     png_ptr->zlib_text_method = method;
  }
  #endif /* WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
  /* end of API added to libpng-1.5.4 */
  
  void PNGAPI
  png_set_write_status_fn(png_structrp png_ptr, png_write_status_ptr write_row_fn)
  {
     if (png_ptr == NULL)
        return;
  
     png_ptr->write_row_fn = write_row_fn;
  }
  
  #ifdef PNG_WRITE_USER_TRANSFORM_SUPPORTED
  void PNGAPI
  png_set_write_user_transform_fn(png_structrp png_ptr, png_user_transform_ptr
      write_user_transform_fn)
  {
     png_debug(1, "in png_set_write_user_transform_fn");
  
     if (png_ptr == NULL)
        return;
  
     png_ptr->transformations |= PNG_USER_TRANSFORM;
     png_ptr->write_user_transform_fn = write_user_transform_fn;
  }
  #endif
  
  
  #ifdef PNG_INFO_IMAGE_SUPPORTED
  void PNGAPI
  png_write_png(png_structrp png_ptr, png_inforp info_ptr,
      int transforms, voidp params)
  {
     if (png_ptr == NULL || info_ptr == NULL)
        return;
  
     if ((info_ptr->valid & PNG_INFO_IDAT) == 0)
     {
        png_app_error(png_ptr, "no rows for png_write_image to write");
        return;
     }
  
     /* Write the file header information. */
     png_write_info(png_ptr, info_ptr);
  
     /* ------ these transformations don't touch the info structure ------- */
  
     /* Invert monochrome pixels */
     if ((transforms & PNG_TRANSFORM_INVERT_MONO) != 0)
  #ifdef PNG_WRITE_INVERT_SUPPORTED
        png_set_invert_mono(png_ptr);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_MONO not supported");
  #endif
  
     /* Shift the pixels up to a legal bit depth and fill in
      * as appropriate to correctly scale the image.
      */
     if ((transforms & PNG_TRANSFORM_SHIFT) != 0)
  #ifdef PNG_WRITE_SHIFT_SUPPORTED
        if ((info_ptr->valid & PNG_INFO_sBIT) != 0)
           png_set_shift(png_ptr, &info_ptr->sig_bit);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_SHIFT not supported");
  #endif
  
     /* Pack pixels into bytes */
     if ((transforms & PNG_TRANSFORM_PACKING) != 0)
  #ifdef PNG_WRITE_PACK_SUPPORTED
        png_set_packing(png_ptr);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_PACKING not supported");
  #endif
  
     /* Swap location of alpha bytes from ARGB to RGBA */
     if ((transforms & PNG_TRANSFORM_SWAP_ALPHA) != 0)
  #ifdef PNG_WRITE_SWAP_ALPHA_SUPPORTED
        png_set_swap_alpha(png_ptr);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ALPHA not supported");
  #endif
  
     /* Remove a filler (X) from XRGB/RGBX/AG/GA into to convert it into
      * RGB, note that the code expects the input color type to be G or RGB; no
      * alpha channel.
      */
     if ((transforms & (PNG_TRANSFORM_STRIP_FILLER_AFTER|
         PNG_TRANSFORM_STRIP_FILLER_BEFORE)) != 0)
     {
  #ifdef PNG_WRITE_FILLER_SUPPORTED
        if ((transforms & PNG_TRANSFORM_STRIP_FILLER_AFTER) != 0)
        {
           if ((transforms & PNG_TRANSFORM_STRIP_FILLER_BEFORE) != 0)
              png_app_error(png_ptr,
                  "PNG_TRANSFORM_STRIP_FILLER: BEFORE+AFTER not supported");
  
           /* Continue if ignored - this is the pre-1.6.10 behavior */
           png_set_filler(png_ptr, 0, PNG_FILLER_AFTER);
        }
  
        else if ((transforms & PNG_TRANSFORM_STRIP_FILLER_BEFORE) != 0)
           png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_STRIP_FILLER not supported");
  #endif
     }
  
     /* Flip BGR pixels to RGB */
     if ((transforms & PNG_TRANSFORM_BGR) != 0)
  #ifdef PNG_WRITE_BGR_SUPPORTED
        png_set_bgr(png_ptr);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_BGR not supported");
  #endif
  
     /* Swap bytes of 16-bit files to most significant byte first */
     if ((transforms & PNG_TRANSFORM_SWAP_ENDIAN) != 0)
  #ifdef PNG_WRITE_SWAP_SUPPORTED
        png_set_swap(png_ptr);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_SWAP_ENDIAN not supported");
  #endif
  
     /* Swap bits of 1-bit, 2-bit, 4-bit packed pixel formats */
     if ((transforms & PNG_TRANSFORM_PACKSWAP) != 0)
  #ifdef PNG_WRITE_PACKSWAP_SUPPORTED
        png_set_packswap(png_ptr);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_PACKSWAP not supported");
  #endif
  
     /* Invert the alpha channel from opacity to transparency */
     if ((transforms & PNG_TRANSFORM_INVERT_ALPHA) != 0)
  #ifdef PNG_WRITE_INVERT_ALPHA_SUPPORTED
        png_set_invert_alpha(png_ptr);
  #else
        png_app_error(png_ptr, "PNG_TRANSFORM_INVERT_ALPHA not supported");
  #endif
  
     /* ----------------------- end of transformations ------------------- */
  
     /* Write the bits */
     png_write_image(png_ptr, info_ptr->row_pointers);
  
     /* It is REQUIRED to call this to finish writing the rest of the file */
     png_write_end(png_ptr, info_ptr);
  
     PNG_UNUSED(params)
  }
  #endif
  
  #ifdef PNG_WRITE_APNG_SUPPORTED
  void PNGAPI
  png_write_frame_head(png_structp png_ptr, png_infop info_ptr,
      png_bytepp row_pointers, png_uint_32 width, png_uint_32 height,
      png_uint_32 x_offset, png_uint_32 y_offset,
      png_uint_16 delay_num, png_uint_16 delay_den, png_byte dispose_op,
      png_byte blend_op)
  {
      png_debug(1, "in png_write_frame_head");
  
      /* there is a chance this has been set after png_write_info was called,
      * so it would be set but not written. is there a way to be sure? */
      if (!(info_ptr->valid & PNG_INFO_acTL))
          png_error(png_ptr, "png_write_frame_head(): acTL not set");
  
      png_write_reset(png_ptr);
  
      png_write_reinit(png_ptr, info_ptr, width, height);
  
      if ( !(png_ptr->num_frames_written == 0 &&
             (png_ptr->apng_flags & PNG_FIRST_FRAME_HIDDEN) ) )
          png_write_fcTL(png_ptr, width, height, x_offset, y_offset,
                         delay_num, delay_den, dispose_op, blend_op);
  
      PNG_UNUSED(row_pointers)
  }
  
  void PNGAPI
  png_write_frame_tail(png_structp png_ptr, png_infop info_ptr)
  {
      png_debug(1, "in png_write_frame_tail");
  
      png_ptr->num_frames_written++;
  
      PNG_UNUSED(info_ptr)
  }
  #endif /* PNG_WRITE_APNG_SUPPORTED */
  
  #ifdef PNG_SIMPLIFIED_WRITE_SUPPORTED
  /* Initialize the write structure - general purpose utility. */
  static int
  png_image_write_init(png_imagep image)
  {
     png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, image,
         png_safe_error, png_safe_warning);
  
     if (png_ptr != NULL)
     {
        png_infop info_ptr = png_create_info_struct(png_ptr);
  
        if (info_ptr != NULL)
        {
           png_controlp control = png_voidcast(png_controlp,
               png_malloc_warn(png_ptr, (sizeof *control)));
  
           if (control != NULL)
           {
              memset(control, 0, (sizeof *control));
  
              control->png_ptr = png_ptr;
              control->info_ptr = info_ptr;
              control->for_write = 1;
  
              image->opaque = control;
              return 1;
           }
  
           /* Error clean up */
           png_destroy_info_struct(png_ptr, &info_ptr);
        }
  
        png_destroy_write_struct(&png_ptr, NULL);
     }
  
     return png_image_error(image, "png_image_write_: out of memory");
  }
  
  /* Arguments to png_image_write_main: */
  typedef struct
  {
     /* Arguments: */
     png_imagep      image;
     png_const_voidp buffer;
     png_int_32      row_stride;
     png_const_voidp colormap;
     int             convert_to_8bit;
     /* Local variables: */
     png_const_voidp first_row;
     ptrdiff_t       row_bytes;
     png_voidp       local_row;
     /* Byte count for memory writing */
     png_bytep        memory;
     png_alloc_size_t memory_bytes; /* not used for STDIO */
     png_alloc_size_t output_bytes; /* running total */
  } png_image_write_control;
  
  /* Write png_uint_16 input to a 16-bit PNG; the png_ptr has already been set to
   * do any necessary byte swapping.  The component order is defined by the
   * png_image format value.
   */
  static int
  png_write_image_16bit(png_voidp argument)
  {
     png_image_write_control *display = png_voidcast(png_image_write_control*,
         argument);
     png_imagep image = display->image;
     png_structrp png_ptr = image->opaque->png_ptr;
  
     png_const_uint_16p input_row = png_voidcast(png_const_uint_16p,
         display->first_row);
     png_uint_16p output_row = png_voidcast(png_uint_16p, display->local_row);
     png_uint_16p row_end;
     const unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
         3 : 1;
     int aindex = 0;
     png_uint_32 y = image->height;
  
     if ((image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
     {
  #   ifdef PNG_SIMPLIFIED_WRITE_AFIRST_SUPPORTED
        if ((image->format & PNG_FORMAT_FLAG_AFIRST) != 0)
        {
           aindex = -1;
           ++input_row; /* To point to the first component */
           ++output_row;
        }
           else
              aindex = (int)channels;
  #     else
           aindex = (int)channels;
  #     endif
     }
  
     else
        png_error(png_ptr, "png_write_image: internal call error");
  
     /* Work out the output row end and count over this, note that the increment
      * above to 'row' means that row_end can actually be beyond the end of the
      * row; this is correct.
      */
     row_end = output_row + image->width * (channels+1);
  
     for (; y > 0; --y)
     {
        png_const_uint_16p in_ptr = input_row;
        png_uint_16p out_ptr = output_row;
  
        while (out_ptr < row_end)
        {
           const png_uint_16 alpha = in_ptr[aindex];
           png_uint_32 reciprocal = 0;
           int c;
  
           out_ptr[aindex] = alpha;
  
           /* Calculate a reciprocal.  The correct calculation is simply
            * component/alpha*65535 << 15. (I.e. 15 bits of precision); this
            * allows correct rounding by adding .5 before the shift.  'reciprocal'
            * is only initialized when required.
            */
           if (alpha > 0 && alpha < 65535)
              reciprocal = ((0xffff<<15)+(alpha>>1))/alpha;
  
           c = (int)channels;
           do /* always at least one channel */
           {
              png_uint_16 component = *in_ptr++;
  
              /* The following gives 65535 for an alpha of 0, which is fine,
               * otherwise if 0/0 is represented as some other value there is more
               * likely to be a discontinuity which will probably damage
               * compression when moving from a fully transparent area to a
               * nearly transparent one.  (The assumption here is that opaque
               * areas tend not to be 0 intensity.)
               */
              if (component >= alpha)
                 component = 65535;
  
              /* component<alpha, so component/alpha is less than one and
               * component*reciprocal is less than 2^31.
               */
              else if (component > 0 && alpha < 65535)
              {
                 png_uint_32 calc = component * reciprocal;
                 calc += 16384; /* round to nearest */
                 component = (png_uint_16)(calc >> 15);
              }
  
              *out_ptr++ = component;
           }
           while (--c > 0);
  
           /* Skip to next component (skip the intervening alpha channel) */
           ++in_ptr;
           ++out_ptr;
        }
  
        png_write_row(png_ptr, png_voidcast(png_const_bytep, display->local_row));
        input_row += (png_uint_16)display->row_bytes/(sizeof (png_uint_16));
     }
  
     return 1;
  }
  
  /* Given 16-bit input (1 to 4 channels) write 8-bit output.  If an alpha channel
   * is present it must be removed from the components, the components are then
   * written in sRGB encoding.  No components are added or removed.
   *
   * Calculate an alpha reciprocal to reverse pre-multiplication.  As above the
   * calculation can be done to 15 bits of accuracy; however, the output needs to
   * be scaled in the range 0..255*65535, so include that scaling here.
   */
  #   define UNP_RECIPROCAL(alpha) ((((0xffff*0xff)<<7)+(alpha>>1))/alpha)
  
  static png_byte
  png_unpremultiply(png_uint_32 component, png_uint_32 alpha,
      png_uint_32 reciprocal/*from the above macro*/)
  {
     /* The following gives 1.0 for an alpha of 0, which is fine, otherwise if 0/0
      * is represented as some other value there is more likely to be a
      * discontinuity which will probably damage compression when moving from a
      * fully transparent area to a nearly transparent one.  (The assumption here
      * is that opaque areas tend not to be 0 intensity.)
      *
      * There is a rounding problem here; if alpha is less than 128 it will end up
      * as 0 when scaled to 8 bits.  To avoid introducing spurious colors into the
      * output change for this too.
      */
     if (component >= alpha || alpha < 128)
        return 255;
  
     /* component<alpha, so component/alpha is less than one and
      * component*reciprocal is less than 2^31.
      */
     else if (component > 0)
     {
        /* The test is that alpha/257 (rounded) is less than 255, the first value
         * that becomes 255 is 65407.
         * NOTE: this must agree with the PNG_DIV257 macro (which must, therefore,
         * be exact!)  [Could also test reciprocal != 0]
         */
        if (alpha < 65407)
        {
           component *= reciprocal;
           component += 64; /* round to nearest */
           component >>= 7;
        }
  
        else
           component *= 255;
  
        /* Convert the component to sRGB. */
        return (png_byte)PNG_sRGB_FROM_LINEAR(component);
     }
  
     else
        return 0;
  }
  
  static int
  png_write_image_8bit(png_voidp argument)
  {
     png_image_write_control *display = png_voidcast(png_image_write_control*,
         argument);
     png_imagep image = display->image;
     png_structrp png_ptr = image->opaque->png_ptr;
  
     png_const_uint_16p input_row = png_voidcast(png_const_uint_16p,
         display->first_row);
     png_bytep output_row = png_voidcast(png_bytep, display->local_row);
     png_uint_32 y = image->height;
     const unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
         3 : 1;
  
     if ((image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
     {
        png_bytep row_end;
        int aindex;
  
  #   ifdef PNG_SIMPLIFIED_WRITE_AFIRST_SUPPORTED
        if ((image->format & PNG_FORMAT_FLAG_AFIRST) != 0)
        {
           aindex = -1;
           ++input_row; /* To point to the first component */
           ++output_row;
        }
  
        else
  #   endif
        aindex = (int)channels;
  
        /* Use row_end in place of a loop counter: */
        row_end = output_row + image->width * (channels+1);
  
        for (; y > 0; --y)
        {
           png_const_uint_16p in_ptr = input_row;
           png_bytep out_ptr = output_row;
  
           while (out_ptr < row_end)
           {
              png_uint_16 alpha = in_ptr[aindex];
              png_byte alphabyte = (png_byte)PNG_DIV257(alpha);
              png_uint_32 reciprocal = 0;
              int c;
  
              /* Scale and write the alpha channel. */
              out_ptr[aindex] = alphabyte;
  
              if (alphabyte > 0 && alphabyte < 255)
                 reciprocal = UNP_RECIPROCAL(alpha);
  
              c = (int)channels;
              do /* always at least one channel */
                 *out_ptr++ = png_unpremultiply(*in_ptr++, alpha, reciprocal);
              while (--c > 0);
  
              /* Skip to next component (skip the intervening alpha channel) */
              ++in_ptr;
              ++out_ptr;
           } /* while out_ptr < row_end */
  
           png_write_row(png_ptr, png_voidcast(png_const_bytep,
               display->local_row));
           input_row += (png_uint_16)display->row_bytes/(sizeof (png_uint_16));
        } /* while y */
     }
  
     else
     {
        /* No alpha channel, so the row_end really is the end of the row and it
         * is sufficient to loop over the components one by one.
         */
        png_bytep row_end = output_row + image->width * channels;
  
        for (; y > 0; --y)
        {
           png_const_uint_16p in_ptr = input_row;
           png_bytep out_ptr = output_row;
  
           while (out_ptr < row_end)
           {
              png_uint_32 component = *in_ptr++;
  
              component *= 255;
              *out_ptr++ = (png_byte)PNG_sRGB_FROM_LINEAR(component);
           }
  
           png_write_row(png_ptr, output_row);
           input_row += (png_uint_16)display->row_bytes/(sizeof (png_uint_16));
        }
     }
  
     return 1;
  }
  
  static void
  png_image_set_PLTE(png_image_write_control *display)
  {
     const png_imagep image = display->image;
     const void *cmap = display->colormap;
     const int entries = image->colormap_entries > 256 ? 256 :
         (int)image->colormap_entries;
  
     /* NOTE: the caller must check for cmap != NULL and entries != 0 */
     const png_uint_32 format = image->format;
     const unsigned int channels = PNG_IMAGE_SAMPLE_CHANNELS(format);
  
  #   if defined(PNG_FORMAT_BGR_SUPPORTED) &&\
        defined(PNG_SIMPLIFIED_WRITE_AFIRST_SUPPORTED)
        const int afirst = (format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
            (format & PNG_FORMAT_FLAG_ALPHA) != 0;
  #   else
  #     define afirst 0
  #   endif
  
  #   ifdef PNG_FORMAT_BGR_SUPPORTED
        const int bgr = (format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
  #   else
  #     define bgr 0
  #   endif
  
     int i, num_trans;
     png_color palette[256];
     png_byte tRNS[256];
  
     memset(tRNS, 255, (sizeof tRNS));
     memset(palette, 0, (sizeof palette));
  
     for (i=num_trans=0; i<entries; ++i)
     {
        /* This gets automatically converted to sRGB with reversal of the
         * pre-multiplication if the color-map has an alpha channel.
         */
        if ((format & PNG_FORMAT_FLAG_LINEAR) != 0)
        {
           png_const_uint_16p entry = png_voidcast(png_const_uint_16p, cmap);
  
           entry += (unsigned int)i * channels;
  
           if ((channels & 1) != 0) /* no alpha */
           {
              if (channels >= 3) /* RGB */
              {
                 palette[i].blue = (png_byte)PNG_sRGB_FROM_LINEAR(255 *
                     entry[(2 ^ bgr)]);
                 palette[i].green = (png_byte)PNG_sRGB_FROM_LINEAR(255 *
                     entry[1]);
                 palette[i].red = (png_byte)PNG_sRGB_FROM_LINEAR(255 *
                     entry[bgr]);
              }
  
              else /* Gray */
                 palette[i].blue = palette[i].red = palette[i].green =
                    (png_byte)PNG_sRGB_FROM_LINEAR(255 * *entry);
           }
  
           else /* alpha */
           {
              png_uint_16 alpha = entry[afirst ? 0 : channels-1];
              png_byte alphabyte = (png_byte)PNG_DIV257(alpha);
              png_uint_32 reciprocal = 0;
  
              /* Calculate a reciprocal, as in the png_write_image_8bit code above
               * this is designed to produce a value scaled to 255*65535 when
               * divided by 128 (i.e. asr 7).
               */
              if (alphabyte > 0 && alphabyte < 255)
                 reciprocal = (((0xffff*0xff)<<7)+(alpha>>1))/alpha;
  
              tRNS[i] = alphabyte;
              if (alphabyte < 255)
                 num_trans = i+1;
  
              if (channels >= 3) /* RGB */
              {
                 palette[i].blue = png_unpremultiply(entry[afirst + (2 ^ bgr)],
                     alpha, reciprocal);
                 palette[i].green = png_unpremultiply(entry[afirst + 1], alpha,
                     reciprocal);
                 palette[i].red = png_unpremultiply(entry[afirst + bgr], alpha,
                     reciprocal);
              }
  
              else /* gray */
                 palette[i].blue = palette[i].red = palette[i].green =
                     png_unpremultiply(entry[afirst], alpha, reciprocal);
           }
        }
  
        else /* Color-map has sRGB values */
        {
           png_const_bytep entry = png_voidcast(png_const_bytep, cmap);
  
           entry += (unsigned int)i * channels;
  
           switch (channels)
           {
              case 4:
                 tRNS[i] = entry[afirst ? 0 : 3];
                 if (tRNS[i] < 255)
                    num_trans = i+1;
                 /* FALLTHROUGH */
              case 3:
                 palette[i].blue = entry[afirst + (2 ^ bgr)];
                 palette[i].green = entry[afirst + 1];
                 palette[i].red = entry[afirst + bgr];
                 break;
  
              case 2:
                 tRNS[i] = entry[1 ^ afirst];
                 if (tRNS[i] < 255)
                    num_trans = i+1;
                 /* FALLTHROUGH */
              case 1:
                 palette[i].blue = palette[i].red = palette[i].green =
                    entry[afirst];
                 break;
  
              default:
                 break;
           }
        }
     }
  
  #   ifdef afirst
  #     undef afirst
  #   endif
  #   ifdef bgr
  #     undef bgr
  #   endif
  
     png_set_PLTE(image->opaque->png_ptr, image->opaque->info_ptr, palette,
         entries);
  
     if (num_trans > 0)
        png_set_tRNS(image->opaque->png_ptr, image->opaque->info_ptr, tRNS,
            num_trans, NULL);
  
     image->colormap_entries = (png_uint_32)entries;
  }
  
  static int
  png_image_write_main(png_voidp argument)
  {
     png_image_write_control *display = png_voidcast(png_image_write_control*,
         argument);
     png_imagep image = display->image;
     png_structrp png_ptr = image->opaque->png_ptr;
     png_inforp info_ptr = image->opaque->info_ptr;
     png_uint_32 format = image->format;
  
     /* The following four ints are actually booleans */
     int colormap = (format & PNG_FORMAT_FLAG_COLORMAP);
     int linear = !colormap && (format & PNG_FORMAT_FLAG_LINEAR); /* input */
     int alpha = !colormap && (format & PNG_FORMAT_FLAG_ALPHA);
     int write_16bit = linear && (display->convert_to_8bit == 0);
  
  #   ifdef PNG_BENIGN_ERRORS_SUPPORTED
        /* Make sure we error out on any bad situation */
        png_set_benign_errors(png_ptr, 0/*error*/);
  #   endif
  
     /* Default the 'row_stride' parameter if required, also check the row stride
      * and total image size to ensure that they are within the system limits.
      */
     {
        const unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
  
        if (image->width <= 0x7fffffffU/channels) /* no overflow */
        {
           png_uint_32 check;
           const png_uint_32 png_row_stride = image->width * channels;
  
           if (display->row_stride == 0)
              display->row_stride = (png_int_32)/*SAFE*/png_row_stride;
  
           if (display->row_stride < 0)
              check = (png_uint_32)(-display->row_stride);
  
           else
              check = (png_uint_32)display->row_stride;
  
           if (check >= png_row_stride)
           {
              /* Now check for overflow of the image buffer calculation; this
               * limits the whole image size to 32 bits for API compatibility with
               * the current, 32-bit, PNG_IMAGE_BUFFER_SIZE macro.
               */
              if (image->height > 0xffffffffU/png_row_stride)
                 png_error(image->opaque->png_ptr, "memory image too large");
           }
  
           else
              png_error(image->opaque->png_ptr, "supplied row stride too small");
        }
  
        else
           png_error(image->opaque->png_ptr, "image row stride too large");
     }
  
     /* Set the required transforms then write the rows in the correct order. */
     if ((format & PNG_FORMAT_FLAG_COLORMAP) != 0)
     {
        if (display->colormap != NULL && image->colormap_entries > 0)
        {
           png_uint_32 entries = image->colormap_entries;
  
           png_set_IHDR(png_ptr, info_ptr, image->width, image->height,
               entries > 16 ? 8 : (entries > 4 ? 4 : (entries > 2 ? 2 : 1)),
               PNG_COLOR_TYPE_PALETTE, PNG_INTERLACE_NONE,
               PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
  
           png_image_set_PLTE(display);
        }
  
        else
           png_error(image->opaque->png_ptr,
               "no color-map for color-mapped image");
     }
  
     else
        png_set_IHDR(png_ptr, info_ptr, image->width, image->height,
            write_16bit ? 16 : 8,
            ((format & PNG_FORMAT_FLAG_COLOR) ? PNG_COLOR_MASK_COLOR : 0) +
            ((format & PNG_FORMAT_FLAG_ALPHA) ? PNG_COLOR_MASK_ALPHA : 0),
            PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
  
     /* Counter-intuitively the data transformations must be called *after*
      * png_write_info, not before as in the read code, but the 'set' functions
      * must still be called before.  Just set the color space information, never
      * write an interlaced image.
      */
  
     if (write_16bit != 0)
     {
        /* The gamma here is 1.0 (linear) and the cHRM chunk matches sRGB. */
        png_set_gAMA_fixed(png_ptr, info_ptr, PNG_GAMMA_LINEAR);
  
        if ((image->flags & PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB) == 0)
           png_set_cHRM_fixed(png_ptr, info_ptr,
               /* color      x       y */
               /* white */ 31270, 32900,
               /* red   */ 64000, 33000,
               /* green */ 30000, 60000,
               /* blue  */ 15000,  6000
           );
     }
  
     else if ((image->flags & PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB) == 0)
        png_set_sRGB(png_ptr, info_ptr, PNG_sRGB_INTENT_PERCEPTUAL);
  
     /* Else writing an 8-bit file and the *colors* aren't sRGB, but the 8-bit
      * space must still be gamma encoded.
      */
     else
        png_set_gAMA_fixed(png_ptr, info_ptr, PNG_GAMMA_sRGB_INVERSE);
  
     /* Write the file header. */
     png_write_info(png_ptr, info_ptr);
  
     /* Now set up the data transformations (*after* the header is written),
      * remove the handled transformations from the 'format' flags for checking.
      *
      * First check for a little endian system if writing 16-bit files.
      */
     if (write_16bit != 0)
     {
        PNG_CONST png_uint_16 le = 0x0001;
  
        if ((*(png_const_bytep) & le) != 0)
           png_set_swap(png_ptr);
     }
  
  #   ifdef PNG_SIMPLIFIED_WRITE_BGR_SUPPORTED
        if ((format & PNG_FORMAT_FLAG_BGR) != 0)
        {
           if (colormap == 0 && (format & PNG_FORMAT_FLAG_COLOR) != 0)
              png_set_bgr(png_ptr);
           format &= ~PNG_FORMAT_FLAG_BGR;
        }
  #   endif
  
  #   ifdef PNG_SIMPLIFIED_WRITE_AFIRST_SUPPORTED
        if ((format & PNG_FORMAT_FLAG_AFIRST) != 0)
        {
           if (colormap == 0 && (format & PNG_FORMAT_FLAG_ALPHA) != 0)
              png_set_swap_alpha(png_ptr);
           format &= ~PNG_FORMAT_FLAG_AFIRST;
        }
  #   endif
  
     /* If there are 16 or fewer color-map entries we wrote a lower bit depth
      * above, but the application data is still byte packed.
      */
     if (colormap != 0 && image->colormap_entries <= 16)
        png_set_packing(png_ptr);
  
     /* That should have handled all (both) the transforms. */
     if ((format & ~(png_uint_32)(PNG_FORMAT_FLAG_COLOR | PNG_FORMAT_FLAG_LINEAR |
           PNG_FORMAT_FLAG_ALPHA | PNG_FORMAT_FLAG_COLORMAP)) != 0)
        png_error(png_ptr, "png_write_image: unsupported transformation");
  
     {
        png_const_bytep row = png_voidcast(png_const_bytep, display->buffer);
        ptrdiff_t row_bytes = display->row_stride;
  
        if (linear != 0)
           row_bytes *= (sizeof (png_uint_16));
  
        if (row_bytes < 0)
           row += (image->height-1) * (-row_bytes);
  
        display->first_row = row;
        display->row_bytes = row_bytes;
     }
  
     /* Apply 'fast' options if the flag is set. */
     if ((image->flags & PNG_IMAGE_FLAG_FAST) != 0)
     {
        png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_NO_FILTERS);
        /* NOTE: determined by experiment using pngstest, this reflects some
         * balance between the time to write the image once and the time to read
         * it about 50 times.  The speed-up in pngstest was about 10-20% of the
         * total (user) time on a heavily loaded system.
         */
  #   ifdef PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED
        png_set_compression_level(png_ptr, 3);
  #   endif
     }
  
     /* Check for the cases that currently require a pre-transform on the row
      * before it is written.  This only applies when the input is 16-bit and
      * either there is an alpha channel or it is converted to 8-bit.
      */
     if ((linear != 0 && alpha != 0 ) ||
         (colormap == 0 && display->convert_to_8bit != 0))
     {
        png_bytep row = png_voidcast(png_bytep, png_malloc(png_ptr,
            png_get_rowbytes(png_ptr, info_ptr)));
        int result;
  
        display->local_row = row;
        if (write_16bit != 0)
           result = png_safe_execute(image, png_write_image_16bit, display);
        else
           result = png_safe_execute(image, png_write_image_8bit, display);
        display->local_row = NULL;
  
        png_free(png_ptr, row);
  
        /* Skip the 'write_end' on error: */
        if (result == 0)
           return 0;
     }
  
     /* Otherwise this is the case where the input is in a format currently
      * supported by the rest of the libpng write code; call it directly.
      */
     else
     {
        png_const_bytep row = png_voidcast(png_const_bytep, display->first_row);
        ptrdiff_t row_bytes = display->row_bytes;
        png_uint_32 y = image->height;
  
        for (; y > 0; --y)
        {
           png_write_row(png_ptr, row);
           row += row_bytes;
        }
     }
  
     png_write_end(png_ptr, info_ptr);
     return 1;
  }
  
  
  static void (PNGCBAPI
  image_memory_write)(png_structp png_ptr, png_bytep/*const*/ data,
      png_size_t size)
  {
     png_image_write_control *display = png_voidcast(png_image_write_control*,
         png_ptr->io_ptr/*backdoor: png_get_io_ptr(png_ptr)*/);
     const png_alloc_size_t ob = display->output_bytes;
  
     /* Check for overflow; this should never happen: */
     if (size <= ((png_alloc_size_t)-1) - ob)
     {
        /* I don't think libpng ever does this, but just in case: */
        if (size > 0)
        {
           if (display->memory_bytes >= ob+size) /* writing */
              memcpy(display->memory+ob, data, size);
  
           /* Always update the size: */
           display->output_bytes = ob+size;
        }
     }
  
     else
        png_error(png_ptr, "png_image_write_to_memory: PNG too big");
  }
  
  static void (PNGCBAPI
  image_memory_flush)(png_structp png_ptr)
  {
     PNG_UNUSED(png_ptr)
  }
  
  static int
  png_image_write_memory(png_voidp argument)
  {
     png_image_write_control *display = png_voidcast(png_image_write_control*,
         argument);
  
     /* The rest of the memory-specific init and write_main in an error protected
      * environment.  This case needs to use callbacks for the write operations
      * since libpng has no built in support for writing to memory.
      */
     png_set_write_fn(display->image->opaque->png_ptr, display/*io_ptr*/,
         image_memory_write, image_memory_flush);
  
     return png_image_write_main(display);
  }
  
  int PNGAPI
  png_image_write_to_memory(png_imagep image, void *memory,
      png_alloc_size_t * PNG_RESTRICT memory_bytes, int convert_to_8bit,
      const void *buffer, png_int_32 row_stride, const void *colormap)
  {
     /* Write the image to the given buffer, or count the bytes if it is NULL */
     if (image != NULL && image->version == PNG_IMAGE_VERSION)
     {
        if (memory_bytes != NULL && buffer != NULL)
        {
           /* This is to give the caller an easier error detection in the NULL
            * case and guard against uninitialized variable problems:
            */
           if (memory == NULL)
              *memory_bytes = 0;
  
           if (png_image_write_init(image) != 0)
           {
              png_image_write_control display;
              int result;
  
              memset(&display, 0, (sizeof display));
              display.image = image;
              display.buffer = buffer;
              display.row_stride = row_stride;
              display.colormap = colormap;
              display.convert_to_8bit = convert_to_8bit;
              display.memory = png_voidcast(png_bytep, memory);
              display.memory_bytes = *memory_bytes;
              display.output_bytes = 0;
  
              result = png_safe_execute(image, png_image_write_memory, &display);
              png_image_free(image);
  
              /* write_memory returns true even if we ran out of buffer. */
              if (result)
              {
                 /* On out-of-buffer this function returns '0' but still updates
                  * memory_bytes:
                  */
                 if (memory != NULL && display.output_bytes > *memory_bytes)
                    result = 0;
  
                 *memory_bytes = display.output_bytes;
              }
  
              return result;
           }
  
           else
              return 0;
        }
  
        else
           return png_image_error(image,
               "png_image_write_to_memory: invalid argument");
     }
  
     else if (image != NULL)
        return png_image_error(image,
            "png_image_write_to_memory: incorrect PNG_IMAGE_VERSION");
  
     else
        return 0;
  }
  
  #ifdef PNG_SIMPLIFIED_WRITE_STDIO_SUPPORTED
  int PNGAPI
  png_image_write_to_stdio(png_imagep image, FILE *file, int convert_to_8bit,
      const void *buffer, png_int_32 row_stride, const void *colormap)
  {
     /* Write the image to the given (FILE*). */
     if (image != NULL && image->version == PNG_IMAGE_VERSION)
     {
        if (file != NULL && buffer != NULL)
        {
           if (png_image_write_init(image) != 0)
           {
              png_image_write_control display;
              int result;
  
              /* This is slightly evil, but png_init_io doesn't do anything other
               * than this and we haven't changed the standard IO functions so
               * this saves a 'safe' function.
               */
              image->opaque->png_ptr->io_ptr = file;
  
              memset(&display, 0, (sizeof display));
              display.image = image;
              display.buffer = buffer;
              display.row_stride = row_stride;
              display.colormap = colormap;
              display.convert_to_8bit = convert_to_8bit;
  
              result = png_safe_execute(image, png_image_write_main, &display);
              png_image_free(image);
              return result;
           }
  
           else
              return 0;
        }
  
        else
           return png_image_error(image,
               "png_image_write_to_stdio: invalid argument");
     }
  
     else if (image != NULL)
        return png_image_error(image,
            "png_image_write_to_stdio: incorrect PNG_IMAGE_VERSION");
  
     else
        return 0;
  }
  
  int PNGAPI
  png_image_write_to_file(png_imagep image, const char *file_name,
      int convert_to_8bit, const void *buffer, png_int_32 row_stride,
      const void *colormap)
  {
     /* Write the image to the named file. */
     if (image != NULL && image->version == PNG_IMAGE_VERSION)
     {
        if (file_name != NULL && buffer != NULL)
        {
           FILE *fp = fopen(file_name, "wb");
  
           if (fp != NULL)
           {
              if (png_image_write_to_stdio(image, fp, convert_to_8bit, buffer,
                  row_stride, colormap) != 0)
              {
                 int error; /* from fflush/fclose */
  
                 /* Make sure the file is flushed correctly. */
                 if (fflush(fp) == 0 && ferror(fp) == 0)
                 {
                    if (fclose(fp) == 0)
                       return 1;
  
                    error = errno; /* from fclose */
                 }
  
                 else
                 {
                    error = errno; /* from fflush or ferror */
                    (void)fclose(fp);
                 }
  
                 (void)remove(file_name);
                 /* The image has already been cleaned up; this is just used to
                  * set the error (because the original write succeeded).
                  */
                 return png_image_error(image, strerror(error));
              }
  
              else
              {
                 /* Clean up: just the opened file. */
                 (void)fclose(fp);
                 (void)remove(file_name);
                 return 0;
              }
           }
  
           else
              return png_image_error(image, strerror(errno));
        }
  
        else
           return png_image_error(image,
               "png_image_write_to_file: invalid argument");
     }
  
     else if (image != NULL)
        return png_image_error(image,
            "png_image_write_to_file: incorrect PNG_IMAGE_VERSION");
  
     else
        return 0;
  }
  #endif /* SIMPLIFIED_WRITE_STDIO */
  #endif /* SIMPLIFIED_WRITE */
  #endif /* WRITE */
  