pngwutil.c

一个国人自己实现图像库的程序（有参考价值）

   if (key_len > 79)
   {
      png_warning(png_ptr, "keyword length must be 1 - 79 characters");
      new_key[79] = '\0';
      key_len = 79;
   }

   return (key_len);
}
#endif

#if defined(PNG_WRITE_tEXt_SUPPORTED)
/* write a tEXt chunk */
void /* PRIVATE */
png_write_tEXt(png_structp png_ptr, png_charp key, png_charp text,
   png_size_t text_len)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_tEXt;
#endif
   png_size_t key_len;
   png_charp new_key;

   png_debug(1, "in png_write_tEXt\n");
   if (key == NULL || (key_len = png_check_keyword(png_ptr, key, &new_key))==0)
   {
      png_warning(png_ptr, "Empty keyword in tEXt chunk");
      return;
   }

   if (text == NULL || *text == '\0')
      text_len = 0;
   else
      text_len = png_strlen(text);

   /* make sure we include the 0 after the key */
   png_write_chunk_start(png_ptr, (png_bytep)png_tEXt, (png_uint_32)key_len+text_len+1);
   /*
    * We leave it to the application to meet PNG-1.0 requirements on the
    * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
    * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
    * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
    */
   png_write_chunk_data(png_ptr, (png_bytep)new_key, key_len + 1);
   if (text_len)
      png_write_chunk_data(png_ptr, (png_bytep)text, text_len);

   png_write_chunk_end(png_ptr);
   png_free(png_ptr, new_key);
}
#endif

#if defined(PNG_WRITE_zTXt_SUPPORTED)
/* write a compressed text chunk */
void /* PRIVATE */
png_write_zTXt(png_structp png_ptr, png_charp key, png_charp text,
   png_size_t text_len, int compression)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_zTXt;
#endif
   png_size_t key_len;
   char buf[1];
   png_charp new_key;
   compression_state comp;

   png_debug(1, "in png_write_zTXt\n");

   if (key == NULL || (key_len = png_check_keyword(png_ptr, key, &new_key))==0)
   {
      png_warning(png_ptr, "Empty keyword in zTXt chunk");
      return;
   }

   if (text == NULL || *text == '\0' || compression==PNG_TEXT_COMPRESSION_NONE)
   {
      png_write_tEXt(png_ptr, new_key, text, (png_size_t)0);
      png_free(png_ptr, new_key);
      return;
   }

   text_len = png_strlen(text);

   png_free(png_ptr, new_key);

   /* compute the compressed data; do it now for the length */
   text_len = png_text_compress(png_ptr, text, text_len, compression,
       &comp);

   /* write start of chunk */
   png_write_chunk_start(png_ptr, (png_bytep)png_zTXt, (png_uint_32)
      (key_len+text_len+2));
   /* write key */
   png_write_chunk_data(png_ptr, (png_bytep)key, key_len + 1);
   buf[0] = (png_byte)compression;
   /* write compression */
   png_write_chunk_data(png_ptr, (png_bytep)buf, (png_size_t)1);
   /* write the compressed data */
   png_write_compressed_data_out(png_ptr, &comp);

   /* close the chunk */
   png_write_chunk_end(png_ptr);
}
#endif

#if defined(PNG_WRITE_iTXt_SUPPORTED)
/* write an iTXt chunk */
void /* PRIVATE */
png_write_iTXt(png_structp png_ptr, int compression, png_charp key,
    png_charp lang, png_charp lang_key, png_charp text)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_iTXt;
#endif
   png_size_t lang_len, key_len, lang_key_len, text_len;
   png_charp new_lang, new_key;
   png_byte cbuf[2];
   compression_state comp;

   png_debug(1, "in png_write_iTXt\n");

   if (key == NULL || (key_len = png_check_keyword(png_ptr, key, &new_key))==0)
   {
      png_warning(png_ptr, "Empty keyword in iTXt chunk");
      return;
   }
   if (lang == NULL || (lang_len = png_check_keyword(png_ptr, lang,
      &new_lang))==0)
   {
      png_warning(png_ptr, "Empty language field in iTXt chunk");
      return;
   }
   lang_key_len = png_strlen(lang_key);
   text_len = png_strlen(text);

   if (text == NULL || *text == '\0')
      text_len = 0;

   /* compute the compressed data; do it now for the length */
   text_len = png_text_compress(png_ptr, text, text_len, compression-2,
      &comp);

   /* make sure we include the compression flag, the compression byte,
    * and the NULs after the key, lang, and lang_key parts */

   png_write_chunk_start(png_ptr, (png_bytep)png_iTXt,
          (png_uint_32)(
        5 /* comp byte, comp flag, terminators for key, lang and lang_key */
        + key_len
        + lang_len
        + lang_key_len
        + text_len));

   /*
    * We leave it to the application to meet PNG-1.0 requirements on the
    * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
    * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
    * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
    */
   png_write_chunk_data(png_ptr, (png_bytep)new_key, key_len + 1);

   /* set the compression flag */
   if (compression == PNG_ITXT_COMPRESSION_NONE || \
       compression == PNG_TEXT_COMPRESSION_NONE)
       cbuf[0] = 0;
   else /* compression == PNG_ITXT_COMPRESSION_zTXt */
       cbuf[0] = 1;
   /* set the compression method */
   cbuf[1] = 0;
   png_write_chunk_data(png_ptr, cbuf, 2);

   png_write_chunk_data(png_ptr, (png_bytep)new_lang, lang_len + 1);
   png_write_chunk_data(png_ptr, (png_bytep)lang_key, lang_key_len+1);
   png_write_chunk_data(png_ptr, '\0', 1);

   png_write_compressed_data_out(png_ptr, &comp);

   png_write_chunk_end(png_ptr);
   png_free(png_ptr, new_key);
   png_free(png_ptr, new_lang);
}
#endif

#if defined(PNG_WRITE_oFFs_SUPPORTED)
/* write the oFFs chunk */
void /* PRIVATE */
png_write_oFFs(png_structp png_ptr, png_int_32 x_offset, png_int_32 y_offset,
   int unit_type)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_oFFs;
#endif
   png_byte buf[9];

   png_debug(1, "in png_write_oFFs\n");
   if (unit_type >= PNG_OFFSET_LAST)
      png_warning(png_ptr, "Unrecognized unit type for oFFs chunk");

   png_save_int_32(buf, x_offset);
   png_save_int_32(buf + 4, y_offset);
   buf[8] = (png_byte)unit_type;

   png_write_chunk(png_ptr, (png_bytep)png_oFFs, buf, (png_size_t)9);
}
#endif

#if defined(PNG_WRITE_pCAL_SUPPORTED)
/* write the pCAL chunk (described in the PNG extensions document) */
void /* PRIVATE */
png_write_pCAL(png_structp png_ptr, png_charp purpose, png_int_32 X0,
   png_int_32 X1, int type, int nparams, png_charp units, png_charpp params)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_pCAL;
#endif
   png_size_t purpose_len, units_len, total_len;
   png_uint_32p params_len;
   png_byte buf[10];
   png_charp new_purpose;
   int i;

   png_debug1(1, "in png_write_pCAL (%d parameters)\n", nparams);
   if (type >= PNG_EQUATION_LAST)
      png_warning(png_ptr, "Unrecognized equation type for pCAL chunk");

   purpose_len = png_check_keyword(png_ptr, purpose, &new_purpose) + 1;
   png_debug1(3, "pCAL purpose length = %d\n", (int)purpose_len);
   units_len = png_strlen(units) + (nparams == 0 ? 0 : 1);
   png_debug1(3, "pCAL units length = %d\n", (int)units_len);
   total_len = purpose_len + units_len + 10;

   params_len = (png_uint_32p)png_malloc(png_ptr, (png_uint_32)(nparams
      *sizeof(png_uint_32)));

   /* Find the length of each parameter, making sure we don't count the
      null terminator for the last parameter. */
   for (i = 0; i < nparams; i++)
   {
      params_len[i] = png_strlen(params[i]) + (i == nparams - 1 ? 0 : 1);
      png_debug2(3, "pCAL parameter %d length = %lu\n", i, params_len[i]);
      total_len += (png_size_t)params_len[i];
   }

   png_debug1(3, "pCAL total length = %d\n", (int)total_len);
   png_write_chunk_start(png_ptr, (png_bytep)png_pCAL, (png_uint_32)total_len);
   png_write_chunk_data(png_ptr, (png_bytep)new_purpose, purpose_len);
   png_save_int_32(buf, X0);
   png_save_int_32(buf + 4, X1);
   buf[8] = (png_byte)type;
   buf[9] = (png_byte)nparams;
   png_write_chunk_data(png_ptr, buf, (png_size_t)10);
   png_write_chunk_data(png_ptr, (png_bytep)units, (png_size_t)units_len);

   png_free(png_ptr, new_purpose);

   for (i = 0; i < nparams; i++)
   {
      png_write_chunk_data(png_ptr, (png_bytep)params[i],
         (png_size_t)params_len[i]);
   }

   png_free(png_ptr, params_len);
   png_write_chunk_end(png_ptr);
}
#endif

#if defined(PNG_WRITE_sCAL_SUPPORTED)
/* write the sCAL chunk */
#if defined(PNG_FLOATING_POINT_SUPPORTED) && !defined(PNG_NO_STDIO)
void /* PRIVATE */
png_write_sCAL(png_structp png_ptr, int unit, double width,double height)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_sCAL;
#endif
   png_size_t total_len;
   char wbuf[32], hbuf[32];

   png_debug(1, "in png_write_sCAL\n");

#if defined(_WIN32_WCE)
/* sprintf() function is not supported on WindowsCE */
   {
      wchar_t wc_buf[32];
      swprintf(wc_buf, TEXT("%12.12e"), width);
      WideCharToMultiByte(CP_ACP, 0, wc_buf, -1, wbuf, 32, NULL, NULL);
      swprintf(wc_buf, TEXT("%12.12e"), height);
      WideCharToMultiByte(CP_ACP, 0, wc_buf, -1, hbuf, 32, NULL, NULL);
   }
#else
   sprintf(wbuf, "%12.12e", width);
   sprintf(hbuf, "%12.12e", height);
#endif
   total_len = 1 + png_strlen(wbuf)+1 + png_strlen(hbuf);

   png_debug1(3, "sCAL total length = %d\n", (int)total_len);
   png_write_chunk_start(png_ptr, (png_bytep)png_sCAL, (png_uint_32)total_len);
   png_write_chunk_data(png_ptr, (png_bytep)&unit, 1);
   png_write_chunk_data(png_ptr, (png_bytep)wbuf, png_strlen(wbuf)+1);
   png_write_chunk_data(png_ptr, (png_bytep)hbuf, png_strlen(hbuf));

   png_write_chunk_end(png_ptr);
}
#else
#ifdef PNG_FIXED_POINT_SUPPORTED
void /* PRIVATE */
png_write_sCAL_s(png_structp png_ptr, int unit, png_charp width,
   png_charp height)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_sCAL;
#endif
   png_size_t total_len;
   char wbuf[32], hbuf[32];

   png_debug(1, "in png_write_sCAL_s\n");

   png_strcpy(wbuf,(const char *)width);
   png_strcpy(hbuf,(const char *)height);
   total_len = 1 + png_strlen(wbuf)+1 + png_strlen(hbuf);

   png_debug1(3, "sCAL total length = %d\n", total_len);
   png_write_chunk_start(png_ptr, (png_bytep)png_sCAL, (png_uint_32)total_len);
   png_write_chunk_data(png_ptr, (png_bytep)&unit, 1);
   png_write_chunk_data(png_ptr, (png_bytep)wbuf, png_strlen(wbuf)+1);
   png_write_chunk_data(png_ptr, (png_bytep)hbuf, png_strlen(hbuf));

   png_write_chunk_end(png_ptr);
}
#endif
#endif
#endif

#if defined(PNG_WRITE_pHYs_SUPPORTED)
/* write the pHYs chunk */
void /* PRIVATE */
png_write_pHYs(png_structp png_ptr, png_uint_32 x_pixels_per_unit,
   png_uint_32 y_pixels_per_unit,
   int unit_type)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_pHYs;
#endif
   png_byte buf[9];

   png_debug(1, "in png_write_pHYs\n");
   if (unit_type >= PNG_RESOLUTION_LAST)
      png_warning(png_ptr, "Unrecognized unit type for pHYs chunk");

   png_save_uint_32(buf, x_pixels_per_unit);
   png_save_uint_32(buf + 4, y_pixels_per_unit);
   buf[8] = (png_byte)unit_type;

   png_write_chunk(png_ptr, (png_bytep)png_pHYs, buf, (png_size_t)9);
}
#endif

#if defined(PNG_WRITE_tIME_SUPPORTED)
/* Write the tIME chunk.  Use either png_convert_from_struct_tm()
 * or png_convert_from_time_t(), or fill in the structure yourself.
 */
void /* PRIVATE */
png_write_tIME(png_structp png_ptr, png_timep mod_time)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_tIME;
#endif
   png_byte buf[7];

   png_debug(1, "in png_write_tIME\n");
   if (mod_time->month  > 12 || mod_time->month  < 1 ||
       mod_time->day    > 31 || mod_time->day    < 1 ||
       mod_time->hour   > 23 || mod_time->second > 60)
   {
      png_warning(png_ptr, "Invalid time specified for tIME chunk");
      return;
   }

   png_save_uint_16(buf, mod_time->year);
   buf[2] = mod_time->month;
   buf[3] = mod_time->day;
   buf[4] = mod_time->hour;
   buf[5] = mod_time->minute;
   buf[6] = mod_time->second;

   png_write_chunk(png_ptr, (png_bytep)png_tIME, buf, (png_size_t)7);
}
#endif

/* initializes the row writing capability of libpng */
void /* PRIVATE */
png_write_start_row(png_structp png_ptr)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   /* arrays to facilitate easy interlacing - use pass (0 - 6) as index */

   /* start of interlace block */
   int png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};

   /* offset to next interlace block */
   int png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};

   /* start of interlace block in the y direction */
   int png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};

   /* offset to next interlace block in the y direction */
   int png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};