pngrutil.c

一个国人自己实现图像库的程序（有参考价值）

   png_byte buf[7];
   png_time mod_time;

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

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Out of place tIME chunk");
   else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_tIME))
   {
      png_warning(png_ptr, "Duplicate tIME chunk");
      png_crc_finish(png_ptr, length);
      return;
   }

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

   if (length != 7)
   {
      png_warning(png_ptr, "Incorrect tIME chunk length");
      png_crc_finish(png_ptr, length);
      return;
   }

   png_crc_read(png_ptr, buf, 7);
   if (png_crc_finish(png_ptr, 0))
      return;

   mod_time.second = buf[6];
   mod_time.minute = buf[5];
   mod_time.hour = buf[4];
   mod_time.day = buf[3];
   mod_time.month = buf[2];
   mod_time.year = png_get_uint_16(buf);

   png_set_tIME(png_ptr, info_ptr, &mod_time);
}
#endif

#if defined(PNG_READ_tEXt_SUPPORTED)
/* Note: this does not properly handle chunks that are > 64K under DOS */
void /* PRIVATE */
png_handle_tEXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_textp text_ptr;
   png_charp key;
   png_charp text;
   png_uint_32 skip = 0;
   png_size_t slength;

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

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before tEXt");

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

#ifdef PNG_MAX_MALLOC_64K
   if (length > (png_uint_32)65535L)
   {
      png_warning(png_ptr, "tEXt chunk too large to fit in memory");
      skip = length - (png_uint_32)65535L;
      length = (png_uint_32)65535L;
   }
#endif

   key = (png_charp)png_malloc(png_ptr, length + 1);
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)key, slength);

   if (png_crc_finish(png_ptr, skip))
   {
      png_free(png_ptr, key);
      return;
   }

   key[slength] = 0x00;

   for (text = key; *text; text++)
      /* empty loop to find end of key */ ;

   if (text != key + slength)
      text++;

   text_ptr = (png_textp)png_malloc(png_ptr, (png_uint_32)sizeof(png_text));
   text_ptr->compression = PNG_TEXT_COMPRESSION_NONE;
   text_ptr->key = key;
#ifdef PNG_iTXt_SUPPORTED
   text_ptr->lang = NULL;
   text_ptr->lang_key = NULL;
   text_ptr->itxt_length = 0;
#endif
   text_ptr->text = text;
   text_ptr->text_length = png_strlen(text);

   png_set_text(png_ptr, info_ptr, text_ptr, 1);

   png_free(png_ptr, key);
   png_free(png_ptr, text_ptr);
}
#endif

#if defined(PNG_READ_zTXt_SUPPORTED)
/* note: this does not correctly handle chunks that are > 64K under DOS */
void /* PRIVATE */
png_handle_zTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_textp text_ptr;
   png_charp chunkdata;
   png_charp text;
   int comp_type;
   png_size_t slength, prefix_len, data_len;

   png_debug(1, "in png_handle_zTXt\n");
   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before zTXt");

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

#ifdef PNG_MAX_MALLOC_64K
   /* We will no doubt have problems with chunks even half this size, but
      there is no hard and fast rule to tell us where to stop. */
   if (length > (png_uint_32)65535L)
   {
     png_warning(png_ptr,"zTXt chunk too large to fit in memory");
     png_crc_finish(png_ptr, length);
     return;
   }
#endif

   chunkdata = (png_charp)png_malloc(png_ptr, length + 1);
     slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)chunkdata, slength);
   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, chunkdata);
      return;
   }

   chunkdata[slength] = 0x00;

   for (text = chunkdata; *text; text++)
      /* empty loop */ ;

   /* zTXt must have some text after the chunkdataword */
   if (text == chunkdata + slength)
   {
      comp_type = PNG_TEXT_COMPRESSION_NONE;
      png_warning(png_ptr, "Zero length zTXt chunk");
   }
   else
   {
       comp_type = *(++text);
       if (comp_type != PNG_TEXT_COMPRESSION_zTXt)
       {
          png_warning(png_ptr, "Unknown compression type in zTXt chunk");
          comp_type = PNG_TEXT_COMPRESSION_zTXt;
       }
       text++;        /* skip the compression_method byte */
   }
   prefix_len = text - chunkdata;

   chunkdata = (png_charp)png_decompress_chunk(png_ptr, comp_type, chunkdata,
                                    (png_size_t)length, prefix_len, &data_len);

   text_ptr = (png_textp)png_malloc(png_ptr, (png_uint_32)sizeof(png_text));
   text_ptr->compression = comp_type;
   text_ptr->key = chunkdata;
#ifdef PNG_iTXt_SUPPORTED
   text_ptr->lang = NULL;
   text_ptr->lang_key = NULL;
   text_ptr->itxt_length = 0;
#endif
   text_ptr->text = chunkdata + prefix_len;
   text_ptr->text_length = data_len;

   png_set_text(png_ptr, info_ptr, text_ptr, 1);

   png_free(png_ptr, text_ptr);
   png_free(png_ptr, chunkdata);
}
#endif

#if defined(PNG_READ_iTXt_SUPPORTED)
/* note: this does not correctly handle chunks that are > 64K under DOS */
void /* PRIVATE */
png_handle_iTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_textp text_ptr;
   png_charp chunkdata;
   png_charp key, lang, text, lang_key;
   int comp_flag;
   int comp_type = 0;
   png_size_t slength, prefix_len, data_len;

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

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before iTXt");

   if (png_ptr->mode & PNG_HAVE_IDAT)
      png_ptr->mode |= PNG_AFTER_IDAT;

#ifdef PNG_MAX_MALLOC_64K
   /* We will no doubt have problems with chunks even half this size, but
      there is no hard and fast rule to tell us where to stop. */
   if (length > (png_uint_32)65535L)
   {
     png_warning(png_ptr,"iTXt chunk too large to fit in memory");
     png_crc_finish(png_ptr, length);
     return;
   }
#endif

   chunkdata = (png_charp)png_malloc(png_ptr, length + 1);
   slength = (png_size_t)length;
   png_crc_read(png_ptr, (png_bytep)chunkdata, slength);
   if (png_crc_finish(png_ptr, 0))
   {
      png_free(png_ptr, chunkdata);
      return;
   }

   chunkdata[slength] = 0x00;

   for (lang = chunkdata; *lang; lang++)
      /* empty loop */ ;
   lang++;        /* skip NUL separator */

   /* iTXt must have a language tag (possibly empty), two compression bytes,
      translated keyword (possibly empty), and possibly some text after the
      keyword */

   if (lang >= chunkdata + slength)
   {
      comp_flag = PNG_TEXT_COMPRESSION_NONE;
      png_warning(png_ptr, "Zero length iTXt chunk");
   }
   else
   {
       comp_flag = *lang++;
       comp_type = *lang++;
   }

   for (lang_key = lang; *lang_key; lang_key++)
      /* empty loop */ ;
   lang_key++;        /* skip NUL separator */

   for (text = lang_key; *text; text++)
      /* empty loop */ ;
   text++;        /* skip NUL separator */

   prefix_len = text - chunkdata;

   key=chunkdata;
   if (comp_flag)
       chunkdata = png_decompress_chunk(png_ptr, comp_type, chunkdata,
          (size_t)length, prefix_len, &data_len);
   else
       data_len=png_strlen(chunkdata + prefix_len);
   text_ptr = (png_textp)png_malloc(png_ptr, (png_uint_32)sizeof(png_text));
   text_ptr->compression = (int)comp_flag + 1;
   text_ptr->lang_key = chunkdata+(lang_key-key);
   text_ptr->lang = chunkdata+(lang-key);
   text_ptr->itxt_length = data_len;
   text_ptr->text_length = 0;
   text_ptr->key = chunkdata;
   text_ptr->text = chunkdata + prefix_len;

   png_set_text(png_ptr, info_ptr, text_ptr, 1);

   png_free(png_ptr, text_ptr);
   png_free(png_ptr, chunkdata);
}
#endif

/* This function is called when we haven't found a handler for a
   chunk.  If there isn't a problem with the chunk itself (ie bad
   chunk name, CRC, or a critical chunk), the chunk is silently ignored
   -- unless the PNG_FLAG_UNKNOWN_CHUNKS_SUPPORTED flag is on in which
   case it will be saved away to be written out later. */
void /* PRIVATE */
png_handle_unknown(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_uint_32 skip = 0;

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

   if (png_ptr->mode & PNG_HAVE_IDAT)
   {
#ifdef PNG_USE_LOCAL_ARRAYS
      PNG_IDAT;
#endif
      if (png_memcmp(png_ptr->chunk_name, png_IDAT, 4))  /* not an IDAT */
         png_ptr->mode |= PNG_AFTER_IDAT;
   }

   png_check_chunk_name(png_ptr, png_ptr->chunk_name);

   if (!(png_ptr->chunk_name[0] & 0x20))
   {
#if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
      if(png_handle_as_unknown(png_ptr, png_ptr->chunk_name) !=
           HANDLE_CHUNK_ALWAYS
#if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
           && png_ptr->read_user_chunk_fn == NULL
#endif
        )
#endif
          png_chunk_error(png_ptr, "unknown critical chunk");
   }

#if defined(PNG_READ_UNKNOWN_CHUNKS_SUPPORTED)
   if (png_ptr->flags & PNG_FLAG_KEEP_UNKNOWN_CHUNKS)
   {
       png_unknown_chunk chunk;

#ifdef PNG_MAX_MALLOC_64K
       if (length > (png_uint_32)65535L)
       {
           png_warning(png_ptr, "unknown chunk too large to fit in memory");
           skip = length - (png_uint_32)65535L;
           length = (png_uint_32)65535L;
       }
#endif
       png_strcpy((png_charp)chunk.name, (png_charp)png_ptr->chunk_name);
       chunk.data = (png_bytep)png_malloc(png_ptr, length);
       chunk.size = (png_size_t)length;
       png_crc_read(png_ptr, (png_bytep)chunk.data, length);
#if defined(PNG_READ_USER_CHUNKS_SUPPORTED)
       if(png_ptr->read_user_chunk_fn != NULL)
       {
          /* callback to user unknown chunk handler */
          if ((*(png_ptr->read_user_chunk_fn)) (png_ptr, &chunk) <= 0)
          {
             if (!(png_ptr->chunk_name[0] & 0x20))
                if(png_handle_as_unknown(png_ptr, png_ptr->chunk_name) !=
                     HANDLE_CHUNK_ALWAYS)
                   png_chunk_error(png_ptr, "unknown critical chunk");
             png_set_unknown_chunks(png_ptr, info_ptr, &chunk, 1);
          }
       }
       else
#endif
          png_set_unknown_chunks(png_ptr, info_ptr, &chunk, 1);
       png_free(png_ptr, chunk.data);
   }
   else
#endif
      skip = length;

   png_crc_finish(png_ptr, skip);

#if !defined(PNG_READ_USER_CHUNKS_SUPPORTED)
   info_ptr = info_ptr; /* quiet compiler warnings about unused info_ptr */
#endif
}

/* This function is called to verify that a chunk name is valid.
   This function can't have the "critical chunk check" incorporated
   into it, since in the future we will need to be able to call user
   functions to handle unknown critical chunks after we check that
   the chunk name itself is valid. */

#define isnonalpha(c) ((c) < 41 || (c) > 122 || ((c) > 90 && (c) < 97))

void /* PRIVATE */
png_check_chunk_name(png_structp png_ptr, png_bytep chunk_name)
{
   png_debug(1, "in png_check_chunk_name\n");
   if (isnonalpha(chunk_name[0]) || isnonalpha(chunk_name[1]) ||
       isnonalpha(chunk_name[2]) || isnonalpha(chunk_name[3]))
   {
      png_chunk_error(png_ptr, "invalid chunk type");
   }
}

/* Combines the row recently read in with the existing pixels in the
   row.  This routine takes care of alpha and transparency if requested.
   This routine also handles the two methods of progressive display
   of interlaced images, depending on the mask value.
   The mask value describes which pixels are to be combined with
   the row.  The pattern always repeats every 8 pixels, so just 8
   bits are needed.  A one indicates the pixel is to be combined,
   a zero indicates the pixel is to be skipped.  This is in addition
   to any alpha or transparency value associated with the pixel.  If
   you want all pixels to be combined, pass 0xff (255) in mask.  */
#ifndef PNG_HAVE_ASSEMBLER_COMBINE_ROW
void /* PRIVATE */
png_combine_row(png_structp png_ptr, png_bytep row, int mask)
{
   png_debug(1,"in png_combine_row\n");
   if (mask == 0xff)
   {
      png_memcpy(row, png_ptr->row_buf + 1,
         (png_size_t)((png_ptr->width *
         png_ptr->row_info.pixel_depth + 7) >> 3));
   }
   else
   {
      switch (png_ptr->row_info.pixel_depth)
      {
         case 1:
         {
            png_bytep sp = png_ptr->row_buf + 1;
            png_bytep dp = row;
            int s_inc, s_start, s_end;
            int m = 0x80;
            int shift;
            png_uint_32 i;
            png_uint_32 row_width = png_ptr->width;

#if defined(PNG_READ_PACKSWAP_SUPPORTED)
            if (png_ptr->transformations & PNG_PACKSWAP)
            {
                s_start = 0;
                s_end = 7;
                s_inc = 1;
            }
            else
#endif
            {
                s_start = 7;
                s_end = 0;
                s_inc = -1;
            }

            shift = s_start;

            for (i = 0; i < row_width; i++)
            {
               if (m & mask)