pngrutil.c

一个国人自己实现图像库的程序（有参考价值）

/* pngrutil.c - utilities to read a PNG file
 *
 * libpng 1.2.1 - December 12, 2001
 * For conditions of distribution and use, see copyright notice in png.h
 * Copyright (c) 1998-2001 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 file contains routines that are only called from within
 * libpng itself during the course of reading an image.
 */

#define PNG_INTERNAL
#include "png.h"

#if defined(_WIN32_WCE)
/* strtod() function is not supported on WindowsCE */
#  ifdef PNG_FLOATING_POINT_SUPPORTED
__inline double strtod(const char *nptr, char **endptr)
{
   double result = 0;
   int len;
   wchar_t *str, *end;

   len = MultiByteToWideChar(CP_ACP, 0, nptr, -1, NULL, 0);
   str = (wchar_t *)malloc(len * sizeof(wchar_t));
   if ( NULL != str )
   {
      MultiByteToWideChar(CP_ACP, 0, nptr, -1, str, len);
      result = wcstod(str, &end);
      len = WideCharToMultiByte(CP_ACP, 0, end, -1, NULL, 0, NULL, NULL);
      *endptr = (char *)nptr + (png_strlen(nptr) - len + 1);
      free(str);
   }
   return result;
}
#  endif
#endif

#ifndef PNG_READ_BIG_ENDIAN_SUPPORTED
/* Grab an unsigned 32-bit integer from a buffer in big-endian format. */
png_uint_32 /* PRIVATE */
png_get_uint_32(png_bytep buf)
{
   png_uint_32 i = ((png_uint_32)(*buf) << 24) +
      ((png_uint_32)(*(buf + 1)) << 16) +
      ((png_uint_32)(*(buf + 2)) << 8) +
      (png_uint_32)(*(buf + 3));

   return (i);
}

#if defined(PNG_READ_pCAL_SUPPORTED) || defined(PNG_READ_oFFs_SUPPORTED)
/* Grab a signed 32-bit integer from a buffer in big-endian format.  The
 * data is stored in the PNG file in two's complement format, and it is
 * assumed that the machine format for signed integers is the same. */
png_int_32 /* PRIVATE */
png_get_int_32(png_bytep buf)
{
   png_int_32 i = ((png_int_32)(*buf) << 24) +
      ((png_int_32)(*(buf + 1)) << 16) +
      ((png_int_32)(*(buf + 2)) << 8) +
      (png_int_32)(*(buf + 3));

   return (i);
}
#endif /* PNG_READ_pCAL_SUPPORTED */

/* Grab an unsigned 16-bit integer from a buffer in big-endian format. */
png_uint_16 /* PRIVATE */
png_get_uint_16(png_bytep buf)
{
   png_uint_16 i = (png_uint_16)(((png_uint_16)(*buf) << 8) +
      (png_uint_16)(*(buf + 1)));

   return (i);
}
#endif /* PNG_READ_BIG_ENDIAN_SUPPORTED */

/* Read data, and (optionally) run it through the CRC. */
void /* PRIVATE */
png_crc_read(png_structp png_ptr, png_bytep buf, png_size_t length)
{
   png_read_data(png_ptr, buf, length);
   png_calculate_crc(png_ptr, buf, length);
}

/* Optionally skip data and then check the CRC.  Depending on whether we
   are reading a ancillary or critical chunk, and how the program has set
   things up, we may calculate the CRC on the data and print a message.
   Returns '1' if there was a CRC error, '0' otherwise. */
int /* PRIVATE */
png_crc_finish(png_structp png_ptr, png_uint_32 skip)
{
   png_size_t i;
   png_size_t istop = png_ptr->zbuf_size;

   for (i = (png_size_t)skip; i > istop; i -= istop)
   {
      png_crc_read(png_ptr, png_ptr->zbuf, png_ptr->zbuf_size);
   }
   if (i)
   {
      png_crc_read(png_ptr, png_ptr->zbuf, i);
   }

   if (png_crc_error(png_ptr))
   {
      if (((png_ptr->chunk_name[0] & 0x20) &&                /* Ancillary */
           !(png_ptr->flags & PNG_FLAG_CRC_ANCILLARY_NOWARN)) ||
          (!(png_ptr->chunk_name[0] & 0x20) &&             /* Critical  */
          (png_ptr->flags & PNG_FLAG_CRC_CRITICAL_USE)))
      {
         png_chunk_warning(png_ptr, "CRC error");
      }
      else
      {
         png_chunk_error(png_ptr, "CRC error");
      }
      return (1);
   }

   return (0);
}

/* Compare the CRC stored in the PNG file with that calculated by libpng from
   the data it has read thus far. */
int /* PRIVATE */
png_crc_error(png_structp png_ptr)
{
   png_byte crc_bytes[4];
   png_uint_32 crc;
   int need_crc = 1;

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

   png_read_data(png_ptr, crc_bytes, 4);

   if (need_crc)
   {
      crc = png_get_uint_32(crc_bytes);
      return ((int)(crc != png_ptr->crc));
   }
   else
      return (0);
}

#if defined(PNG_READ_zTXt_SUPPORTED) || defined(PNG_READ_iTXt_SUPPORTED) || \
    defined(PNG_READ_iCCP_SUPPORTED)
/*
 * Decompress trailing data in a chunk.  The assumption is that chunkdata
 * points at an allocated area holding the contents of a chunk with a
 * trailing compressed part.  What we get back is an allocated area
 * holding the original prefix part and an uncompressed version of the
 * trailing part (the malloc area passed in is freed).
 */
png_charp /* PRIVATE */
png_decompress_chunk(png_structp png_ptr, int comp_type,
                              png_charp chunkdata, png_size_t chunklength,
                              png_size_t prefix_size, png_size_t *newlength)
{
   static char msg[] = "Error decoding compressed text";
   png_charp text = NULL;
   png_size_t text_size;

   if (comp_type == PNG_COMPRESSION_TYPE_BASE)
   {
      int ret = Z_OK;
      png_ptr->zstream.next_in = (png_bytep)(chunkdata + prefix_size);
      png_ptr->zstream.avail_in = (uInt)(chunklength - prefix_size);
      png_ptr->zstream.next_out = png_ptr->zbuf;
      png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;

      text_size = 0;
      text = NULL;

      while (png_ptr->zstream.avail_in)
      {
         ret = inflate(&png_ptr->zstream, Z_PARTIAL_FLUSH);
         if (ret != Z_OK && ret != Z_STREAM_END)
         {
            if (png_ptr->zstream.msg != NULL)
               png_warning(png_ptr, png_ptr->zstream.msg);
            else
               png_warning(png_ptr, msg);
            inflateReset(&png_ptr->zstream);
            png_ptr->zstream.avail_in = 0;

            if (text ==  NULL)
            {
               text_size = prefix_size + sizeof(msg) + 1;
               text = (png_charp)png_malloc(png_ptr, text_size);
               png_memcpy(text, chunkdata, prefix_size);
            }

            text[text_size - 1] = 0x00;

            /* Copy what we can of the error message into the text chunk */
            text_size = (png_size_t)(chunklength - (text - chunkdata) - 1);
            text_size = sizeof(msg) > text_size ? text_size : sizeof(msg);
            png_memcpy(text + prefix_size, msg, text_size + 1);
            break;
         }
         if (!png_ptr->zstream.avail_out || ret == Z_STREAM_END)
         {
            if (text == NULL)
            {
               text_size = prefix_size +
                   png_ptr->zbuf_size - png_ptr->zstream.avail_out;
               text = (png_charp)png_malloc(png_ptr, text_size + 1);
               png_memcpy(text + prefix_size, png_ptr->zbuf,
                    text_size - prefix_size);
               png_memcpy(text, chunkdata, prefix_size);
               *(text + text_size) = 0x00;
            }
            else
            {
               png_charp tmp;

               tmp = text;
               text = (png_charp)png_malloc(png_ptr, (png_uint_32)(text_size +
                  png_ptr->zbuf_size - png_ptr->zstream.avail_out + 1));
               png_memcpy(text, tmp, text_size);
               png_free(png_ptr, tmp);
               png_memcpy(text + text_size, png_ptr->zbuf,
                  (png_ptr->zbuf_size - png_ptr->zstream.avail_out));
               text_size += png_ptr->zbuf_size - png_ptr->zstream.avail_out;
               *(text + text_size) = 0x00;
            }
            if (ret == Z_STREAM_END)
               break;
            else
            {
               png_ptr->zstream.next_out = png_ptr->zbuf;
               png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
            }
         }
      }
      if (ret != Z_STREAM_END)
      {
#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
         char umsg[50];

         if (ret == Z_BUF_ERROR)
            sprintf(umsg,"Buffer error in compressed datastream in %s chunk",
                png_ptr->chunk_name);
         else if (ret == Z_DATA_ERROR)
            sprintf(umsg,"Data error in compressed datastream in %s chunk",
                png_ptr->chunk_name);
         else
            sprintf(umsg,"Incomplete compressed datastream in %s chunk",
                png_ptr->chunk_name);
         png_warning(png_ptr, umsg);
#else
         png_warning(png_ptr,
            "Incomplete compressed datastream in chunk other than IDAT");
#endif
         text_size=prefix_size;
         if (text ==  NULL)
         {
            text = (png_charp)png_malloc(png_ptr, text_size+1);
            png_memcpy(text, chunkdata, prefix_size);
         }
         *(text + text_size) = 0x00;
      }

      inflateReset(&png_ptr->zstream);
      png_ptr->zstream.avail_in = 0;

      png_free(png_ptr, chunkdata);
      chunkdata = text;
      *newlength=text_size;
   }
   else /* if (comp_type != PNG_COMPRESSION_TYPE_BASE) */
   {
#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
      char umsg[50];

      sprintf(umsg, "Unknown zTXt compression type %d", comp_type);
      png_warning(png_ptr, umsg);
#else
      png_warning(png_ptr, "Unknown zTXt compression type");
#endif

      *(chunkdata + prefix_size) = 0x00;
      *newlength=prefix_size;
   }

   return chunkdata;
}
#endif

/* read and check the IDHR chunk */
void /* PRIVATE */
png_handle_IHDR(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_byte buf[13];
   png_uint_32 width, height;
   int bit_depth, color_type, compression_type, filter_type;
   int interlace_type;

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

   if (png_ptr->mode & PNG_HAVE_IHDR)
      png_error(png_ptr, "Out of place IHDR");

   /* check the length */
   if (length != 13)
      png_error(png_ptr, "Invalid IHDR chunk");

   png_ptr->mode |= PNG_HAVE_IHDR;

   png_crc_read(png_ptr, buf, 13);
   png_crc_finish(png_ptr, 0);

   width = png_get_uint_32(buf);
   height = png_get_uint_32(buf + 4);
   bit_depth = buf[8];
   color_type = buf[9];
   compression_type = buf[10];
   filter_type = buf[11];
   interlace_type = buf[12];


   /* set internal variables */
   png_ptr->width = width;
   png_ptr->height = height;
   png_ptr->bit_depth = (png_byte)bit_depth;
   png_ptr->interlaced = (png_byte)interlace_type;
   png_ptr->color_type = (png_byte)color_type;
#if defined(PNG_MNG_FEATURES_SUPPORTED)
   png_ptr->filter_type = (png_byte)filter_type;
#endif

   /* find number of channels */
   switch (png_ptr->color_type)
   {
      case PNG_COLOR_TYPE_GRAY:
      case PNG_COLOR_TYPE_PALETTE:
         png_ptr->channels = 1;
         break;
      case PNG_COLOR_TYPE_RGB:
         png_ptr->channels = 3;
         break;
      case PNG_COLOR_TYPE_GRAY_ALPHA:
         png_ptr->channels = 2;
         break;
      case PNG_COLOR_TYPE_RGB_ALPHA:
         png_ptr->channels = 4;
         break;
   }

   /* set up other useful info */
   png_ptr->pixel_depth = (png_byte)(png_ptr->bit_depth *
   png_ptr->channels);
   png_ptr->rowbytes = ((png_ptr->width *
      (png_uint_32)png_ptr->pixel_depth + 7) >> 3);
   png_debug1(3,"bit_depth = %d\n", png_ptr->bit_depth);
   png_debug1(3,"channels = %d\n", png_ptr->channels);
   png_debug1(3,"rowbytes = %lu\n", png_ptr->rowbytes);
   png_set_IHDR(png_ptr, info_ptr, width, height, bit_depth,
      color_type, interlace_type, compression_type, filter_type);
}

/* read and check the palette */
void /* PRIVATE */
png_handle_PLTE(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_color palette[PNG_MAX_PALETTE_LENGTH];
   int num, i;
#ifndef PNG_NO_POINTER_INDEXING
   png_colorp pal_ptr;
#endif

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

   if (!(png_ptr->mode & PNG_HAVE_IHDR))
      png_error(png_ptr, "Missing IHDR before PLTE");
   else if (png_ptr->mode & PNG_HAVE_IDAT)
   {
      png_warning(png_ptr, "Invalid PLTE after IDAT");
      png_crc_finish(png_ptr, length);
      return;
   }
   else if (png_ptr->mode & PNG_HAVE_PLTE)
      png_error(png_ptr, "Duplicate PLTE chunk");

   png_ptr->mode |= PNG_HAVE_PLTE;

   if (!(png_ptr->color_type&PNG_COLOR_MASK_COLOR))
   {
      png_warning(png_ptr,
        "Ignoring PLTE chunk in grayscale PNG");
      png_crc_finish(png_ptr, length);
      return;
   }
#if !defined(PNG_READ_OPT_PLTE_SUPPORTED)
   if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
   {
      png_crc_finish(png_ptr, length);
      return;
   }
#endif

   if (length > 3*PNG_MAX_PALETTE_LENGTH || length % 3)
   {
      if (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
      {
         png_warning(png_ptr, "Invalid palette chunk");
         png_crc_finish(png_ptr, length);
         return;
      }
      else
      {
         png_error(png_ptr, "Invalid palette chunk");
      }
   }

   num = (int)length / 3;

#ifndef PNG_NO_POINTER_INDEXING
   for (i = 0, pal_ptr = palette; i < num; i++, pal_ptr++)
   {
      png_byte buf[3];