pngwutil.c

一个国人自己实现图像库的程序（有参考价值）

                png_ptr->usr_bit_depth);
      if (sbit->red == 0 || sbit->red > maxbits ||
          sbit->green == 0 || sbit->green > maxbits ||
          sbit->blue == 0 || sbit->blue > maxbits)
      {
         png_warning(png_ptr, "Invalid sBIT depth specified");
         return;
      }
      buf[0] = sbit->red;
      buf[1] = sbit->green;
      buf[2] = sbit->blue;
      size = 3;
   }
   else
   {
      if (sbit->gray == 0 || sbit->gray > png_ptr->usr_bit_depth)
      {
         png_warning(png_ptr, "Invalid sBIT depth specified");
         return;
      }
      buf[0] = sbit->gray;
      size = 1;
   }

   if (color_type & PNG_COLOR_MASK_ALPHA)
   {
      if (sbit->alpha == 0 || sbit->alpha > png_ptr->usr_bit_depth)
      {
         png_warning(png_ptr, "Invalid sBIT depth specified");
         return;
      }
      buf[size++] = sbit->alpha;
   }

   png_write_chunk(png_ptr, (png_bytep)png_sBIT, buf, size);
}
#endif

#if defined(PNG_WRITE_cHRM_SUPPORTED)
/* write the cHRM chunk */
#ifdef PNG_FLOATING_POINT_SUPPORTED
void /* PRIVATE */
png_write_cHRM(png_structp png_ptr, double white_x, double white_y,
   double red_x, double red_y, double green_x, double green_y,
   double blue_x, double blue_y)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_cHRM;
#endif
   png_byte buf[32];
   png_uint_32 itemp;

   png_debug(1, "in png_write_cHRM\n");
   /* each value is saved in 1/100,000ths */
   if (white_x < 0 || white_x > 0.8 || white_y < 0 || white_y > 0.8 ||
       white_x + white_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM white point specified");
#if !defined(PNG_NO_CONSOLE_IO)
      fprintf(stderr,"white_x=%f, white_y=%f\n",white_x, white_y);
#endif
      return;
   }
   itemp = (png_uint_32)(white_x * 100000.0 + 0.5);
   png_save_uint_32(buf, itemp);
   itemp = (png_uint_32)(white_y * 100000.0 + 0.5);
   png_save_uint_32(buf + 4, itemp);

   if (red_x < 0 || red_x > 0.8 || red_y < 0 || red_y > 0.8 ||
       red_x + red_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM red point specified");
      return;
   }
   itemp = (png_uint_32)(red_x * 100000.0 + 0.5);
   png_save_uint_32(buf + 8, itemp);
   itemp = (png_uint_32)(red_y * 100000.0 + 0.5);
   png_save_uint_32(buf + 12, itemp);

   if (green_x < 0 || green_x > 0.8 || green_y < 0 || green_y > 0.8 ||
       green_x + green_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM green point specified");
      return;
   }
   itemp = (png_uint_32)(green_x * 100000.0 + 0.5);
   png_save_uint_32(buf + 16, itemp);
   itemp = (png_uint_32)(green_y * 100000.0 + 0.5);
   png_save_uint_32(buf + 20, itemp);

   if (blue_x < 0 || blue_x > 0.8 || blue_y < 0 || blue_y > 0.8 ||
       blue_x + blue_y > 1.0)
   {
      png_warning(png_ptr, "Invalid cHRM blue point specified");
      return;
   }
   itemp = (png_uint_32)(blue_x * 100000.0 + 0.5);
   png_save_uint_32(buf + 24, itemp);
   itemp = (png_uint_32)(blue_y * 100000.0 + 0.5);
   png_save_uint_32(buf + 28, itemp);

   png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
}
#endif
#ifdef PNG_FIXED_POINT_SUPPORTED
void /* PRIVATE */
png_write_cHRM_fixed(png_structp png_ptr, png_fixed_point white_x,
   png_fixed_point white_y, png_fixed_point red_x, png_fixed_point red_y,
   png_fixed_point green_x, png_fixed_point green_y, png_fixed_point blue_x,
   png_fixed_point blue_y)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_cHRM;
#endif
   png_byte buf[32];

   png_debug(1, "in png_write_cHRM\n");
   /* each value is saved in 1/100,000ths */
   if (white_x > 80000L || white_y > 80000L || white_x + white_y > 100000L)
   {
      png_warning(png_ptr, "Invalid fixed cHRM white point specified");
#if !defined(PNG_NO_CONSOLE_IO)
      fprintf(stderr,"white_x=%ld, white_y=%ld\n",white_x, white_y);
#endif
      return;
   }
   png_save_uint_32(buf, (png_uint_32)white_x);
   png_save_uint_32(buf + 4, (png_uint_32)white_y);

   if (red_x > 80000L || red_y > 80000L || red_x + red_y > 100000L)
   {
      png_warning(png_ptr, "Invalid cHRM fixed red point specified");
      return;
   }
   png_save_uint_32(buf + 8, (png_uint_32)red_x);
   png_save_uint_32(buf + 12, (png_uint_32)red_y);

   if (green_x > 80000L || green_y > 80000L || green_x + green_y > 100000L)
   {
      png_warning(png_ptr, "Invalid fixed cHRM green point specified");
      return;
   }
   png_save_uint_32(buf + 16, (png_uint_32)green_x);
   png_save_uint_32(buf + 20, (png_uint_32)green_y);

   if (blue_x > 80000L || blue_y > 80000L || blue_x + blue_y > 100000L)
   {
      png_warning(png_ptr, "Invalid fixed cHRM blue point specified");
      return;
   }
   png_save_uint_32(buf + 24, (png_uint_32)blue_x);
   png_save_uint_32(buf + 28, (png_uint_32)blue_y);

   png_write_chunk(png_ptr, (png_bytep)png_cHRM, buf, (png_size_t)32);
}
#endif
#endif

#if defined(PNG_WRITE_tRNS_SUPPORTED)
/* write the tRNS chunk */
void /* PRIVATE */
png_write_tRNS(png_structp png_ptr, png_bytep trans, png_color_16p tran,
   int num_trans, int color_type)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_tRNS;
#endif
   png_byte buf[6];

   png_debug(1, "in png_write_tRNS\n");
   if (color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (num_trans <= 0 || num_trans > (int)png_ptr->num_palette)
      {
         png_warning(png_ptr,"Invalid number of transparent colors specified");
         return;
      }
      /* write the chunk out as it is */
      png_write_chunk(png_ptr, (png_bytep)png_tRNS, trans, (png_size_t)num_trans);
   }
   else if (color_type == PNG_COLOR_TYPE_GRAY)
   {
      /* one 16 bit value */
      if(tran->gray >= (1 << png_ptr->bit_depth))
      {
         png_warning(png_ptr,
           "Ignoring attempt to write tRNS chunk out-of-range for bit_depth");
         return;
      }
      png_save_uint_16(buf, tran->gray);
      png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)2);
   }
   else if (color_type == PNG_COLOR_TYPE_RGB)
   {
      /* three 16 bit values */
      png_save_uint_16(buf, tran->red);
      png_save_uint_16(buf + 2, tran->green);
      png_save_uint_16(buf + 4, tran->blue);
      if(png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
         {
            png_warning(png_ptr,
              "Ignoring attempt to write 16-bit tRNS chunk when bit_depth is 8");
            return;
         }
      png_write_chunk(png_ptr, (png_bytep)png_tRNS, buf, (png_size_t)6);
   }
   else
   {
      png_warning(png_ptr, "Can't write tRNS with an alpha channel");
   }
}
#endif

#if defined(PNG_WRITE_bKGD_SUPPORTED)
/* write the background chunk */
void /* PRIVATE */
png_write_bKGD(png_structp png_ptr, png_color_16p back, int color_type)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_bKGD;
#endif
   png_byte buf[6];

   png_debug(1, "in png_write_bKGD\n");
   if (color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if (
#if defined(PNG_MNG_FEATURES_SUPPORTED)
          (png_ptr->num_palette ||
          (!(png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE))) &&
#endif
         back->index > png_ptr->num_palette)
      {
         png_warning(png_ptr, "Invalid background palette index");
         return;
      }
      buf[0] = back->index;
      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)1);
   }
   else if (color_type & PNG_COLOR_MASK_COLOR)
   {
      png_save_uint_16(buf, back->red);
      png_save_uint_16(buf + 2, back->green);
      png_save_uint_16(buf + 4, back->blue);
      if(png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]))
         {
            png_warning(png_ptr,
              "Ignoring attempt to write 16-bit bKGD chunk when bit_depth is 8");
            return;
         }
      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)6);
   }
   else
   {
      if(back->gray >= (1 << png_ptr->bit_depth))
      {
         png_warning(png_ptr,
           "Ignoring attempt to write bKGD chunk out-of-range for bit_depth");
         return;
      }
      png_save_uint_16(buf, back->gray);
      png_write_chunk(png_ptr, (png_bytep)png_bKGD, buf, (png_size_t)2);
   }
}
#endif

#if defined(PNG_WRITE_hIST_SUPPORTED)
/* write the histogram */
void /* PRIVATE */
png_write_hIST(png_structp png_ptr, png_uint_16p hist, int num_hist)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_hIST;
#endif
   int i;
   png_byte buf[3];

   png_debug(1, "in png_write_hIST\n");
   if (num_hist > (int)png_ptr->num_palette)
   {
      png_debug2(3, "num_hist = %d, num_palette = %d\n", num_hist,
         png_ptr->num_palette);
      png_warning(png_ptr, "Invalid number of histogram entries specified");
      return;
   }

   png_write_chunk_start(png_ptr, (png_bytep)png_hIST, (png_uint_32)(num_hist * 2));
   for (i = 0; i < num_hist; i++)
   {
      png_save_uint_16(buf, hist[i]);
      png_write_chunk_data(png_ptr, buf, (png_size_t)2);
   }
   png_write_chunk_end(png_ptr);
}
#endif

#if defined(PNG_WRITE_TEXT_SUPPORTED) || defined(PNG_WRITE_pCAL_SUPPORTED) || \
    defined(PNG_WRITE_iCCP_SUPPORTED) || defined(PNG_WRITE_sPLT_SUPPORTED)
/* Check that the tEXt or zTXt keyword is valid per PNG 1.0 specification,
 * and if invalid, correct the keyword rather than discarding the entire
 * chunk.  The PNG 1.0 specification requires keywords 1-79 characters in
 * length, forbids leading or trailing whitespace, multiple internal spaces,
 * and the non-break space (0x80) from ISO 8859-1.  Returns keyword length.
 *
 * The new_key is allocated to hold the corrected keyword and must be freed
 * by the calling routine.  This avoids problems with trying to write to
 * static keywords without having to have duplicate copies of the strings.
 */
png_size_t /* PRIVATE */
png_check_keyword(png_structp png_ptr, png_charp key, png_charpp new_key)
{
   png_size_t key_len;
   png_charp kp, dp;
   int kflag;
   int kwarn=0;

   png_debug(1, "in png_check_keyword\n");
   *new_key = NULL;

   if (key == NULL || (key_len = png_strlen(key)) == 0)
   {
      png_warning(png_ptr, "zero length keyword");
      return ((png_size_t)0);
   }

   png_debug1(2, "Keyword to be checked is '%s'\n", key);

   *new_key = (png_charp)png_malloc(png_ptr, (png_uint_32)(key_len + 2));

   /* Replace non-printing characters with a blank and print a warning */
   for (kp = key, dp = *new_key; *kp != '\0'; kp++, dp++)
   {
      if (*kp < 0x20 || (*kp > 0x7E && (png_byte)*kp < 0xA1))
      {
#if !defined(PNG_NO_STDIO) && !defined(_WIN32_WCE)
         char msg[40];

         sprintf(msg, "invalid keyword character 0x%02X", *kp);
         png_warning(png_ptr, msg);
#else
         png_warning(png_ptr, "invalid character in keyword");
#endif
         *dp = ' ';
      }
      else
      {
         *dp = *kp;
      }
   }
   *dp = '\0';

   /* Remove any trailing white space. */
   kp = *new_key + key_len - 1;
   if (*kp == ' ')
   {
      png_warning(png_ptr, "trailing spaces removed from keyword");

      while (*kp == ' ')
      {
        *(kp--) = '\0';
        key_len--;
      }
   }

   /* Remove any leading white space. */
   kp = *new_key;
   if (*kp == ' ')
   {
      png_warning(png_ptr, "leading spaces removed from keyword");

      while (*kp == ' ')
      {
        kp++;
        key_len--;
      }
   }

   png_debug1(2, "Checking for multiple internal spaces in '%s'\n", kp);

   /* Remove multiple internal spaces. */
   for (kflag = 0, dp = *new_key; *kp != '\0'; kp++)
   {
      if (*kp == ' ' && kflag == 0)
      {
         *(dp++) = *kp;
         kflag = 1;
      }
      else if (*kp == ' ')
      {
         key_len--;
         kwarn=1;
      }
      else
      {
         *(dp++) = *kp;
         kflag = 0;
      }
   }
   *dp = '\0';
   if(kwarn)
      png_warning(png_ptr, "extra interior spaces removed from keyword");

   if (key_len == 0)
   {
      png_free(png_ptr, *new_key);
      *new_key=NULL;
      png_warning(png_ptr, "Zero length keyword");
   }