pngpread.c

一个国人自己实现图像库的程序（有参考价值）

      png_ptr->skip_length -= save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }
   if (!png_ptr->skip_length)
   {
      if (png_ptr->buffer_size < 4)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_crc_finish(png_ptr, 0);
      png_ptr->process_mode = PNG_READ_CHUNK_MODE;
   }
}

void /* PRIVATE */
png_push_fill_buffer(png_structp png_ptr, png_bytep buffer, png_size_t length)
{
   png_bytep ptr;

   ptr = buffer;
   if (png_ptr->save_buffer_size)
   {
      png_size_t save_size;

      if (length < png_ptr->save_buffer_size)
         save_size = length;
      else
         save_size = png_ptr->save_buffer_size;

      png_memcpy(ptr, png_ptr->save_buffer_ptr, save_size);
      length -= save_size;
      ptr += save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->save_buffer_size -= save_size;
      png_ptr->save_buffer_ptr += save_size;
   }
   if (length && png_ptr->current_buffer_size)
   {
      png_size_t save_size;

      if (length < png_ptr->current_buffer_size)
         save_size = length;
      else
         save_size = png_ptr->current_buffer_size;

      png_memcpy(ptr, png_ptr->current_buffer_ptr, save_size);
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }
}

void /* PRIVATE */
png_push_save_buffer(png_structp png_ptr)
{
   if (png_ptr->save_buffer_size)
   {
      if (png_ptr->save_buffer_ptr != png_ptr->save_buffer)
      {
         png_size_t i,istop;
         png_bytep sp;
         png_bytep dp;

         istop = png_ptr->save_buffer_size;
         for (i = 0, sp = png_ptr->save_buffer_ptr, dp = png_ptr->save_buffer;
            i < istop; i++, sp++, dp++)
         {
            *dp = *sp;
         }
      }
   }
   if (png_ptr->save_buffer_size + png_ptr->current_buffer_size >
      png_ptr->save_buffer_max)
   {
      png_size_t new_max;
      png_bytep old_buffer;

      new_max = png_ptr->save_buffer_size + png_ptr->current_buffer_size + 256;
      old_buffer = png_ptr->save_buffer;
      png_ptr->save_buffer = (png_bytep)png_malloc(png_ptr,
         (png_uint_32)new_max);
      png_memcpy(png_ptr->save_buffer, old_buffer, png_ptr->save_buffer_size);
      png_free(png_ptr, old_buffer);
      png_ptr->save_buffer_max = new_max;
   }
   if (png_ptr->current_buffer_size)
   {
      png_memcpy(png_ptr->save_buffer + png_ptr->save_buffer_size,
         png_ptr->current_buffer_ptr, png_ptr->current_buffer_size);
      png_ptr->save_buffer_size += png_ptr->current_buffer_size;
      png_ptr->current_buffer_size = 0;
   }
   png_ptr->save_buffer_ptr = png_ptr->save_buffer;
   png_ptr->buffer_size = 0;
}

void /* PRIVATE */
png_push_restore_buffer(png_structp png_ptr, png_bytep buffer,
   png_size_t buffer_length)
{
   png_ptr->current_buffer = buffer;
   png_ptr->current_buffer_size = buffer_length;
   png_ptr->buffer_size = buffer_length + png_ptr->save_buffer_size;
   png_ptr->current_buffer_ptr = png_ptr->current_buffer;
}

void /* PRIVATE */
png_push_read_IDAT(png_structp png_ptr)
{
#ifdef PNG_USE_LOCAL_ARRAYS
   PNG_IDAT;
#endif
   if (!(png_ptr->mode & PNG_HAVE_CHUNK_HEADER))
   {
      png_byte chunk_length[4];

      if (png_ptr->buffer_size < 8)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_push_fill_buffer(png_ptr, chunk_length, 4);
      png_ptr->push_length = png_get_uint_32(chunk_length);

      png_reset_crc(png_ptr);
      png_crc_read(png_ptr, png_ptr->chunk_name, 4);
      png_ptr->mode |= PNG_HAVE_CHUNK_HEADER;

      if (png_memcmp(png_ptr->chunk_name, (png_bytep)png_IDAT, 4))
      {
         png_ptr->process_mode = PNG_READ_CHUNK_MODE;
         if (!(png_ptr->flags & PNG_FLAG_ZLIB_FINISHED))
            png_error(png_ptr, "Not enough compressed data");
         return;
      }

      png_ptr->idat_size = png_ptr->push_length;
   }
   if (png_ptr->idat_size && png_ptr->save_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->idat_size < (png_uint_32)png_ptr->save_buffer_size)
      {
         save_size = (png_size_t)png_ptr->idat_size;
         /* check for overflow */
         if((png_uint_32)save_size != png_ptr->idat_size)
            png_error(png_ptr, "save_size overflowed in pngpread");
      }
      else
         save_size = png_ptr->save_buffer_size;

      png_calculate_crc(png_ptr, png_ptr->save_buffer_ptr, save_size);
      png_process_IDAT_data(png_ptr, png_ptr->save_buffer_ptr, save_size);

      png_ptr->idat_size -= save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->save_buffer_size -= save_size;
      png_ptr->save_buffer_ptr += save_size;
   }
   if (png_ptr->idat_size && png_ptr->current_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->idat_size < (png_uint_32)png_ptr->current_buffer_size)
      {
         save_size = (png_size_t)png_ptr->idat_size;
         /* check for overflow */
         if((png_uint_32)save_size != png_ptr->idat_size)
            png_error(png_ptr, "save_size overflowed in pngpread");
      }
      else
         save_size = png_ptr->current_buffer_size;

      png_calculate_crc(png_ptr, png_ptr->current_buffer_ptr, save_size);
      png_process_IDAT_data(png_ptr, png_ptr->current_buffer_ptr, save_size);

      png_ptr->idat_size -= save_size;
      png_ptr->buffer_size -= save_size;
      png_ptr->current_buffer_size -= save_size;
      png_ptr->current_buffer_ptr += save_size;
   }
   if (!png_ptr->idat_size)
   {
      if (png_ptr->buffer_size < 4)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_crc_finish(png_ptr, 0);
      png_ptr->mode &= ~PNG_HAVE_CHUNK_HEADER;
   }
}

void /* PRIVATE */
png_process_IDAT_data(png_structp png_ptr, png_bytep buffer,
   png_size_t buffer_length)
{
   int ret;

   if ((png_ptr->flags & PNG_FLAG_ZLIB_FINISHED) && buffer_length)
      png_error(png_ptr, "Extra compression data");

   png_ptr->zstream.next_in = buffer;
   png_ptr->zstream.avail_in = (uInt)buffer_length;
   for(;;)
   {
      ret = inflate(&png_ptr->zstream, Z_PARTIAL_FLUSH);
      if (ret != Z_OK)
      {
         if (ret == Z_STREAM_END)
         {
            if (png_ptr->zstream.avail_in)
               png_error(png_ptr, "Extra compressed data");
            if (!(png_ptr->zstream.avail_out))
            {
               png_push_process_row(png_ptr);
            }

            png_ptr->mode |= PNG_AFTER_IDAT;
            png_ptr->flags |= PNG_FLAG_ZLIB_FINISHED;
            break;
         }
         else if (ret == Z_BUF_ERROR)
            break;
         else
            png_error(png_ptr, "Decompression Error");
      }
      if (!(png_ptr->zstream.avail_out))
      {
         png_push_process_row(png_ptr);
         png_ptr->zstream.avail_out = (uInt)png_ptr->irowbytes;
         png_ptr->zstream.next_out = png_ptr->row_buf;
      }
      else
         break;
   }
}

void /* PRIVATE */
png_push_process_row(png_structp png_ptr)
{
   png_ptr->row_info.color_type = png_ptr->color_type;
   png_ptr->row_info.width = png_ptr->iwidth;
   png_ptr->row_info.channels = png_ptr->channels;
   png_ptr->row_info.bit_depth = png_ptr->bit_depth;
   png_ptr->row_info.pixel_depth = png_ptr->pixel_depth;

   png_ptr->row_info.rowbytes = ((png_ptr->row_info.width *
      (png_uint_32)png_ptr->row_info.pixel_depth + 7) >> 3);

   png_read_filter_row(png_ptr, &(png_ptr->row_info),
      png_ptr->row_buf + 1, png_ptr->prev_row + 1,
      (int)(png_ptr->row_buf[0]));

   png_memcpy_check(png_ptr, png_ptr->prev_row, png_ptr->row_buf,
      png_ptr->rowbytes + 1);

   if (png_ptr->transformations)
      png_do_read_transformations(png_ptr);

#if defined(PNG_READ_INTERLACING_SUPPORTED)
   /* blow up interlaced rows to full size */
   if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))
   {
      if (png_ptr->pass < 6)
/*       old interface (pre-1.0.9):
         png_do_read_interlace(&(png_ptr->row_info),
            png_ptr->row_buf + 1, png_ptr->pass, png_ptr->transformations);
 */
         png_do_read_interlace(png_ptr);

    switch (png_ptr->pass)
    {
         case 0:
         {
            int i;
            for (i = 0; i < 8 && png_ptr->pass == 0; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr); /* updates png_ptr->pass */
            }
            if (png_ptr->pass == 2) /* pass 1 might be empty */
            {
               for (i = 0; i < 4 && png_ptr->pass == 2; i++)
               {
                  png_push_have_row(png_ptr, png_bytep_NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }
	    if (png_ptr->pass == 4 && png_ptr->height <= 4)
	    {
	        for (i = 0; i < 2 && png_ptr->pass == 4; i++)
                {
                   png_push_have_row(png_ptr, png_bytep_NULL);
                   png_read_push_finish_row(png_ptr);
                }
            }
            if (png_ptr->pass == 6 && png_ptr->height <= 4)
            {
                png_push_have_row(png_ptr, png_bytep_NULL);
                png_read_push_finish_row(png_ptr);
            }
            break;
         }
         case 1:
         {
            int i;
            for (i = 0; i < 8 && png_ptr->pass == 1; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }
            if (png_ptr->pass == 2) /* skip top 4 generated rows */
            {
               for (i = 0; i < 4 && png_ptr->pass == 2; i++)
               {
                  png_push_have_row(png_ptr, png_bytep_NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }
            break;
         }
         case 2:
         {
            int i;
            for (i = 0; i < 4 && png_ptr->pass == 2; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }
            for (i = 0; i < 4 && png_ptr->pass == 2; i++)
            {
               png_push_have_row(png_ptr, png_bytep_NULL);
               png_read_push_finish_row(png_ptr);
            }
            if (png_ptr->pass == 4) /* pass 3 might be empty */
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, png_bytep_NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }
            break;
         }
         case 3:
         {
            int i;
            for (i = 0; i < 4 && png_ptr->pass == 3; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }
            if (png_ptr->pass == 4) /* skip top two generated rows */
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, png_bytep_NULL);
                  png_read_push_finish_row(png_ptr);
               }
            }
            break;
         }
         case 4:
         {
            int i;
            for (i = 0; i < 2 && png_ptr->pass == 4; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }
            for (i = 0; i < 2 && png_ptr->pass == 4; i++)
            {
               png_push_have_row(png_ptr, png_bytep_NULL);
               png_read_push_finish_row(png_ptr);
            }
            if (png_ptr->pass == 6) /* pass 5 might be empty */
            {
               png_push_have_row(png_ptr, png_bytep_NULL);
               png_read_push_finish_row(png_ptr);
            }
            break;
         }
         case 5:
         {
            int i;
            for (i = 0; i < 2 && png_ptr->pass == 5; i++)
            {
               png_push_have_row(png_ptr, png_ptr->row_buf + 1);
               png_read_push_finish_row(png_ptr);
            }
            if (png_ptr->pass == 6) /* skip top generated row */
            {
               png_push_have_row(png_ptr, png_bytep_NULL);
               png_read_push_finish_row(png_ptr);
            }
            break;
         }
         case 6:
         {
            png_push_have_row(png_ptr, png_ptr->row_buf + 1);
            png_read_push_finish_row(png_ptr);
            if (png_ptr->pass != 6)
               break;
            png_push_have_row(png_ptr, png_bytep_NULL);
            png_read_push_finish_row(png_ptr);
         }
      }
   }
   else
#endif
   {
      png_push_have_row(png_ptr, png_ptr->row_buf + 1);
      png_read_push_finish_row(png_ptr);
   }
}

void /* PRIVATE */
png_read_push_finish_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 */
   const int FARDATA png_pass_start[] = {0, 4, 0, 2, 0, 1, 0};

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

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

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

   /* Width of interlace block.  This is not currently used - if you need
    * it, uncomment it here and in png.h
   const int FARDATA png_pass_width[] = {8, 4, 4, 2, 2, 1, 1};
   */

   /* Height of interlace block.  This is not currently used - if you need
    * it, uncomment it here and in png.h
   const int FARDATA png_pass_height[] = {8, 8, 4, 4, 2, 2, 1};
   */
#endif

   png_ptr->row_number++;
   if (png_ptr->row_number < png_ptr->num_rows)
      return;

   if (png_ptr->interlaced)
   {
      png_ptr->row_number = 0;
      png_memset_check(png_ptr, png_ptr->prev_row, 0,
         png_ptr->rowbytes + 1);
      do
      {
         png_ptr->pass++;
         if ((png_ptr->pass == 1 && png_ptr->width < 5) ||
             (png_ptr->pass == 3 && png_ptr->width < 3) ||
             (png_ptr->pass == 5 && png_ptr->width < 2))
           png_ptr->pass++;

         if (png_ptr->pass >= 7)
            break;

         png_ptr->iwidth = (png_ptr->width +
            png_pass_inc[png_ptr->pass] - 1 -
            png_pass_start[png_ptr->pass]) /
            png_pass_inc[png_ptr->pass];

         png_ptr->irowbytes = ((png_ptr->iwidth *
            png_ptr->pixel_depth + 7) >> 3) + 1;

         if (png_ptr->transformations & PNG_INTERLACE)
            break;

         png_ptr->num_rows = (png_ptr->height +
            png_pass_yinc[png_ptr->pass] - 1 -
            png_pass_ystart[png_ptr->pass]) /
            png_pass_yinc[png_ptr->pass];

      } while (png_ptr->iwidth == 0 || png_ptr->num_rows == 0);
   }
}

#if defined(PNG_READ_tEXt_SUPPORTED)
void /* PRIVATE */
png_push_handle_tEXt(png_structp png_ptr, png_infop info_ptr, png_uint_32
   length)
{
   if (!(png_ptr->mode & PNG_HAVE_IHDR) || (png_ptr->mode & PNG_HAVE_IEND))
      {