libpng/pngpread.c

/* pngpread.c - read a png file in push mode

   libpng 1.0 beta 6 - version 0.96
   For conditions of distribution and use, see copyright notice in png.h
   Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
   Copyright (c) 1996, 1997 Andreas Dilger
   May 12, 1997
   */

#define PNG_INTERNAL
#include "png.h"

#ifdef PNG_PROGRESSIVE_READ_SUPPORTED

void
png_process_data(png_structp png_ptr, png_infop info_ptr,
   png_bytep buffer, png_size_t buffer_size)
{
   png_push_restore_buffer(png_ptr, buffer, buffer_size);

   while (png_ptr->buffer_size)
   {
      png_process_some_data(png_ptr, info_ptr);
   }
}

/* What we do with the incoming data depends on what we were previously
 * doing before we ran out of data...
 */
void
png_process_some_data(png_structp png_ptr, png_infop info_ptr)
{
   switch (png_ptr->process_mode)
   {
      case PNG_READ_SIG_MODE:
      {
         png_push_read_sig(png_ptr, info_ptr);
         break;
      }
      case PNG_READ_CHUNK_MODE:
      {
         png_push_read_chunk(png_ptr, info_ptr);
         break;
      }
      case PNG_READ_IDAT_MODE:
      {
         png_push_read_IDAT(png_ptr);
         break;
      }
#if defined(PNG_READ_tEXt_SUPPORTED)
      case PNG_READ_tEXt_MODE:
      {
         png_push_read_tEXt(png_ptr, info_ptr);
         break;
      }
#endif
#if defined(PNG_READ_zTXt_SUPPORTED)
      case PNG_READ_zTXt_MODE:
      {
         png_push_read_zTXt(png_ptr, info_ptr);
         break;
      }
#endif
      case PNG_SKIP_MODE:
      {
         png_push_crc_finish(png_ptr);
         break;
      }
      default:
      {
         png_ptr->buffer_size = 0;
         break;
      }
   }
}

/* Read any remaining signature bytes from the stream and compare them with
 * the correct PNG signature.  It is possible that this routine is called
 * with bytes already read from the signature, whether because they have been
 * checked by the calling application, or from multiple calls to this routine.
 */
void
png_push_read_sig(png_structp png_ptr, png_infop info_ptr)
{
   png_size_t num_checked = png_ptr->sig_bytes,
             num_to_check = 8 - num_checked;

   if (png_ptr->buffer_size < num_to_check)
   {
      num_to_check = png_ptr->buffer_size;
   }

   png_push_fill_buffer(png_ptr, &(info_ptr->signature[num_checked]), 
      num_to_check);
   png_ptr->sig_bytes += num_to_check;

   if (png_sig_cmp(info_ptr->signature, num_checked, num_to_check))
   {
      if (num_checked < 4 &&
          png_sig_cmp(info_ptr->signature, num_checked, num_to_check - 4))
         png_error(png_ptr, "Not a PNG file");
      else
         png_error(png_ptr, "PNG file corrupted by ASCII conversion");
   }
   else
   {
      if (png_ptr->sig_bytes >= 8)
      {
         png_ptr->process_mode = PNG_READ_CHUNK_MODE;
      }
   }
}

void
png_push_read_chunk(png_structp png_ptr, png_infop info_ptr)
{
   /* First we make sure we have enough data for the 4 byte chunk name
      and the 4 byte chunk length before proceeding with decoding the
      chunk data.  To fully decode each of these chunks, we also make
      sure we have enough data in the buffer for the 4 byte CRC at the
      end of every chunk (except IDAT, which is handled separately). */
   if (!(png_ptr->flags & PNG_FLAG_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->flags |= PNG_FLAG_HAVE_CHUNK_HEADER;
   }

   if (!png_memcmp(png_ptr->chunk_name, png_IHDR, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_IHDR(png_ptr, info_ptr, png_ptr->push_length);
   }
   else if (!png_memcmp(png_ptr->chunk_name, png_PLTE, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_PLTE(png_ptr, info_ptr, png_ptr->push_length);
   }
   else if (!png_memcmp(png_ptr->chunk_name, png_IDAT, 4))
   {
      /* If we reach an IDAT chunk, this means we have read all of the
         header chunks, and we can start reading the image (or if this
         is called after the image has been read - we have an error). */
      if (png_ptr->mode & PNG_HAVE_IDAT)
      {
         if (png_ptr->push_length == 0)
            return;

         if (png_ptr->mode & PNG_AFTER_IDAT)
            png_error(png_ptr, "Too many IDAT's found");
      }

      png_ptr->idat_size = png_ptr->push_length;
      png_ptr->mode |= PNG_HAVE_IDAT;
      png_ptr->process_mode = PNG_READ_IDAT_MODE;
      png_push_have_info(png_ptr, info_ptr);
      png_ptr->zstream.avail_out = (uInt)png_ptr->irowbytes;
      png_ptr->zstream.next_out = png_ptr->row_buf;
      return;
   }
   else if (!png_memcmp(png_ptr->chunk_name, png_IEND, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_IEND(png_ptr, info_ptr, png_ptr->push_length);
      png_ptr->process_mode = PNG_READ_DONE_MODE;
      png_push_have_end(png_ptr, info_ptr);
   }
#if defined(PNG_READ_gAMA_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_gAMA, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_gAMA(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_sBIT_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_sBIT, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_sBIT(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_cHRM_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_cHRM, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_cHRM(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_tRNS_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_tRNS, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_tRNS(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_bKGD_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_bKGD, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_bKGD(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_hIST_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_hIST, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_hIST(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_pHYs_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_pHYs, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_pHYs(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_oFFs_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_oFFs, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_oFFs(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_pCAL_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_pCAL, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_pCAL(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_tIME_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_tIME, 4))
   {
      if (png_ptr->push_length + 4 > png_ptr->buffer_size)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_handle_tIME(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_tEXt_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_tEXt, 4))
   {
      png_push_handle_tEXt(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
#if defined(PNG_READ_zTXt_SUPPORTED)
   else if (!png_memcmp(png_ptr->chunk_name, png_zTXt, 4))
   {
      png_push_handle_zTXt(png_ptr, info_ptr, png_ptr->push_length);
   }
#endif
   else
   {
      png_push_handle_unknown(png_ptr, info_ptr, png_ptr->push_length);
   }

   png_ptr->flags &= ~PNG_FLAG_HAVE_CHUNK_HEADER;
}

void
png_push_crc_skip(png_structp png_ptr, png_uint_32 skip)
{
   png_ptr->process_mode = PNG_SKIP_MODE;
   png_ptr->skip_length = skip;
}

void
png_push_crc_finish(png_structp png_ptr)
{
   if (png_ptr->skip_length && png_ptr->save_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->skip_length < (png_uint_32)png_ptr->save_buffer_size)
         save_size = (png_size_t)png_ptr->skip_length;
      else
         save_size = png_ptr->save_buffer_size;

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

      png_ptr->skip_length -= 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->skip_length && png_ptr->current_buffer_size)
   {
      png_size_t save_size;

      if (png_ptr->skip_length < (png_uint_32)png_ptr->current_buffer_size)
         save_size = (png_size_t)png_ptr->skip_length;
      else
         save_size = png_ptr->current_buffer_size;

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

      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
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
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;
         png_bytep sp;
         png_bytep dp;

         for (i = 0, sp = png_ptr->save_buffer_ptr, dp = png_ptr->save_buffer;
            i < png_ptr->save_buffer_size;
            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, 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
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
png_push_read_IDAT(png_structp png_ptr)
{
   if (!(png_ptr->flags & PNG_FLAG_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->flags |= PNG_FLAG_HAVE_CHUNK_HEADER;

      if (png_memcmp(png_ptr->chunk_name, 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_ptr->idat_size;
      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_ptr->idat_size;
      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->flags &= ~PNG_FLAG_HAVE_CHUNK_HEADER;
   }
}

void
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;
   while(1)
   {
      ret = inflate(&png_ptr->zstream, Z_PARTIAL_FLUSH);
      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 if (ret != Z_OK)
         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
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(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)
         png_do_read_interlace(&(png_ptr->row_info),
            png_ptr->row_buf + 1, png_ptr->pass, png_ptr->transformations);

      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);
            }
            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)
            {
               for (i = 0; i < 4 && png_ptr->pass == 2; i++)
               {
                  png_push_have_row(png_ptr, 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, 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)
            {
               for (i = 0; i < 2 && png_ptr->pass == 4; i++)
               {
                  png_push_have_row(png_ptr, 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, 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)
            {
               png_push_have_row(png_ptr, 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, 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
png_read_push_finish_row(png_structp png_ptr)
{
   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(png_ptr->prev_row, 0, png_ptr->rowbytes + 1);
      do
      {
         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))
         {
            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];
            if (!(png_ptr->num_rows))
               continue;
         }
         if (png_ptr->transformations & PNG_INTERLACE)
            break;
      } while (png_ptr->iwidth == 0);
   }
}

#if defined(PNG_READ_tEXt_SUPPORTED)
void
png_push_handle_tEXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   if (png_ptr->mode == PNG_BEFORE_IHDR || png_ptr->mode & PNG_HAVE_IEND)
      png_error(png_ptr, "Out of place tEXt");

#ifdef PNG_MAX_MALLOC_64K
   png_ptr->skip_length = 0;  /* This may not be necessary */

   if (length > 65535L)  /* We can't hold the entire string in memory */
   {
      png_warning(png_ptr, "tEXt chunk too large to fit in memory");
      png_ptr->skip_length = length - 65535L;
      length = 65535L;
   }
#endif

   png_ptr->current_text = (png_charp)png_malloc(png_ptr, length+1);
   png_ptr->current_text[length] = '\0';
   png_ptr->current_text_ptr = png_ptr->current_text;
   png_ptr->current_text_size = length;
   png_ptr->current_text_left = length;
   png_ptr->process_mode = PNG_READ_tEXt_MODE;
}

void
png_push_read_tEXt(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr->buffer_size && png_ptr->current_text_left)
   {
      png_size_t text_size;

      if (png_ptr->buffer_size < png_ptr->current_text_left)
         text_size = png_ptr->buffer_size;
      else
         text_size = png_ptr->current_text_left;
      png_crc_read(png_ptr, (png_bytep)png_ptr->current_text_ptr, text_size);
      png_ptr->current_text_left -= text_size;
      png_ptr->current_text_ptr += text_size;
   }
   if (!(png_ptr->current_text_left))
   {
      png_textp text_ptr;
      png_charp text;
      png_charp key;

      if (png_ptr->buffer_size < 4)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_push_crc_finish(png_ptr);

#if defined(PNG_MAX_MALLOC_64K)
      if (png_ptr->skip_length)
         return;
#endif

      key = png_ptr->current_text;
      png_ptr->current_text = 0;

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

      if (text != key + png_ptr->current_text_size)
         text++;

      text_ptr = (png_textp)png_malloc(png_ptr, sizeof(png_text));
      text_ptr->compression = PNG_TEXT_COMPRESSION_NONE;
      text_ptr->key = key;
      text_ptr->text = text;

      png_set_text(png_ptr, info_ptr, text_ptr, 1);

      png_free(png_ptr, text_ptr);
   }
}
#endif

#if defined(PNG_READ_zTXt_SUPPORTED)
void
png_push_handle_zTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   if (png_ptr->mode == PNG_BEFORE_IHDR || png_ptr->mode & PNG_HAVE_IEND)
      png_error(png_ptr, "Out of place zTXt");

#ifdef PNG_MAX_MALLOC_64K
   /* We can't handle zTXt chunks > 64K, since we don't have enough space
    * to be able to store the uncompressed data.  Actually, the threshold
    * is probably around 32K, but it isn't as definite as 64K is.
    */
   if (length > 65535L)
   {
      png_warning(png_ptr, "zTXt chunk too large to fit in memory");
      png_push_crc_skip(png_ptr, length);
      return;
   }
#endif

   png_ptr->current_text = (png_charp)png_malloc(png_ptr, length+1);
   png_ptr->current_text[length] = '\0';
   png_ptr->current_text_ptr = png_ptr->current_text;
   png_ptr->current_text_size = length;
   png_ptr->current_text_left = length;
   png_ptr->process_mode = PNG_READ_zTXt_MODE;
}

void
png_push_read_zTXt(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr->buffer_size && png_ptr->current_text_left)
   {
      png_size_t text_size;

      if (png_ptr->buffer_size < (png_uint_32)png_ptr->current_text_left)
         text_size = png_ptr->buffer_size;
      else
         text_size = png_ptr->current_text_left;
      png_crc_read(png_ptr, (png_bytep)png_ptr->current_text_ptr, text_size);
      png_ptr->current_text_left -= text_size;
      png_ptr->current_text_ptr += text_size;
   }
   if (!(png_ptr->current_text_left))
   {
      png_textp text_ptr;
      png_charp text;
      png_charp key;
      int ret;
      png_size_t text_size, key_size;

      if (png_ptr->buffer_size < 4)
      {
         png_push_save_buffer(png_ptr);
         return;
      }

      png_push_crc_finish(png_ptr);

      key = png_ptr->current_text;
      png_ptr->current_text = 0;

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

      /* zTXt can't have zero text */
      if (text == key + png_ptr->current_text_size)
      {
         png_free(png_ptr, key);
         return;
      }

      text++;

      if (*text != PNG_TEXT_COMPRESSION_zTXt) /* check compression byte */
      {
         png_free(png_ptr, key);
         return;
      }

      text++;

      png_ptr->zstream.next_in = (png_bytep )text;
      png_ptr->zstream.avail_in = (uInt)(png_ptr->current_text_size -
         (text - key));
      png_ptr->zstream.next_out = png_ptr->zbuf;
      png_ptr->zstream.avail_out = png_ptr->zbuf_size;

      key_size = text - key;
      text_size = 0;
      text = NULL;
      ret = Z_STREAM_END;

      while (png_ptr->zstream.avail_in)
      {
         ret = inflate(&png_ptr->zstream, Z_PARTIAL_FLUSH);
         if (ret != Z_OK && ret != Z_STREAM_END)
         {
            inflateReset(&png_ptr->zstream);
            png_ptr->zstream.avail_in = 0;
            png_free(png_ptr, key);
            png_free(png_ptr, text);
            return;
         }
         if (!(png_ptr->zstream.avail_out) || ret == Z_STREAM_END)
         {
            if (text == NULL)
            {
               text = (png_charp)png_malloc(png_ptr,
                  png_ptr->zbuf_size - png_ptr->zstream.avail_out +
                     key_size + 1);
               png_memcpy(text + key_size, png_ptr->zbuf,
                  png_ptr->zbuf_size - png_ptr->zstream.avail_out);
               png_memcpy(text, key, key_size);
               text_size = key_size + png_ptr->zbuf_size -
                  png_ptr->zstream.avail_out;
               *(text + text_size) = '\0';
            }
            else
            {
               png_charp tmp;

               tmp = text;
               text = png_malloc(png_ptr, 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) = '\0';
            }
            if (ret != Z_STREAM_END)
            {
               png_ptr->zstream.next_out = png_ptr->zbuf;
               png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
            }
         }
         else
         {
            break;
         }

         if (ret == Z_STREAM_END)
            break;
      }

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

      if (ret != Z_STREAM_END)
      {
         png_free(png_ptr, key);
         png_free(png_ptr, text);
         return;
      }

      png_free(png_ptr, key);
      key = text;
      text += key_size;
      text_size -= key_size;

      text_ptr = (png_textp)png_malloc(png_ptr, sizeof(png_text));
      text_ptr->compression = PNG_TEXT_COMPRESSION_zTXt;
      text_ptr->key = key;
      text_ptr->text = text;

      png_set_text(png_ptr, info_ptr, text_ptr, 1);

      png_free(png_ptr, text_ptr);
   }
}
#endif

/* This function is called when we haven't found a handler for this
   chunk.  In the future we will have code here which can handle
   user-defined callback functions for unknown chunks before they are
   ignored or cause an error.  If there isn't a problem with the
   chunk itself (ie a bad chunk name or a critical chunk), the chunk
   is (currently) silently ignored. */
void
png_push_handle_unknown(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
{
   png_check_chunk_name(png_ptr, png_ptr->chunk_name);

   if (!(png_ptr->chunk_name[0] & 0x20))
   {
      char msg[40];

      sprintf(msg, "Unknown critical chunk %s", png_ptr->chunk_name);
      png_error(png_ptr, msg);
   }

   png_push_crc_skip(png_ptr, length);
}

void
png_push_have_info(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr->info_fn != NULL)
      (*(png_ptr->info_fn))(png_ptr, info_ptr);
}

void
png_push_have_end(png_structp png_ptr, png_infop info_ptr)
{
   if (png_ptr->end_fn != NULL)
      (*(png_ptr->end_fn))(png_ptr, info_ptr);
}

void
png_push_have_row(png_structp png_ptr, png_bytep row)
{
   if (png_ptr->row_fn != NULL)
      (*(png_ptr->row_fn))(png_ptr, row, png_ptr->row_number,
         (int)png_ptr->pass);
}

void
png_progressive_combine_row (png_structp png_ptr,
   png_bytep old_row, png_bytep new_row)
{
   if (new_row != NULL)
      png_combine_row(png_ptr, old_row, png_pass_dsp_mask[png_ptr->pass]);
}

void
png_set_progressive_read_fn(png_structp png_ptr, png_voidp progressive_ptr,
   png_progressive_info_ptr info_fn, png_progressive_row_ptr row_fn,
   png_progressive_end_ptr end_fn)
{
   png_ptr->info_fn = info_fn;
   png_ptr->row_fn = row_fn;
   png_ptr->end_fn = end_fn;

   png_set_read_fn(png_ptr, progressive_ptr, png_push_fill_buffer);
}

png_voidp
png_get_progressive_ptr(png_structp png_ptr)
{
   return png_ptr->io_ptr;
}

#endif /* PNG_PROGRESSIVE_READ_SUPPORTED */