pngwrite.c

   
/* pngwrite.c - general routines to write a PNG file

   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
   */

/* get internal access to png.h */
#define PNG_INTERNAL
#include "png.h"

/* Writes all the PNG information.  This is the suggested way to use the
 * library.  If you have a new chunk to add, make a function to write it,
 * and put it in the correct location here.  If you want the chunk written
 * after the image data, put it in png_write_end().  I strongly encurage
 * you to supply a PNG_INFO_ flag, and check info_ptr->valid before writing
 * the chunk, as that will keep the code from breaking if you want to just
 * write a plain PNG file.  If you have long comments, I suggest writing
 * them in png_write_end(), and compressing them.
 */
void
png_write_info(png_structp png_ptr, png_infop info_ptr)
{
   int i;

   png_debug(1, "in png_write_info\n");
   png_write_sig(png_ptr); /* write PNG signature */
   /* write IHDR information. */
   png_write_IHDR(png_ptr, info_ptr->width, info_ptr->height,
      info_ptr->bit_depth, info_ptr->color_type, info_ptr->compression_type,
      info_ptr->filter_type, info_ptr->interlace_type);
   /* the rest of these check to see if the valid field has the appropriate
      flag set, and if it does, writes the chunk. */
#if defined(PNG_WRITE_gAMA_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_gAMA)
      png_write_gAMA(png_ptr, info_ptr->gamma);
#endif
#if defined(PNG_WRITE_sBIT_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_sBIT)
      png_write_sBIT(png_ptr, &(info_ptr->sig_bit), info_ptr->color_type);
#endif
#if defined(PNG_WRITE_cHRM_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_cHRM)
      png_write_cHRM(png_ptr,
         info_ptr->x_white, info_ptr->y_white,
         info_ptr->x_red, info_ptr->y_red,
         info_ptr->x_green, info_ptr->y_green,
         info_ptr->x_blue, info_ptr->y_blue);
#endif
   if (info_ptr->valid & PNG_INFO_PLTE)
      png_write_PLTE(png_ptr, info_ptr->palette,
         (png_uint_32)info_ptr->num_palette);
   else if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      png_error(png_ptr, "Valid palette required for paletted images\n");
#if defined(PNG_WRITE_tRNS_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_tRNS)
      png_write_tRNS(png_ptr, info_ptr->trans, &(info_ptr->trans_values),
         info_ptr->num_trans, info_ptr->color_type);
#endif
#if defined(PNG_WRITE_bKGD_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_bKGD)
      png_write_bKGD(png_ptr, &(info_ptr->background), info_ptr->color_type);
#endif
#if defined(PNG_WRITE_hIST_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_hIST)
      png_write_hIST(png_ptr, info_ptr->hist, info_ptr->num_palette);
#endif
#if defined(PNG_WRITE_oFFs_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_oFFs)
      png_write_oFFs(png_ptr, info_ptr->x_offset, info_ptr->y_offset,
         info_ptr->offset_unit_type);
#endif
#if defined(PNG_WRITE_pCAL_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_pCAL)
      png_write_pCAL(png_ptr, info_ptr->pcal_purpose, info_ptr->pcal_X0,
         info_ptr->pcal_X1, info_ptr->pcal_type, info_ptr->pcal_nparams,
         info_ptr->pcal_units, info_ptr->pcal_params);
#endif
#if defined(PNG_WRITE_pHYs_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_pHYs)
      png_write_pHYs(png_ptr, info_ptr->x_pixels_per_unit,
         info_ptr->y_pixels_per_unit, info_ptr->phys_unit_type);
#endif
#if defined(PNG_WRITE_tIME_SUPPORTED)
   if (info_ptr->valid & PNG_INFO_tIME)
   {
      png_write_tIME(png_ptr, &(info_ptr->mod_time));
      png_ptr->flags |= PNG_FLAG_WROTE_tIME;
   }
#endif
#if defined(PNG_WRITE_tEXt_SUPPORTED) || defined(PNG_WRITE_zTXt_SUPPORTED)
   /* Check to see if we need to write text chunks */
   for (i = 0; i < info_ptr->num_text; i++)
   {
      png_debug2(2, "Writing header text chunk %d, type %d\n", i,
         info_ptr->text[i].compression);
      /* If we want a compressed text chunk */
      if (info_ptr->text[i].compression >= PNG_TEXT_COMPRESSION_zTXt)
      {
#if defined(PNG_WRITE_zTXt_SUPPORTED)
         /* write compressed chunk */
         png_write_zTXt(png_ptr, info_ptr->text[i].key,
            info_ptr->text[i].text, info_ptr->text[i].text_length,
            info_ptr->text[i].compression);
#else
         png_warning(png_ptr, "Unable to write compressed text\n");
#endif
         /* Mark this chunk as written */
         info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
      }
      else if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
      {
#if defined(PNG_WRITE_tEXt_SUPPORTED)
         /* write uncompressed chunk */
         png_write_tEXt(png_ptr, info_ptr->text[i].key,
            info_ptr->text[i].text, info_ptr->text[i].text_length);
#else
         png_warning(png_ptr, "Unable to write uncompressed text\n");
#endif
         /* Mark this chunk as written */
         info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
      }
   }
#endif
}

/* Writes the end of the PNG file.  If you don't want to write comments or
   time information, you can pass NULL for info.  If you already wrote these
   in png_write_info(), do not write them again here.  If you have long
   comments, I suggest writing them here, and compressing them. */
void
png_write_end(png_structp png_ptr, png_infop info_ptr)
{
   png_debug(1, "in png_write_end\n");
   if (!(png_ptr->mode & PNG_HAVE_IDAT))
      png_error(png_ptr, "No IDATs written into file");

   /* see if user wants us to write information chunks */
   if (info_ptr != NULL)
   {
      int i; /* local index variable */
#if defined(PNG_WRITE_tIME_SUPPORTED)
      /* check to see if user has supplied a time chunk */
      if (info_ptr->valid & PNG_INFO_tIME &&
         !(png_ptr->flags & PNG_FLAG_WROTE_tIME))
         png_write_tIME(png_ptr, &(info_ptr->mod_time));
#endif
#if defined(PNG_WRITE_tEXt_SUPPORTED) || defined(PNG_WRITE_zTXt_SUPPORTED)
      /* loop through comment chunks */
      for (i = 0; i < info_ptr->num_text; i++)
      {
         png_debug2(2, "Writing trailer text chunk %d, type %d\n", i,
            info_ptr->text[i].compression);
         if (info_ptr->text[i].compression >= PNG_TEXT_COMPRESSION_zTXt)
         {
#if defined(PNG_WRITE_zTXt_SUPPORTED)
            /* write compressed chunk */
            png_write_zTXt(png_ptr, info_ptr->text[i].key,
               info_ptr->text[i].text, info_ptr->text[i].text_length,
               info_ptr->text[i].compression);
#else
            png_warning(png_ptr, "Unable to write compressed text\n");
#endif
            /* Mark this chunk as written */
            info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_zTXt_WR;
         }
         else if (info_ptr->text[i].compression == PNG_TEXT_COMPRESSION_NONE)
         {
#if defined(PNG_WRITE_tEXt_SUPPORTED)
            /* write uncompressed chunk */
            png_write_tEXt(png_ptr, info_ptr->text[i].key,
               info_ptr->text[i].text, info_ptr->text[i].text_length);
#else
            png_warning(png_ptr, "Unable to write uncompressed text\n");
#endif

            /* Mark this chunk as written */
            info_ptr->text[i].compression = PNG_TEXT_COMPRESSION_NONE_WR;
         }
      }
#endif
   }

   png_ptr->mode |= PNG_AFTER_IDAT;

   /* write end of PNG file */
   png_write_IEND(png_ptr);
}

#if defined(PNG_WRITE_tIME_SUPPORTED)
void
png_convert_from_struct_tm(png_timep ptime, struct tm FAR * ttime)
{
   png_debug(1, "in png_convert_from_struct_tm\n");
   ptime->year = (png_uint_16)(1900 + ttime->tm_year);
   ptime->month = (png_byte)(ttime->tm_mon + 1);
   ptime->day = (png_byte)ttime->tm_mday;
   ptime->hour = (png_byte)ttime->tm_hour;
   ptime->minute = (png_byte)ttime->tm_min;
   ptime->second = (png_byte)ttime->tm_sec;
}

void
png_convert_from_time_t(png_timep ptime, time_t ttime)
{
   struct tm *tbuf;

   png_debug(1, "in png_convert_from_time_t\n");
   tbuf = gmtime(&ttime);
   png_convert_from_struct_tm(ptime, tbuf);
}
#endif

/* Initialize png_ptr structure, and allocate any memory needed */
png_structp
png_create_write_struct(png_const_charp user_png_ver, voidp error_ptr,
   png_error_ptr error_fn, png_error_ptr warn_fn)
{
   png_structp png_ptr;
#ifdef USE_FAR_KEYWORD
   jmp_buf jmpbuf;
#endif
   png_debug(1, "in png_create_write_struct\n");
   if ((png_ptr = (png_structp)png_create_struct(PNG_STRUCT_PNG)) == NULL)
   {
      return (png_structp)NULL;
   }
#ifdef USE_FAR_KEYWORD
   if (setjmp(jmpbuf))
#else
   if (setjmp(png_ptr->jmpbuf))
#endif
   {
      png_free(png_ptr, png_ptr->zbuf);
      png_destroy_struct(png_ptr);
      return (png_structp)NULL;
   }
#ifdef USE_FAR_KEYWORD
   png_memcpy(png_ptr->jmpbuf,jmpbuf,sizeof(jmp_buf));
#endif
   png_set_error_fn(png_ptr, error_ptr, error_fn, warn_fn);

   /* Libpng 0.90 and later are binary incompatible with libpng 0.89, so
    * we must recompile any applications that use any older library version.
    * For versions after libpng 1.0, we will be compatible, so we need
    * only check the first digit.
    */
   if (user_png_ver == NULL || user_png_ver[0] != png_libpng_ver[0] ||
       (png_libpng_ver[0] == '0' && user_png_ver[2] < '9'))
   {
      png_error(png_ptr,
         "Incompatible libpng version in application and library");
   }

   /* initialize zbuf - compression buffer */
   png_ptr->zbuf_size = PNG_ZBUF_SIZE;
   png_ptr->zbuf = png_malloc(png_ptr, png_ptr->zbuf_size);

   png_set_write_fn(png_ptr, NULL, NULL, NULL);

   return (png_ptr);
}


/* Initialize png_ptr structure, and allocate any memory needed */
void
png_write_init(png_structp png_ptr)
{
   jmp_buf tmp_jmp; /* to save current jump buffer */

   png_debug(1, "in png_write_init\n");
   /* save jump buffer and error functions */
   png_memcpy(tmp_jmp, png_ptr->jmpbuf, sizeof (jmp_buf));

   /* reset all variables to 0 */
   png_memset(png_ptr, 0, sizeof (png_struct));

   /* restore jump buffer */
   png_memcpy(png_ptr->jmpbuf, tmp_jmp, sizeof (jmp_buf));

   /* initialize zbuf - compression buffer */
   png_ptr->zbuf_size = PNG_ZBUF_SIZE;
   png_ptr->zbuf = png_malloc(png_ptr, png_ptr->zbuf_size);
   png_set_write_fn(png_ptr, NULL, NULL, NULL);

#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
   png_set_filter_heuristics(png_ptr, PNG_FILTER_HEURISTIC_DEFAULT,
      1, NULL, NULL);
#endif
}

/* write a few rows of image data.  If the image is interlaced,
   either you will have to write the 7 sub images, or, if you
   have called png_set_interlace_handling(), you will have to
   "write" the image seven times */
void
png_write_rows(png_structp png_ptr, png_bytepp row,
   png_uint_32 num_rows)
{
   png_uint_32 i; /* row counter */
   png_bytepp rp; /* row pointer */

   png_debug(1, "in png_write_rows\n");
   /* loop through the rows */
   for (i = 0, rp = row; i < num_rows; i++, rp++)
   {
      png_write_row(png_ptr, *rp);
   }
}

/* write the image.  You only need to call this function once, even
   if you are writing an interlaced image. */
void
png_write_image(png_structp png_ptr, png_bytepp image)
{
   png_uint_32 i; /* row index */
   int pass, num_pass; /* pass variables */
   png_bytepp rp; /* points to current row */

   png_debug(1, "in png_write_image\n");
   /* intialize interlace handling.  If image is not interlaced,
      this will set pass to 1 */
   num_pass = png_set_interlace_handling(png_ptr);
   /* loop through passes */
   for (pass = 0; pass < num_pass; pass++)
   {
      /* loop through image */
      for (i = 0, rp = image; i < png_ptr->height; i++, rp++)
      {
         png_write_row(png_ptr, *rp);
      }
   }
}

/* called by user to write a row of image data */
void
png_write_row(png_structp png_ptr, png_bytep row)
{
   png_debug(1, "in png_write_row\n");
   /* initialize transformations and other stuff if first time */
   if (png_ptr->row_number == 0 && png_ptr->pass == 0)
   {
      png_write_start_row(png_ptr);
   }

#if defined(PNG_WRITE_INTERLACING_SUPPORTED)
   /* if interlaced and not interested in row, return */
   if (png_ptr->interlaced && (png_ptr->transformations & PNG_INTERLACE))
   {
      switch (png_ptr->pass)
      {
         case 0:
            if (png_ptr->row_number & 7)
            {
               png_write_finish_row(png_ptr);
               return;
            }
            break;
         case 1:
            if ((png_ptr->row_number & 7) || png_ptr->width < 5)
            {
               png_write_finish_row(png_ptr);
               return;
            }
            break;
         case 2:
            if ((png_ptr->row_number & 7) != 4)
            {
               png_write_finish_row(png_ptr);
               return;
            }
            break;
         case 3:
            if ((png_ptr->row_number & 3) || png_ptr->width < 3)
            {
               png_write_finish_row(png_ptr);
               return;
            }
            break;
         case 4:
            if ((png_ptr->row_number & 3) != 2)
            {
               png_write_finish_row(png_ptr);
               return;
            }
            break;
         case 5:
            if ((png_ptr->row_number & 1) || png_ptr->width < 2)
            {
               png_write_finish_row(png_ptr);
               return;
            }
            break;
         case 6:
            if (!(png_ptr->row_number & 1))
            {
               png_write_finish_row(png_ptr);
               return;
            }
            break;
      }
   }
#endif

   /* set up row info for transformations */
   png_ptr->row_info.color_type = png_ptr->color_type;
   png_ptr->row_info.width = png_ptr->usr_width;
   png_ptr->row_info.channels = png_ptr->usr_channels;
   png_ptr->row_info.bit_depth = png_ptr->usr_bit_depth;
   png_ptr->row_info.pixel_depth = (png_byte)(png_ptr->row_info.bit_depth *
      png_ptr->row_info.channels);
   png_ptr->row_info.rowbytes = ((png_ptr->row_info.width *
      (png_uint_32)png_ptr->row_info.pixel_depth + 7) >> 3);

   png_debug1(4, "row_info->color_type = %d\n", png_ptr->row_info.color_type);
   png_debug1(4, "row_info->width = %d\n", png_ptr->row_info.width);
   png_debug1(4, "row_info->channels = %d\n", png_ptr->row_info.channels);
   png_debug1(4, "row_info->bit_depth = %d\n", png_ptr->row_info.bit_depth);
   png_debug1(4, "row_info->pixel_depth = %d\n", png_ptr->row_info.pixel_depth);
   png_debug1(4, "row_info->rowbytes = %d\n", png_ptr->row_info.rowbytes);

   /* Copy user's row into buffer, leaving room for filter byte. */
   png_memcpy(png_ptr->row_buf + 1, row, png_ptr->row_info.rowbytes);

#if defined(PNG_WRITE_INTERLACING_SUPPORTED)
   /* handle interlacing */
   if (png_ptr->interlaced && png_ptr->pass < 6 &&
      (png_ptr->transformations & PNG_INTERLACE))
   {
      png_do_write_interlace(&(png_ptr->row_info),
         png_ptr->row_buf + 1, png_ptr->pass);
      /* this should always get caught above, but still ... */
      if (!(png_ptr->row_info.width))
      {
         png_write_finish_row(png_ptr);
         return;
      }
   }
#endif

   /* handle other transformations */
   if (png_ptr->transformations)
      png_do_write_transformations(png_ptr);

   /* Find a filter if necessary, filter the row and write it out. */
   png_write_find_filter(png_ptr, &(png_ptr->row_info));
}

#if defined(PNG_WRITE_FLUSH_SUPPORTED)
/* Set the automatic flush interval or 0 to turn flushing off */
void
png_set_flush(png_structp png_ptr, int nrows)
{
   png_debug(1, "in png_set_flush\n");
   png_ptr->flush_dist = (nrows < 0 ? 0 : nrows);
}

/* flush the current output buffers now */
void
png_write_flush(png_structp png_ptr)
{
   int wrote_IDAT;

   png_debug(1, "in png_write_flush\n");
   /* We have already written out all of the data */
   if (png_ptr->row_number >= png_ptr->num_rows)
     return;

   do
   {
      int ret;

      /* compress the data */
      ret = deflate(&png_ptr->zstream, Z_SYNC_FLUSH);
      wrote_IDAT = 0;

      /* check for compression errors */
      if (ret != Z_OK)
      {
         if (png_ptr->zstream.msg != NULL)
            png_error(png_ptr, png_ptr->zstream.msg);
         else
            png_error(png_ptr, "zlib error");
      }

      if (!(png_ptr->zstream.avail_out))
      {
         /* write the IDAT and reset the zlib output buffer */
         png_write_IDAT(png_ptr, png_ptr->zbuf,
                        png_ptr->zbuf_size);
         png_ptr->zstream.next_out = png_ptr->zbuf;
         png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
         wrote_IDAT = 1;
      }
   } while(wrote_IDAT == 1);

   /* If there is any data left to be output, write it into a new IDAT */
   if (png_ptr->zbuf_size != png_ptr->zstream.avail_out)
   {
      /* write the IDAT and reset the zlib output buffer */
      png_write_IDAT(png_ptr, png_ptr->zbuf,
                     png_ptr->zbuf_size - png_ptr->zstream.avail_out);
      png_ptr->zstream.next_out = png_ptr->zbuf;
      png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
   }
   png_ptr->flush_rows = 0;
   png_flush(png_ptr);
}
#endif /* PNG_WRITE_FLUSH_SUPPORTED */

/* free all memory used by the write */
void
png_destroy_write_struct(png_structpp png_ptr_ptr, png_infopp info_ptr_ptr)
{
   png_structp png_ptr = NULL;
   png_infop info_ptr = NULL;

   png_debug(1, "in png_destroy_write_struct\n");
   if (png_ptr_ptr != NULL)
      png_ptr = *png_ptr_ptr;

   if (info_ptr_ptr != NULL)
      info_ptr = *info_ptr_ptr;

   if (info_ptr != NULL)
   {
      png_destroy_struct((png_voidp)info_ptr);
      *info_ptr_ptr = (png_infop)NULL;
   }

   if (png_ptr != NULL)
   {
      png_write_destroy(png_ptr);
      png_destroy_struct((png_voidp)png_ptr);
      *png_ptr_ptr = (png_structp)NULL;
   }
}


/* Free any memory used in png_ptr struct (old method) */
void
png_write_destroy(png_structp png_ptr)
{
   jmp_buf tmp_jmp; /* save jump buffer */
   png_error_ptr error_fn;
   png_error_ptr warning_fn;
   png_voidp error_ptr;

   png_debug(1, "in png_write_destroy\n");
   /* free any memory zlib uses */
   deflateEnd(&png_ptr->zstream);

   /* free our memory.  png_free checks NULL for us. */
   png_free(png_ptr, png_ptr->zbuf);
   png_free(png_ptr, png_ptr->row_buf);
   png_free(png_ptr, png_ptr->prev_row);
   png_free(png_ptr, png_ptr->sub_row);
   png_free(png_ptr, png_ptr->up_row);
   png_free(png_ptr, png_ptr->avg_row);
   png_free(png_ptr, png_ptr->paeth_row);
#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
   png_free(png_ptr, png_ptr->prev_filters);
   png_free(png_ptr, png_ptr->filter_weights);
   png_free(png_ptr, png_ptr->inv_filter_weights);
   png_free(png_ptr, png_ptr->filter_costs);
   png_free(png_ptr, png_ptr->inv_filter_costs);
#endif /* PNG_WRITE_WEIGHTED_FILTER_SUPPORTED */

   /* reset structure */
   png_memcpy(tmp_jmp, png_ptr->jmpbuf, sizeof (jmp_buf));

   error_fn = png_ptr->error_fn;
   warning_fn = png_ptr->warning_fn;
   error_ptr = png_ptr->error_ptr;

   png_memset(png_ptr, 0, sizeof (png_struct));

   png_ptr->error_fn = error_fn;
   png_ptr->warning_fn = warning_fn;
   png_ptr->error_ptr = error_ptr;

   png_memcpy(png_ptr->jmpbuf, tmp_jmp, sizeof (jmp_buf));
}

/* Allow the application to select one or more row filters to use. */
void
png_set_filter(png_structp png_ptr, int method, int filters)
{
   png_debug(1, "in png_set_filter\n");
   /* We allow 'method' only for future expansion of the base filter method. */
   if (method == PNG_FILTER_TYPE_BASE)
   {
      switch (filters & (PNG_ALL_FILTERS | 0x07))
      {
         case 5:
         case 6:
         case 7: png_warning(png_ptr, "Unknown row filter for method 0");
         case PNG_FILTER_VALUE_NONE:  png_ptr->do_filter=PNG_FILTER_NONE; break;
         case PNG_FILTER_VALUE_SUB:   png_ptr->do_filter=PNG_FILTER_SUB;  break;
         case PNG_FILTER_VALUE_UP:    png_ptr->do_filter=PNG_FILTER_UP;   break;
         case PNG_FILTER_VALUE_AVG:   png_ptr->do_filter=PNG_FILTER_AVG;  break;
         case PNG_FILTER_VALUE_PAETH: png_ptr->do_filter=PNG_FILTER_PAETH;break;
         default: png_ptr->do_filter = (png_byte)filters; break;
      }

      /* If we have allocated the row_buf, this means we have already started
       * with the image and we should have allocated all of the filter buffers
       * that have been selected.  If prev_row isn't already allocated, then
       * it is too late to start using the filters that need it, since we
       * will be missing the data in the previous row.  If an application
       * wants to start and stop using particular filters during compression,
       * it should start out with all of the filters, and then add and
       * remove them after the start of compression.
       */
      if (png_ptr->row_buf != NULL)
      {
         if (png_ptr->do_filter & PNG_FILTER_SUB && png_ptr->sub_row == NULL)
         {
            png_ptr->sub_row = (png_bytep)png_malloc(png_ptr,
               png_ptr->rowbytes + 1);
            png_ptr->sub_row[0] = PNG_FILTER_VALUE_SUB;
         }

         if (png_ptr->do_filter & PNG_FILTER_UP && png_ptr->up_row == NULL)
         {
            if (png_ptr->prev_row == NULL)
            {
               png_warning(png_ptr, "Can't add Up filter after starting");
               png_ptr->do_filter &= ~PNG_FILTER_UP;
            }
            else
            {
               png_ptr->up_row = (png_bytep)png_malloc(png_ptr,
                  png_ptr->rowbytes + 1);
               png_ptr->up_row[0] = PNG_FILTER_VALUE_UP;
            }
         }

         if (png_ptr->do_filter & PNG_FILTER_AVG && png_ptr->avg_row == NULL)
         {
            if (png_ptr->prev_row == NULL)
            {
               png_warning(png_ptr, "Can't add Average filter after starting");
               png_ptr->do_filter &= ~PNG_FILTER_AVG;
            }
            else
            {
               png_ptr->avg_row = (png_bytep)png_malloc(png_ptr,
                  png_ptr->rowbytes + 1);
               png_ptr->avg_row[0] = PNG_FILTER_VALUE_AVG;
            }
         }

         if (png_ptr->do_filter & PNG_FILTER_PAETH &&
             png_ptr->paeth_row == NULL)
         {
            if (png_ptr->prev_row == NULL)
            {
               png_warning(png_ptr, "Can't add Paeth filter after starting");
               png_ptr->do_filter &= ~PNG_FILTER_PAETH;
            }
            else
            {
               png_ptr->paeth_row = (png_bytep )png_malloc(png_ptr,
                  png_ptr->rowbytes + 1);
               png_ptr->paeth_row[0] = PNG_FILTER_VALUE_PAETH;
            }
         }

         if (png_ptr->do_filter == PNG_NO_FILTERS)
            png_ptr->do_filter = PNG_FILTER_NONE;
      }
   }
   else
      png_error(png_ptr, "Unknown custom filter method");
}

/* This allows us to influence the way in which libpng chooses the "best"
 * filter for the current scanline.  While the "minimum-sum-of-absolute-
 * differences metric is relatively fast and effective, there is some
 * question as to whether it can be improved upon by trying to keep the
 * filtered data going to zlib more consistent, hopefully resulting in
 * better compression. */
#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)      /* GRR 970116 */
void
png_set_filter_heuristics(png_structp png_ptr, int heuristic_method,
   int num_weights, png_doublep filter_weights,
   png_doublep filter_costs)
{
   int i;

   png_debug(1, "in png_set_filter_heuristics\n");
   if (heuristic_method >= PNG_FILTER_HEURISTIC_LAST)
   {
      png_warning(png_ptr, "Unknown filter heuristic method");
      return;
   }

   if (heuristic_method == PNG_FILTER_HEURISTIC_DEFAULT)
   {
      heuristic_method = PNG_FILTER_HEURISTIC_UNWEIGHTED;
   }

   if (num_weights < 0 || filter_weights == NULL ||
      heuristic_method == PNG_FILTER_HEURISTIC_UNWEIGHTED)
   {
      num_weights = 0;
   }

   png_ptr->num_prev_filters = num_weights;
   png_ptr->heuristic_method = heuristic_method;

   if (num_weights > 0)
   {
      if (png_ptr->prev_filters == NULL)
      {
         png_ptr->prev_filters = (png_bytep)png_malloc(png_ptr,
            sizeof(png_byte) * num_weights);

         /* To make sure that the weighting starts out fairly */
         for (i = 0; i < num_weights; i++)
         {
            png_ptr->prev_filters[i] = 255;
         }
      }

      if (png_ptr->filter_weights == NULL)
      {
         png_ptr->filter_weights = (png_uint_16p)png_malloc(png_ptr,
            sizeof(png_uint_16) * num_weights);

         png_ptr->inv_filter_weights = (png_uint_16p)png_malloc(png_ptr,
            sizeof(png_uint_16) * num_weights);

         for (i = 0; i < num_weights; i++)
         {
            png_ptr->inv_filter_weights[i] =
            png_ptr->filter_weights[i] = PNG_WEIGHT_FACTOR;
         }
      }

      for (i = 0; i < num_weights; i++)
      {
         if (filter_weights[i] < 0.0)
         {
            png_ptr->inv_filter_weights[i] =
            png_ptr->filter_weights[i] = PNG_WEIGHT_FACTOR;
         }
         else
         {
            png_ptr->inv_filter_weights[i] =
               (png_uint_16)((double)PNG_WEIGHT_FACTOR*filter_weights[i]+0.5);
            png_ptr->filter_weights[i] =
               (png_uint_16)((double)PNG_WEIGHT_FACTOR/filter_weights[i]+0.5);
         }
      }
   }

   /* If, in the future, there are other filter methods, this would
    * need to be based on png_ptr->filter.
    */
   if (png_ptr->filter_costs == NULL)
   {
      png_ptr->filter_costs = (png_uint_16p)png_malloc(png_ptr,
         sizeof(png_uint_16) * PNG_FILTER_VALUE_LAST);

      png_ptr->inv_filter_costs = (png_uint_16p)png_malloc(png_ptr,
         sizeof(png_uint_16) * PNG_FILTER_VALUE_LAST);

      for (i = 0; i < PNG_FILTER_VALUE_LAST; i++)
      {
         png_ptr->inv_filter_costs[i] =
         png_ptr->filter_costs[i] = PNG_COST_FACTOR;
      }
   }

   /* Here is where we set the relative costs of the different filters.  We
    * should take the desired compression level into account when setting
    * the costs, so that Paeth, for instance, has a high relative cost at low
    * compression levels, while it has a lower relative cost at higher
    * compression settings.  The filter types are in order of increasing
    * relative cost, so it would be possible to do this with an algorithm.
    */
   for (i = 0; i < PNG_FILTER_VALUE_LAST; i++)
   {
      if (filter_costs == NULL || filter_costs[i] < 0.0)
      {
         png_ptr->inv_filter_costs[i] =
         png_ptr->filter_costs[i] = PNG_COST_FACTOR;
      }
      else if (filter_costs[i] >= 1.0)
      {
         png_ptr->inv_filter_costs[i] =
            (png_uint_16)((double)PNG_COST_FACTOR / filter_costs[i] + 0.5);
         png_ptr->filter_costs[i] =
            (png_uint_16)((double)PNG_COST_FACTOR * filter_costs[i] + 0.5);
      }
   }
}
#endif /* PNG_WRITE_WEIGHTED_FILTER_SUPPORTED */

void
png_set_compression_level(png_structp png_ptr, int level)
{
   png_debug(1, "in png_set_compression_level\n");
   png_ptr->flags |= PNG_FLAG_ZLIB_CUSTOM_LEVEL;
   png_ptr->zlib_level = level;
}

void
png_set_compression_mem_level(png_structp png_ptr, int mem_level)
{
   png_debug(1, "in png_set_compression_mem_level\n");
   png_ptr->flags |= PNG_FLAG_ZLIB_CUSTOM_MEM_LEVEL;
   png_ptr->zlib_mem_level = mem_level;
}

void
png_set_compression_strategy(png_structp png_ptr, int strategy)
{
   png_debug(1, "in png_set_compression_strategy\n");
   png_ptr->flags |= PNG_FLAG_ZLIB_CUSTOM_STRATEGY;
   png_ptr->zlib_strategy = strategy;
}

void
png_set_compression_window_bits(png_structp png_ptr, int window_bits)
{
   if (window_bits > 15)
      png_warning(png_ptr, "Only compression windows <= 32k supported by PNG");
   png_ptr->flags |= PNG_FLAG_ZLIB_CUSTOM_WINDOW_BITS;
   png_ptr->zlib_window_bits = window_bits;
}

void
png_set_compression_method(png_structp png_ptr, int method)
{
   png_debug(1, "in png_set_compression_method\n");
   if (method != 8)
      png_warning(png_ptr, "Only compression method 8 is supported by PNG");
   png_ptr->flags |= PNG_FLAG_ZLIB_CUSTOM_METHOD;
   png_ptr->zlib_method = method;
}