pngwutil.c

hl2 source code. Do not use it illegal.

#else
   if (pass < 6)
#endif
   {
      /* each pixel depth is handled separately */
      switch (row_info->pixel_depth)
      {
         case 1:
         {
            png_bytep sp;
            png_bytep dp;
            int shift;
            int d;
            int value;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;

            dp = row;
            d = 0;
            shift = 7;
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               sp = row + (png_size_t)(i >> 3);
               value = (int)(*sp >> (7 - (int)(i & 7))) & 0x1;
               d |= (value << shift);

               if (shift == 0)
               {
                  shift = 7;
                  *dp++ = (png_byte)d;
                  d = 0;
               }
               else
                  shift--;

            }
            if (shift != 7)
               *dp = (png_byte)d;
            break;
         }
         case 2:
         {
            png_bytep sp;
            png_bytep dp;
            int shift;
            int d;
            int value;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;

            dp = row;
            shift = 6;
            d = 0;
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               sp = row + (png_size_t)(i >> 2);
               value = (*sp >> ((3 - (int)(i & 3)) << 1)) & 0x3;
               d |= (value << shift);

               if (shift == 0)
               {
                  shift = 6;
                  *dp++ = (png_byte)d;
                  d = 0;
               }
               else
                  shift -= 2;
            }
            if (shift != 6)
                   *dp = (png_byte)d;
            break;
         }
         case 4:
         {
            png_bytep sp;
            png_bytep dp;
            int shift;
            int d;
            int value;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;

            dp = row;
            shift = 4;
            d = 0;
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               sp = row + (png_size_t)(i >> 1);
               value = (*sp >> ((1 - (int)(i & 1)) << 2)) & 0xf;
               d |= (value << shift);

               if (shift == 0)
               {
                  shift = 4;
                  *dp++ = (png_byte)d;
                  d = 0;
               }
               else
                  shift -= 4;
            }
            if (shift != 4)
               *dp = (png_byte)d;
            break;
         }
         default:
         {
            png_bytep sp;
            png_bytep dp;
            png_uint_32 i;
            png_uint_32 row_width = row_info->width;
            png_size_t pixel_bytes;

            /* start at the beginning */
            dp = row;
            /* find out how many bytes each pixel takes up */
            pixel_bytes = (row_info->pixel_depth >> 3);
            /* loop through the row, only looking at the pixels that
               matter */
            for (i = png_pass_start[pass]; i < row_width;
               i += png_pass_inc[pass])
            {
               /* find out where the original pixel is */
               sp = row + (png_size_t)i * pixel_bytes;
               /* move the pixel */
               if (dp != sp)
                  png_memcpy(dp, sp, pixel_bytes);
               /* next pixel */
               dp += pixel_bytes;
            }
            break;
         }
      }
      /* set new row width */
      row_info->width = (row_info->width +
         png_pass_inc[pass] - 1 -
         png_pass_start[pass]) /
         png_pass_inc[pass];
         row_info->rowbytes = ((row_info->width *
            row_info->pixel_depth + 7) >> 3);
   }
}
#endif

/* This filters the row, chooses which filter to use, if it has not already
 * been specified by the application, and then writes the row out with the
 * chosen filter.
 */
#define PNG_MAXSUM (~((png_uint_32)0) >> 1)
#define PNG_HISHIFT 10
#define PNG_LOMASK ((png_uint_32)0xffffL)
#define PNG_HIMASK ((png_uint_32)(~PNG_LOMASK >> PNG_HISHIFT))
void
png_write_find_filter(png_structp png_ptr, png_row_infop row_info)
{
   png_bytep prev_row, best_row, row_buf;
   png_uint_32 mins, bpp;
   png_byte filter_to_do = png_ptr->do_filter;
   png_uint_32 row_bytes = row_info->rowbytes;
#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
   int num_p_filters = (int)png_ptr->num_prev_filters;
#endif

   png_debug(1, "in png_write_find_filter\n");
   /* find out how many bytes offset each pixel is */
   bpp = (row_info->pixel_depth + 7) / 8;

   prev_row = png_ptr->prev_row;
   best_row = row_buf = png_ptr->row_buf;
   mins = PNG_MAXSUM;

   /* The prediction method we use is to find which method provides the
    * smallest value when summing the absolute values of the distances
    * from zero, using anything >= 128 as negative numbers.  This is known
    * as the "minimum sum of absolute differences" heuristic.  Other
    * heuristics are the "weighted minimum sum of absolute differences"
    * (experimental and can in theory improve compression), and the "zlib
    * predictive" method (not implemented yet), which does test compressions
    * of lines using different filter methods, and then chooses the
    * (series of) filter(s) that give minimum compressed data size (VERY
    * computationally expensive).
    *
    * GRR 980525:  consider also
    *   (1) minimum sum of absolute differences from running average (i.e.,
    *       keep running sum of non-absolute differences & count of bytes)
    *       [track dispersion, too?  restart average if dispersion too large?]
    *  (1b) minimum sum of absolute differences from sliding average, probably
    *       with window size <= deflate window (usually 32K)
    *   (2) minimum sum of squared differences from zero or running average
    *       (i.e., ~ root-mean-square approach)
    */


   /* We don't need to test the 'no filter' case if this is the only filter
    * that has been chosen, as it doesn't actually do anything to the data.
    */
   if (filter_to_do & PNG_FILTER_NONE &&
       filter_to_do != PNG_FILTER_NONE)
   {
      png_bytep rp;
      png_uint_32 sum = 0;
      png_uint_32 i;
      int v;

      for (i = 0, rp = row_buf + 1; i < row_bytes; i++, rp++)
      {
         v = *rp;
         sum += (v < 128) ? v : 256 - v;
      }

#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
      if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
      {
         png_uint_32 sumhi, sumlo;
         int j;
         sumlo = sum & PNG_LOMASK;
         sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK; /* Gives us some footroom */

         /* Reduce the sum if we match any of the previous rows */
         for (j = 0; j < num_p_filters; j++)
         {
            if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_NONE)
            {
               sumlo = (sumlo * png_ptr->filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
               sumhi = (sumhi * png_ptr->filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
            }
         }

         /* Factor in the cost of this filter (this is here for completeness,
          * but it makes no sense to have a "cost" for the NONE filter, as
          * it has the minimum possible computational cost - none).
          */
         sumlo = (sumlo * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
            PNG_COST_SHIFT;
         sumhi = (sumhi * png_ptr->filter_costs[PNG_FILTER_VALUE_NONE]) >>
            PNG_COST_SHIFT;

         if (sumhi > PNG_HIMASK)
            sum = PNG_MAXSUM;
         else
            sum = (sumhi << PNG_HISHIFT) + sumlo;
      }
#endif
      mins = sum;
   }

   /* sub filter */
   if (filter_to_do == PNG_FILTER_SUB)
   /* it's the only filter so no testing is needed */
   {
      png_bytep rp, lp, dp;
      png_uint_32 i;
      for (i = 0, rp = row_buf + 1, dp = png_ptr->sub_row + 1; i < bpp;
           i++, rp++, dp++)
      {
         *dp = *rp;
      }
      for (lp = row_buf + 1; i < row_bytes;
         i++, rp++, lp++, dp++)
      {
         *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
      }
      best_row = png_ptr->sub_row;
   }

   else if (filter_to_do & PNG_FILTER_SUB)
   {
      png_bytep rp, dp, lp;
      png_uint_32 sum = 0, lmins = mins;
      png_uint_32 i;
      int v;

#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
      /* We temporarily increase the "minimum sum" by the factor we
       * would reduce the sum of this filter, so that we can do the
       * early exit comparison without scaling the sum each time.
       */
      if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
      {
         int j;
         png_uint_32 lmhi, lmlo;
         lmlo = lmins & PNG_LOMASK;
         lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;

         for (j = 0; j < num_p_filters; j++)
         {
            if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
            {
               lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
               lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
            }
         }

         lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
            PNG_COST_SHIFT;
         lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
            PNG_COST_SHIFT;

         if (lmhi > PNG_HIMASK)
            lmins = PNG_MAXSUM;
         else
            lmins = (lmhi << PNG_HISHIFT) + lmlo;
      }
#endif

      for (i = 0, rp = row_buf + 1, dp = png_ptr->sub_row + 1; i < bpp;
           i++, rp++, dp++)
      {
         v = *dp = *rp;

         sum += (v < 128) ? v : 256 - v;
      }
      for (lp = row_buf + 1; i < row_info->rowbytes;
         i++, rp++, lp++, dp++)
      {
         v = *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);

         sum += (v < 128) ? v : 256 - v;

         if (sum > lmins)  /* We are already worse, don't continue. */
            break;
      }

#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
      if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
      {
         int j;
         png_uint_32 sumhi, sumlo;
         sumlo = sum & PNG_LOMASK;
         sumhi = (sum >> PNG_HISHIFT) & PNG_HIMASK;

         for (j = 0; j < num_p_filters; j++)
         {
            if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_SUB)
            {
               sumlo = (sumlo * png_ptr->inv_filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
               sumhi = (sumhi * png_ptr->inv_filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
            }
         }

         sumlo = (sumlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
            PNG_COST_SHIFT;
         sumhi = (sumhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_SUB]) >>
            PNG_COST_SHIFT;

         if (sumhi > PNG_HIMASK)
            sum = PNG_MAXSUM;
         else
            sum = (sumhi << PNG_HISHIFT) + sumlo;
      }
#endif

      if (sum < mins)
      {
         mins = sum;
         best_row = png_ptr->sub_row;
      }
   }

   /* up filter */
   if (filter_to_do == PNG_FILTER_UP)
   {
      png_bytep rp, dp, pp;
      png_uint_32 i;

      for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
           pp = prev_row + 1; i < row_bytes;
           i++, rp++, pp++, dp++)
      {
         *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
      }
      best_row = png_ptr->up_row;
   }

   else if (filter_to_do & PNG_FILTER_UP)
   {
      png_bytep rp, dp, pp;
      png_uint_32 sum = 0, lmins = mins;
      png_uint_32 i;
      int v;


#if defined(PNG_WRITE_WEIGHTED_FILTER_SUPPORTED)
      if (png_ptr->heuristic_method == PNG_FILTER_HEURISTIC_WEIGHTED)
      {
         int j;
         png_uint_32 lmhi, lmlo;
         lmlo = lmins & PNG_LOMASK;
         lmhi = (lmins >> PNG_HISHIFT) & PNG_HIMASK;

         for (j = 0; j < num_p_filters; j++)
         {
            if (png_ptr->prev_filters[j] == PNG_FILTER_VALUE_UP)
            {
               lmlo = (lmlo * png_ptr->inv_filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
               lmhi = (lmhi * png_ptr->inv_filter_weights[j]) >>
                  PNG_WEIGHT_SHIFT;
            }
         }

         lmlo = (lmlo * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
            PNG_COST_SHIFT;
         lmhi = (lmhi * png_ptr->inv_filter_costs[PNG_FILTER_VALUE_UP]) >>
            PNG_COST_SHIFT;