pngwtran.c

/* pngwtran.c - transforms the data in a row for PNG writers
 *
 * libpng 1.00.97
 * 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 28, 1997
 */

#define PNG_INTERNAL
#include "png.h"

/* Transform the data according to the users wishes.  The order of
 * transformations is significant.
 */
void
png_do_write_transformations(png_structp png_ptr)
{
   png_debug(1, "in png_do_write_transformations\n");
#if defined(PNG_WRITE_FILLER_SUPPORTED)
   if (png_ptr->transformations & PNG_FILLER)
      png_do_strip_filler(&(png_ptr->row_info), png_ptr->row_buf + 1,
         png_ptr->flags);
#endif
#if defined(PNG_WRITE_PACK_SUPPORTED)
   if (png_ptr->transformations & PNG_PACK)
      png_do_pack(&(png_ptr->row_info), png_ptr->row_buf + 1,
         (png_uint_32)png_ptr->bit_depth);
#endif
#if defined(PNG_WRITE_SHIFT_SUPPORTED)
   if (png_ptr->transformations & PNG_SHIFT)
      png_do_shift(&(png_ptr->row_info), png_ptr->row_buf + 1,
         &(png_ptr->shift));
#endif
#if defined(PNG_WRITE_SWAP_SUPPORTED)
   if (png_ptr->transformations & PNG_SWAP_BYTES)
      png_do_swap(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif
#if defined(PNG_WRITE_SWAP_ALPHA_SUPPORTED)
   if (png_ptr->transformations & PNG_SWAP_ALPHA)
      png_do_write_swap_alpha(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif
#if defined(PNG_WRITE_BGR_SUPPORTED)
   if (png_ptr->transformations & PNG_BGR)
      png_do_bgr(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif
#if defined(PNG_WRITE_INVERT_SUPPORTED)
   if (png_ptr->transformations & PNG_INVERT_MONO)
      png_do_invert(&(png_ptr->row_info), png_ptr->row_buf + 1);
#endif
}

#if defined(PNG_WRITE_PACK_SUPPORTED)
/* Pack pixels into bytes.  Pass the true bit depth in bit_depth.  The
 * row_info bit depth should be 8 (one pixel per byte).  The channels
 * should be 1 (this only happens on grayscale and paletted images).
 */
void
png_do_pack(png_row_infop row_info, png_bytep row, png_uint_32 bit_depth)
{
   png_debug(1, "in png_do_pack\n");
   if (row_info->bit_depth == 8 &&
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL &&
#endif
      row_info->channels == 1)
   {
      switch ((int)bit_depth)
      {
         case 1:
         {
            png_bytep sp, dp;
            int mask, v;
            png_uint_32 i;

            sp = row;
            dp = row;
            mask = 0x80;
            v = 0;
            for (i = 0; i < row_info->width; i++)
            {
               if (*sp != 0)
                  v |= mask;
               sp++;
               if (mask > 1)
                  mask >>= 1;
               else
               {
                  mask = 0x80;
                  *dp = (png_byte)v;
                  dp++;
                  v = 0;
               }
            }
            if (mask != 0x80)
               *dp = (png_byte)v;
            break;
         }
         case 2:
         {
            png_bytep sp, dp;
            int shift, v;
            png_uint_32 i;

            sp = row;
            dp = row;
            shift = 6;
            v = 0;
            for (i = 0; i < row_info->width; i++)
            {
               png_byte value;

               value = (png_byte)(*sp & 0x3);
               v |= (value << shift);
               if (shift == 0)
               {
                  shift = 6;
                  *dp = (png_byte)v;
                  dp++;
                  v = 0;
               }
               else
                  shift -= 2;
               sp++;
            }
            if (shift != 6)
               *dp = (png_byte)v;
            break;
         }
         case 4:
         {
            png_bytep sp, dp;
            int shift, v;
            png_uint_32 i;

            sp = row;
            dp = row;
            shift = 4;
            v = 0;
            for (i = 0; i < row_info->width; i++)
            {
               png_byte value;

               value = (png_byte)(*sp & 0xf);
               v |= (value << shift);

               if (shift == 0)
               {
                  shift = 4;
                  *dp = (png_byte)v;
                  dp++;
                  v = 0;
               }
               else
                  shift -= 4;

               sp++;
            }
            if (shift != 4)
               *dp = (png_byte)v;
            break;
         }
      }
      row_info->bit_depth = (png_byte)bit_depth;
      row_info->pixel_depth = (png_byte)(bit_depth * row_info->channels);
      row_info->rowbytes =
         ((row_info->width * row_info->pixel_depth + 7) >> 3);
   }
}
#endif

#if defined(PNG_WRITE_SHIFT_SUPPORTED)
/* Shift pixel values to take advantage of whole range.  Pass the
 * true number of bits in bit_depth.  The row should be packed
 * according to row_info->bit_depth.  Thus, if you had a row of
 * bit depth 4, but the pixels only had values from 0 to 7, you
 * would pass 3 as bit_depth, and this routine would translate the
 * data to 0 to 15.
 */
void
png_do_shift(png_row_infop row_info, png_bytep row, png_color_8p bit_depth)
{
   png_debug(1, "in png_do_shift\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL &&
#else
   if (
#endif
      row_info->color_type != PNG_COLOR_TYPE_PALETTE)
   {
      int shift_start[4], shift_dec[4];
      png_uint_32 channels;

      channels = 0;
      if (row_info->color_type & PNG_COLOR_MASK_COLOR)
      {
         shift_start[channels] = row_info->bit_depth - bit_depth->red;
         shift_dec[channels] = bit_depth->red;
         channels++;
         shift_start[channels] = row_info->bit_depth - bit_depth->green;
         shift_dec[channels] = bit_depth->green;
         channels++;
         shift_start[channels] = row_info->bit_depth - bit_depth->blue;
         shift_dec[channels] = bit_depth->blue;
         channels++;
      }
      else
      {
         shift_start[channels] = row_info->bit_depth - bit_depth->gray;
         shift_dec[channels] = bit_depth->gray;
         channels++;
      }
      if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
      {
         shift_start[channels] = row_info->bit_depth - bit_depth->alpha;
         shift_dec[channels] = bit_depth->alpha;
         channels++;
      }

      /* with low row dephts, could only be grayscale, so one channel */
      if (row_info->bit_depth < 8)
      {
         png_bytep bp;
         png_uint_32 i;
         png_byte mask;

         if (bit_depth->gray == 1 && row_info->bit_depth == 2)
            mask = 0x55;
         else if (row_info->bit_depth == 4 && bit_depth->gray == 3)
            mask = 0x11;
         else
            mask = 0xff;

         for (bp = row, i = 0; i < row_info->rowbytes; i++, bp++)
         {
            png_uint_16 v;
            int j;

            v = *bp;
            *bp = 0;
            for (j = shift_start[0]; j > -shift_dec[0]; j -= shift_dec[0])
            {
               if (j > 0)
                  *bp |= (png_byte)((v << j) & 0xff);
               else
                  *bp |= (png_byte)((v >> (-j)) & mask);
            }
         }
      }
      else if (row_info->bit_depth == 8)
      {
         png_bytep bp;
         png_uint_32 i;

         for (bp = row, i = 0; i < row_info->width; i++)
         {
            png_uint_32 c;

            for (c = 0; c < channels; c++, bp++)
            {
               png_uint_16 v;
               int j;

               v = *bp;
               *bp = 0;
               for (j = shift_start[c]; j > -shift_dec[c]; j -= shift_dec[c])
               {
                  if (j > 0)
                     *bp |= (png_byte)((v << j) & 0xff);
                  else
                     *bp |= (png_byte)((v >> (-j)) & 0xff);
               }
            }
         }
      }
      else
      {
         png_bytep bp;
         png_uint_32 i;

         for (bp = row, i = 0; i < row_info->width * row_info->channels; i++)
         {
            png_uint_32 c;

            for (c = 0; c < channels; c++, bp += 2)
            {
               png_uint_16 value, v;
               int j;

               v = ((png_uint_16)(*bp) << 8) + *(bp + 1);
               value = 0;
               for (j = shift_start[c]; j > -shift_dec[c]; j -= shift_dec[c])
               {
                  if (j > 0)
                     value |= (png_uint_16)((v << j) & (png_uint_16)0xffff);
                  else
                     value |= (png_uint_16)((v >> (-j)) & (png_uint_16)0xffff);
               }
               *bp = (png_byte)(value >> 8);
               *(bp + 1) = (png_byte)(value & 0xff);
            }
         }
      }
   }
}
#endif

#if defined(PNG_WRITE_SWAP_ALPHA_SUPPORTED)
void
png_do_write_swap_alpha(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_write_swap_alpha\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL)
#endif
   {
      if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
      {
         /* This converts from ARGB to RGBA */
         if (row_info->bit_depth == 8)
         {
            png_bytep sp, dp;
            png_byte save;
            png_uint_32 i;

            for (i = 0, sp = dp = row; i < row_info->width; i++)
            {
               save = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = save;
            }
         }
         /* This converts from AARRGGBB to RRGGBBAA */
         else
         {
            png_bytep sp, dp;
            png_byte save[2];
            png_uint_32 i;

            for (i = 0, sp = dp = row; i < row_info->width; i++)
            {
               save[0] = *(sp++);
               save[1] = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = save[0];
               *(dp++) = save[1];
            }
         }
      }
      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
      {
         /* This converts from AG to GA */
         if (row_info->bit_depth == 8)
         {
            png_bytep sp, dp;
            png_byte save;
            png_uint_32 i;

            for (i = 0, sp = dp = row; i < row_info->width; i++)
            {
               save = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = save;
            }
         }
         /* This converts from AAGG to GGAA */
         else
         {
            png_bytep sp, dp;
            png_byte save[2];
            png_uint_32 i;

            for (i = 0, sp = dp = row; i < row_info->width; i++)
            {
               save[0] = *(sp++);
               save[1] = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = *(sp++);
               *(dp++) = save[0];
               *(dp++) = save[1];
            }
         }
      }
   }
}
#endif