text: 
  /* pngwtran.c - transforms the data in a row for PNG writers
   *
   * Last changed in libpng 1.2.37 [June 4, 2009]
   * Copyright (c) 1998-2009 Glenn Randers-Pehrson
   * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
   * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
   *
   * This code is released under the libpng license.
   * For conditions of distribution and use, see the disclaimer
   * and license in png.h
   */
  
  #define PNG_INTERNAL
  #include "png.h"
  #ifdef PNG_WRITE_SUPPORTED
  
  /* Transform the data according to the user's wishes.  The order of
   * transformations is significant.
   */
  void /* PRIVATE */
  png_do_write_transformations(png_structp png_ptr)
  {
     png_debug(1, "in png_do_write_transformations");
  
     if (png_ptr == NULL)
        return;
  
  #if defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
     if (png_ptr->transformations & PNG_USER_TRANSFORM)
        if (png_ptr->write_user_transform_fn != NULL)
          (*(png_ptr->write_user_transform_fn)) /* User write transform function */
            (png_ptr,                    /* png_ptr */
             &(png_ptr->row_info),       /* row_info:     */
               /*  png_uint_32 width;          width of row */
               /*  png_uint_32 rowbytes;       number of bytes in row */
               /*  png_byte color_type;        color type of pixels */
               /*  png_byte bit_depth;         bit depth of samples */
               /*  png_byte channels;          number of channels (1-4) */
               /*  png_byte pixel_depth;       bits per pixel (depth*channels) */
             png_ptr->row_buf + 1);      /* start of pixel data for row */
  #endif
  #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_PACKSWAP_SUPPORTED)
     if (png_ptr->transformations & PNG_PACKSWAP)
        png_do_packswap(&(png_ptr->row_info), png_ptr->row_buf + 1);
  #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_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_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_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_INVERT_ALPHA_SUPPORTED)
     if (png_ptr->transformations & PNG_INVERT_ALPHA)
        png_do_write_invert_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 /* PRIVATE */
  png_do_pack(png_row_infop row_info, png_bytep row, png_uint_32 bit_depth)
  {
     png_debug(1, "in png_do_pack");
     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;
              png_uint_32 row_width = row_info->width;
  
              sp = row;
              dp = row;
              mask = 0x80;
              v = 0;
  
              for (i = 0; i < row_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;
              png_uint_32 row_width = row_info->width;
  
              sp = row;
              dp = row;
              shift = 6;
              v = 0;
              for (i = 0; i < row_width; i++)
              {
                 png_byte value;
  
                 value = (png_byte)(*sp & 0x03);
                 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;
              png_uint_32 row_width = row_info->width;
  
              sp = row;
              dp = row;
              shift = 4;
              v = 0;
              for (i = 0; i < row_width; i++)
              {
                 png_byte value;
  
                 value = (png_byte)(*sp & 0x0f);
                 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 = PNG_ROWBYTES(row_info->pixel_depth,
           row_info->width);
     }
  }
  #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 /* PRIVATE */
  png_do_shift(png_row_infop row_info, png_bytep row, png_color_8p bit_depth)
  {
     png_debug(1, "in png_do_shift");
  #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];
        int 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 depths, could only be grayscale, so one channel */
        if (row_info->bit_depth < 8)
        {
           png_bytep bp = row;
           png_uint_32 i;
           png_byte mask;
           png_uint_32 row_bytes = row_info->rowbytes;
  
           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 (i = 0; i < row_bytes; 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 = row;
           png_uint_32 i;
           png_uint_32 istop = channels * row_info->width;
  
           for (i = 0; i < istop; i++, bp++)
           {
  
              png_uint_16 v;
              int j;
              int c = (int)(i%channels);
  
              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;
           png_uint_32 istop = channels * row_info->width;
  
           for (bp = row, i = 0; i < istop; i++)
           {
              int c = (int)(i%channels);
              png_uint_16 value, v;
              int j;
  
              v = (png_uint_16)(((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++ = (png_byte)(value & 0xff);
           }
        }
     }
  }
  #endif
  
  #if defined(PNG_WRITE_SWAP_ALPHA_SUPPORTED)
  void /* PRIVATE */
  png_do_write_swap_alpha(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_write_swap_alpha");
  #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_uint_32 i;
              png_uint_32 row_width = row_info->width;
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 png_byte save = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = save;
              }
           }
           /* This converts from AARRGGBB to RRGGBBAA */
           else
           {
              png_bytep sp, dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 png_byte save[2];
                 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_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 png_byte save = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = save;
              }
           }
           /* This converts from AAGG to GGAA */
           else
           {
              png_bytep sp, dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 png_byte save[2];
                 save[0] = *(sp++);
                 save[1] = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = save[0];
                 *(dp++) = save[1];
              }
           }
        }
     }
  }
  #endif
  
  #if defined(PNG_WRITE_INVERT_ALPHA_SUPPORTED)
  void /* PRIVATE */
  png_do_write_invert_alpha(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_write_invert_alpha");
  #if defined(PNG_USELESS_TESTS_SUPPORTED)
     if (row != NULL && row_info != NULL)
  #endif
     {
        if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
        {
           /* This inverts the alpha channel in RGBA */
           if (row_info->bit_depth == 8)
           {
              png_bytep sp, dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 /* Does nothing
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 */
                 sp+=3; dp = sp;
                 *(dp++) = (png_byte)(255 - *(sp++));
              }
           }
           /* This inverts the alpha channel in RRGGBBAA */
           else
           {
              png_bytep sp, dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 /* Does nothing
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 */
                 sp+=6; dp = sp;
                 *(dp++) = (png_byte)(255 - *(sp++));
                 *(dp++) = (png_byte)(255 - *(sp++));
              }
           }
        }
        else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
        {
           /* This inverts the alpha channel in GA */
           if (row_info->bit_depth == 8)
           {
              png_bytep sp, dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 *(dp++) = *(sp++);
                 *(dp++) = (png_byte)(255 - *(sp++));
              }
           }
           /* This inverts the alpha channel in GGAA */
           else
           {
              png_bytep sp, dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              for (i = 0, sp = dp = row; i < row_width; i++)
              {
                 /* Does nothing
                 *(dp++) = *(sp++);
                 *(dp++) = *(sp++);
                 */
                 sp+=2; dp = sp;
                 *(dp++) = (png_byte)(255 - *(sp++));
                 *(dp++) = (png_byte)(255 - *(sp++));
              }
           }
        }
     }
  }
  #endif
  
  #if defined(PNG_MNG_FEATURES_SUPPORTED)
  /* Undoes intrapixel differencing  */
  void /* PRIVATE */
  png_do_write_intrapixel(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_write_intrapixel");
     if (
  #if defined(PNG_USELESS_TESTS_SUPPORTED)
         row != NULL && row_info != NULL &&
  #endif
         (row_info->color_type & PNG_COLOR_MASK_COLOR))
     {
        int bytes_per_pixel;
        png_uint_32 row_width = row_info->width;
        if (row_info->bit_depth == 8)
        {
           png_bytep rp;
           png_uint_32 i;
  
           if (row_info->color_type == PNG_COLOR_TYPE_RGB)
              bytes_per_pixel = 3;
           else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
              bytes_per_pixel = 4;
           else
              return;
  
           for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
           {
              *(rp)   = (png_byte)((*rp     - *(rp+1))&0xff);
              *(rp+2) = (png_byte)((*(rp+2) - *(rp+1))&0xff);
           }
        }
        else if (row_info->bit_depth == 16)
        {
           png_bytep rp;
           png_uint_32 i;
  
           if (row_info->color_type == PNG_COLOR_TYPE_RGB)
              bytes_per_pixel = 6;
           else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
              bytes_per_pixel = 8;
           else
              return;
  
           for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
           {
              png_uint_32 s0   = (*(rp  ) << 8) | *(rp+1);
              png_uint_32 s1   = (*(rp+2) << 8) | *(rp+3);
              png_uint_32 s2   = (*(rp+4) << 8) | *(rp+5);
              png_uint_32 red  = (png_uint_32)((s0 - s1) & 0xffffL);
              png_uint_32 blue = (png_uint_32)((s2 - s1) & 0xffffL);
              *(rp  ) = (png_byte)((red >> 8) & 0xff);
              *(rp+1) = (png_byte)(red & 0xff);
              *(rp+4) = (png_byte)((blue >> 8) & 0xff);
              *(rp+5) = (png_byte)(blue & 0xff);
           }
        }
     }
  }
  #endif /* PNG_MNG_FEATURES_SUPPORTED */
  #endif /* PNG_WRITE_SUPPORTED */
  