    /* pngwtran.c - transforms the data in a row for PNG writers
     *
     * Copyright (c) 2018 Cosmin Truta
     * Copyright (c) 1998-2002,2004,2006-2016,2018 Glenn Randers-Pehrson
     * Copyright (c) 1996-1997 Andreas Dilger
     * 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
     */

    #include "pngpriv.h"

    #ifdef PNG_WRITE_SUPPORTED
    #ifdef PNG_WRITE_TRANSFORMS_SUPPORTED

    #ifdef 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).
     */
    static void
    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 &&
          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;
                unsigned int shift;
                int 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;
                unsigned int shift;
                int 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;
             }

             default:
                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

    #ifdef 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.
     */
    static void
    png_do_shift(png_row_infop row_info, png_bytep row,
        png_const_color_8p bit_depth)
    {
       png_debug(1, "in png_do_shift");

       if (row_info->color_type != PNG_COLOR_TYPE_PALETTE)
       {
          int shift_start[4], shift_dec[4];
          unsigned int channels = 0;

          if ((row_info->color_type & PNG_COLOR_MASK_COLOR) != 0)
          {
             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) != 0)
          {
             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;
             size_t i;
             unsigned int mask;
             size_t 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++)
             {
                int j;
                unsigned int v, out;

                v = *bp;
                out = 0;

                for (j = shift_start[0]; j > -shift_dec[0]; j -= shift_dec[0])
                {
                   if (j > 0)
                      out |= v << j;

                   else
                      out |= (v >> (-j)) & mask;
                }

                *bp = (png_byte)(out & 0xff);
             }
          }

          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++)
             {
                unsigned int c = i%channels;
                int j;
                unsigned int v, out;

                v = *bp;
                out = 0;

                for (j = shift_start[c]; j > -shift_dec[c]; j -= shift_dec[c])
                {
                   if (j > 0)
                      out |= v << j;

                   else
                      out |= v >> (-j);
                }

                *bp = (png_byte)(out & 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++)
             {
                unsigned int c = i%channels;
                int j;
                unsigned int value, v;

                v = png_get_uint_16(bp);
                value = 0;

                for (j = shift_start[c]; j > -shift_dec[c]; j -= shift_dec[c])
                {
                   if (j > 0)
                      value |= v << j;

                   else
                      value |= v >> (-j);
                }
                *bp++ = (png_byte)((value >> 8) & 0xff);
                *bp++ = (png_byte)(value & 0xff);
             }
          }
       }
    }
    #endif

    #ifdef PNG_WRITE_SWAP_ALPHA_SUPPORTED
    static void
    png_do_write_swap_alpha(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_write_swap_alpha");

       {
          if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
          {
             if (row_info->bit_depth == 8)
             {
                /* This converts from ARGB to RGBA */
                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;
                }
             }

    #ifdef PNG_WRITE_16BIT_SUPPORTED
             else
             {
                /* This converts from AARRGGBB to RRGGBBAA */
                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];
                }
             }
    #endif /* WRITE_16BIT */
          }

          else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
          {
             if (row_info->bit_depth == 8)
             {
                /* This converts from AG to GA */
                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;
                }
             }

    #ifdef PNG_WRITE_16BIT_SUPPORTED
             else
             {
                /* This converts from AAGG to GGAA */
                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 /* WRITE_16BIT */
          }
       }
    }
    #endif

    #ifdef PNG_WRITE_INVERT_ALPHA_SUPPORTED
    static void
    png_do_write_invert_alpha(png_row_infop row_info, png_bytep row)
    {
       png_debug(1, "in png_do_write_invert_alpha");

       {
          if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
          {
             if (row_info->bit_depth == 8)
             {
                /* This inverts the alpha channel in RGBA */
                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++));
                }
             }

    #ifdef PNG_WRITE_16BIT_SUPPORTED
             else
             {
                /* This inverts the alpha channel in RRGGBBAA */
                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++));
                }
             }
    #endif /* WRITE_16BIT */
          }

          else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
          {
             if (row_info->bit_depth == 8)
             {
                /* This inverts the alpha channel in GA */
                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++));
                }
             }

    #ifdef PNG_WRITE_16BIT_SUPPORTED
             else
             {
                /* This inverts the alpha channel in GGAA */
                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 /* WRITE_16BIT */
          }
       }
    }
    #endif

    /* Transform the data according to the user's wishes.  The order of
     * transformations is significant.
     */
    void /* PRIVATE */
    png_do_write_transformations(png_structrp png_ptr, png_row_infop row_info)
    {
       png_debug(1, "in png_do_write_transformations");

       if (png_ptr == NULL)
          return;

    #ifdef PNG_WRITE_USER_TRANSFORM_SUPPORTED
       if ((png_ptr->transformations & PNG_USER_TRANSFORM) != 0)
          if (png_ptr->write_user_transform_fn != NULL)
             (*(png_ptr->write_user_transform_fn)) /* User write transform
                                                     function */
                 (png_ptr,  /* png_ptr */
                 row_info,  /* row_info: */
                    /*  png_uint_32 width;       width of row */
                    /*  size_t 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

    #ifdef PNG_WRITE_FILLER_SUPPORTED
       if ((png_ptr->transformations & PNG_FILLER) != 0)
          png_do_strip_channel(row_info, png_ptr->row_buf + 1,
              !(png_ptr->flags & PNG_FLAG_FILLER_AFTER));
    #endif

    #ifdef PNG_WRITE_PACKSWAP_SUPPORTED
       if ((png_ptr->transformations & PNG_PACKSWAP) != 0)
          png_do_packswap(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_WRITE_PACK_SUPPORTED
       if ((png_ptr->transformations & PNG_PACK) != 0)
          png_do_pack(row_info, png_ptr->row_buf + 1,
              (png_uint_32)png_ptr->bit_depth);
    #endif

    #ifdef PNG_WRITE_SWAP_SUPPORTED
    #  ifdef PNG_16BIT_SUPPORTED
       if ((png_ptr->transformations & PNG_SWAP_BYTES) != 0)
          png_do_swap(row_info, png_ptr->row_buf + 1);
    #  endif
    #endif

    #ifdef PNG_WRITE_SHIFT_SUPPORTED
       if ((png_ptr->transformations & PNG_SHIFT) != 0)
          png_do_shift(row_info, png_ptr->row_buf + 1,
               &(png_ptr->shift));
    #endif

    #ifdef PNG_WRITE_SWAP_ALPHA_SUPPORTED
       if ((png_ptr->transformations & PNG_SWAP_ALPHA) != 0)
          png_do_write_swap_alpha(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_WRITE_INVERT_ALPHA_SUPPORTED
       if ((png_ptr->transformations & PNG_INVERT_ALPHA) != 0)
          png_do_write_invert_alpha(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_WRITE_BGR_SUPPORTED
       if ((png_ptr->transformations & PNG_BGR) != 0)
          png_do_bgr(row_info, png_ptr->row_buf + 1);
    #endif

    #ifdef PNG_WRITE_INVERT_SUPPORTED
       if ((png_ptr->transformations & PNG_INVERT_MONO) != 0)
          png_do_invert(row_info, png_ptr->row_buf + 1);
    #endif
    }
    #endif /* WRITE_TRANSFORMS */
    #endif /* WRITE */