pngtrans.c

/* pngtrans.c - transforms the data in a row (used by both readers and writers)
 *
 * Last changed in libpng 1.6.33 [September 28, 2017]
 * Copyright (c) 1998-2002,2004,2006-2017 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
 */

#include "pngpriv.h"

#if defined(PNG_READ_SUPPORTED) || defined(PNG_WRITE_SUPPORTED)

#if defined(PNG_READ_BGR_SUPPORTED) || defined(PNG_WRITE_BGR_SUPPORTED)
/* Turn on BGR-to-RGB mapping */
void PNGAPI
png_set_bgr(png_structrp png_ptr)
{
   png_debug(1, "in png_set_bgr");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_BGR;
}
#endif

#if defined(PNG_READ_SWAP_SUPPORTED) || defined(PNG_WRITE_SWAP_SUPPORTED)
/* Turn on 16-bit byte swapping */
void PNGAPI
png_set_swap(png_structrp png_ptr)
{
   png_debug(1, "in png_set_swap");

   if (png_ptr == NULL)
      return;

   if (png_ptr->bit_depth == 16)
      png_ptr->transformations |= PNG_SWAP_BYTES;
}
#endif

#if defined(PNG_READ_PACK_SUPPORTED) || defined(PNG_WRITE_PACK_SUPPORTED)
/* Turn on pixel packing */
void PNGAPI
png_set_packing(png_structrp png_ptr)
{
   png_debug(1, "in png_set_packing");

   if (png_ptr == NULL)
      return;

   if (png_ptr->bit_depth < 8)
   {
      png_ptr->transformations |= PNG_PACK;
#     ifdef PNG_WRITE_SUPPORTED
         png_ptr->usr_bit_depth = 8;
#     endif
   }
}
#endif

#if defined(PNG_READ_PACKSWAP_SUPPORTED)||defined(PNG_WRITE_PACKSWAP_SUPPORTED)
/* Turn on packed pixel swapping */
void PNGAPI
png_set_packswap(png_structrp png_ptr)
{
   png_debug(1, "in png_set_packswap");

   if (png_ptr == NULL)
      return;

   if (png_ptr->bit_depth < 8)
      png_ptr->transformations |= PNG_PACKSWAP;
}
#endif

#if defined(PNG_READ_SHIFT_SUPPORTED) || defined(PNG_WRITE_SHIFT_SUPPORTED)
void PNGAPI
png_set_shift(png_structrp png_ptr, png_const_color_8p true_bits)
{
   png_debug(1, "in png_set_shift");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_SHIFT;
   png_ptr->shift = *true_bits;
}
#endif

#if defined(PNG_READ_INTERLACING_SUPPORTED) || \
    defined(PNG_WRITE_INTERLACING_SUPPORTED)
int PNGAPI
png_set_interlace_handling(png_structrp png_ptr)
{
   png_debug(1, "in png_set_interlace handling");

   if (png_ptr != 0 && png_ptr->interlaced != 0)
   {
      png_ptr->transformations |= PNG_INTERLACE;
      return (7);
   }

   return (1);
}
#endif

#if defined(PNG_READ_FILLER_SUPPORTED) || defined(PNG_WRITE_FILLER_SUPPORTED)
/* Add a filler byte on read, or remove a filler or alpha byte on write.
 * The filler type has changed in v0.95 to allow future 2-byte fillers
 * for 48-bit input data, as well as to avoid problems with some compilers
 * that don't like bytes as parameters.
 */
void PNGAPI
png_set_filler(png_structrp png_ptr, png_uint_32 filler, int filler_loc)
{
   png_debug(1, "in png_set_filler");

   if (png_ptr == NULL)
      return;

   /* In libpng 1.6 it is possible to determine whether this is a read or write
    * operation and therefore to do more checking here for a valid call.
    */
   if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0)
   {
#     ifdef PNG_READ_FILLER_SUPPORTED
         /* On read png_set_filler is always valid, regardless of the base PNG
          * format, because other transformations can give a format where the
          * filler code can execute (basically an 8 or 16-bit component RGB or G
          * format.)
          *
          * NOTE: usr_channels is not used by the read code!  (This has led to
          * confusion in the past.)  The filler is only used in the read code.
          */
         png_ptr->filler = (png_uint_16)filler;
#     else
         png_app_error(png_ptr, "png_set_filler not supported on read");
         PNG_UNUSED(filler) /* not used in the write case */
         return;
#     endif
   }

   else /* write */
   {
#     ifdef PNG_WRITE_FILLER_SUPPORTED
         /* On write the usr_channels parameter must be set correctly at the
          * start to record the number of channels in the app-supplied data.
          */
         switch (png_ptr->color_type)
         {
            case PNG_COLOR_TYPE_RGB:
               png_ptr->usr_channels = 4;
               break;

            case PNG_COLOR_TYPE_GRAY:
               if (png_ptr->bit_depth >= 8)
               {
                  png_ptr->usr_channels = 2;
                  break;
               }

               else
               {
                  /* There simply isn't any code in libpng to strip out bits
                   * from bytes when the components are less than a byte in
                   * size!
                   */
                  png_app_error(png_ptr,
                      "png_set_filler is invalid for"
                      " low bit depth gray output");
                  return;
               }

            default:
               png_app_error(png_ptr,
                   "png_set_filler: inappropriate color type");
               return;
         }
#     else
         png_app_error(png_ptr, "png_set_filler not supported on write");
         return;
#     endif
   }

   /* Here on success - libpng supports the operation, set the transformation
    * and the flag to say where the filler channel is.
    */
   png_ptr->transformations |= PNG_FILLER;

   if (filler_loc == PNG_FILLER_AFTER)
      png_ptr->flags |= PNG_FLAG_FILLER_AFTER;

   else
      png_ptr->flags &= ~PNG_FLAG_FILLER_AFTER;
}

/* Added to libpng-1.2.7 */
void PNGAPI
png_set_add_alpha(png_structrp png_ptr, png_uint_32 filler, int filler_loc)
{
   png_debug(1, "in png_set_add_alpha");

   if (png_ptr == NULL)
      return;

   png_set_filler(png_ptr, filler, filler_loc);
   /* The above may fail to do anything. */
   if ((png_ptr->transformations & PNG_FILLER) != 0)
      png_ptr->transformations |= PNG_ADD_ALPHA;
}

#endif

#if defined(PNG_READ_SWAP_ALPHA_SUPPORTED) || \
    defined(PNG_WRITE_SWAP_ALPHA_SUPPORTED)
void PNGAPI
png_set_swap_alpha(png_structrp png_ptr)
{
   png_debug(1, "in png_set_swap_alpha");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_SWAP_ALPHA;
}
#endif

#if defined(PNG_READ_INVERT_ALPHA_SUPPORTED) || \
    defined(PNG_WRITE_INVERT_ALPHA_SUPPORTED)
void PNGAPI
png_set_invert_alpha(png_structrp png_ptr)
{
   png_debug(1, "in png_set_invert_alpha");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_INVERT_ALPHA;
}
#endif

#if defined(PNG_READ_INVERT_SUPPORTED) || defined(PNG_WRITE_INVERT_SUPPORTED)
void PNGAPI
png_set_invert_mono(png_structrp png_ptr)
{
   png_debug(1, "in png_set_invert_mono");

   if (png_ptr == NULL)
      return;

   png_ptr->transformations |= PNG_INVERT_MONO;
}

/* Invert monochrome grayscale data */
void /* PRIVATE */
png_do_invert(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_invert");

  /* This test removed from libpng version 1.0.13 and 1.2.0:
   *   if (row_info->bit_depth == 1 &&
   */
   if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
   {
      png_bytep rp = row;
      png_size_t i;
      png_size_t istop = row_info->rowbytes;

      for (i = 0; i < istop; i++)
      {
         *rp = (png_byte)(~(*rp));
         rp++;
      }
   }

   else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
      row_info->bit_depth == 8)
   {
      png_bytep rp = row;
      png_size_t i;
      png_size_t istop = row_info->rowbytes;

      for (i = 0; i < istop; i += 2)
      {
         *rp = (png_byte)(~(*rp));
         rp += 2;
      }
   }

#ifdef PNG_16BIT_SUPPORTED
   else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA &&
      row_info->bit_depth == 16)
   {
      png_bytep rp = row;
      png_size_t i;
      png_size_t istop = row_info->rowbytes;

      for (i = 0; i < istop; i += 4)
      {
         *rp = (png_byte)(~(*rp));
         *(rp + 1) = (png_byte)(~(*(rp + 1)));
         rp += 4;
      }
   }
#endif
}
#endif

#ifdef PNG_16BIT_SUPPORTED
#if defined(PNG_READ_SWAP_SUPPORTED) || defined(PNG_WRITE_SWAP_SUPPORTED)
/* Swaps byte order on 16-bit depth images */
void /* PRIVATE */
png_do_swap(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_swap");

   if (row_info->bit_depth == 16)
   {
      png_bytep rp = row;
      png_uint_32 i;
      png_uint_32 istop= row_info->width * row_info->channels;

      for (i = 0; i < istop; i++, rp += 2)
      {
#ifdef PNG_BUILTIN_BSWAP16_SUPPORTED
         /* Feature added to libpng-1.6.11 for testing purposes, not
          * enabled by default.
          */
         *(png_uint_16*)rp = __builtin_bswap16(*(png_uint_16*)rp);
#else
         png_byte t = *rp;
         *rp = *(rp + 1);
         *(rp + 1) = t;
#endif
      }
   }
}
#endif
#endif

#if defined(PNG_READ_PACKSWAP_SUPPORTED)||defined(PNG_WRITE_PACKSWAP_SUPPORTED)
static PNG_CONST png_byte onebppswaptable[256] = {
   0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0,
   0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
   0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
   0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
   0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4,
   0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
   0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC,
   0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
   0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
   0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
   0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA,
   0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
   0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6,
   0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
   0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
   0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
   0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1,
   0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
   0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9,
   0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
   0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
   0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
   0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED,
   0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
   0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3,
   0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
   0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
   0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
   0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7,
   0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
   0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF,
   0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
};

static PNG_CONST png_byte twobppswaptable[256] = {
   0x00, 0x40, 0x80, 0xC0, 0x10, 0x50, 0x90, 0xD0,
   0x20, 0x60, 0xA0, 0xE0, 0x30, 0x70, 0xB0, 0xF0,
   0x04, 0x44, 0x84, 0xC4, 0x14, 0x54, 0x94, 0xD4,
   0x24, 0x64, 0xA4, 0xE4, 0x34, 0x74, 0xB4, 0xF4,
   0x08, 0x48, 0x88, 0xC8, 0x18, 0x58, 0x98, 0xD8,
   0x28, 0x68, 0xA8, 0xE8, 0x38, 0x78, 0xB8, 0xF8,
   0x0C, 0x4C, 0x8C, 0xCC, 0x1C, 0x5C, 0x9C, 0xDC,
   0x2C, 0x6C, 0xAC, 0xEC, 0x3C, 0x7C, 0xBC, 0xFC,
   0x01, 0x41, 0x81, 0xC1, 0x11, 0x51, 0x91, 0xD1,
   0x21, 0x61, 0xA1, 0xE1, 0x31, 0x71, 0xB1, 0xF1,
   0x05, 0x45, 0x85, 0xC5, 0x15, 0x55, 0x95, 0xD5,
   0x25, 0x65, 0xA5, 0xE5, 0x35, 0x75, 0xB5, 0xF5,
   0x09, 0x49, 0x89, 0xC9, 0x19, 0x59, 0x99, 0xD9,
   0x29, 0x69, 0xA9, 0xE9, 0x39, 0x79, 0xB9, 0xF9,
   0x0D, 0x4D, 0x8D, 0xCD, 0x1D, 0x5D, 0x9D, 0xDD,
   0x2D, 0x6D, 0xAD, 0xED, 0x3D, 0x7D, 0xBD, 0xFD,
   0x02, 0x42, 0x82, 0xC2, 0x12, 0x52, 0x92, 0xD2,
   0x22, 0x62, 0xA2, 0xE2, 0x32, 0x72, 0xB2, 0xF2,
   0x06, 0x46, 0x86, 0xC6, 0x16, 0x56, 0x96, 0xD6,
   0x26, 0x66, 0xA6, 0xE6, 0x36, 0x76, 0xB6, 0xF6,
   0x0A, 0x4A, 0x8A, 0xCA, 0x1A, 0x5A, 0x9A, 0xDA,
   0x2A, 0x6A, 0xAA, 0xEA, 0x3A, 0x7A, 0xBA, 0xFA,
   0x0E, 0x4E, 0x8E, 0xCE, 0x1E, 0x5E, 0x9E, 0xDE,
   0x2E, 0x6E, 0xAE, 0xEE, 0x3E, 0x7E, 0xBE, 0xFE,
   0x03, 0x43, 0x83, 0xC3, 0x13, 0x53, 0x93, 0xD3,
   0x23, 0x63, 0xA3, 0xE3, 0x33, 0x73, 0xB3, 0xF3,
   0x07, 0x47, 0x87, 0xC7, 0x17, 0x57, 0x97, 0xD7,
   0x27, 0x67, 0xA7, 0xE7, 0x37, 0x77, 0xB7, 0xF7,
   0x0B, 0x4B, 0x8B, 0xCB, 0x1B, 0x5B, 0x9B, 0xDB,
   0x2B, 0x6B, 0xAB, 0xEB, 0x3B, 0x7B, 0xBB, 0xFB,
   0x0F, 0x4F, 0x8F, 0xCF, 0x1F, 0x5F, 0x9F, 0xDF,
   0x2F, 0x6F, 0xAF, 0xEF, 0x3F, 0x7F, 0xBF, 0xFF
};

static PNG_CONST png_byte fourbppswaptable[256] = {
   0x00, 0x10, 0x20, 0x30, 0x40, 0x50, 0x60, 0x70,
   0x80, 0x90, 0xA0, 0xB0, 0xC0, 0xD0, 0xE0, 0xF0,
   0x01, 0x11, 0x21, 0x31, 0x41, 0x51, 0x61, 0x71,
   0x81, 0x91, 0xA1, 0xB1, 0xC1, 0xD1, 0xE1, 0xF1,
   0x02, 0x12, 0x22, 0x32, 0x42, 0x52, 0x62, 0x72,
   0x82, 0x92, 0xA2, 0xB2, 0xC2, 0xD2, 0xE2, 0xF2,
   0x03, 0x13, 0x23, 0x33, 0x43, 0x53, 0x63, 0x73,
   0x83, 0x93, 0xA3, 0xB3, 0xC3, 0xD3, 0xE3, 0xF3,
   0x04, 0x14, 0x24, 0x34, 0x44, 0x54, 0x64, 0x74,
   0x84, 0x94, 0xA4, 0xB4, 0xC4, 0xD4, 0xE4, 0xF4,
   0x05, 0x15, 0x25, 0x35, 0x45, 0x55, 0x65, 0x75,
   0x85, 0x95, 0xA5, 0xB5, 0xC5, 0xD5, 0xE5, 0xF5,
   0x06, 0x16, 0x26, 0x36, 0x46, 0x56, 0x66, 0x76,
   0x86, 0x96, 0xA6, 0xB6, 0xC6, 0xD6, 0xE6, 0xF6,
   0x07, 0x17, 0x27, 0x37, 0x47, 0x57, 0x67, 0x77,
   0x87, 0x97, 0xA7, 0xB7, 0xC7, 0xD7, 0xE7, 0xF7,
   0x08, 0x18, 0x28, 0x38, 0x48, 0x58, 0x68, 0x78,
   0x88, 0x98, 0xA8, 0xB8, 0xC8, 0xD8, 0xE8, 0xF8,
   0x09, 0x19, 0x29, 0x39, 0x49, 0x59, 0x69, 0x79,
   0x89, 0x99, 0xA9, 0xB9, 0xC9, 0xD9, 0xE9, 0xF9,
   0x0A, 0x1A, 0x2A, 0x3A, 0x4A, 0x5A, 0x6A, 0x7A,
   0x8A, 0x9A, 0xAA, 0xBA, 0xCA, 0xDA, 0xEA, 0xFA,
   0x0B, 0x1B, 0x2B, 0x3B, 0x4B, 0x5B, 0x6B, 0x7B,
   0x8B, 0x9B, 0xAB, 0xBB, 0xCB, 0xDB, 0xEB, 0xFB,
   0x0C, 0x1C, 0x2C, 0x3C, 0x4C, 0x5C, 0x6C, 0x7C,
   0x8C, 0x9C, 0xAC, 0xBC, 0xCC, 0xDC, 0xEC, 0xFC,
   0x0D, 0x1D, 0x2D, 0x3D, 0x4D, 0x5D, 0x6D, 0x7D,
   0x8D, 0x9D, 0xAD, 0xBD, 0xCD, 0xDD, 0xED, 0xFD,
   0x0E, 0x1E, 0x2E, 0x3E, 0x4E, 0x5E, 0x6E, 0x7E,
   0x8E, 0x9E, 0xAE, 0xBE, 0xCE, 0xDE, 0xEE, 0xFE,
   0x0F, 0x1F, 0x2F, 0x3F, 0x4F, 0x5F, 0x6F, 0x7F,
   0x8F, 0x9F, 0xAF, 0xBF, 0xCF, 0xDF, 0xEF, 0xFF
};

/* Swaps pixel packing order within bytes */
void /* PRIVATE */
png_do_packswap(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_packswap");

   if (row_info->bit_depth < 8)
   {
      png_bytep rp;
      png_const_bytep end, table;

      end = row + row_info->rowbytes;

      if (row_info->bit_depth == 1)
         table = onebppswaptable;

      else if (row_info->bit_depth == 2)
         table = twobppswaptable;

      else if (row_info->bit_depth == 4)
         table = fourbppswaptable;

      else
         return;

      for (rp = row; rp < end; rp++)
         *rp = table[*rp];
   }
}
#endif /* PACKSWAP || WRITE_PACKSWAP */

#if defined(PNG_WRITE_FILLER_SUPPORTED) || \
    defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
/* Remove a channel - this used to be 'png_do_strip_filler' but it used a
 * somewhat weird combination of flags to determine what to do.  All the calls
 * to png_do_strip_filler are changed in 1.5.2 to call this instead with the
 * correct arguments.
 *
 * The routine isn't general - the channel must be the channel at the start or
 * end (not in the middle) of each pixel.
 */
void /* PRIVATE */
png_do_strip_channel(png_row_infop row_info, png_bytep row, int at_start)
{
   png_bytep sp = row; /* source pointer */
   png_bytep dp = row; /* destination pointer */
   png_bytep ep = row + row_info->rowbytes; /* One beyond end of row */

   /* At the start sp will point to the first byte to copy and dp to where
    * it is copied to.  ep always points just beyond the end of the row, so
    * the loop simply copies (channels-1) channels until sp reaches ep.
    *
    * at_start:        0 -- convert AG, XG, ARGB, XRGB, AAGG, XXGG, etc.
    *            nonzero -- convert GA, GX, RGBA, RGBX, GGAA, RRGGBBXX, etc.
    */

   /* GA, GX, XG cases */
   if (row_info->channels == 2)
   {
      if (row_info->bit_depth == 8)
      {
         if (at_start != 0) /* Skip initial filler */
            ++sp;
         else          /* Skip initial channel and, for sp, the filler */
         {
            sp += 2; ++dp;
         }

         /* For a 1 pixel wide image there is nothing to do */
         while (sp < ep)
         {
            *dp++ = *sp; sp += 2;
         }

         row_info->pixel_depth = 8;
      }

      else if (row_info->bit_depth == 16)
      {
         if (at_start != 0) /* Skip initial filler */
            sp += 2;
         else          /* Skip initial channel and, for sp, the filler */
         {
            sp += 4; dp += 2;
         }

         while (sp < ep)
         {
            *dp++ = *sp++; *dp++ = *sp; sp += 3;
         }

         row_info->pixel_depth = 16;
      }

      else
         return; /* bad bit depth */

      row_info->channels = 1;

      /* Finally fix the color type if it records an alpha channel */
      if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
         row_info->color_type = PNG_COLOR_TYPE_GRAY;
   }

   /* RGBA, RGBX, XRGB cases */
   else if (row_info->channels == 4)
   {
      if (row_info->bit_depth == 8)
      {
         if (at_start != 0) /* Skip initial filler */
            ++sp;
         else          /* Skip initial channels and, for sp, the filler */
         {
            sp += 4; dp += 3;
         }

         /* Note that the loop adds 3 to dp and 4 to sp each time. */
         while (sp < ep)
         {
            *dp++ = *sp++; *dp++ = *sp++; *dp++ = *sp; sp += 2;
         }

         row_info->pixel_depth = 24;
      }

      else if (row_info->bit_depth == 16)
      {
         if (at_start != 0) /* Skip initial filler */
            sp += 2;
         else          /* Skip initial channels and, for sp, the filler */
         {
            sp += 8; dp += 6;
         }

         while (sp < ep)
         {
            /* Copy 6 bytes, skip 2 */
            *dp++ = *sp++; *dp++ = *sp++;
            *dp++ = *sp++; *dp++ = *sp++;
            *dp++ = *sp++; *dp++ = *sp; sp += 3;
         }

         row_info->pixel_depth = 48;
      }

      else
         return; /* bad bit depth */

      row_info->channels = 3;

      /* Finally fix the color type if it records an alpha channel */
      if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
         row_info->color_type = PNG_COLOR_TYPE_RGB;
   }

   else
      return; /* The filler channel has gone already */

   /* Fix the rowbytes value. */
   row_info->rowbytes = (png_size_t)(dp-row);
}
#endif

#if defined(PNG_READ_BGR_SUPPORTED) || defined(PNG_WRITE_BGR_SUPPORTED)
/* Swaps red and blue bytes within a pixel */
void /* PRIVATE */
png_do_bgr(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_bgr");

   if ((row_info->color_type & PNG_COLOR_MASK_COLOR) != 0)
   {
      png_uint_32 row_width = row_info->width;
      if (row_info->bit_depth == 8)
      {
         if (row_info->color_type == PNG_COLOR_TYPE_RGB)
         {
            png_bytep rp;
            png_uint_32 i;

            for (i = 0, rp = row; i < row_width; i++, rp += 3)
            {
               png_byte save = *rp;
               *rp = *(rp + 2);
               *(rp + 2) = save;
            }
         }

         else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
         {
            png_bytep rp;
            png_uint_32 i;

            for (i = 0, rp = row; i < row_width; i++, rp += 4)
            {
               png_byte save = *rp;
               *rp = *(rp + 2);
               *(rp + 2) = save;
            }
         }
      }

#ifdef PNG_16BIT_SUPPORTED
      else if (row_info->bit_depth == 16)
      {
         if (row_info->color_type == PNG_COLOR_TYPE_RGB)
         {
            png_bytep rp;
            png_uint_32 i;

            for (i = 0, rp = row; i < row_width; i++, rp += 6)
            {
               png_byte save = *rp;
               *rp = *(rp + 4);
               *(rp + 4) = save;
               save = *(rp + 1);
               *(rp + 1) = *(rp + 5);
               *(rp + 5) = save;
            }
         }

         else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
         {
            png_bytep rp;
            png_uint_32 i;

            for (i = 0, rp = row; i < row_width; i++, rp += 8)
            {
               png_byte save = *rp;
               *rp = *(rp + 4);
               *(rp + 4) = save;
               save = *(rp + 1);
               *(rp + 1) = *(rp + 5);
               *(rp + 5) = save;
            }
         }
      }
#endif
   }
}
#endif /* READ_BGR || WRITE_BGR */

#if defined(PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED) || \
    defined(PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED)
/* Added at libpng-1.5.10 */
void /* PRIVATE */
png_do_check_palette_indexes(png_structrp png_ptr, png_row_infop row_info)
{
   if (png_ptr->num_palette < (1 << row_info->bit_depth) &&
      png_ptr->num_palette > 0) /* num_palette can be 0 in MNG files */
   {
      /* Calculations moved outside switch in an attempt to stop different
       * compiler warnings.  'padding' is in *bits* within the last byte, it is
       * an 'int' because pixel_depth becomes an 'int' in the expression below,
       * and this calculation is used because it avoids warnings that other
       * forms produced on either GCC or MSVC.
       */
      int padding = PNG_PADBITS(row_info->pixel_depth, row_info->width);
      png_bytep rp = png_ptr->row_buf + row_info->rowbytes - 1;

      switch (row_info->bit_depth)
      {
         case 1:
         {
            /* in this case, all bytes must be 0 so we don't need
             * to unpack the pixels except for the rightmost one.
             */
            for (; rp > png_ptr->row_buf; rp--)
            {
              if ((*rp >> padding) != 0)
                 png_ptr->num_palette_max = 1;
              padding = 0;
            }

            break;
         }

         case 2:
         {
            for (; rp > png_ptr->row_buf; rp--)
            {
              int i = ((*rp >> padding) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 2) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 4) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 6) & 0x03);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              padding = 0;
            }

            break;
         }

         case 4:
         {
            for (; rp > png_ptr->row_buf; rp--)
            {
              int i = ((*rp >> padding) & 0x0f);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              i = (((*rp >> padding) >> 4) & 0x0f);

              if (i > png_ptr->num_palette_max)
                 png_ptr->num_palette_max = i;

              padding = 0;
            }

            break;
         }

         case 8:
         {
            for (; rp > png_ptr->row_buf; rp--)
            {
               if (*rp > png_ptr->num_palette_max)
                  png_ptr->num_palette_max = (int) *rp;
            }

            break;
         }

         default:
            break;
      }
   }
}
#endif /* CHECK_FOR_INVALID_INDEX */

#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
#ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
void PNGAPI
png_set_user_transform_info(png_structrp png_ptr, png_voidp
   user_transform_ptr, int user_transform_depth, int user_transform_channels)
{
   png_debug(1, "in png_set_user_transform_info");

   if (png_ptr == NULL)
      return;

#ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
   if ((png_ptr->mode & PNG_IS_READ_STRUCT) != 0 &&
      (png_ptr->flags & PNG_FLAG_ROW_INIT) != 0)
   {
      png_app_error(png_ptr,
          "info change after png_start_read_image or png_read_update_info");
      return;
   }
#endif

   png_ptr->user_transform_ptr = user_transform_ptr;
   png_ptr->user_transform_depth = (png_byte)user_transform_depth;
   png_ptr->user_transform_channels = (png_byte)user_transform_channels;
}
#endif

/* This function returns a pointer to the user_transform_ptr associated with
 * the user transform functions.  The application should free any memory
 * associated with this pointer before png_write_destroy and png_read_destroy
 * are called.
 */
#ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
png_voidp PNGAPI
png_get_user_transform_ptr(png_const_structrp png_ptr)
{
   if (png_ptr == NULL)
      return (NULL);

   return png_ptr->user_transform_ptr;
}
#endif

#ifdef PNG_USER_TRANSFORM_INFO_SUPPORTED
png_uint_32 PNGAPI
png_get_current_row_number(png_const_structrp png_ptr)
{
   /* See the comments in png.h - this is the sub-image row when reading an
    * interlaced image.
    */
   if (png_ptr != NULL)
      return png_ptr->row_number;

   return PNG_UINT_32_MAX; /* help the app not to fail silently */
}

png_byte PNGAPI
png_get_current_pass_number(png_const_structrp png_ptr)
{
   if (png_ptr != NULL)
      return png_ptr->pass;
   return 8; /* invalid */
}
#endif /* USER_TRANSFORM_INFO */
#endif /* READ_USER_TRANSFORM || WRITE_USER_TRANSFORM */
#endif /* READ || WRITE */