pngtrans.c

一个国人自己实现图像库的程序（有参考价值）

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};

/* 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\n");
   if (
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL &&
#endif
       row_info->bit_depth < 8)
   {
      png_bytep rp, 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 /* PNG_READ_PACKSWAP_SUPPORTED or PNG_WRITE_PACKSWAP_SUPPORTED */

#if defined(PNG_WRITE_FILLER_SUPPORTED) || \
    defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
/* remove filler or alpha byte(s) */
void /* PRIVATE */
png_do_strip_filler(png_row_infop row_info, png_bytep row, png_uint_32 flags)
{
   png_debug(1, "in png_do_strip_filler\n");
#if defined(PNG_USELESS_TESTS_SUPPORTED)
   if (row != NULL && row_info != NULL)
#endif
   {
/*
      if (row_info->color_type == PNG_COLOR_TYPE_RGB ||
          row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
*/
      png_bytep sp=row;
      png_bytep dp=row;
      png_uint_32 row_width=row_info->width;
      png_uint_32 i;

      if (row_info->channels == 4)
      {
         if (row_info->bit_depth == 8)
         {
            /* This converts from RGBX or RGBA to RGB */
            if (flags & PNG_FLAG_FILLER_AFTER)
            {
               dp+=3; sp+=4;
               for (i = 1; i < row_width; i++)
               {
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  sp++;
               }
            }
            /* This converts from XRGB or ARGB to RGB */
            else
            {
               for (i = 0; i < row_width; i++)
               {
                  sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
               }
            }
            row_info->pixel_depth = 24;
            row_info->rowbytes = row_width * 3;
         }
         else /* if (row_info->bit_depth == 16) */
         {
            if (flags & PNG_FLAG_FILLER_AFTER)
            {
               /* This converts from RRGGBBXX or RRGGBBAA to RRGGBB */
               sp += 8; dp += 6;
               for (i = 1; i < row_width; i++)
               {
                  /* This could be (although png_memcpy is probably slower):
                  png_memcpy(dp, sp, 6);
                  sp += 8;
                  dp += 6;
                  */

                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  sp += 2;
               }
            }
            else
            {
               /* This converts from XXRRGGBB or AARRGGBB to RRGGBB */
               for (i = 0; i < row_width; i++)
               {
                  /* This could be (although png_memcpy is probably slower):
                  png_memcpy(dp, sp, 6);
                  sp += 8;
                  dp += 6;
                  */

                  sp+=2;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
               }
            }
            row_info->pixel_depth = 48;
            row_info->rowbytes = row_width * 6;
         }
         row_info->channels = 3;
         row_info->color_type &= ~PNG_COLOR_MASK_ALPHA;
      }
/*
      else if (row_info->color_type == PNG_COLOR_TYPE_GRAY ||
               row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
*/
      else if (row_info->channels == 2)
      {
         if (row_info->bit_depth == 8)
         {
            /* This converts from GX or GA to G */
            if (flags & PNG_FLAG_FILLER_AFTER)
            {
               for (i = 0; i < row_width; i++)
               {
                  *dp++ = *sp++;
                  sp++;
               }
            }
            /* This converts from XG or AG to G */
            else
            {
               for (i = 0; i < row_width; i++)
               {
                  sp++;
                  *dp++ = *sp++;
               }
            }
            row_info->pixel_depth = 8;
            row_info->rowbytes = row_width;
         }
         else /* if (row_info->bit_depth == 16) */
         {
            if (flags & PNG_FLAG_FILLER_AFTER)
            {
               /* This converts from GGXX or GGAA to GG */
               sp += 4; dp += 2;
               for (i = 1; i < row_width; i++)
               {
                  *dp++ = *sp++;
                  *dp++ = *sp++;
                  sp += 2;
               }
            }
            else
            {
               /* This converts from XXGG or AAGG to GG */
               for (i = 0; i < row_width; i++)
               {
                  sp += 2;
                  *dp++ = *sp++;
                  *dp++ = *sp++;
               }
            }
            row_info->pixel_depth = 16;
            row_info->rowbytes = row_width * 2;
         }
         row_info->channels = 1;
         row_info->color_type &= ~PNG_COLOR_MASK_ALPHA;
      }
   }
}
#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\n");
   if (
#if defined(PNG_USELESS_TESTS_SUPPORTED)
       row != NULL && row_info != NULL &&
#endif
       (row_info->color_type & PNG_COLOR_MASK_COLOR))
   {
      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;
            }
         }
      }
      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 /* PNG_READ_BGR_SUPPORTED or PNG_WRITE_BGR_SUPPORTED */

#if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
    defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED) || \
    defined(PNG_LEGACY_SUPPORTED)
void PNGAPI
png_set_user_transform_info(png_structp png_ptr, png_voidp
   user_transform_ptr, int user_transform_depth, int user_transform_channels)
{
   png_debug(1, "in png_set_user_transform_info\n");
#if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
   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;
#else
   if(user_transform_ptr || user_transform_depth || user_transform_channels)
      png_warning(png_ptr,
        "This version of libpng does not support user transform info");
#endif
}
#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.
 */
png_voidp PNGAPI
png_get_user_transform_ptr(png_structp png_ptr)
{
#if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
   return ((png_voidp)png_ptr->user_transform_ptr);
#else
   if(png_ptr)
     return (NULL);
   return (NULL);
#endif
}