PNG_FLAG_ZLIB_CUSTOM_LEVEL 1403 3rdparty/libpng/pngwrite.c    png_ptr->flags |= PNG_FLAG_ZLIB_CUSTOM_LEVEL;
PNG_FLAG_ZLIB_CUSTOM_LEVEL  848 3rdparty/libpng/pngwutil.c    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_LEVEL))