PNG_FLAG_ZTXT_CUSTOM_METHOD 1551 3rdparty/libpng/pngwrite.c    png_ptr->flags |= PNG_FLAG_ZTXT_CUSTOM_METHOD;
PNG_FLAG_ZTXT_CUSTOM_METHOD  874 3rdparty/libpng/pngwutil.c    if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_METHOD))