So I've had this creative world going for years now and it's become this beautiful mountain village with the aim of having many areas around it to travel to as well. However it's always been vanilla and I accidentally opened it in modded mode just now (I have some world altering mods like Biomes o plenty). Hadn't played for a while, so it prompted me to back up which I did, from 1.15.1 to 1.15.2 I think.
Anyway realised my mistake almost immediately and closed game, and moved the backup file into place which I'm now playing on as I've lost nothing regardless. The backup gave me the same warning about not having played since 1.15.1, and it showed the old date (december if I remember correctly) as the date last played - so does this mean I've correctly fixed my stupid mistake of loading up the modded world and reverted the game back to a state of before I did that? No risk of glitches because of this? And it's still a save file that's never been loaded with mods?
Sorry haha I know I'm just a bit obsessive - but would really appreciate the help! Please and thank you
Don't think it's relevant but the resource pack I think stayed the same as when I messed up and loaded it up modded (was messing around with resource packs), even when I loaded up the backup - however think I'm right in thinking the resource pack works separately in that respect?
It is unlikely that opening a vanilla world in a modded version and going back will cause any issues as long as no mod items/block/entities/etc were crafted/spawned or new chunks were generated, or a mod like Cubic chunks which changes the save format was used, and even if the mod adds new NBT data or the like vanilla will simply ignore it (based on personal experience with modding 1.6.4 and my first world, which I use some of my own mods on, including adding a couple new blocks and a "LightUpdated" NBT tag in the chunk data, but there are no issues with loading it in vanilla as long as the blocks aren't present, which otherwise simply disappear; since I only use them to carry more resources while caving there are no persistent modded blocks in the world).
The only caveat is that newer versions, since 1.13, are far more sensitive to invalid save data and will simply throw away entire chunks with any bad data (not sure if this includes unknown blocks/etc; there is/used to be (1.6.4 source) code that specifically checked a chunk after it was loaded to remove any unknown blocks. Part of the issues newer versions have may stem from the fact they save a "data version" for each chunk which indicates the last version it was saved in and the game doesn't know how to handle unknown (newer) versions).
In any case, this is why you should always make separate profiles with separate game directories for every version, vanilla or modded, that you play - IMO, the launcher should automatically do this for anything other than "latest version", there are also issues with data files like options.txt being read by different versions, especially when downgrading, which is not supported in any form (a leading cause of crashes or bizarre behavior is due to changing versions which read options.txt differently - most reinstallations could have been prevented by simply deleting this file, or using a separate game directory).
Thanks for the help! I'm worried that maybe (although very unlikely) I managed to load new chunks in the modded version, or change things underground etc. However, am I right in thinking that going back to the backup I made before playing, from 1.15.1, in December I think, would have completely cancelled out anything like that? Cheers
If you had COFHCore (the library mod that Thermal Engineering and other TeamCOFH mods use) I think it may have retrogenned the modded ores into the world. I know there's a command to force this to happen, but I dunno if it does this automatically. I don't know of any other mod that retrogens anything, but some mods add mobs/entities and AI changes that could still have affected your world (ie, mobs breaking/placing blocks, mobs picking up or changing blocks, black hole singularities that suck up and destroy blocks around them, etc).
A backup restoration would revert all of this, assuming it was from a point prior to your mistake. Such a backup would also undo any legit work you may have done in the interirm, though.