MCPE-154323Parity issue: Carvers do not generate in the same place in Java and Bedrock
May relate to MCPE-143895.
The bug
Despite noise caves generating in largely the same positions in Java Edition as they do in Bedrock Edition (if not identically), the position of traditional carvers still differs even on the same seed.
While some generation disparities may still be expected between editions (such as configured features, which are unstable between different versions on the same edition anyway), carvers are a stable enough feature such that consistency between editions would be expected, however this is not the case.
How to reproduce
Having both editions and a keen eye would reveal this for any seed.
I've specifically tested this with the seed 107038380838084 due to its iconic cave systems which make their presence known rather quickly (MC-111378). At the coordinates -137, 68, 34, a section of cave exists in Java Edition which is completely absent in Bedrock Edition. Turning 180 degrees from it and wandering away from it reveals a small noise cave opening that can be seen in both editions and appears to be shaped identically.
Expected results
Carvers would appear in the same places in both the Java and Bedrock editions, just like noise caves are.
Actual results
Their positions are completely different.
Linked Issues
MC-250445
LowAttachments9
Created Issue:
Parity issue: Carvers do not generate in the same place in Java and Bedrock
May relate to
MCPE-143895.The bug
Despite noise caves generating in largely the same positions in Java Edition as they do in Bedrock Edition (if not identically), the position of traditional carvers still differs even on the same seed.
While some generation disparities may still be expected between editions (such as configured features, which are unstable between different versions on the same edition anyway), carvers are a stable enough feature such that consistency between editions would be expected, however this is not the case.
How to reproduce
Having both editions and a keen eye would reveal this for any seed.
I've specifically tested this with the seed 107038380838084 due to its iconic cave systems which make their presence known rather quickly (
MC-111378). At the coordinates -137, 68, 34, a section of cave exists in Java Edition which is completely absent in Bedrock Edition. Turning 180 degrees from it and wandering away from it reveals a small noise cave opening that can be seen in both editions and appears to be shaped identically.Expected results
Carvers would appear in the same places in both the Java and Bedrock editions, just like noise caves are.
Actual results
Their positions are completely different.
Attachments5
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relates to
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The bug
The generation of carvers only appears to use the bottom 48 bits of the world seed, and ignores the top 2^16. As a result, the arrangement of carvers in one world will be shared by another 65,535 worlds, despite noise caves differing.
As it appears that Mojang intended to eliminate such similarities with the fixing of MC-236650, the fact that this remains is likely a bug.
How to reproduce
This can be seen by generating a world with a desired seed, locating a carver-based cave, then generating another world with an integer multiple of 281474976710656 added to the seed and flying to the same location. Assuming that the carver's generation has not been interrupted by another cave, not being underground or some other factor, the basic cave layout should appear identical.
The screenshots provided with this ticket use the seeds 1 and 281474976710657, with coordinates provided.
Expected results
The carvers would appear completely different for all 2^64 seeds.
Actual results
The carvers are a complete match for seeds constructed in this way.
How to fix
Carvers should be made to also respect the upper 16 bits in the world seed as to eliminate duplicate caves like these.
If the carver RNG is redone, it should also be reworked in the same way in Bedrock Edition as to fix MCPE-154323. Such a change could also fix MC-111378 and MCPE-95011.
Further notes
This likely affects world generation as far back as Beta 1.8, and possibly even earlier (in b1.8 to 1.6.4, it affected the entire world like with MC-236650, but from 1.7 onwards only affects carvers and other minor details): https://www.minecraftforum.net/forums/minecraft-java-edition/seeds/2229720-can-two-different-seeds-produce-identical-worlds
Very closely relates to MC-250445. Likely also relates to MC-111378, MC-236650, MCPE-18739, MCPE-95011 and MCPE-154323.
This is specifically the Bedrock Edition equivalent of MC-250445; the differences between these two tickets constitute MCPE-154323.
The bug
Bedrock Edition recently expanded to allow for the main world generation to support 64-bit seeds. However, this only appears to affect the superficial terrain shape and noise caves; it appears that carvers will end up being the same for very many seeds.
How to reproduce
A keen eye can be used to reproduce this on any seed - just create a world with a desired seed, locate a carver cave, then create another world with a seed which has an integer multiple of 4294967296 added to the previous seed and go to those exact coordinates. Assuming that the cave's generation hasn't been interrupted by something like an aquifer, surface terrain or a structure, the cave's basic shape should be identical.
I've specifically opted to use the seed 1669320484, which becomes 5964287780 when 4294967296 is added to it. The choice of this seed is due to the very unique cave generation it results in (MCPE-95011), which makes the similarities between the two seeds incredibly obvious. The weird cave generation is not the focus of this bug report - I'm just using it since it makes the matching caves across different seeds obvious.
Expected results
Cave generation would use all 64 bits of the seed, just like the rest of terrain does.
Actual results
It only uses the lower 32 bits of the seed. As a result, any given carver layout will be shared by another 4,294,967,295 other seeds.
How to fix
Carvers should be made to also respect the upper 32 bits in the world seed as to eliminate duplicate caves like these.
If the carver RNG is redone, it should also be reworked in the same way in Java Edition as to fix MC-250445 and MCPE-154323. Such a change could also fix MC-111378 and MCPE-95011.