[MC-131327] Opaque blocks at the top of subchunks (chunk sections) do not increase the world height to the next subchunk

How to reproduce

Create a new superflat world with void preset
Make it night time by running this: /time set midnight
Fill a layer of stone at layer 63: /fill ~ 63 ~ ~20 63 ~20 stone
→ ❌ No hostile mobs are spawning
Fill a layer of stone at any other layer: /fill ~ 30 ~ ~20 30 ~20 stone
→ ✔ Mobs are spawning correctly on this layer

Note: This bug was introduced in 18w19a

Linked issues

blocks 1

MC-68565 Monsters spawn at daytime at y=256 and don't burn Resolved

relates to 1

MC-55172 Mobs do not spawn at the heights 16, 32, 48, 64, 80... (Multiples of 16) Resolved

Attachments

Comments 25

FaRo1 2018-06-14T18:06:38Z

Only 63? Not 62, not 64, not 127, only 63? Then it might have something to do with sea level (squid spawning etc.), because I don't know anything else that is fixed on level 63.

Misode 2018-06-14T18:10:04Z

Yes, blocks at 63 and mobs spawning at 64 is the only layer it happens with.

NeunEinser 2018-06-14T18:27:05Z

It definetly seems to have to do with sub chunks and if there are blocks above. If you have a layer of stone at the top of a sub chunk and nothing above, no mob can spawn there.
They do spawn at layer 63, if there is also a layer of stone at 66.
Simply adding one stone block per chunk at layer 64 does not change anything tho, even tho the sub chunk level should now be raised. So maybe it's when the higest block of the highest subchunk as sky light access?

Tested what I described above at layers 15, 31, 47, 63 and 127

Pau Olivares 2018-06-14T18:29:18Z

Confirmed for MC 1.13-pre1.

Fabian Röling: the affected layer is 63. I tried to reproduce this bug with other layers but nothing.

As you said, it might have something to do with sea level.

Eta740 2018-06-14T18:31:15Z

Subchunks are calculated individually for x/z since 1.9 or 1.10. Maybe the height map is not being adjusted properly when there's an opaque block at the top of a subchunk (previously, an opaque block at the top of a subchunk would also make the subchunk above it eligible for spawning)

To test this theory, try it at any other place where y = 16n - 1 (so 15, 31, 47, 63 etc) and see if you get the same results.

15 more comments

NeunEinser 2018-06-14T18:37:33Z

@unknown Yeah, I did that. I checked 127 for >63 and all sub chunk borders <= 63

NeunEinser 2018-06-14T18:41:25Z

Actually, due to this bug MC-68565 does no longer happen, because mobs cannot spawn there at all now. The actual cause of MC-68565 si probably not fixed, tho.

McModknower 2018-06-14T19:33:09Z

I tested it with a 16*16 Platform of stone in a chunk:

at height 63 => no Mobs
at height 62/64 => Mobs
at height 63 with one block in the subchunk above => no Mobs
at height 63 with a Platform at 79(16 Blocks higher) => Mobs on 63, but not 79
at height 63 with a Platform at 78(15 Blocks higher) => Mobs on 63 and 78

It looks like it is as @Eta740 said it already:

Maybe the height map is not being adjusted properly when there's an opaque block at the top of a subchunk.

Pau Olivares 2018-06-14T19:39:54Z

I tested it too. Eta740 is right.

Acheron River 2018-06-21T17:06:31Z

Eta's theory confirmed by one more tester!

Error is present at all sub chunk borders.

FaRo1 2018-06-21T17:13:08Z

Is this correct?

Eta740 2018-06-21T17:17:21Z

In that case, title should be changed to "Opaque blocks at the top of subchunks (chunk sections) do not increase the world height to the next subchunk" or something similar. Also, summary is misleading, since empty subchunks should not attempt to spawn mobs other than this 1 exception.

FaRo1 2018-06-21T17:57:42Z

Better? I don't really see a problem with the description.

Pau Olivares 2018-07-04T21:06:55Z

Cannot reproduce in MC 1.13-pre6. Can someone alse try to reproduce it?

NeunEinser 2018-07-04T21:36:57Z

Can still reproduce.

Pau Olivares 2018-07-05T09:37:33Z

I can't, weird... I'll try to reproduce it again.

Ray 2018-07-13T13:25:17Z

[media]

Still doesn't allow mobs to spawn on those blocks by border.

AJMFactsheets 2018-07-16T04:24:14Z

I did a similar test to Ray in 1.13-pre8 and got the same results. I feel this could also cause erratic spawning at sub-chunks near the surface, creating areas where mobs don't spawn at all.

AJMFactsheets 2018-07-17T02:39:16Z

This bug seems to be fixed for 1.13-pre9. In my testing, mobs spawned on all platforms regardless of whether they were below, at, or above a subchunk.

Greg Milson 2018-07-20T02:41:29Z

Is this still an issue in release 1.13?

FaRo1 2018-07-20T06:34:19Z

If someone knew, they would add the version or comment. There are currently 3436 open bugs that do not have the version 1.13 added yet. Please don't comment on all of them.
And please remember that every comment on a report sends as many mails as the number next to "watch this issue", in this report 23 at once.

ZombieBaby 2018-07-20T13:20:41Z

Can confirm the 'how to reproduce' doesn't work in major version 1.13. To the best of my testing, this has been fixed.

kumasasa 2018-07-21T03:27:37Z

Will wait for comment of @unknown before resolving as fixed.

Misode 2018-08-01T23:17:11Z

@unknown Sorry for this late response but I wasn't able to test this until now. I can indeed confirm that this is fixed in the major version 1.13.

kumasasa 2018-08-01T23:31:06Z

No problem, the ticket won't run away 😛