[MC-41631] Tall entities (enderman, ghast, large slime/magma cube, open shulker) don't activate some tripwire from another sub-chunk

The bug

When an entity is inside a sub-chunk (which is marked with blue lines when you have F3+G enabled) and it touches tripwire from sub-chunk above, this tripwire won't activate if it is two blocks higher than the border of the sub-chunk (for example a ghast at y=207 (16*13-1) does not trigger tripwire at y=210 (16*13+2)), but triggers tripwire at y=209 and 208.

Currently affects:

Ghast
Enderman
Slime and Magma Cube with Size:5 or bigger
Open Shulker

Also happens horizontally - in this case only 3 tripwire lines can be activated and it only affects slimes/magma cubes with Size:12 or bigger

Steps to Reproduce

1. Create a Superflat world with the preset

3;207*minecraft:stone;0;

2. Create a ghast cage (blocks around a 4x4x4 area to trap a spawned ghast) at ground level.

3. Place a line of tripwire through the top of the inner area.
4. Spawn a ghast inside.

Linked issues

relates to 1

MC-254614 Shulkers at Y levels that are a multiple of 16 don't activate pressure plates or tripwire below them Reopened

Attachments

Ghast + Tripwire.zip

Ghast Tripwire (world).zip

Ghast Tripwire Sieve.zip

MC-41631 Open Shulker Reproduce.mp4

probably_fixed4.mp4

Comments 15

Deleted account 2014-02-12T23:45:17Z

Is this still a concern in the current Minecraft version 14w06b / Launcher version 1.3.9 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Itouch2 2014-02-18T12:01:11Z

Change your map. It works everywhere for me (with another map).

Deleted account 2014-04-20T13:44:22Z

Is this still a concern in the current Minecraft version 1.7.9 / Launcher version 1.3.11 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

fienxjox 2014-07-29T20:45:27Z

Is this still a concern in the current Minecraft version 14w30c or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Mark McKenzie 2014-07-31T00:41:39Z

Same results with a matching world created from scratch in 14w31a (launcher 1.5.1, java 7 update 65) - the ghast trapped at ground level will not trigger the tripwire, but the whole setup one layer higher or lower works fine.

I did not re-test the attached world, and I don't remember where the engineering world where I first found the bug is, so I can't check that one.

The preset screen in 14w31a kept resetting the old custom preset after entering it, clicking Use Preset and then Done; the preset 3;207*minecraft:stone;1;1 works and I have updated the instructions above.

5 more comments

Sonicwave 2014-10-06T02:49:49Z

Cannot reproduce in 1.8.

galaxy_2alex 2014-10-26T12:53:24Z

Is this still a concern in the current Minecraft version 1.8.1 Prerelease 3 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

KingSupernova 2015-03-12T03:43:04Z

Cannot reproduce in 1.8.3. As you can see in the screenshot, the tripwire is at Y=10, the ghast was summoned at Y=7, and it's triggering the tripwire.

Mark McKenzie 2015-03-14T02:25:53Z

This issue is only known to happen at one particular combination of ghast height and tripwire height. The title was originally vague because I didn't (and still don't) know if this problem could be reproduced at any other particular combination of heights; I figured a title that was too specific might cause people to overlook that unknown, but apparently they aren't reading the important detail clearly listed in the description.

If you can't reproduce a bug, please don't post that you couldn't reproduce it until you've checked that you didn't miss something important in the description. A vague statement of inability to reproduce will mislead others looking over the problem and make those who have already reproduced the problem have to check it again (possibly leading to a vicious circle); giving details from the reproduction attempt helps to identify the problem but can also cause noise if it neither correctly tests the issue nor identifies another arrangement as also producing the problem ("Problem doesn't occur at <conditions not claimed to cause problem>" vs "Problem also found with <different conditions>").

It's reasonable for reviewers to not want to immediately download an untrusted file but I will add a demonstration world from 1.8.3, and a new screenshot showing the altitude in the debug overlay (in addition to the ghasts on each side already showing that the problem does not occur at every height).

This problem also occurs in Minecraft 1.3.1 (the first release featuring tripwire) but the Affected Versions field doesn't support adding a version that old.

Mark McKenzie 2015-03-14T08:39:03Z

This appears to be a modular arithmetic issue, presumably in how the game checks if tripwire in one section is triggered by an entity in the lower section. A ghast at any height h (integer or floating point) with (h mod 16) > 14.0625 will fail to trigger tripwire in the third layer of the next section up, and if (h mod 16) > 15.0625, tripwire in the fourth layer should also trigger but fails to (eg. a ghast summoned at Y=15.5 will trigger tripwire in layers 16 and 17 but fails to trigger tripwire in layers 18 and 19).

I may upload a demonstration world tomorrow (no promises).

KingSupernova 2015-03-14T09:09:20Z

Sorry, I assumed that the 207 coordinate was just an example, since the title just said it didn't trigger tripwire at all. Confirmed in 1.8.3.

Mark McKenzie 2015-03-14T17:24:29Z

I uploaded a Minecraft 1.8.3 world (Ghast Tripwire Sieve.zip) with a self-replicating setup to test multiple combinations of ghast and tripwire elevation.

Mark McKenzie 2015-03-14T17:36:23Z

Added screenshots of the test setup showing one of multiple locations where tripwire is failing to trigger (another spot 16 layers upward can be seen in the distance).

kumasasa 2016-10-22T05:49:52Z

Is this still an issue in the most recent versions (currently that is 1.10.2, or 16w42a) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time.

ampolive 2021-08-13T13:01:40Z

Can confirm in 1.17.1.