Dwarf Fortress Bug Tracker - Dwarf Fortress
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0004814Dwarf FortressCreaturespublic2011-08-08 13:222015-01-12 09:07
0004814: Building destroyers are unable to destroy adjacent buildings
Building destroyers that find themselves immediately adjacent (rather than 2 tiles away) from a valid target for building destruction sit there trying to destroy the building, but the building never takes any damage. The creature will sit there at 1 tile distant even if it can path to a position 2 tiles away, even if it can path to another valid building for destruction, even if it can path to a valid but unseen dwarf. It will move from its impossible job only when a dwarf comes both close and visible.
a) Trap some building destroyers. I used demons because I had them around and because they're still aggressive post-siege. Undead would also work well, with wooden doors.

b) Build the cage. Build a door adjacent to the cage. Link the cage to a lever.

c) Optional: lock the door. (If you don't, a mechanism or cage is likely to prop the door open, but it has exactly the same effect: the building destroyer uselessly pounds on the propped open door.)

d) Throw the lever, watch the building destroyer. Inspect your door after, say, a year.
Almost certainly a bug, placed here in the interest of completeness, but it's only going to come up in extraordinarily rare situations, and it lets players do some fun constructions with building destroyers. Not a big deal.
building destroyer, BUILDINGDESTROYER
Issue History
2011-08-08 13:22vasilnNew Issue
2011-08-08 13:25vasilnTag Attached: building destroyer
2011-08-08 13:39vasilnNote Added: 0018458
2011-08-10 07:44kwielandNote Added: 0018466
2011-08-10 08:06vasilnNote Added: 0018467
2011-08-10 09:34vasilnNote Edited: 0018467bug_revision_view_page.php?bugnote_id=0018467#r6905
2013-09-22 17:35FootkerchiefTag Attached: BUILDINGDESTROYER
2015-01-12 07:16PatrikLundellNote Added: 0031904
2015-01-12 09:07FootkerchiefAssigned To => Footkerchief
2015-01-12 09:07FootkerchiefStatusnew => confirmed

2011-08-08 13:39   
I should have labeled this "...unable to destroy adjacent doors." I haven't tested with non-door buildings.

And btw, it doesn't matter if you unlock the door after releasing the building destroyer-- the creatures still sit there, unable to destroy, unwilling to pass.
2011-08-10 07:44   
Is there an exit? I've not seen this, and I've released lots of building destroyers and had them destroy doors. I did have military in the room at the time, though, and a path to exit. Does this matter?
2011-08-10 08:06   
(edited on: 2011-08-10 09:34)
I've tried it both with and without exits. It doesn't matter. It does matter if military is in the room, as BDs will ignore buildings in favor of creatures. So if for instance you uncage it from next to a door, with a dwarf around, it'll path to that dwarf, and if it wins, it'll likely be 2 or more tiles from the door, so it can destroy it-- but if no dwarf is around, it won't be able to destroy the door.

Trolls (and ogres) might behave differently, as post-siege, they try to escape off-map. Not sure if building destruction is their first priority then. I could test it pretty easily.

BTW, I have now tested this for horizontal bars as well: destroyable from 2 tiles, cannot be destroyed when adjacent.

EDIT: It may be relevant that the only path available in my tests was through the adjacent door, although it made no difference if the door was locked or not.

2015-01-12 07:16   
I disagree that the problem is a minor one, since it basically leads to titans/FBs, etc, that you're not equipped to kill with dwarves will sit there and besiege you infinitely until you send someone on a suicide mission to dislodge it. You cannot release your civilian alert burrows, since that will undoubtedly lead to a civilian straying close to the monster, releasing it in the midst of civilian targets.
Since I have encountered this issue previously, I was prepared for it when a Giantess appeared in a 0.40.23 fortress. The monster went directly to my trap construction, but did NOT stop two tiles away from the door, but instead continued an additional tile to stand in front of the door (the movement was straight, as it had to cross a a moat bridge first, and the door was straight in front of the bridge). Admittedly, I did not wait, but killed it using the menacing spike trap it was standing on by hand cranking the lever connected to the trap, but when I did NOT have any such device (0.40.13 or something like that), the Titan just stood there, without any degradation of the door happening despite me waiting for quite a few weeks.
I don't know if it matters, but 2 tiles in front of the door was a 2 tile raising drawbridge (lowered). In the previous encounter the corresponding drawbridge was directly in front of the door.

The Giantess arrived from the West:

W = Wall
B,b = Bridge
D = Locked Door
T = Trap
Inside the building the menacing spike traps are on repeat action, so the INTENDED working is for building destroyer and door passers to get through the first door and get killed by the trap array inside, and if it's too tough, the bridges should be able to lock it in while it is destroying the second door.

I also had a similar case where a Cyclops appeared, climbed a stair and stood diagonally (1 tile) outside the door that held a war dog locked in on the other side. Again, it just stood there. Crashing the game and repeating with the door unlocked, the dog panicked and fled, the Cyclops then proceeded to stand two tiles away from the door, destroyed the door and the floor grate inside, and then, after waiting a while, proceeded on to my trade depot entrance as I believe the proper behavior is.