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[itg]

While trying to cave in a portion of the edge of the map in my fort, I stumbled across a neat little bug: when you mark a raised drawbridge for deconstruction, then cancel the job, the bridge "forgets" that it was raised and allows liquids to pass through it. Ten minutes later, I had a prototype weapon.

Spoiler: The weapon at t=0 ticks, ~40 ticks, ~200 ticks (click to show/hide)

Spoiler: Below the surface (click to show/hide)

The concept is simple: create a hole in the ground (see the blue square in the pictures), block it off with a raising bridge, and hook it up to a pressurized magma source (use a pump at a higher level than the magma hole). When enemies are near, mark the bridge for deconstruction, then immediately cancel the order (q-x-s). Response is instantaneous, and you don't have to worry about your idiot lever puller going on break. To reset, simply lower the bridge with a lever, then raise it again.

The same trick can be used to create player-operated switches. Build a raising bridge, put liquid on one side, then put a liquid-triggered pressure plate on the other.

[Urist McRas]

Wait, you have designed a magma contraption that can be triggered without those drunken insane idiots? That's cheating!

Seriously, thank for you science, could be useful.

[Urist Da Vinci]

Honestly, player-operated switches and (potentially) building-destroyer-proof anti-swimming fluid filters are the more intriguing applications. A self-resetting player-operated switch would be golden.

So when you give the deconstruction order (and then cancel the order) to a raised, raisable bridge (not a retracting bridge) then it thinks it is lowered (for the purposes of fluids and perhaps other things?)?

If you did this with a retracting bridge or raising bridge that covers a floor hole, would it block fluids after the "exploit"? I wonder if it is a reversion to "no bridge" or "default bridge"? Are doors, floodgates, hatches, etc. affected?

[itg]

Honestly, player-operated switches and (potentially) building-destroyer-proof anti-swimming fluid filters are the more intriguing applications. A self-resetting player-operated switch would be golden.

I think a self-resetting player-operated switch is very possible. I'm thinking of trying a minecart loop with a pressure plate to lower the bridge and a plate to re-raise it and send the signal.

So when you give the deconstruction order (and then cancel the order) to a raised, raisable bridge (not a retracting bridge) then it thinks it is lowered (for the purposes of fluids and perhaps other things?)?...

If you did this with a retracting bridge or raising bridge that covers a floor hole, would it block fluids after the "exploit"? I wonder if it is a reversion to "no bridge" or "default bridge"?

Having done a few more tests, I can say it's not quite either of those things, actually. The bridge lets fluids and objects through horizontally, but not vertically, i.e the bridge acts as a floor. The tiles of the bridge that "disappear" when you raise it don't interact with anything.

Dwarves can move through these bridges if forced (e.g. by cave-in), but they seem totally unwilling to path through them.

Are doors, floodgates, hatches, etc. affected?

So far, the exploit only seems to work with raised bridges. I tried it with doors and floodgates (open and closed), as well as retracting bridges, to no effect.

[Urist Da Vinci]

...
Having done a few more tests, I can say it's not quite either of those things, actually. The bridge lets fluids and objects through horizontally, but not vertically, i.e the bridge acts as a floor. The tiles of the bridge that "disappear" when you raise it don't interact with anything.

Dwarves can move through these bridges if forced (e.g. by cave-in), but they seem totally unwilling to path through them.
...

That sounds similar to the "bridges encased in obsidian then dug out" thing.

Will foreign creatures path through the "deconstruction exploit" bridges?
Can Dwarves see hostiles through the bridges?
Can minecarts, and/or dwarves on minecarts drive through the bridges?
Does the exploit persist after saving and loading the game?

[TruePikachu]

In theory, this could be expanded to any control by means of using water and a pressure plate.

I propose a challenge: someone should design a compact pair of these which can reset each other.

[itg]

...
Having done a few more tests, I can say it's not quite either of those things, actually. The bridge lets fluids and objects through horizontally, but not vertically, i.e the bridge acts as a floor. The tiles of the bridge that "disappear" when you raise it don't interact with anything.

Dwarves can move through these bridges if forced (e.g. by cave-in), but they seem totally unwilling to path through them.
...

That sounds similar to the "bridges encased in obsidian then dug out" thing.

Will foreign creatures path through the "deconstruction exploit" bridges?
Can Dwarves see hostiles through the bridges?
Can minecarts, and/or dwarves on minecarts drive through the bridges?
Does the exploit persist after saving and loading the game?

Foreign creatures do NOT path through the "disabled" bridges.
Dwarf CAN see hostiles through the bridges.
Minecarts with or without dwarves go through the bridges just fine.
The exploit DOES persist after saving and reloading.

[Urist Da Vinci]

Got to my DFHack tools.

Reference material (valid building tile occupancy types):

Code: [Select]

        <enum-item name='None' comment='no building'/>
        <enum-item name='Planned' comment='nothing built yet'/>
        <enum-item name='Passable'/>
        <enum-item name='Obstacle' comment='workshop tile; ~fortification'/>
        <enum-item name='Well'/>
        <enum-item name='Floored' comment='depot; lowered bridge'/>
        <enum-item name='Impassable'/>
        <enum-item name='Dynamic' comment='doors, grates, etc'/>

The lowered bridge is type 5 (Floored), the raised bridge is type 6 (Impassible), and the exploited bridge is type 3 (Obstacle).

It should have most of the properties of an unwalkable workshop tile.

[itg]

That sounds exactly right. Where does that "enum-item name" stuff come from, out of curiosity?

The next question is, why would the exploited bridge be set to type 3? It's not obvious how that could be an accident.

[wierd]

Wild guess:

When the bridge gets the deconstruct order, and time passes 1 tick, it gets assigned the new state, since partial deconstruction state would presumably have that designation.

Eg, the type gets set at the BEGINNING of each construct/deconstruct stage.


So, for construction:
Planned->Obstacle->(finish), with the pathing type set at the beginning of each stage.

And for deconstruction:
(Finish)->Obstacle->Planned, with the pathing type set at the beginning of each stage.

this makes me wonder about walls as well.

[itg]

I made a working auto-resetting player-operated switch. This proof-of-concept design combines the bridge exploit with the bridge "wedging" trick from the lunar calendar thread. This design can be compacted considerably, and hopefully a no-power version can be created.

Spoiler: auto-resetting player-operated switch (click to show/hide)

The minecart sits on a roller until the bridge is "disabled," letting the cart slip through and activate the pressure plate. The plate/impulse ramp combo is necessary to re-raise the bridge, and incidentally, it's the ideal setup for linking to other bridges and floodgates in your fort.

This system doesn't work so well with doors and hatches. It opens them momentarily, but there's no way for it to make them stay open.

Wild guess:

When the bridge gets the deconstruct order, and time passes 1 tick, it gets assigned the new state, since partial deconstruction state would presumably have that designation.

Eg, the type gets set at the BEGINNING of each construct/deconstruct stage.


So, for construction:
Planned->Obstacle->(finish), with the pathing type set at the beginning of each stage.

And for deconstruction:
(Finish)->Obstacle->Planned, with the pathing type set at the beginning of each stage.

this makes me wonder about walls as well.

I'm sure it's something along those lines, but it's odd that the state change happens only when you cancel the order. If you don't cancel it, the bridge stays in wall state until a dwarf actually starts to tear it down.

[MDFification]

Itig, surely you've earned an honorary engineering degree at some university by now, haven't you?

Also ever consider making a masterpost with links to all of your science?

---

The minecart thing is promising. It might be possible (through clever management of burrows and military scheduling/equipping) to send fully armed and armored dwarfs through the bridge, allowing you to fight sieges while simultaniously turtling.
That being said, this is a bit exploit-y for my tastes. Finding it was dwarfy enough to justify it's use, but still.

[Urist Da Vinci]

...
The minecart thing is promising. It might be possible (through clever management of burrows and military scheduling/equipping) to send fully armed and armored dwarfs through the bridge, allowing you to fight sieges while simultaniously turtling.
That being said, this is a bit exploit-y for my tastes. Finding it was dwarfy enough to justify it's use, but still.

It IS possible to send flying minecarts with dwarves through fortifications without using any exploits.

The main advantage of this bridge exploit is that it can be selectively turned into a permeable barrier at any time.

[thegoatgod_pan]

The main advantage of this bridge exploit is that it can be selectively turned into a permeable barrier at any time.

!!!!invention!!!!

I love when the forum has a scientific breakthrough!

This is a big development.  Not only does this optimize magma mines nicely, but it opens amazing possibilities for freezing traps.

If you can activate the flow of water selectively you can freeze discrete, chosen  squares: targeted frost death, instead of the good-old fill-the-whole-tunnel-with-ice-and-send-in-the-miners.

[itg]

Itig, surely you've earned an honorary engineering degree at some university by now, haven't you?

Also ever consider making a masterpost with links to all of your science?

---

The minecart thing is promising. It might be possible (through clever management of burrows and military scheduling/equipping) to send fully armed and armored dwarfs through the bridge, allowing you to fight sieges while simultaniously turtling.
That being said, this is a bit exploit-y for my tastes. Finding it was dwarfy enough to justify it's use, but still.

I was thinking it might be nice to make/revive a general compendium of dwarven science, actually. I noticed an old thread by Girlinhat that fits the bill, if she's interested in updating/maintaining it. Otherwise, I could make a new one.

The main advantage of this bridge exploit is that it can be selectively turned into a permeable barrier at any time.

!!!!invention!!!!

I love when the forum has a scientific breakthrough!

This is a big development.  Not only does this optimize magma mines nicely, but it opens amazing possibilities for freezing traps.

If you can activate the flow of water selectively you can freeze discrete, chosen  squares: targeted frost death, instead of the good-old fill-the-whole-tunnel-with-ice-and-send-in-the-miners.

I like the sound of that. I'm envisioning a carbon freezing chamber for misbehaving nobles.