Editing User:Vasiln/Build order

I once did some careful examination of a creature triggering a pressure plate linked to various buildings built either before or after the pressure plate.  I added those findings to the [[pressure plate]] page.  However, some of the things I found felt inconsistent with [[User:Hussell|Hussell's]] findings regarding build order.  In particular, he found that build order of [[gear assembly|gear assemblies]] affected the period of his [[repeater]]s, whereas I found that gear assemblies were always triggered on the same tick, regardless of whether they were built before or after the triggering pressure plate.  Also, I found that the delay of pressure plates was 99 ticks, rather than the traditionally accepted 100.

These findings have always kind of bothered me, but I think I have a hypothesis that explains it.

==The Grand Unified Hypothesis of Build Order==

Every tick, the game evaluates every creature and building in sequence.  Here's the order in which it does so (according to my hypothesis):

*1) Every creature checks its [[speed]] to determine whether it can move to the next tile in its path.  If it can, it moves.  If its next tile is occupied or inaccessible, it recomputes path.
*2) Power needs are computed for power generators.  If power needs are greater than power output, power generators are considered unpowered.  (This one requires a lot of research).
*3) Every variable-state building is evaluated (more on this later).
*4) Every tile of [[water]] is evaluated to determine whether it should flow (or maybe teleport), and it does so, if it should.

The important part of this is step 2.  In particular, buildings are evaluated in the reverse order to which they were built.  If you build a pressure plate, then a [[door]], the game will first run the door's ''think'' function, then run the plate's ''think'' function.

Here are the ''think'' functions for various variable state buildings, as far as I can tell:

====Door====
*If a ''close'' signal has been generated for this door, close the door.
*Note that the door doesn't itself evaluate ''open'' signals!
====Pressure plate====
*If triggering criteria are met, and the device most recently sent a ''close'' signal, send an ''open'' signal.  Additionally, open any doors or [[hatch cover|hatches]] linked to this pressure plate, and toggle any linked gear assemblies.
*If triggering criteria are met and the device most recently sent an ''open'' signal, don't do anything, except remember this tick.
*If triggering criteria are not met, and it has been exactly 99 ticks since triggering criteria were met, send a ''close'' signal.  Additionally, toggle any linked gear assemblies.
*If triggering criteria are not met, and it has been greater than or less than 99 ticks since triggering criteria were met, don't do anything.
====Bridge====
*If no open or close scheduled for this device, check for a signal.  If ''open'', schedule an open in 100 ticks.  If ''close'', schedule a close in <s>99</s> 100 ticks.
*if no signal, or an open or close is already scheduled, don't do anything.
====Screw Pump====
*If the pump is adjacent to a powered gear assembly, there is fluid in its intake tile, and there is no fluid in an acceptable output tile, destroy the water in its intake tile and generate an equivalent amount of water in the first acceptable output tile.
*Otherwise, don't do anything.
====Gear Assembly====
*If gear assembly is adjacent to a device with power and is engaged, consider this tile powered.
*If gear assembly is not adjacent to a device with power or is not engaged, do not consider this tile powered.
*Note that gear assemblies do not evaluate signals!
====Other Furniture====
I believe that the think functions described earlier apply to all other forms of furniture.  Hatches use the same think function as doors.  Grates, bars, and floodgates use the same think function as bridges.  <s>[[Lever]]s require a special note: I believe they function the same way as a pressure plate.  However, there's a chance that the dwarf pulling them actually sends the signals, in which case you would expect to see levers functioning as if they were always built before the furniture they trigger.</s>  Levers do not function like other furniture!  It is the dwarf that sends open and close signals, rather than the furniture, which means that signals from levers are always evaluated before any other buildings.  Levers automatically open doors and toggle gear assemblies, since those are not functions of the furniture themselves.

===How this reconciles Hussell's clock and my goblin repeater===
This model of build order demonstrates how a gear assembly can both be engaged at the end of a tick, yet a pump attached to that gear assembly may or may not yet be powered, based on the order in which the two components were built.  That disconnect between my data and Hussell's been bothering me, and this hypothesis explains both results.

==Predictions==
Now that I've got a working hypothesis (including bits that I'm not very sure of, for instance, exactly when non-dwarves are evaluated, exactly how power is evaluated, exactly when flow is evaluated), it's time to make some predictions.

===Formulating data===
====200-step repeater====
Let's examine the behavior of Hussell's [[user:Hussell/ClockRepeater|200 step repeater]] in terms of my theory.  Reprinted here:
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Just to clarify, pressure plates trigger on 2+/7 water, and are linked to the gear assembly of the same color.  Device is built in the following order: first the upper pump, then the lower pump, then the gear assemblies, then the pressure plates.  Beginning state has 7/7 water in the left-hand reservoir, both gears disengaged.  At t=0, we engage the green gear via lever.  Let's examine, ''in order'', the events happening during important ticks.

 T=0: Red plate already activated, no action.  Green gear becomes powered.  Lower pump moves water to right.
 T=1: Red plate schedules a close to occur at T=99.  Green plate toggles green gear.  Green gear becomes unpowered.  Lower pump stops pumping.
 T=99: Red plate sends a close to red gear.  Red gear becomes powered. Upper pump moves water to the left.
 T=100: Green plate schedules a close to occur at T=199.
 T~=125: Water lands on red plate.  Red plate sends an open to red gear.  Red gear becomes unpowered.
 T=199: Green plate toggles green gear.  Green gear becomes powered.  Lower pump moves water to the right.
 T=200: Red plate schedules a close for T=299.  Green plate toggles green gear.  Green gear becomes unpowered.
 T=299: Red plate toggles red gear.  Red gear becomes powered.  Upper pump moves water to the left.

Do you see?  Hussell's clock '''would not work''' unless pressure plates sent signals 99 ticks after becoming disengaged!

====Pressure plate trigger data====

Here, I'm just going to link you to http://mkv25.net/dfma/movie-2363-timingdetails.

<s>Actually, on reviewing that, it doesn't necessarily demonstrate what I want it to.  This could be due to imperfect frame-by-frame capture for movies, or it could be because I screwed up.  I will have to confirm.</s>  Yes, it does demonstrate the effects, you just have to slow it down to a rate below 1 to see all of the frames.

====Dropping a dwarf takes 7 ticks====
Creatures fall at a constant rate of 6 ticks.  However, when you drop a dwarf, it takes 7 ticks for the dwarf to fall the first z-level.  This, according to my hypothesis, is because the dwarf doesn't know the ground isn't there during the tick the floor disappears, because the ground doesn't disappear during the dwarf's ''think'', it disappears later, during the hatch's ''think''.

===Testable Predictions===
====Screw pumps and pressure plates====
The following design, seen from the side, can behave multiple ways, depending on build order.

 # %% #  Return pump
 # %%^#  Feed pump, plate (1+/7 water)
 # ####  7/7 reservoir
 ###

*1) Build return, feed, then plate.  Plate doesn't trigger.  Water is moved first from the feed, then to return, and stays in the reservoir.
*2) Feed, return, then plate.  Plate doesn't trigger first tick, but triggers on the next tick.  Water is moved first from the return, then the feed, and so stays on top of the pressure plate.
*3) Return, plate, then feed.  Plate triggers, although water remains in the reservoir.
*4) Feed, plate, then return.  Plate doesn't trigger, although water remains on top of the plate.
*5) Plate, return, feed.  Plate doesn't trigger, and water remains in the reservoir.
*6) Plate, feed, return.  Plate triggers, and water stays on top of the plate.

Those are the predictions.  Time to test!

=====Findings=====
I forgot to take gravity into account in my predictions.  Water takes a certain amount of time to fall, and until it falls fully into the reservoir, it cannot be pumped back by the feed.  This changes where we expect water to sit, but it doesn't change our predictions regarding pressure plate activation.
*1) Plate doesn't trigger.  Water stays in the reservoir side.  Meets predictions.
*2) Plate triggers.  Water stays mostly in the reservoir side.  That's because it takes time to fall to get pumped by the feed again.  I missed the first tick, can't say whether it only triggered on the second tick.
*3) Plate doesn't trigger.  Doesn't meet predictions.  Will rebuild to verify.
*4) Plate triggers.  Doesn't meet predictions.  Will rebuild to verify.
*5) Plate doesn't trigger.
*6) Plate triggers.

Note that both feed and destination tiles are muddy.  I'll DFHack unmuddy them to see if water is actually never touching a the ground on the machines.

After rebuild, 3 triggers, and 4 doesn't trigger.  I figure I screwed up build order originally.  Note that it doesn't look to me like Hack can unmuddy specific tiles, so I didn't test that.

So far, so good.  Predictions are as expected.

====Levers====
Next prediction is regarding levers.  I anticipate that levers behave the same way as pressure plates in regards to build order.  Those predictions are established on the pressure plate page, and my hypothesis tells me to expect them.  I'm going to test bridges, doors, and gear assemblies (as those represent the three build types in my hypothesis).  Note that it's hard for me to establish exactly when a lever is activated, so I'm instead just going to compare the open and close signals of furniture built before and after the lever.
*1) Both doors open at the same time, but the door built after the lever closes 1 tick later.
*2) Both gear assemblies open and close at the same time.
*3) The bridge built earlier opens and closes 1 tick before the bridge built later.

=====Findings=====
Findings did not meet predictions.  Buildings responded identically, regardless of build order.
*At tick=-1, there is an active "pull lever" job at the lever.
*At tick=0, there is no active "pull lever" job.  Doors open or close, and gears engage or disengage.
*At tick=100, bridges open or close.

There are two interesting parts to this finding.  First, lever signals are being evaluated before all other signals-- I believe it's happening in the dwarf phase, with completion of the lever pull task.  <s>Second, open and close signals are being acknowledged by bridges at the same time-- 100 ticks after receipt of signal.  Is there some way to rectify this with the behavior of bridges linked to pressure plates?</s>  Of course there is-- it is the 99 tick delay associated with pressure plates that is responsible for the 199 tick closing of bridges, not the bridges themselves.

====Gear assemblies====
Consider the following machine:
 # %%*#  Return pump, return gear
 #*%%^#  Feed gear, feed pump, plate (1+/7 water)
 # ####  7/7 reservoir
 ###

Both gears begin disengaged, linked to a lever that has just been pulled (t=-1, queued pull job; t=0, no queued job)

We expect that power won't be transferred to pumps on the tick it's received by a gear assembly '''unless''' that gear assembly is built after the pump to which it's transferring power.

*1) Build plate, then feed pump, return pump, feed gear, return gear.  Both pumps are in operation on the first tick (t=0), and feed pumps last.  Plate triggers on t=0.
*1.1) Build plate, then feed pump, return pump, return gear, feed gear.  Exactly as with 1).
*1.2) Plate, feed pump, feed gear, return pump, return gear.  Exactly as with 1).
*2) Plate, then return pump, then feed pump, return gear, feed gear.  Both pumps operate at t=0, but return pumps last.  Plate doesn't trigger.
*2.1) Plate, return pump, feed pump, feed gear, return gear.  Exactly as with 2).
*2.2) Plate, return pump, return gear, feed pump, feed gear.  Exactly as with 2).
*3) Plate, return gear, return pump, feed pump, feed gear.  On tick 0, feed is powered and return is not.  Plate triggers on t=0.  At t=1, return gear activates, plate sends ''close'' at t=99.
*4) Plate, feed gear, feed pump, return pump, return gear.  On tick 0, return is powered and feed is not-- no trigger at t=0.  At t=1, feed becomes powered, and plate triggers.


I'm not going to test 1.1, 1.2, 2.1, or 2.2.  I will test the others.  Particularly notable is the behavior of 3.

====Lever vs pressure plate activated bridges====
To verify my lever findings, and compare to my pressure plate findings, I'm going to make two bridges, such that they are both activated at the same time, but one via lever, while the other via bridge.

*1) Build the machine demonstrated in the above gear assembly test.  Use build order 1.
*2) Build a lever and a bridge.  Link the lever both to the bridge, and to both gear assemblies.  Build order shouldn't matter, but we'll build the lever first.
*3) Build a bridge.  Link the plate to the bridge.

Predicted: The plate activated bridge will open 1 tick before the lever activated bridge.

====Water flow====
This is a simple one, and I'm going to use Hack to test it.

# ## 7/7 water
# ^# 7/7 water, plate triggers on 2+
####

Predicted: Plate does not trigger on first tick, but triggers on second tick.