Game AI stuff (1.5)

[ReluctantSamurai]

From what I've observed, the Middle East appears to have more than it's share of path-finding problems. In looking at the RTW map in it's entirety, perhaps it's just my imagination, but there seems to be a lot more twisting and winding of roads through mountains and rough terrain than anywhere else I've never cataloged it, but just like Carthage seems to get buried under a slew of path-finding problems in the Western Med, Seleucia mirrors that problem in the Eastern Med. They rarely ever target the nearest rebel town of Palmyra (in the east), or Halicarnassus (in the west). Getting into the Lycia province is the most puzzling, as it's just a stone's throw across the river

movement costs may matter indirectly as finding the fastest path through difficult but not impassable terrain is an obstacle also, just not as much of one as impassable terrain - so roads and difficult terrain may have an effect there

Although it involves considerably more tinkering, increasing movement rates might be a good follow-up to map alterations in aiding path-finding problems...

I'm thinking a better solution may be the exact opposite and give the unwanted direction a close by region with very high unrest instead. So instead of a dozen armies crawling over the desert towards a very distant settlement the AI just has one army constantly retaking the same close by settlement.

That's just evil

as the Persian Royal Road (in terms of RTW regions) went Babylon-Hatra-Cappadocia so Hatra as a crossroads region seems appropriate.

Although it's a topic for a different thread, the Persian Royal Road was as advanced as anything the Romans built. I had some links somewhere covering the topic, and it makes for some fascinating reading (and caused me to give the Parthians the "Paved Road-building" capability).

In any case, fabulous work

[nikolai1962]

From what I've observed, the Middle East appears to have more than it's share of path-finding problems.

agree - that whole quarter of the map and the bit around massilia/lugdunensis are the two worst imo

They rarely ever target the nearest rebel town of Palmyra (in the east), or Halicarnassus (in the west). Getting into the Lycia province is the most puzzling, as it's just a stone's throw across the river

yes, it's the strangest thing as when pontus takes sardis they usually go on to take halicarnussus with no problem so it's not a persistent clipping type problem, it's something else. there's a few places like that which i've never managed to figure out but i'm hoping they're a side effect of problems elsewhere and so will eventually clear as other problems are cleared.

Although it involves considerably more tinkering, increasing movement rates might be a good follow-up to map alterations in aiding path-finding problems...

Yes definitely - increasing MP fixes a lot of problems on its own. I kept them at 80 while doing this as i specifically wanted to see where the AI gets stuck so I could try and fix it but the plan was always to increase MP when i was done, Although I'll probably do it by giving movement traits to AI generals.

Although it's a topic for a different thread, the Persian Royal Road was as advanced as anything the Romans built

yes, knowledge getting lost after a civ collapse and then reinvented somewhere else

In any case, fabulous work

Thanks, I'm pretty pleased to be honest as I can finally enjoy the game again.

In fact took a break from map editing to play a bit before moving on to the next stage - trying to ensure every settlement is within pathing range. Will be interesting to see if that fixes the remaining unexplainable problems or just creates new ones :)

[nikolai1962]

breakthrough on the multi-region movement - kicking myself as it's obvious once you see it but I didn't have such a clear example before...

adding some regions in parts of the vanilla map to make sure all settlements in adjacent regions are within pathing range of each other and got a situation where Hasdrubal regularly got stuck on the single blue tile by the mouse cursor in the middle of the image below (en route from Carthage via the Leptis Magna region to the desert region in the lower right corner .)



(I knew the army started in Carthage cos it was Hasdrubal and not a randomly named captain and he hadn't moved out of Carthage yet.)

(nb portions of the map like this where 3+ regions join at a point are prime contenders for the region clipping bug.)

looking at the settlement to settlement path from Carthage to the settlement in the target region there are no obvious issues



however they are not adjacent regions so if we assume the AI uses region to region movement in this situation what might that be? assuming the game knows the region to region path is Carthage region ->Leptis Magna region-> desert region then let's say it's first move is to calculate the fastest path to the closest border tile of the region adjacent to the target region (i.e. Leptis Magna region) which by eye looks like it would be this.



the fastest path from that tile to the target settlement also seems okay



however the path to the closest tile in the target region clips



placing an impassable tile in the right spot should stop the path clipping and fix the problem



which it does (at least from that direction).



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this is actually a more general case of the region clipping previously mentioned in that the fastest path between two *adjacent* settlements will in most (all?) cases automatically include the fastest path from start settlement to closest passable tile in target region.

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from past observation my theory was the AI used region to region movement to get to an adjacent region and then switched to finding a path to the settlement itself but this example suggests it paths to get in the actual target region first. this kind of pathing glitch happens a lot but it's usually hard to be sure what the precise cause is as unless it happens in the first few moves you generally don't know where the AI army was when it was assigned its target but in this case by lucky accident the combination of a) the odd shape of the target region in this example (a temporary thing while i juggled region borders) and b) it being Hasdrubal and very early in the game made it obvious.

[nikolai1962]

the previous post implies that in multi-region movement the key is not the overall settlement to settlement path but

a) the armies start tile to the nearest (or fastest to reach) tile of the next region in the region-to-region path

b) the path from that resulting tile to the fastest border tile of the next region in the chain

and finally

c) the path from the resulting border tile in the target region to the target settlement

an example of where this can happen

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on the vanilla map the distance from campus alanni to a border tile of the caucasus regions is beyond path finding distance



(nb there's no way to know if the game's internal max path finding distance for AI armies is the distance allowed the player using their right-click movement but it's the only clue available)

(nb AI armies won't always be assigned targets from a settlement tile - they could be in any tile in the source region - but they often are in the settlement or the waiting spot outside the settlement (usually the tile SW of the settlement if it's not blocked) so measuring from the settlement is a good first iteration)

from the other direction the path from a caucasus region settlement to a steppe border tile is well within range



and the steppe border tile to the settlement is within range also



there are multiple ways to fix this:
- move the campus alanni settlement down
- push the border of the caucasus regions up
- add an extra region
all of which can create new pathing problems so need to check afterwards.

I added an extra region - imaginatively titled campus_alanni02



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another example

on the vanilla map the arabia settlement is distant from some of its adjacent settlements so the borders of those regions are pushed out such that the distance for the nearest border tile to the arabia settlement is within range e.g. vanilla Palmyra region



and vanilla Bostra region



however now i'm pretty sure i can fix most pathing problems i've reactivated one of my original aims which was to make regions (or a cluster of regions) have the same shape as the roman provinces they eventually became a part of so that if you're playing Roman you can make your empire look like historical maps and as a result made the distance between the Palmyra border tile -> Arabia settlement too far.



No problem though - easily fixed as long as you know what to look for.

[ReluctantSamurai]

A lot of this is much like the process of map creating in Pacific General that I did. Play-testing the map to make sure units behaved correctly was a large part of the time involved. The finished map often had many, many alterations from the beta version...

[nikolai1962]

yes exactly - we can't change the AI code but we can change the map to cope better with the flaws in the existing AI code

[nikolai1962]

a type of glitch, a minor addendum and a major breakthrough

1) a type of glitch

generally if the AI is stuck it can be hard to spot as often it is just one stack among many but then there's the other kind



this can happen when
a) a faction has only one potential adjacent land target and the army assigned to it is stuck
b) a faction has no potential land targets and the a naval landing has glitched
c) a faction temporarily has no adjacent land targets cos it's at peace with all it's neighbors - this generally only happens briefly after defeating one enemy faction and before starting a new war with a neighbor

in this case it was (c) - Macedon has just defeated Greece and was at peace with all its other neighbors

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2) a minor addendum

the fastest way to clear most path-finding glitches is to check the settlement-to-settlement path between adjacent regions looking for any clipping issues however

vanilla Macedon: army in Larissa moves out to city "waiting spot" (usually the tile SW of settlement unless it's blocked) and waits, getting extra units from Larissa each turn and getting the Captain promoted to general (the AI will often promote a captain of a stack that has been assigned a target settlement)

261BC



and waits 254BC



and waits 226BC



eventually (209BC) another faction takes the target settlement (Athens)



and the stack moves



but after 100+ turns of not expanding and paying the upkeep for a full stack that isn't doing anything it's a bit late



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Solution

if you look at the fastest path from Larissa to Athens it seems okay



and to be thorough the fastest path from Larissa's waiting spot to Athens also



but if you move the mouse around the tiles adjacent to the target settlement rather than the settlement itself the path clips the Corinth region



also, just to be thorough again, on the assumption the AI doesn't calc settlement to settlement but 1) start tile to fastest path to a passable tile in the target region and then 2) from that tile to the target settlement then check that too - which clips also if for whatever reason the path finding chooses to go that way around the mountain



on the assumption the path-finding does go that way for some reason it is easily fixed by giving the tile it clips through to the Athens region - which seems to work

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so the expanded sequence is

1) check the fastest path settlement-to-settlement doesn't clip
2) check the fastest path from the start settlement's waiting spot to the target settlement doesn't clip
3) check the fastest paths to tiles adjacent to the target settlement don't clip
4) lastly check the fastest path from the start settlement to a passable tile in the target region is not different from the fastest path overall

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example of last point

the fastest path from Narbo to Lugdunum seems okay



(actually it's not as although the diagonal from Narbo region to Lug region doesn't clip, the underlying orthogonal path can only go either right and up or up and right and the latter is blocked by the mountain tile so the orthogonal path clips the Massilia region - however it can easily be fixed by removing that corner tile from Massilia)

however the fastest path from Narbo to the nearest passable tile in Lugdunensis is like this



and the fastest path from that tile within Lugdunensis region to Lugdunum clips back into Narbo region.