Implementing forces in Unit Motion (HELP WANTED)

[Atrik]

1 hour ago, nifa said:

The ship's movement looks really natural.

My favorite too  Hopefully it can be a good starting point to make naval battles very different then land battles.

1 hour ago, nifa said:

(on the elephant attack too late, on the catapult impact too early?). I think it's nice and I wanna encourage anyone who is able to test it

Right.

 

Edited September 22 by Atrik

[guerringuerrin]

10 minutes ago, nifa said:

Too bad it's not possible to make a mod, unfortunately I don't have it compiled.

Having people who can compile is important for testing many things. I can help you with that if you want to do it some day

[Atrik]

2 hours ago, nifa said:

The timing in the other two videos might be not 100 percent on point (on the elephant attack too late, on the catapult impact too early?)

 

Better?

Also another demo about cavalry movement now :

[Thalatta]

11 hours ago, Atrik said:

Already ships not going through each other is an astronomical improvement (although realistically, for the more direct impacts the ram would perforate the other ship and reversing would be needed to separate them). I hope the same could be implemented for land units, making their movements more natural and their tactics more relevant.

[Atrik]

4 hours ago, Thalatta said:

although realistically, for the more direct impacts the ram would perforate the other ship and reversing would be needed to separate them). I hope the same could be implemented for land units, making their movements more natural and their tactics more relevant.

You are such a gigantic troll 
But I'll bump on it still, and give some nerdy details.

The collisions between units are not indeed like solid bodies that are impossible to overlap, even with this PR, this will remain true for most units. It's more a spring-like push that tries to make units keep distance to each others. This pushing just use a distance-to-center repulsion force.

What's introduced here for boats and elephants is a different stronger pushing and that actually take the unit's shape into account. This is why on the video you see that the hulls act like actual solid bodies. However simulating this, is ~x1.5 time costlier then the simple radial spring pushing. So because that, for small units, the difference in visible behavior would be minor, better go with the simple pushing, and use the better one only for big units that get the most benefits from it.

A fun fact is that before this PR, all units were treated the same, so you did had still this radial-pushing for boats (the collisions were spring-like and only a small circle at the center of the boat was even acting as the hitbox) but it was still much bigger then for, say infantry.
To detect if units were colliding, the map had a grid that allowed each unit to search a limited area where it might be actually colliding with other units. This grid size had to be proportional to the largest pushing unit of the game : boats - who's pushing effects where questionable anyway.
Even if you played on mainland map with no ships whatsoever, the grid was sized to work for boats too. And your unit had to check their distance with much more other units they needed to.
So you can say that the lag you experience on mainland, was partially due to ships.

This along a few other optimizations with the pushing and more resilient obstruction handling, make the PR a performance improvement for common scenarios (yey!).

[Thalatta]

49 minutes ago, Atrik said:

You are such a gigantic troll 

Hardly , just pointing out history, realism, and possible improvements, more so considering many have stated a preference for tactics and formations becoming more relevant, which units not going through each other would automatically provide, in good part

 

49 minutes ago, Atrik said:

The collisions between units are not indeed like solid bodies that are impossible to overlap, even with this PR, this will remain true for most units. It's more a spring-like push that tries to make units keep distance to each others. This pushing just use a distance-to-center repulsion force.

What's introduced here for boats and elephants is a different stronger pushing and that actually take the unit's shape into account. This is why on the video you see that the hulls act like actual solid bodies. However simulating this, is ~x1.5 time costlier then the simple radial spring pushing. So because that, for small units, the difference in visible behavior would be minor, better go with the simple pushing, and use the better one only for big units that get the most benefits from it.

Sure, but it's a theory/practise issue. Shouldn't increasing the radial repulsion force at a given distance (in physical terms, the elastic constant k, or stiffness) of land units achieve a more "solid" effect? Would this be costlier to simulate? I wonder how your cavalry turning would look in that case, for example.

[Atrik]

1 hour ago, Thalatta said:

Shouldn't increasing the radial repulsion force at a given distance (in physical terms, the elastic constant k, or stiffness) of land units achieve a more "solid" effect?

You can see how "solid effect" of "stiffness" impact the boats in the video. You get super cool effects when there are a few ones, but a lot of them result in them taking a lot of time to settle. It's fine for boats as you rarely think of crowds of boats, and I just made a scene for this in the video to show that it works, and still look good for them.
But if you have a crowd of infantry constantly wiggling and taking forever to settle, this would look very bad. Hence the spring.

 

1 hour ago, Thalatta said:

I wonder how your cavalry turning would look in that case, for example.

Inertia and pushing aren't the same thing. But for navigating on open terrain, this wouldn't change much. However if you try to funnel "solid" physical bodies into a choke-point, they obviously take a while more to achieve the same movement.
So if ever we wanted to make cavalry "solid bodies", with this PR it's only just one tweak in their template. But because big crowds of them cost more to simulate and that moving them around take longer if they are in high number, it should be accompanied by an increase of cost/population for example. The pros are that they will have much more realistic charge effects, like you see with elephants, but cavalry have less contact area and are moving much faster, the physic outcome would be different too (like a cavalry can trow fewer infantry units away but at higher velocity). So this is just a balancing change, out of scope.

Even without proper "charge", -so just using the old pushing  pretty much as it was, the inertia improves physics for cavalry fighting at no additional cost. The cavalry can push away other spread units thanks to it's superior weight, and also push its target by a little - even if ideally it would be more, and the cavalry would be smart enough to take more advantage of it instead of stopping once in front of it's target.

 

Edited Tuesday at 16:57 by Atrik

[Thalatta]

24 minutes ago, Atrik said:

Inertia and pushing aren't the same thing. But for navigating on open terrain, this wouldn't change much.

Of course they aren't the same thing, those would somewhat correspond to independent Newton's laws after all. I was referring to the effects of their combination. What I noticed is that when cavalry change direction they go a bit into each other, and I wondered how their movement would change without doing so. But you say both "it wouldn't much" and "cost more to simulate", along with representing a "balancing change", the latter I think should be considered since far too many sword infantry seemed to be having a go at that poor elephant (avoidance and ranged attacks, mainly javelins if I remember correctly, is how the Romans dealt with them), although of course that's another discussion, but good if "with this PR it's only just one tweak".

[guerringuerrin]

 

@Atrik!  I’ve been testing the PR. I haven’t noticed any functional bugs. Everything I’m noticing is related to tweaks for the units values. So I’ll share my impressions of their current behavior. 

In general, the units feel more “heavy” to me. I find it somewhat appealing, but I think it will all depend on the fine-tuning that’s done. I think some degree of overlapping could also be fine to make unit bumping feel less noticeable.

I don’t think civilians and infantry should have such a gradual rotation, at least not when they’re moving individually. I hope I can explain what I mean. I don’t know anything about crowd movement, but I have the feeling that their turns should become wider as the size of the group increases, with this being more of a consequence of them bumping into each other.

Maybe civilians could also be allowed to overlap with each other a little more.

I’m sharing a few videos showing different situations. Unfortunately, we still can’t test multiplayer, so I did my best to simulate a battle.

 

Woodcutting. Notice the woman on the left who gets stuck and can’t reach her destination, around the end of the video. I’ve never tested this with the vanilla version, so I can’t really compare whether this happens there as well..

Spoiler

Mining brothers:

Spoiler

 

Here I get the feeling that the elephants are trampling the horses. Some horses appear to be standing still while being pushed around, or simply remain stationary, as if they can’t find a path to their targets. The trampling looks interesting, but the horses remain stuck for too long.
 

Spoiler

 

And the elephants seem to have this infinite pushing loop. I assume you’ve already noticed it. 
 

Spoiler

 

Edited Wednesday at 20:16 by guerringuerrin

[nifa]

On 22/09/2026 at 3:07 AM, Atrik said:

 

 

 

Better?

Also another demo about cavalry movement now :

 

Thanks, yes it's better. Calvary movement looks smooth too. In the catapult video those 2 guys walking in circles looks strange, but I guess it has nothing to do with the question here.

On 22/09/2026 at 12:36 AM, guerringuerrin said:

Having people who can compile is important for testing many things. I can help you with that if you want to do it some day

Yes I want to do that some day when I have more time, thanks for the offer, I will get back to you

[Atrik]

2 hours ago, guerringuerrin said:

I don’t think civilians and infantry should have such a gradual rotation, at least not when they’re moving individually.

9 minutes ago, nifa said:

In the catapult video those 2 guys walking in circles looks strange,

Noted, yes after some playtesting also with @Effervescent it was clear that we should make infantry have more agile movements, which is mainly suppressing restrictions on turning. We also had interesting talks about using the new parameter "MaxAngle" to have ranged units in general start the attack prepareTime/animation while turning (they start drawing an arrow while they turn, so it makes micro interesting).
 

3 hours ago, guerringuerrin said:

Maybe civilians could also be allowed to overlap with each other a little more.

I think i did increase the value of pushing a tiny bit, but maybe before reverting I would try to see if you think it's better with the lowered Inertia effects (they are more agile so maybe it would fix it for you).

 

3 hours ago, guerringuerrin said:

Here I get the feeling that the elephants are trampling the horses. Some horses appear to be standing still while being pushed around, or simply remain stationary, as if they can’t find a path to their targets. The trampling looks interesting, but the horses remain stuck for too long.

I guess I did set a "stagger recovery rate" very low in the templates  So you are right.

 

3 hours ago, guerringuerrin said:

And the elephants seem to have this infinite pushing loop. I assume you’ve already noticed it. 

I didn't, but I should have saw it come.  Yes this is one bug that is from this PR obviously, I can address that. The other ones I'm not too sure, the woodcutters getting stuck happens a lot to me in MP.

Thank you so much for the feedbacks! I have a much clearer idea of what this PR needs now. Mostly tweaking the templates and fixing the big boys club dances.

[Thalatta]

On 22/09/2026 at 6:55 PM, Atrik said:

constantly wiggling and taking forever to settle

5 hours ago, guerringuerrin said:

seem to have this infinite pushing loop

2 hours ago, nifa said:

guys walking in circles looks strange

I wonder if this could be solved, instead of removing how "solid" units are, by changing something else, like not reacting to repositioning so fast and simultaneously when close by (maybe hard to require), or being more permissive on supposed destinations if an obstacle is there (one can always reform after obstacles are removed if a specific formation is wanted, for which showing and shaping it by dragging the mouse at the destination like Rise of Nations and Total War would be useful, and has been asked).

Edited Thursday at 00:49 by Thalatta

[nifa]

14 minutes ago, Atrik said:

We also had interesting talks about using the new parameter "MaxAngle" to have ranged units in general start the attack prepareTime/animation while turning (they start drawing an arrow while they turn, so it makes micro interesting).

This seems interesting!

Another thought I had when watching the elephant videos (probably unrelated): All soldiers going back to idle at the same time when the elephant dies looks so abruptly, maybe there could be some randomness (like some cheering, some idle) or random delay.

[parizaad]

The ship movement is really nice, and the inertia makes the collisions feel much more natural.
It’s a shame it can’t be tested as a mod, but the demo videos still give a good idea of the changes.
Hope more people can compile it and give feedback on the PR.

[Effervescent]

Hi,

Let me start by expressing how much I love the unit motions. The inertia aspect bring more depth to the units, and with the newly tweaked values, it's a good balance between realism and unit control ability (also micro).

I especially love the turns cavalry make. that really gives the vibes of medieval cavalry going for raids.
The unit animation sync needs to be handled though, so that the stop-animation syncs with units stopping, by that's a minor thing.

As for the elephants. O.M.G. That thing is so fun to play. Elephants pushing and trampling units is so fun, and I wouldn't be surprised if this changes births a few elephant lovers in-game.

The infantry units having different values from cavs and eles makes the most sense to me, tbh. It gives infantry agility, and tighter controls which their qudra-pedal brothers can only dream of.

I'll try to recruit more testers for this and see how people feel about this in general, but I for one really love this and hope this gets pushed in the next alpha.

Cheers.
 

[guerringuerrin]

New tests on the latest iteration. The bouncing elephants bug is now much harder to reproduce.

When trying to gather them at the same point, the issue is much less pronounced than before:
 

Spoiler

However, I was able to reproduce it in the following situations:

 

 

Walking around corners:

I think the bouncing effect is triggered when two or more units become blocked by objects or other units of similar strength. You can see in one part of the video that a single elephant gets blocked, but nothing happens because it has enough space to bounce. Later in the video, however, more than one elephant gets blocked from all sides, and that's when the bouncing starts.

Yesterday we talked a bit about adding some kind of diminishing return calculation to reduce the bouncing effect as it keeps repeating. This could be a relatively low-cost solution in terms of performance that might address the issue.

Spoiler

 

Moving through narrow paths:

This is perhaps the most important issue to address. At some point, they should be able to "agree" on who gets through first. Common sense tells the user to destroy the house first before trying to pass, and it's perfectly valid for a successful attack to depend on the player's ability to move their units through narrow paths or turtle bases. However, it is still noticeable that more than half of the elephants get stuck in a space they should be able to pass through relatively easily:

Spoiler

 

It makes sense that they don't turn as quickly as they do in vanilla and that, as a consequence, their attacks and movement take longer to execute. After all, we're talking about a huge animal. Somewhat slower and, in a way, "clumsy" movement is to be expected.

Beyond continuing to tune the elephants' physical values, I think it would be worth considering some degree of overlapping. Not as much as what currently exists in vanilla, but enough to help reduce some of the clumsiness and to emulate a slight "compression" of their bodies when they are packed together. After all, they are organic bodies with some degree of flexibility, not rigid objects like tanks.

Could we also try making their hitbox oval rather than square? This might help reduce collisions between them even further.


 

This last comment is outside the scope of this PR, but I think it's worth mentioning:

This testing also made me wonder whether it's desirable for elephants to prioritize attacking nearby units over buildings. In the video example, I send the elephants to attack the fortress directly. Then I press H to make them attack freely. The elephants prioritize attacking the units, but the ones in the back can't reach them and end up bouncing around without dealing any damage.

Elephants are perhaps the only "hybrid" unit in the game, in the sense that, although they are not classified as siege units, they can still destroy buildings quite effectively. Perhaps we should consider giving them a smaller target acquisition range, so that in situations like this, they choose to attack buildings instead.

Edited 1 hour ago by guerringuerrin