What is the state of the UE4 physics engine in 2018 and where is it headed in the future (Apeiron)?

If you have been paying attention you may have noticed things have been happening in the UE4 code-base regarding physics. If you have read the physics technical notes for the 4.21 release you will note that physics things are now happening under a unified physics interface. Additionally, if you poke around in the source you will notice an experimental new physics interface called “Apeiron”, see “PhysInterface_Apeiron.h”](

UE4 has already had source access to Physx for some time now, so my speculation is that the recent announcement about Physx going open-source was probably not a big shake-up for Epic. But what is interesting, are some of the features boasted by Physx 4.0, such as the supposedly more stable, “temporal Gauss-Seidel solver” and “joint articulations”. These would be great to have in-engine. My body and my physic’s bodies are ready for some better stability :slight_smile:

So, with these changes happening in UE4 and industry, it does raise several questions for developers who are heavily involved with physics:

  1. What is “Apeiron?”
  2. Is Physx 4.0 coming to UE4? If so, any hints on a version release target?
  3. Why is there no physics section on the forum? (Edit: I guess there is) Configuring physics is fiddly. Haha.

Quite a bunch of programmers working in EpicGames are literally “scientists”… I wouldn’t be surprised if they come up with their own thing built from the ground up.
Specially when we know that PhysX takes a considerable hit on framerate budget for big maps like Fortnite’s (physics often fails hard in that game, bullets pass through, etc)

Be aware the experimental interface is now on version Chaos in the latest branch.
Aperion and now Chaos are just part of the interface change over.

The release notes kind of tell you why and what the interface is, and at the bottom sort of explain why there’s an experimental folder.

When physx 3.4 came out, it had already been available in the UE4 source for months.
Unfortunately I don’t see anything glaring in the source that says 4.0 is happening soon.

But it’s possible the interface was built with 4.0 in mind. And it’s probably not a coincidence that the interface came out and then 4.0 was announced.

We just have to wait and see what happens.

Well with the Chaos GDC 2019 video just dropped, that was interesting.

Right off the bat,

Purely my speculation here, but my thoughts are we probably won’t see an upgrade to PhysX 4.0 anytime soon.

Keen to have a look at Chaos in 4.23 though.

i tried the chaos preview in 4.23 it wasnt really a preview at all but more of a half broken somewhat implemented system. it was also different from the one the dude used in the presentation found on youtube. kinda tragic its like the apex destruction feature back in 2012 i was so hyped then started to figure out i had to stitch together dll files from different sites that wasnt documented just to get it working. if you wanna see my destruction game im making its cryosoldier on youtube username silverskateboarder. i assume we’re gonna be waiting quite some time until chaos works but i hope im wrong and i hope it doesnt crash like it does in the 4.23 branch that took 4 hours to compile.

Unreleased UE4 versions on github are all experimental, you can’t expect them to be ready to go like the official releases. The official UE 4.23 release should happen soon anyway and even if Chaos APIs will still be in early preview or preview more like an advanced alpha or a beta version they surely will fix all needed dependencies and make it usable enough to let more developers test it out otherwise there would be no reason to release an early preview in 4.23 at all if Chaos is not stable enough to use it in order to get it fixed and production ready for 4.24. More users feedback they could get quicker they should be able to fix all the reported bugs which is what is needed to make any API become production ready.
I really hope they will be quick and make it production ready by then because having to wait for 4.26 or 4.28 would mean 12 months to 18 months more waiting and that would be really bad for anyone that needs to replace the legacy PhysX with Chaos …

@DarkS474 Hopefully it will not take that much time to have it out of experimental and early access. Epic too has need for that to work asap for their own future projects and they already know it is coming with a great hype from the gamedev community and probably even higher than the hype from the archviz community in relation to realtime raytracing.

I hope so too. Although I will keep using PhysX to setup BP (with nativization I will need or I would have to rewrite in pure C++ for performance reasons as needed) static meshes to destructibles runtime swapping indeed having Chaos destructibles instead along with Niagara particles would mean a huge performance boost even because the new APIs can use the GPU and aren’t limited to CPU. Anyway I still need quite some time to figure out how to properly write and make batch scripting with Python for creating destructibles and I will need to do many tests to ensure the fastest swapping algorithm I can write from the various example codes and studying UE APIs as needed. But as soon as I will have completed all that I will start assembling the level maps with world composition for my first game and I hope that later on removing PhysX destructibles by replacing them with Chaos ones could be very easy to do. I will probably avoid adding particles effects to the PhysX version anyway because if Chaos will be production ready in the next 12 months then I might be able to avoid being forced to release the game with PhysX at all.
Your Cloudscape Seasons I bought some time ago I will add to the maps when I will have almost completed everything so by then I might need your help to configure it properly.

Sure thing. We are closing in the next release (which is quite tiresome to test in all condition scenarios) and the new rain/storm, snow/blizzard, thunder and lightning systems are really nice. Hopefully will help construct very dramatic scenes, including the tornado effect we are working on.