Box3D, an open source 3D physics engine
makepanic
464 points
106 comments
July 01, 2026
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Discussion Highlights (20 comments)
HexDecOctBin
I do wonder how it compares against Jolt. Both seem to have a good pedigree, one from Valve and Eric Catto, and another used in Horizon games.
RobLach
Box2D was a foundation for a lot of interesting physics oriented indie games in my day. I wonder if the landscape is empty enough for a resurgence.
minraws
I feel like Box2D, was pretty good for the time, I didn't feel like it aged quite as well, mostly because where the solutions built internally went, but hoping box3d is great for it's time as well, would love lots of fun physics engines.
nasso_dev
> On the Valve side, Rubikon continues to evolve and Dirk has developed optimizations (similar to those in Box3D) in a new engine called Ragnarok. Look for that in future Valve games. wait....
alex_suzuki
Some years ago, I used Box2D from Python to get a couple of bodies moving naturally in a 2D plane, lightly disturbed by random impulses (like water lilies in a pond when it's raining). It was a fun project and working with Box2D was pleasant. Looking forward to using Box3D!
tancop
i love that we went from bullet being the only real option for open source 3D physics to jolt, rapier, avian, nvidia physx and now box3d.
dude250711
> ...native physics engine (called Chaos)... I have to say, based on those videos, that is one accurately-named engine.
dym_sh
Box>:3Drawr
999900000999
I went ahead and wishlisted his legend of California game. Probably won’t use Box3D, I’m not a fan of low level programming. I will look forward to the abstraction layers above it
neals
Made look up some of my game stuff from back in the day, but the apps are not in the store (after 15 years, to be expected) oh well...
LoganDark
I first heard of Box3D when s&box loudly ripped out the Source 2 physics engine in favor of it (along with ripping out all cross-platform rendering code, etc). Nice to see it really is open-source now.
gafferongames
Yeah this library is great. Use it!!!
utopiah
I'm a bit familiar with Rapier (and before that Cannon and Ammo) so how does it compare? PS: FWIW made my own physics engine in 3D space just few weeks ago (and shared it here). OK ok ... it's just a 1-liner that brings an object down at regular interval but it's surprising how well it works already! I recommend you give it a go as from a learning perspective it's really fun.
MomsAVoxell
Oh I'm so ready for this.. I've had some success with Box2D in the past, it's well and truly one of the top bits of F/OSS out there. Box3D-based Spectre VR? It's so happening. (Shades of Tanarus ..) EDIT: holy smokes, the transition to recording and playback in the Legend of California demo (Unreal Engine-based) is quite a jarring leap. If you at first get the impression things are quite basic, be sure to get into at least 18:00 into the demo video, it gets pretty wild .. recording and playback is awesome.
dom96
Funny to see this just a few days after I’ve started building a Tron-like 3D game for the browser using Jolt[1]. So far Jolt is working pretty well but I’ll certainly be taking a look at this. 1 - I’ve been sitting on this domain for years: https://lightcycles.io
jackling
Glad to see the release, Box2D has some of the best code I've ever read. It's interesting to see that Box3D was originally a fork of a physics engine made by Dirk. Dirk is one of the best presenters in GDC, and so influential in Physics Engine space, nice to see how he's continuing to push the latest and greatest forward.
adalacelove
Physics simulation is a dangerous rabbit hole. Even if you focus just on rigid bodies and just physical plausibility there are plenty of open problems related to collision detection and collision resolution. Convex approximations and/or decompositions for geometry and hand tuning of solvers are the norm, balancing robustness and precision against speed.
kidfiji
I remember reading about it in S&Box's (Source-2-based game engine) blog a while back - glad to see it released out to the public!
Jeaye
Yes! This is exciting to see. Erin Catto is such a cool hacker. Thank you, Erin, for sharing your code with the open source community. There wasn't anything about determinism in the announcement, but I'd really love to see some more about that, too. Trying to use Unity's built-in physics to make a networked billiards game is quite troubling, when none of the clients can happily agree on what happened.
tikotus
Oh, nice! What a wonderful surprise! Very easy to build, and quite small. A release build of the library is 916K (on macos at least). I have a game engine that compiles to WASM for web, and having 3D physics has been a challenge. 3D physics libraries tend to be large and hard to compile. I didn't try yet, but compiling this into a WASM library with emscripten should be easy, and it's likely small enough to be justifiable for a simple web game.