I used to work at Rovio (the creator of Angry Birds). Everyone was telling the story of a talk given by Peter Vesterbacka, the head of marketing. When it was time for questions, a man from the audience asked what physics engine the game uses. Vesterbacka gives the correct answer, Box2D, to which the person replied with another question. "Why isn't it mentioned in the credits? And by the way, I'm Erin Catto, the creator of Box2D." To this Vesterbacka replied "Come talk to me after the show". Maybe that's when Erin was given the hoodie? Also, his name was soon added to the credits.
But one thing amazed us all. It was impressive that the marketing guy knew which physics engine was used!
To the larger point, do you know if Rovio did support/pay Eric in any other way than that hoodie?
Angry Birds generated $500M [0], supposedly.
I would also not be surprised if the Rovio developers, designers, testers, etc. who worked on this game did not get a share of that $500M pie - I actually assume they didn't.
But still, you know. Dare I say it - what about "fairness"? :-)
I find it odd how we frame fairness in regards to open source software. He licensed his software as MIT. It says anyone can you use it without owing the author anything. So how is it unfair?
To be clear, I think that open source maintainers deserve much more, but I don't understand why we rarely inspect the licenses as the source of the problem.
He got his name in the credits. The question was if he is owed anything else. The contract he created says he was not. I’m simply suggesting he might need a different contract.
If the comment above is correct, he was only added to the credits after he had to ask for it after the fact.
So the ONLY thing the license asked for is to be named and that was supposedly violated. So a multi million dollar company can just violate a generous license and then after a fact cling to this exact license while arguing to not pay a single cent more than the license asked for. Alright...
But you probably depend on over 500 open source libraries and tools, mostly ones you're not aware of. (Do you ever use a linux VM to run or just develop your stuff? Ever use git or curl etc? Did you know that tools and components in turn use other open-source libraries that you didn't pay for?) The main reason you use such things is so that you don't have to worry about this question.
That’s a fine perspective, but the whole point of law is to guarantee outcomes. The license could easily say “if you make more than $500M, you must pay me $1M”. Why is that not an acceptable solution here?
Have you ever taken part in a legal dispute? The "whole point of law is to guarantee outcomes" sounds like someone who has not.
The easiest, most "acceptable solution" is to obviously throw the oss maintainer who made your hundreds of millions possible a bone. It's not that complicated. Why you find this such an odd notion I find rather strange.
An interesting approach is the dual GPL and commercial license. This is used for example by the CGAL geometry library [1]. In this case, a user of the library has the choice of either paying for the library, or open sourcing the code of their software.
Sure, but contracts is the remedy society has developed to the problem that there are lots of indecent people around (not to mention that reasonable persons can disagree without being unreasonable).
Because there’s a clear mismatch between the value generated from Box2d vs the value the creator receives, and that’s common for open-source in general.
It would be common decency to donate even a small portion of that $500 million, even if the license technically doesn’t require it.
MIT is simple, open, and common which is a big benefit for indie projects, small studios, and anyone with limited legal resources.
It means there’s lots of info on the internet explaining how to use the license and they can be relatively certain they won’t accidentally fall into some legal trap or misinterpret the license. It also means there’s legal precedent around the license.
All that to say, custom licenses are actually a big issue for small players.
You seem to be confusing what is legally/contractually required with what is fair. Fairness, in general, isn't defined by law or contracts, although some laws try to codify it.
There weren't many free and open source 3D physics engines to begin with. The ancient forefathers are ODE, Bullet and Newton Dynamics (all first released in the early 2000s), then nothing(?) for nearly two decades until Jolt in 2021 and now Box3D.
Any addition to this small and exclusive list is very welcome :)
I remember trying this back in 2004 or so when i was making my first real 3D game engine, but i ended up abandoning it because i was trying to use it on 64bit Linux and the source code had typecasts between pointers and (32bit) ints all over the place :-P.
That was fixed later and apparently the engine was used in a few commercial games during the 2000s and early 2010s.
This is so cool! I also tried replicating Incredibots during the pandemic, but abandoned it in favor of 3d stuff.
I remember every day as a kid logging on to find new vehicles, challenges, rube-goldberg machines. Some content archives are still online, but don't scratch that itch as an adult. For its time, Incredibots really nailed the sweet spot between expressiveness and ease to create content.
Box2D is still pretty darn good! Definitely recommended for 2D physics game projects. The C APIs for Box2D and now Box3D are just so nice to work with.
As an ML researcher, I know box2d because it underpins many of the standard reinforcement learning environments (in OpenAI Gym) that we use to benchmark methods, like Lunar Lander or Car Racing: https://gymnasium.farama.org/environments/box2d/car_racing/
Thanks to Erin for such a useful piece of software!
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.
I was looking for the same thing. There is a replay mechanism, so it seems to be deterministic. But with floating point physics, not across platforms. Though -ffast-math is unsupported according to the documentation, so maybe it is intended to be deterministic across platforms? https://box2d.org/documentation3d/recording.html
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.
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.
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.
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.
I'm a big fan of jolt because they have a more incremental way of snapshotting physics state which really reduces the amount of serialization and memory you have to do if you want to implement deterministic netcode.
> 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.
Considering the years, that X must mean we're skipping straight to ten! Gabe is a former MS employee, so of course counting problems are cropping up occasionally.
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.
Love to see this! I got started with Box2D back in probably 2006ish. Great to see Erin is still working on this stuff. Thank you Erin for the great libraries!
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!
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
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.
Have you tried the latest Box2D (it started as the experimental Box2c)? It’s pretty good afaict. It may not be what you want specifically in your 2D game, as often people prefer more arcade-like mechanics than the physics it tries to deliver.
I have been using an in-house/handrolled physics engine for the last few years so not sure if something has changed, but being able to modify the physics engine for arcade or other non-realistic style games was a big let down over time as well.
Basically optimizing your game for feel was quite hard with Box2D in general.
For a long time there wasn't deformers in Box2D (not sure if it's in there now), I hacked by own but I was a dumb 17yo and it was a horrid mess back in the day. Maybe AI could do better than the old me, but I gave up pretty quickly after not getting good results.
So basically lack of support for non-rigid bodies and lack of easy customisability made it not age well for someone like me.
But I know people who have had performance issues with it when building large maps/worlds as well so there are other issues.
Again all of these could have been fixed if they paid more attention to it, more dev time, but it was free so I couldn't really ask for more as a broke student.
And best part was you could run it on any hardware, I remember cooking up a small 2d demo on a rpi back in the day. Fun times.
I just fired it up, couldn't find anything related to soft body or deformers, neither does there seem to be anything regarding common issues around 2d platformer features character mover is sort of moving in that direction does seem to provide better controls over how I would setup slide/jump and stuff, but still seems like not a great choice for a 2d game that I would like to build.
The biggest issue with overly generalized 2d physics systems is ideally they should be built as patch works and provide escape hatches as the default, since in most 2d games you don't want real world physics.
Angry birds and early 2010 games were an exception when real world esque physics was the well interesting thing. Example Angry Birds, and Cut The Rope.
The above blog even seems to suggest that soft constraints were added recently which is well surprising.
I just feel like Box2D is very lacking albeit less now.
Let me give you an example imagine you want box2d to allow applying weird forces to player most of the time, but you also don't want to allow the player to clip through at certain movements and speeds to avoid weird cases where your character hits a wall and loses all momentum because that's how the physics should work, or it forces some rotational momentum which you have disabled...
Again in a lot of these character controllers you always end up with custom physics setups either way, and this is where I feel like box2d was especially lacking they seem to have worked on it with character mover, but it seems just very late.
Again I have used a lot of it in the past for making shitty flash style games, and it has been great but I honestly don't think there is a great use for it as it stands today in the projects I like to work on.
Ofc it's also largely because I find writing my own physics engine to be easier than picking up a library, and I would probably copy some of the code verbatim if needed for collision optimizations and stuff, but Box2D just feels a tad behind the times.
Again I am not a big time dev, and I am certain since Godot ships Box2D there must be a lot of users of it, but I just don't care enough at this point.
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.
Well - simply see it as a feature. A horror game
where poltergeists infiltrate objects. Stephen
King even wrote some book about that, and that got
a B movie too.
Also shame on the Unreal engine to have such huge
bugs and nobody fixing it. Still, I like the idea
of horror movies more. Finally poltergeist makes
a come back - it was a really scary movie when I
was young.
Thank you. I agree, Box3D is great! Maybe Erin will even add rollback determinism at some point. That would be a huge step forward for network physics rollback!
Probably people who don't register the name. Your comment adds nothing and is the kind that always ends on the bottom of the thread, so you shouldn't take it personally.
Great website, though. I'm fixing my time step all day.
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.
https://kotaku.com/this-guy-created-angry-birds-physics-and-...
But one thing amazed us all. It was impressive that the marketing guy knew which physics engine was used!
Angry Birds generated $500M [0], supposedly.
I would also not be surprised if the Rovio developers, designers, testers, etc. who worked on this game did not get a share of that $500M pie - I actually assume they didn't.
But still, you know. Dare I say it - what about "fairness"? :-)
[0] https://gameworldobserver.com/2023/02/28/angry-birds-2-reven...
To be clear, I think that open source maintainers deserve much more, but I don't understand why we rarely inspect the licenses as the source of the problem.
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
That's what he was asking for, a mention in the credits.
So the ONLY thing the license asked for is to be named and that was supposedly violated. So a multi million dollar company can just violate a generous license and then after a fact cling to this exact license while arguing to not pay a single cent more than the license asked for. Alright...
The easiest, most "acceptable solution" is to obviously throw the oss maintainer who made your hundreds of millions possible a bone. It's not that complicated. Why you find this such an odd notion I find rather strange.
[1]: https://doc.cgal.org/latest/Manual/license.html
It would be common decency to donate even a small portion of that $500 million, even if the license technically doesn’t require it.
It means there’s lots of info on the internet explaining how to use the license and they can be relatively certain they won’t accidentally fall into some legal trap or misinterpret the license. It also means there’s legal precedent around the license.
All that to say, custom licenses are actually a big issue for small players.
I wonder if the landscape is empty enough for a resurgence.
Any addition to this small and exclusive list is very welcome :)
I remember trying this back in 2004 or so when i was making my first real 3D game engine, but i ended up abandoning it because i was trying to use it on 64bit Linux and the source code had typecasts between pointers and (32bit) ints all over the place :-P.
That was fixed later and apparently the engine was used in a few commercial games during the 2000s and early 2010s.
I spent many of my teenage and early adult years trying to replicate it in HTML5. Finally got the Open Source version of IB2 largely ported during COVID: https://github.com/JoshTheDerf/Incredibots-2-HTML5-Open-Sour...
I remember every day as a kid logging on to find new vehicles, challenges, rube-goldberg machines. Some content archives are still online, but don't scratch that itch as an adult. For its time, Incredibots really nailed the sweet spot between expressiveness and ease to create content.
Thanks to Erin for such a useful piece of software!
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.
EDIT: Clarified meaning about ffast-math
This is absolutely fantastic!
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.
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.
1 - I’ve been sitting on this domain for years: https://lightcycles.io
https://github.com/snackdotgame/jolt-ts
I also have an open source character controller for it
https://github.com/snackdotgame/jolt-ts-character-controller
I'm a big fan of jolt because they have a more incremental way of snapshotting physics state which really reduces the amount of serialization and memory you have to do if you want to implement deterministic netcode.
wait....
Box3D
3D
3
Hope!
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.
For a long time there wasn't deformers in Box2D (not sure if it's in there now), I hacked by own but I was a dumb 17yo and it was a horrid mess back in the day. Maybe AI could do better than the old me, but I gave up pretty quickly after not getting good results.
So basically lack of support for non-rigid bodies and lack of easy customisability made it not age well for someone like me.
But I know people who have had performance issues with it when building large maps/worlds as well so there are other issues.
Again all of these could have been fixed if they paid more attention to it, more dev time, but it was free so I couldn't really ask for more as a broke student.
And best part was you could run it on any hardware, I remember cooking up a small 2d demo on a rpi back in the day. Fun times.
https://box2d.org/posts/2025/04/box2d-3.1/
It became the current box2d implementation, now after version 3.0, it was entirely rewritten in C, it works differently.
The biggest issue with overly generalized 2d physics systems is ideally they should be built as patch works and provide escape hatches as the default, since in most 2d games you don't want real world physics.
Angry birds and early 2010 games were an exception when real world esque physics was the well interesting thing. Example Angry Birds, and Cut The Rope.
The above blog even seems to suggest that soft constraints were added recently which is well surprising.
I just feel like Box2D is very lacking albeit less now.
Let me give you an example imagine you want box2d to allow applying weird forces to player most of the time, but you also don't want to allow the player to clip through at certain movements and speeds to avoid weird cases where your character hits a wall and loses all momentum because that's how the physics should work, or it forces some rotational momentum which you have disabled...
Again in a lot of these character controllers you always end up with custom physics setups either way, and this is where I feel like box2d was especially lacking they seem to have worked on it with character mover, but it seems just very late.
Again I have used a lot of it in the past for making shitty flash style games, and it has been great but I honestly don't think there is a great use for it as it stands today in the projects I like to work on.
Ofc it's also largely because I find writing my own physics engine to be easier than picking up a library, and I would probably copy some of the code verbatim if needed for collision optimizations and stuff, but Box2D just feels a tad behind the times.
Again I am not a big time dev, and I am certain since Godot ships Box2D there must be a lot of users of it, but I just don't care enough at this point.
I have to say, based on those videos, that is one accurately-named engine.
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.
Well - simply see it as a feature. A horror game where poltergeists infiltrate objects. Stephen King even wrote some book about that, and that got a B movie too.
Also shame on the Unreal engine to have such huge bugs and nobody fixing it. Still, I like the idea of horror movies more. Finally poltergeist makes a come back - it was a really scary movie when I was young.
Great website, though. I'm fixing my time step all day.