Box3D: Erin Catto extends Box2D into an open source 3D engine
Erin Catto, whose Box2D powers the physics in Angry Birds and countless indie games, has released Box3D, a 3D rigid-body engine that began as a fork of Valve's in-house Rubikon.
Box3D keeps almost the same architecture as Box2D, the C17 code, C API, sub-stepping solver and continuous collision, then adds triangle-mesh, height-field and baked compound collision for 3D worlds.
Its unusual origin: it began as a fork of Dirk Gregorius's Rubikon-Lite, the hobby cousin of the engine Valve built for Half-Life: Alyx, and still carries that code in convex-hull generation.
A game-networking veteran's whole review was 'Use it!!!'; another builder asked where the determinism guarantees actually are.
A 3D engine built on Box2D's bones
Box3D is an open source 3D rigid-body physics engine, and its author is blunt about the lineage: the core architecture is almost identical to Box2D. It shares the C17 codebase, the C API, the sub-stepping solver, continuous collision detection and multithreading, then adds the pieces 3D games actually need: triangle-mesh collision, height-field collision and baked compound collision.
Under the hood are graph coloring for large islands, a wide-SIMD contact solver, large-world support using doubles for position, and recording and replay.
The origin story is unusual. Box3D began as a fork of Dirk Gregorius's Rubikon-Lite, the hobby cousin of Rubikon, the physics engine Valve built for Half-Life: Alyx; the released code still carries Rubikon-Lite in its convex-hull generation and some collision algorithms. Gregorius, meanwhile, is folding similar optimizations into a new Valve engine called Ragnarok. Box3D is free to use now, with pull requests planned later (probably behind a CLA) and development funded through GitHub Sponsors and Patreon.
How does it stack up against Jolt?
The first question in the thread is comparison, since open-source 3D physics is suddenly crowded with Jolt, Rapier, PhysX and now this. The creator of the Nim programming language is mid-project and hedging:
"Funny to see this just a few days after I've started building a Tron-like 3D game for the browser using Jolt … I'll certainly be taking a look at this."
The endorsement from the founder of Network Next ran to three words:
"Yeah this library is great. Use it!!!"
For web games the standout is size. A game developer whose engine compiles to WASM measured it:
"A release build of the library is 916K (on macos at least)."
One gap stood out to the creator of jank, a Clojure dialect on LLVM, who fights nondeterminism in networked games:
"There wasn't anything about determinism in the announcement, but I'd really love to see some more about that, too."
For a networked billiards game where every client must agree on each collision, that unanswered question is the whole ballgame.
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