tnayuki/unity-physicsbox3d

Unity-PhysicsBox3D connects the Unity game engine to Box3D, a newer open-source physics engine created by Erin Catto, and directly compares its performance against Unity's built-in PhysX physics system. Physics engines handle how objects fall, collide, and settle in a game, and this project lets a developer see, side by side, how the two engines perform under the same conditions. The binding is designed for speed. Instead of updating each object's position one at a time, it gathers all the moved objects from the physics engine in a single batch and writes their new positions back to Unity in parallel using Unity's Burst compiler, which speeds up math-heavy code. It also plugs Box3D's internal multithreading into Unity's own job system, so the physics work runs alongside Unity's other background tasks instead of spawning its own separate threads. The README includes benchmark results from tests run on an Apple Silicon Mac using a falling tower of objects. With sleep enabled, meaning objects that settle down stop being actively calculated, Box3D was measured as one and a half to over two and a half times faster than PhysX, largely because Box3D recognizes settled objects and puts them to sleep more quickly. With sleep disabled, forcing both engines to keep calculating everything, the two engines perform similarly at lower object counts, with Box3D pulling ahead as more objects are added. Setup only works on macOS in the Unity Editor, since the physics engine is compiled into a native Mac plugin. Getting started means cloning the repository with its submodules, running a build script that uses clang, and opening the project in Unity 6.3 or newer. Two example scenes are included: one that benchmarks both engines side by side with an on-screen display, and one purely for visually comparing how objects behave under each engine. This project itself is released into the public domain under the Unlicense, though the Box3D engine it depends on is separately MIT-licensed.