+ Physics engines allow you to simulate physical phenomena like gravity, collisions, and forces within + your 3D capabilities. In a typical three.js scene, objects are moved by directly modifying their + position or rotation. When using a physics engine, however, you create a parallel physics world + where bodies react to forces and collisions. You then synchronize the three.js meshes with these + physics bodies on every frame, creating the illusion of a physically simulated environment. +
+ ++ It should be noted that the physics engine does not necessarily have to be updated every frame. + Usually, to keep experiences consistent, physics are updated at fixed time steps. For instance, it could + be that we are running the game loop at 60fps but the physics engine at 30fps (that is 1/30=3.33ms) + while updating the three.js meshes' transforms (e.g., positions and rotations) with the most recent + state from the physics engine. +
+ ++ Physics simulations are particularly useful for games, interactive visualizations, and any + application requiring realistic object behavior, such as objects falling, bouncing, or sliding. +
+ ++ There are three main ways to integrate a physics engine into a three.js project: +
+ ++ Three.js provides wrapper classes for several popular physics engines in the + examples/jsm/physics directory. These addons simplify the setup process by handling the + initialization of the physics world and the synchronization of meshes. +
+ ++ Available addons include: +
+ ++ These addons effectively hide much of the complexity of the underlying engines. For standard use + cases, they offer a very quick way to get started. +
+ ++ Many physics engines are written directly in JavaScript or TypeScript and are designed to work + easily with the web ecosystem. Libraries like cannon-es are popular choices because they are + lightweight and easy to integrate specifically with three.js. +
+ ++ When using these libraries, you instantiate the physics world and bodies yourself, then manually + copy the position and quaternion from the physics body to the three.js mesh in your animation loop. +
+ + ++ It should also be noted that there are a couple of 3D physics engines that are seemingly written in JS/TS but are in reality calling other standalone 3D physics engines. For example: +
++ For maximum performance, stability, and precision, especially with complex simulations, you can use physics engines written in + C++ or Rust (or any other language that supports WASM) that have been compiled to WebAssembly (WASM). Engines like Ammo.js (a port of + Bullet Physics) and Rapier fall into this category. +
+ ++ While this approach offers the most features and best performance, it often requires more setup code + to handle the WASM memory management and interaction with the physics API directly. +
+ ++ Some of these multi-platform 3D physics engines have a ready-to-use WASM port, including: +
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