Rapier — Fast 2D and 3D Physics Engine in Rust

Introduction

Rapier is a set of 2D and 3D physics simulation libraries written in Rust with first-class WebAssembly support. It provides rigid body dynamics, collision detection, and joint constraints suitable for games, robotics simulations, and interactive applications.

What Rapier Does

• Simulates rigid body dynamics with gravity, forces, and impulses
• Detects collisions between convex shapes, trimeshes, and heightfields
• Supports joints and constraints including revolute, prismatic, and fixed types
• Provides continuous collision detection (CCD) to prevent tunneling
• Exposes a deterministic simulation mode for lockstep multiplayer

Architecture Overview

Rapier is built on the nalgebra linear algebra library and uses an island-based constraint solver with SIMD acceleration. The collision detection pipeline implements a broad-phase sweep-and-prune algorithm followed by narrow-phase GJK/EPA queries. The engine compiles natively to Rust targets and to WebAssembly via wasm-bindgen, sharing the same core simulation code across platforms.

Self-Hosting & Configuration

• Add rapier2d or rapier3d as a Cargo dependency for Rust projects
• Use the @dimforge/rapier2d or rapier3d npm packages for JavaScript/WASM
• Configure gravity, timestep, and solver iterations via IntegrationParameters
• Enable CCD on fast-moving bodies to prevent objects passing through walls
• Use debug rendering with Bevy or other engines via the rapier-debug-render feature

Key Features

• Cross-platform via native Rust and WebAssembly compilation
• Deterministic simulation for reproducible physics across clients
• Bevy integration through the bevy_rapier plugin for game development
• Event system for collision start/stop and contact force reporting
• Serialization support for saving and restoring simulation state

Comparison with Similar Tools

• Box2D — mature 2D engine but C++ only, no built-in Rust or WASM support
• Bullet — feature-rich 3D engine but heavier and more complex API
• PhysX — high-performance but proprietary NVIDIA SDK
• Cannon.js — JavaScript-native physics but slower than WASM-based Rapier
• Avian (formerly heron) — Bevy-specific wrapper but Rapier powers it underneath

FAQ

Q: Can Rapier handle soft bodies or fluids? A: No. Rapier focuses on rigid body simulation. For soft bodies, consider complementary libraries.

Q: Is the WASM build slower than native Rust? A: WASM performance is typically 1.5-3x slower than native, but still fast enough for real-time game physics in the browser.

Q: Does Rapier support multithreading? A: Yes. The parallel feature enables rayon-based multithreaded simulation on native targets.

Q: What game engines integrate with Rapier? A: Bevy (via bevy_rapier), Godot (via godot-rapier), and any engine that can call Rust or WASM code.

Sources

• https://github.com/dimforge/rapier
• https://rapier.rs