Choosing a Physics Engine for A-Frame: Cannon.js, Ammo.js, or Oimo.js?

Decision to Make

When building an interactive 3D scene in A‑Frame that requires realistic motion, you must pick a physics engine. A‑Frame bundles three popular options – Cannon.js, Ammo.js, and Oimo.js – each with its own strengths and trade‑offs. This guide helps you decide which engine best fits your project’s constraints and shows how to switch engines and validate the result.

Project Constraints

• Target Platforms: Modern browsers with WebAssembly support (Chrome, Edge, Safari). Ammo.js requires WebAssembly; others work in pure JavaScript.
• Scene Complexity: Ranges from a handful of objects to hundreds of dynamic bodies.
• Feature Needs: Basic rigid‑body physics, advanced constraints, or soft‑body simulation.
• Bundle Size & Load Time: Acceptable size < 200 KB for initial load.
• License Compatibility: All engines are permissive (MIT or BSD‑3), but check your project’s license.

Compact Comparison Table

Engine	API Simplicity	Feature Set	Performance (Dynamic Objects)	Bundle Size	Community & Docs
Cannon.js	Very simple – type: "dynamic" etc.	Rigid body, basic constraints, no soft‑body.	Good for <200 objects; slows after 300.	~30 KB (JS only)	Large community, many examples.
Ammo.js	Verbosity – requires ammo.js API calls.	Full Bullet features: ragdoll, soft‑body, constraints.	Best for <500 objects; slower startup.	~200 KB (WASM + JS glue)	Active, but docs scattered.
Oimo.js	Mid‑level – less verbose than Ammo.	Rigid body, some constraints, no soft‑body.	Fastest for >200 objects.	~35 KB (JS only)	Smaller community, limited docs.

Trade‑Offs Explained

• API Simplicity vs. Feature Richness
  Use Cannon.js if you need a quick prototype with standard rigid bodies. Ammo.js gives you the most features but requires more code and a deeper understanding of Bullet’s API.
• Performance vs. Bundle Size
  Oimo.js shines in large scenes but offers fewer constraints. If you need ragdolls or soft bodies, Ammo.js is the only viable choice, accepting a larger bundle.
• Browser Support
  Ammo.js falls back to a JavaScript version if WebAssembly is unavailable, but the fallback is noticeably slower. For legacy browsers, stick with Cannon or Oimo.
• Community & Documentation
  While Cannon.js has the most community code, Ammo.js has official documentation through the Bullet project. Oimo.js has fewer resources, so debugging may be harder.

Concrete Implementation: Switching Engines

Below is a minimal A‑Frame scene that demonstrates how to swap physics engines by changing the src of the physics-system component. The scene contains a falling cube and a static ground plane.

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8"
    <title>Physics Engine Switch Demo</title>
    <script src="https://aframe.io/releases/1.5.0/aframe.min.js"
    </head>
  <body>
    <a-scene physics-body="gravity: -9.8" physics-system="debug: true"
    <a-entity position="0 2 0" geometry="primitive: box; depth:1; height:1; width:1" material="color: blue" physics-body="type: dynamic"
    </a-entity>
    <a-entity geometry="primitive: plane; width:10; height:10" rotation="-90 0 0" material="color: green" physics-body="type: static"
    </a-entity>
  </a-scene>
</body>
</html>