What Is the Typical File Size of Ammo.js

When integrating 3D physics into web applications, understanding the library’s footprint is crucial for maintaining fast page load times. This article provides a breakdown of the typical file size of the ammo.js physics engine, compares its WebAssembly (WASM) and asm.js builds, and explains how compression and custom builds can optimize its footprint for production environments.

Typical File Sizes of Ammo.js

Because ammo.js is a direct port of the robust, C++ Bullet Physics engine compiled via Emscripten, its file size is significantly larger than lightweight, native JavaScript physics libraries. The footprint varies depending on the build type you use:

1. WebAssembly (WASM) Build (Recommended)

The WebAssembly version is the modern standard for web applications because of its superior performance. It is split into two files: * WASM Binary (ammo.wasm): Typically between 700 KB and 900 KB uncompressed. * JavaScript Wrapper (ammo.js): Typically between 100 KB and 200 KB uncompressed. * Total Uncompressed Footprint: Roughly 800 KB to 1.1 MB.

2. asm.js Build (Legacy / Fallback)

The asm.js version is a highly optimized subset of JavaScript used as a fallback for older browsers that do not support WebAssembly. * JavaScript File (ammo.js): Typically between 1.5 MB and 2.5 MB uncompressed.

The Impact of Network Compression

While the uncompressed sizes may seem large, the actual data transferred over the network to a user’s browser is much smaller when server-side compression is enabled:

• Gzip Compression: Reduces the WASM and JS wrapper combined transfer size to approximately 250 KB to 350 KB.
• Brotli Compression: Offers even higher compression ratios, often reducing the total transfer size of the WASM build to under 200 KB.

Why Is Ammo.js So Large?

The size of ammo.js is directly related to its capabilities. Unlike smaller libraries designed specifically for the web (such as Cannon.js or Oimo.js), ammo.js includes the full suite of Bullet Physics features. This includes advanced rigid body dynamics, soft body physics, vehicle simulations, complex collision shapes, and constraint solvers.

How to Reduce the Ammo.js Footprint

If the default file size is too restrictive for your project, you can reduce it using the following optimization techniques:

1. Custom Builds (Interface Definition Language - IDL): ammo.js uses WebIDL to define which C++ functions are exposed to JavaScript. By editing the ammo.idl file and rebuilding the library, you can exclude features you do not use (such as soft bodies or specific collision algorithms) to significantly shrink the final file size.
2. Deferred Loading: Load the ammo.js library asynchronously or only when the physics-based portion of your application is initiated, ensuring that the initial website load remains fast.