Draco.js

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QUICK START

git clone https://github.com/AnalystCorrect/draco.js-875.git
cd draco.js-875
npm install
npm start

A pure-JavaScript Draco mesh loader for three.js. It's a drop-in DRACOLoader that decodes Draco-compressed triangle meshes — both the EdgeBreaker connectivity used by glTF's KHR_draco_mesh_compression and Draco's sequential connectivity — directly in JavaScript.

Live demo →

Why a JS port instead of the official WASM build?

• Small — ~22 KB gzipped (69 KB minified), vs ~100 KB gzipped for the draco3d WASM decoder + glue (~4.6× smaller).
• Simple to ship — one ES module. No .wasm fetch, no worker/glue setup, no cross-origin or CSP headaches.
• Fast — on substantial meshes it's within ~1.0–1.4× of the WASM decoder, and effectively at parity on the largest ones, with byte-for-byte identical output (see Correctness).

On the largest meshes (e.g. a 358k-face glTF) the two are about even; WASM keeps a lead of up to ~1.35× on smaller and mid-size meshes. You trade, at most, a modest amount of decode speed for a much smaller, simpler-to-deploy loader.

Status

Targets Draco bitstream version 2.2 — what current Draco encoders and glTF exporters produce.

Not implemented:

• Point-cloud decoding (sequential and KD-tree) — only triangle meshes are decoded.
• Metadata content — geometry metadata is parsed (so metadata-bearing files still decode correctly) but is not surfaced on the returned geometry.
• Older bitstreams (< 2.2) — not a support goal, though many still decode.

Correctness

Output is byte-for-byte identical to Google's reference draco3d WASM element-by-element — face indices and every per-point attribute value match times decoding and guards against output regressions via a sha256 of the decoded geometry.

Project layout

src/          decoder source, mirroring draco/src/draco/ file-for-file
build/        bundled output (build/DRACOLoader.js + .min.js)
tools/        bench.mjs (timing + regression) and verify-wasm.mjs (WASM parity)
libs/         three.js's WASM Draco loader, vendored for the comparison
samples/      .drc and Draco-compressed .glb test models
index.html    JS-vs-WASM comparison viewer

Credits

• Decoder logic is a port of Google Draco (Apache-2.0); it mirrors the original C++ file structure.
• DRACOLoader.js follows the API of three.js's DRACOLoader (MIT) so it drops into GLTFLoader unchanged.