Repo: https://github.com/ParthPatel00/WhatTheDiff

Drag-drop two 3D model files and instantly see what changed, visually and structurally. No 3D software needed. Built for game and design teams.

Native macOS desktop app. Supports .glb files. Runs entirely on-device, no server, no auth, no uploads.

Built at SJHacks 2026.

Compare before and after models with synced cameras and structural stats.

Blend both models into a single viewport. Toggle between A only, B only, or a blended view to spot differences.

A only (red)	B only (green)	Blended

Automated 6-angle comparison with per-angle diff percentages.

This repo has three reference documents. Read them in this order before writing code:

1. SPEC.md — single source of truth for what to build. Tech stack, architecture, MVP feature specs with inline code patterns, and a critical gotchas section (15 items) documenting silent-failure traps. Every implementation decision that deviates from the obvious default is justified inline.
2. PHASES.md — how the work is divided into independent phases. Each phase lists deliverables, dependencies, and a "done when" checklist.
3. DEMO.md — 2-3 minute demo script. Only relevant at the end of the build.

If you are an AI agent implementing a phase: read SPEC.md in full first, then read only the phase you are assigned in PHASES.md. Do not skim the gotchas section.

If you are a human picking up work: read PHASES.md first to see what's free, then consult SPEC.md for technical detail.

Next.js 14 App Router, TypeScript, Tailwind, Three.js, gltf-transform, Zustand. See SPEC.md § Tech stack for version pins and rationale.

The app lives under frontend/. All commands must be run from there.

cd frontend
npm install
npm run dev

Open http://localhost:3000 and drop two .glb files.

Build the Next.js app first, then run Electron against it:

cd frontend
npm run build

cd ../electron
npx electron .

To package a distributable macOS app:

cd electron
npm run build:mac

After a git commit that touches .glb files, the hook automatically opens both versions in the local diff viewer.

Install the hook in any repo containing .glb files:

cd cli
npm install
node bin/whathediff.js install-hook

Compare two files directly (no git required):

node bin/whathediff.js --a old.glb --b new.glb

Remove the hook:

node bin/whathediff.js uninstall-hook

Set WHATHEDIFF_VIEWER_URL in .env to override the default viewer URL (http://localhost:3000).

Use KhronosGroup/glTF-Sample-Assets. DamagedHelmet is the canonical test model. See SPEC.md § Test models for required test cases.