# Port a Three.js game to Unity and keep the hand-tuned physics

PaperChase agent use case (free feed entry), version 1.0. Source: [@froessell on X](https://x.com/froessell/status/2114310224391655453), 2026-10-25.

## What they did

The builder wanted Drift Lane on iOS and Android. They asked Claude Code to choose between two racing engines from the Unity Asset Store. After reading the existing code, it recommended skipping both, because the handling came from about 170 lines of tuned physics that neither engine would reproduce. It ported that code directly. For the UI, a ChatGPT concept image went to Claude Design for a first draft, then Claude Code rebuilt the screens in Unity.

## Worth knowing

Ask the agent to read your code before it picks a framework, and say what must not change (here, the driving feel). A direct port of a small, tuned core often beats adopting a big engine. The game is still in progress.

## Workflow template

```text
Apply this workflow to [your project]:
1. Name the part of your game whose feel must not change and point the agent at it
2. Ask the agent to compare candidate engines against that code before installing anything
3. Port the core logic first and test it side by side with the original
4. Do the UI as a separate pass from a concept image
5. Keep the old build so you can compare feel on the same input
Stop and ask me before anything irreversible: deploys, payments, sends or deletes.
```

## Steps

1. **Name the part of your game whose feel must not change and point the ag.** Name the part of your game whose feel must not change and point the agent at it
2. **Ask the agent to compare candidate engines against that code before in.** Ask the agent to compare candidate engines against that code before installing anything
3. **Port the core logic first and test it side by side with the original.** Port the core logic first and test it side by side with the original
4. **Do the UI as a separate pass from a concept image.** Do the UI as a separate pass from a concept image
5. **Keep the old build so you can compare feel on the same input.** Keep the old build so you can compare feel on the same input

## Credit

Workflow reported by @froessell on X: https://x.com/froessell/status/2114310224391655453

Summary and template written by PaperChaseWebb in our own words. Questions: mgmt@paperchasewebb.com