# How Lantern Fox Built a Deterministic Co-op Roguelite

Lantern Fox is a six-person indie studio developing *Below the Brine*, a cooperative roguelite about salvaging machinery from a flooded city. The team began with a familiar stack—Unity, C#, and Steamworks—but quickly discovered that four-player networking affected nearly every design decision. Physics-heavy debris, procedural rooms, and hundreds of simulated creatures looked great in prototypes, yet produced unacceptable bandwidth usage and frequent desynchronization.

## Simulation Before Presentation

The studio separated gameplay state from visual presentation. A fixed-timestep simulation now handles movement, damage, inventory, and enemy decisions using integer values wherever practical. Animation, particles, and audio remain client-side and interpolate between confirmed simulation frames. This architecture made the game less dependent on frame rate and allowed developers to replay recorded input streams when diagnosing bugs.

```yaml
simulation:
  tick_rate: 30
  snapshot_interval: 6
  input_buffer_frames: 3
  deterministic_seed: true
```

## Procedural Generation on a Budget

Rather than synchronizing every generated object, the host sends a world seed plus a compact list of exceptions, such as destroyed doors or relocated loot. Each client runs the same room-generation pipeline locally. To keep generation deterministic across platforms, Lantern Fox replaced engine-provided random calls with a small custom generator and added automated tests that compare room hashes on Windows, macOS, and Linux.

## Tools for a Small Team

With no dedicated tools programmer, the studio invests in editor utilities only when they remove recurring work. Designers can validate encounter budgets, preview seeded maps, and export reproduction packages containing logs, inputs, and simulation checksums. These packages reduced many networking bug reports from multi-day investigations to repeatable failures that programmers could inspect immediately.

## Shipping Without Losing the Game

The technical constraints ultimately improved the design. Enemies use clearer attack patterns because their logic must fit within the simulation budget, while debris is cosmetic unless it affects navigation. Lantern Fox still profiles every weekly build on modest hardware, but the team no longer treats optimization as a final production phase. For a small studio, performance, tooling, and game design have become the same continuous process.