# Architecture

How Board turns a physical Piece on the glass into data your game can use. This page is SDK-neutral: the pipeline is the same whether you build with Unity, the Web SDK, or Godot. For the classes and entry points a specific SDK exposes, see that SDK’s own architecture page.

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## The touch pipeline

```
Physical Piece / finger
        │
        ▼
Capacitive touch sensor  ──►  Touch controller (raw capacitance frames)
        │
        ▼
On-device ML (dedicated NPU)  ──►  Glyph recognition + contact tracking
        │
        ▼
Board OS touch service  ──►  noise rejection, smoothing, persistence
        │
        ▼
SDK (Unity / Web / Godot)  ──►  your game
```

Two things make this different from ordinary multi-touch:

- **The ML runs on dedicated hardware.** Glyph recognition and contact tracking happen on a separate NPU, so they don’t compete with your game for CPU or GPU. Touch stays responsive no matter how busy your render loop is.
- **The OS owns the touch pipeline, not your app.** Inference, noise rejection, and tracking live in a Board OS service. Every SDK is a thin client over the same service, which is why all three report the same contact model.

See [Touch](https://docs.dev.board.fun/learn/touch-system) for how recognition, noise rejection, and unlimited contacts work, and [Pieces](https://docs.dev.board.fun/learn/pieces) for how Glyphs encode Piece identity.

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## What every SDK exposes

Each SDK presents the same capabilities, named idiomatically for its engine:

| Capability | What it covers |
| --- | --- |
| **Touch input** | Active contacts (fingers and Pieces), Glyph recognition, phases, orientation, touch state |
| **Session & players** | Active profile, player list, guests, profile switcher |
| **Save games** | Persistent per-app storage with player associations and quotas |
| **Pause screen** | Integration with Board’s system pause overlay and custom buttons |

The data they hand you is the same; the way you receive it differs by engine (Unity polls each frame, the Web SDK delivers a callback, Godot emits a signal). The shared shape of a contact is documented once in [Contact Model](https://docs.dev.board.fun/guides/touch-input#the-contact-model), including the per-SDK coordinate and orientation conventions.

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## Per-SDK architecture

- [Unity SDK Architecture](https://docs.dev.board.fun/unity/architecture) — `BoardInput`, `BoardSession`, `BoardApplication`, `BoardSaveGameManager`, and the `Board.*` namespaces.
- [Web SDK Architecture](https://docs.dev.board.fun/web/architecture) — the `Board` object, the platform bridge, and the six domain modules.
- [Godot SDK Architecture](https://docs.dev.board.fun/godot/architecture) — the `Board` autoload and its module singletons.

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