Fame Boy

A Game Boy (DMG) emulator written in F#. Try it out in the browser here!

Features

• Supports most of the popular Game Boy games with sound (incl. Tetris, Pokémon, Mario, Zelda, and more!).
• Runs in the browser with a touch-friendly fully responsive design built with Fable.
• Cross-platform too, it runs natively on Windows, macOS, and Linux (and others) with Raylib.
• Zero-dependency F# core with robust typing and built with functional programming in mind.

About

I wrote about the architecture and my general experience in a blog post: I built a Game Boy emulator in F#

This project was a way for me to learn more about computer hardware. The original Game Boy felt like the perfect target: well-defined in scope while still complex enough to learn about a real system, and chock-full of nostalgia.

Along the way, I mostly optimised for readability, idiomatic F#, and having fun in the process, rather than chasing perfect hardware accuracy or maximum performance.

Limitations

There are still a few gaps with the real hardware that I may or may not get to (but would like to).

• No Game Boy Color support.
• Limited emulator configuration (no fast-forward, key remapping, or custom palettes).
• Missing battery saves (SRAM) and save states.
• Hardware inaccuracies (e.g. CPU instruction-level rather than M-cycle-level timing, scanline-based rendering rather than pixel FIFOs, and missing a few hardware features/bugs).

Repo structure

• FameBoy - Core emulator library (CPU, PPU, memory, cartridges, IO)
• FameBoy.Raylib - Native desktop frontend using Raylib
• FameBoy.Web - Browser frontend using Fable and Vite
• FameBoy.Test - Unit and integration tests
• FameBoy.Benchmark, FameBoy.Benchmark.Web - Performance benchmarking projects

Getting Started

Prerequisites

• .NET 10 SDK
• Node.js (for the web projects only)

Running it locally

Desktop

dotnet run --project src/FameBoy.Raylib -- <rom-file-path> [scale]

scale is an optional positive integer that controls the window size multiplier (default: 4).

Web

cd src/FameBoy.Web
npm install
npm run dev

This starts both Fable and Vite in watch mode.

Testing

The unit tests cover most of the core emulator, and the integration tests run the emulator with the dmg-acid2 and Blargg cpu_instrs test ROMs, then compare the PPU's framebuffer with a known correct framebuffer.

To run the tests:

dotnet test

Benchmarks

More details on the benchmarks and results in my blog post.

Desktop

The benchmark includes a few ROMs to run the emulator with in headless mode with BenchmarkDotNet.

./benchmark.ps1

Or directly:

cd src/FameBoy.Benchmark
dotnet run -c release

Web

There is also a basic Node.js benchmarking project using the same test ROMs and structure as the native benchmarking to better estimate browser performance.

./benchmark-web.ps1

Or directly:

cd src/FameBoy.Benchmark.Web
npm run bench

Controls

Game Boy	Key
D-pad	W / A / S / D
A	K
B	J
Start	N
Select	B

The web version also supports mouse/touch.

License

The Fame Boy source code is licensed under the MIT License.

This project redistributes an unmodified copy of Tobu Tobu Girl DX by Simon Larsen, included under its original MIT/CC-BY licensing terms and is not covered by the above license.