gboy.ts

A Game Boy emulator in TypeScript, designed for the browser and serverless environments.

The emulator runs headlessly with no DOM or Canvas dependency. Frames render to a raw Uint8Array RGBA buffer that can be encoded to PNG/JPEG or rendered to a terminal.

npm | Website

Terminal screenshot:

Quick Start

# Install
bun install

# Run tests
bun test

# Debug a ROM in the terminal
bun run debug path/to/rom.gb --watch

Examples

Example	Path	Description
Vite Browser	examples/vite-browser/	Client-side emulation via Web Worker + bidc
Next.js	examples/nextjs/	Server-side emulation with App Router API routes
Screenshot	examples/screenshot.ts	CLI tool to capture a PNG from any ROM

Browser Demo (Worker + bidc)

Run the browser demo (Vite + Web Worker):

# From repo root:
bun install
bun --cwd examples/vite-browser install

# Start demo:
bun run demo:browser

Then open the printed local URL, load a .gb/.gbc ROM, and use keyboard controls:

• Arrows: D-pad
• Z / X: A / B
• Enter / Backspace: Start / Select
• Space: pause/resume

The browser worker protocol is powered by bidc.

Next.js Demo (App Router)

A full Next.js App Router example with server-side emulation and a Game Boy UI. Stores data in memory; move to e.g. Redis for statefulness.

# From repo root:
bun install
bun --cwd examples/nextjs install

# Place a ROM in the example directory:
cp path/to/rom.gb examples/nextjs/rom.gb

# Start the dev server:
bun run demo:nextjs

The app exposes four API routes:

Route	Method	Description
/api/frame	GET	Returns the current frame as PNG (?advance=N)
/api/input	POST	Sends a button press, returns the resulting frame
/api/reset	POST	Resets the game, returns the first frame
/api/state	GET	Returns game info (title, ROM size, frame count)

Controls are the same as the browser demo (arrows, Z/X, Enter, Backspace, Space).

Debug CLI

bun run debug <rom-path> [options]

Options

Flag	Default	Description
--format <fmt>	green-half	Render format (see below)
--width <n>	80	Output width in characters
--frames <n>	300	Frames to run (batch mode)
--interval <n>	-	Print every N frames (batch mode)
--press <btn>	-	Press button at midpoint (batch mode)
--stats	off	Show framebuffer stats
--watch	off	Interactive mode

Render Formats

Format	Description
green-half	Truecolor DMG green palette + half-block chars (highest quality)
green	Truecolor DMG green, 1 char per pixel
ansi-half	256-color grayscale + half-blocks
ansi	256-color grayscale backgrounds
ascii	Punctuation shading: .:-=+*#%@
blocks	Unicode blocks: ░▓█
half-blocks	Unicode half-blocks (no color)

Interactive Controls (--watch mode)

Key	Action
Arrow keys	D-pad
Z	A button
X	B button
Enter	Start
Backspace	Select
Space	Pause / Resume
] or F	Speed up (1x / 2x / 4x / 8x / 16x)
[ or D	Slow down
1-5	Set speed directly
S	Step one frame (while paused)
I	Toggle stats overlay
R	Reset emulator
Q / Ctrl+C	Quit

Programmatic Usage

import { Emulator, Button } from "./src/emulator";

// Load ROM
const rom = new Uint8Array(await Bun.file("pokemon.gb").arrayBuffer());
const emu = new Emulator(rom);

// Run frames
emu.runFrames(60);

// Handle input
emu.pressButton(Button.A);
emu.runFrames(5);
emu.releaseButton(Button.A);

// Get framebuffer (160x144 RGBA)
const fb = emu.getFramebuffer(); // Uint8Array, 92160 bytes

// Save state (excludes ROM data)
const state = emu.serialize();
await Bun.write("save.state", state);

// Restore state
const saved = new Uint8Array(await Bun.file("save.state").arrayBuffer());
const emu2 = Emulator.deserialize(rom, saved);
emu2.runFrames(1); // continues where it left off

Browser Imports

Use the browser-safe entrypoint when bundling for the browser:

import { BrowserEmulatorClient, Button } from "gboy-ts/browser";

gboy-ts/browser excludes Node-only exports like PNG encoding.

Serialization

State serialization is designed for frequent save/load in serverless:

• ROM data is never included in serialized state
• Save state is ~110KB (CPU: 13B, MMU: 18KB, PPU: 92KB, Timer: 12B, Joypad: 9B, Cartridge: 8B + RAM)

Known Limitations

• No DMA timing - OAM DMA transfer is not cycle-accurate

Tests

bun test
bun test --watch      # Watch mode
bun test src/__tests__/cpu-alu.test.ts   # Run specific test file