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* ROMs will be rounded up to the nearest 32KiB and filled with zeroes.
* Still attempt to run the game even if the GB header info isn't valid.
* Don't print any non-ascii characters in the title

Partial fix for #43.

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A simple GB/GBC emulator.


  • Runs in the browser using WebAssembly
  • Hacky-but-passable CGB support!
  • Mostly-there Super GB support!
  • Cycle accurate, passes many timing tests (see below)
  • Supports MBC1, MBC1M, MMM01, MBC2, MBC3, MBC5 and HuC1
  • Save/load battery backup
  • Save/load emulator state to file
  • Fast-forward, pause and step one frame
  • Rewind and seek to specific cycle
  • Disable/enable each audio channel
  • Disable/enable BG, Window and Sprite layers
  • Convenient Python test harness using hashes to validate
  • (WIP) Debugger with various visualizations (see below)

DMG Screenshots

Bionic Commando Donkey Kong Kirby's Dreamland 2 Mole Mania Mario's Picross Trip World Wario Land Game Boy Wars Is That a Demo in Your Pocket?

CGB Screenshots

Dragon Warrior Hamtaro Metal Gear Solid It Came From Planet Zilog Survival Kids Aevilia Toki Tori Wario 3

SGB Screenshots

Donkey Kong Kirby's Dreamland 2 Mole Mania

Debugger Screenshots

Debugger OBJ Map Tile Data Breakpoints

Embedding binjgb in your own web page

Copy the folowing files to your webserver:

  • docs/binjgb.js
  • docs/binjgb.wasm
  • docs/simple.html
  • docs/simple.js
  • docs/simple.css
  • your .gb or .gbc file

simple.html will fill the entire page, so if you don't want that, you should put it into an iframe.

The emulator will also display an on-screen gamepad if the device supports touch events.

You can configure the emulator by editing simple.js:

Constant name Description
ROM_FILENAME The path to your .gb or .gbc file
ENABLE_REWIND Whether to enable rewinding with the backspace key
ENABLE_PAUSE Whether to enable pausing with the space bar
ENABLE_SWITCH_PALETTES Whether to enable switching palettes with [ and ]
OSGP_DEADZONE How wide to make the deadzone for the onscreen gamepad, as a decimal between between 0 and 1
CGB_COLOR_CURVE How to tint the CGB colors so they look more like a real CGB.
  • 0: none
  • 1: Use Sameboy's "Emulate Hardware" colors
  • 2: Use Gambatte/Gameboy Online colors
DEFAULT_PALETTE_IDX Which palette to use by default, as an index into PALETTES
PALETTES An array of built-in palette IDs, between 0 and 83. Useful if you only want the player to switch between a few of the built-in palettes

See simple.js for more info.


Use a recursive clone, to include the submodules:

$ git clone --recursive

If you've already cloned without initializing submodules, you can run this:

$ git submodule update --init


Requires CMake and SDL2. Debugger uses dear imgui, (included as a git submodule).

Building (Linux/Mac)

If you run make, it will run CMake for you and put the output in the bin/ directory.

$ make
$ bin/binjgb

You can also just use cmake directly:

$ mkdir build
$ cd build
$ cmake ..
$ make

Building (Windows)

When building on Windows, you'll probably have to set the SDL2 directory:

> mkdir build
> cd build
> cmake .. -G "Visual Studio 15 2017" -DSDL2_ROOT_DIR="C:\path\to\SDL\"

Then load this solution into Visual Studio and build it. Make sure to build the INSTALL target, so the exectuables are built to the bin directory.

Building WebAssembly

You can build binjgb as a WebAssembly module. You'll need an incoming build of emscripten. See and

Put a symlink to Emscripten in the emscripten directory, then run make.

$ ln -s ${PATH_TO_EMSCRIPTEN} emscripten
$ make wasm

Or set Makefile variables via command line:

$ make wasm EMSCRIPTEN_CMAKE="/path/to/Emscripten.cmake"

Changing the Build Configuration

If you change the build config (e.g. update the submodules), you may need to run CMake again. The simplest way to do this is to remove the out/ directory.

$ rm -rf out/
$ make


$ bin/binjgb <filename>
$ bin/binjgb-debugger <filename>


Action Key
Quit Esc
Save state F6
Load state F9
Toggle fullscreen F11
Disable audio channel 1-4 1-4
Disable BG layer B
Disable Window layer W
Disable OBJ (sprites) O
Fast-forward Lshift
Rewind Backspace
Pause Space
Step one frame N

INI file

Binjgb tries to read from binjgb.ini on startup for configuration. The following keys are supported:

# Load this file automatically on startup

# Set the audio frequency in Hz

# Set the number of audio frames per buffer
# lower=better latency, more pops/clicks
# higher=worse latency, fewer pops/clicks

# Set to the index of a builtin palette
# (valid numbers are 0..82)

# Force the emulator to run in DMG (original gameboy) mode.
# 0=Don't force DMG
# 1=Force DMG

# The number of video frames to display before storing a full dump of
# the emulator state in the rewind buffer. Probably best to leave this
# alone

# The number of megabytes to allocate to the rewind buffer.
# lower=less memory usage, less rewind time
# higher=more memory usage, more rewind time

# The speed at which to rewind the game, as a scale.
# 1=rewind at 1x
# 2=rewind at 2x
# etc.

# How much to scale the emulator window at startup.

# What to set the random seed to when initializing memory. Using 0
# disables memory randomization.

# Whether to display the SGB border or not.
# 0=Don't display SGB border
# 1=Display SGB border, even if it doesn't exist.

The INI file is loaded before parsing the command line flags, so you can use the command line to override the values in the INI file.

Running tests

Run scripts/ to download and build the necessary testsuites. This works on Linux and Mac, not sure about Windows.

scripts/ will only run the tests that match a filter passed on the command line. Some examples:

# Run all tests
$ scripts/

# Run all tests mooneye tests
$ scripts/ mooneye

# Run all gpu tests
$ scripts/ gpu

Test status

See test results