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gen2recomp

An early-stage Godot 4 reimplementation of the Generation 2 Game Boy Color games, with native builds planned for desktop and mobile platforms.

Github

gen2recomp

gen2recomp is a work-in-progress, native Godot 4 reimplementation of the Generation 2 Game Boy Color games: Gold, Silver and Crystal. The project is published in the gen2recomp repository.

This is not an emulator, a static recompilation or a disassembly. The engine is being written from scratch in GDScript. Your own cartridge dump is used as an asset database: it is verified, decoded into a local cache and then released. No game data is included in the repository.

Current status

gen2recomp is still in an early development stage. The import gate and the first half of the importer are implemented and tested. A verified cartridge can already be decoded into species data, moves, items, types, palettes, Pokémon sprites, the font and text box borders. Sprites and text can be drawn on a real 160x144 screen.

The overworld, battle system, audio and mod loader are not implemented yet, so there is nothing playable here today. The first alpha release is coming soon. Until then, the repository is the place to follow development and try the project from source.

What you will be able to do

Once the project reaches alpha, the Releases page will provide already-built executables for supported platforms. The project is targeting Windows, macOS, Linux, Android and iOS with Godot's GL Compatibility renderer.

The current source already supports these workflows:

  • Verify a supported cartridge dump by SHA-1.
  • Import cartridge data into a cache stored in Godot's user:// directory.
  • Preview decoded sprites, fonts and text box frames.
  • Dump decoded tables such as species, moves, items and types.
  • Open the sprite and text viewers in the Godot editor.
  • Run the automated tests without loading a real cartridge.

Before you start

You need:

  • Godot 4.8 or newer.
  • A cartridge dump that you are legally allowed to use.
  • A clone of the gen2recomp repository.

The project does not distribute ROMs, save files or extracted game assets. Put your own cartridge dumps in the repository's roms/ folder. Matching is based on SHA-1, never on the filename, and an unknown dump is refused instead of being imported on a best-effort basis.

Quick start from source

Clone the repository and enable its commit guard once per clone:

git clone https://github.com/Decryptu/gen2recomp.git
cd gen2recomp
git config core.hooksPath .githooks

Place a supported cartridge dump in roms/, then verify it:

godot --headless --path . -s res://tools/verify_rom.gd

Import the verified cartridge into the local cache:

godot --headless --path . -s res://tools/import_rom.gd

The import normally takes under a second per game. The cache is derived from your cartridge and stays in Godot's user:// directory rather than being written into the project. Add --verify to run the checks without writing anything.

Supported cartridges

The current importer recognises these dumps:

GameSHA-1
Gold (USA/Europe)d8b8a3600a465308c9953dfa04f0081c05bdcb94
Silver (USA/Europe)49b163f7e57702bc939d642a18f591de55d92dae
Crystal (USA/Europe Rev 1)f2f52230b536214ef7c9924f483392993e226cfb

Explore the imported data

Generate a contact sheet of decoded sprites with:

godot --headless --path . -s res://tools/preview_pics.gd -- gold /tmp/gold.png front

Use font or frames instead of front to preview the decoded font or text box borders. You can also print decoded tables:

godot --headless --path . -s res://tools/dump_tables.gd -- gold moves

The table command accepts species, moves, items, types or all.

Run the viewers

Open game/render/pic_viewer.tscn in Godot and press Play to inspect imported sprites. Use Left and Right to change species, S to toggle shiny sprites and B to switch between front and back sprites.

Open game/render/text_viewer.tscn to inspect text rendering. Space advances the text box, F cycles through the eight borders and C displays the full font.

The game screen is rendered at 160x144 and scaled by a whole number so the original pixel grid stays sharp.

Run the tests

The project uses GUT for its unit and integration tests:

godot --headless -s res://addons/gut/gut_cmdln.gd -gdir=res://tests -ginclude_subdirs -gexit

The suite uses synthetic files and a known SHA-1 test vector, so it does not need a real cartridge. An exit code of 0 means the tests passed.

Links

The engine source is MIT licensed. The original games are not included or redistributed and remain the property of their respective owners.