RSDKv4-Decompilation

About

Sonic the Hedgehog (1991) and its sequel Sonic the Hedgehog 2 (1992) are Sega Genesis platform games in which Sonic races through side-scrolling levels collecting rings to stop Doctor Robotnik; Sonic 2 introduced Sonic's sidekick Tails and a multiplayer mode. This is a complete decompilation of Retro Engine v4, covering both the game engine and the 2013 remaster menus for Sonic 1 and Sonic 2. It requires assets from an official release, via Sonic Origins on Steam, Epic Games Store, Switch, iOS, or Android, to run. Beyond reproducing the originals, it adds a built-in script compiler, a mod loader and API, and a custom networking system that recreates Sonic 2's 2-player VS mode online.

How it differs from the original

Adds a custom online multiplayer system, with a self-hosted Python server, recreating Sonic 2's 2-player VS mode; lets the normally-unlockable Egg Gauntlet Zone be selected directly from the Time Attack menu; and includes Sonic Mania-style debug and dev-menu tools not present in the original releases.

Getting started

Requires official Sonic 1/2 game assets from a legitimate release. Clone the repository recursively and build with CMake. To play Sonic 2's online multiplayer, run the included Python server script and configure the host and port in settings.ini; the developers note this networking feature is more a proof of concept, and connections can be unreliable.

Known issues & limitations

• compatibility: The multiplayer server is unstable and unreliable for connecting to opponents.
• The multiplayer server is a proof of concept and is very unstable, so connections to opponents may be unreliable.
• Unofficial platform branches are not supported and may not be up to date.
• The C++ server in the Server folder is deprecated and no longer works.

What you need to run it

Features

• The project includes a mod loader and API for playing mods, with features such as save-file redirection, custom achievements, and XML GameConfig data.
• The game uses a settings.ini file to load settings.
• The game can dim the screen when idle; users can disable dimming or set how long it takes to begin.

How to install

1. Obtain an official copy of the game to get its assets; use the linked guide to find the required assets.
2. To transfer a save from an official Android mobile version, copy SGame.bin into the project folder and name it SData.bin.

Controls

• Press ESC to open the dev menu from anywhere when it is enabled in the config.
• With the dev menu enabled, F1 loads the first scene in the Presentation stage list, usually the title screen.
• With the dev menu enabled, F2 and F3 load the previous and next scene in the current stage list.

Additional notes

Compatibility

Save files from the Android 'pre-forever' mobile release can be copied in and renamed to work with this decompilation.

FAQ

What is RSDKv4-Decompilation?

RSDKv4-Decompilation is an open-source decompilation of Sonic 2 and Sonic the Hedgehog. Source code reconstructed from the original game's compiled binary, so the game can be understood, rebuilt and ported.

Do I need the original game files to run RSDKv4-Decompilation?

Yes. The project does not include the original game's assets, so you need your own copy. Requires assets from an official release of Sonic 1 & Sonic 2 (via Sonic Origins on Steam, Epic Games Store, Nintendo Switch, iOS, or Android).