About
Sonic CD is a 1993 platform game developed by Sega for the Sega CD, in which Sonic must protect the extraterrestrial Little Planet from Doctor Robotnik; it introduced time travel as a gameplay mechanic and the characters Amy Rose and Metal Sonic. This is a complete, open-source decompilation of Retro Engine v3, the engine originally used to build Sonic CD. It requires assets from an official release of Sonic CD (available via Sonic Origins on Steam, Epic Games Store, Switch, iOS, or Android) to run, since no original game assets are included. Compared to the original PC release, it offers a pixel-perfect display, fully remappable controls, and a native x64 build; compared to the mobile versions, it uses the PC version's rendering backend with full palette support. It also adds a built-in mod loader and API, a settings.ini configuration file, and debug tools ported from Sonic Mania.
How it differs from the original
Adds features the original releases did not have: fully remappable controls, a mod loader and API with save-file redirection, Sonic Mania-style debug menus and idle-screen dimming, and, unlike the mobile ports, the PC version's rendering backend with correct water palette effects.
Getting started
Requires official Sonic CD game assets, obtainable only through a legitimate release of the game (Steam or Epic via Sonic Origins, Nintendo Switch, iOS, or Android — note that only the Steam release's video files are supported). Clone the repository recursively and build with CMake; unofficial forks add Switch and 3DS support.