Sonic CD Decomp: A 2011 Remaster Rebuilt With a Dev Menu

By Indie Kings | October 28, 2026

Updated October 28, 2026: RSDKModding/RSDKv3-Decompilation, a complete decompilation of the Retro Engine version 3 that powers the 2011 Sonic CD remaster, merged a change on October 26, 2026 that checks the render type in the window info callback. The repository has been running since April 2020, has 36 contributors, 713 stars and 203 forks, and its build produces a native Windows executable that needs the retail game's assets but none of its code.

Image: a Sega CD Model 1, the add-on that hosted the original Sonic CD, via Wikimedia Commons.

What the decompilation actually is

Sonic CD has an unusual history. The 1993 Sega CD original was built on Sega's own engine, and the 2011 remaster that brought the game to modern platforms was built on Retro Engine v3, a framework by Christian Whitehead that recreated the game's physics and added widescreen support. RSDKv3-Decompilation takes the second of those and rebuilds it from source. The README is precise about the dependency: without assets from an official release, the decompilation will not run, and it lists the places those assets can legally come from, including Steam, the Epic Games Store through Sonic Origins, the Switch version of Origins, and the iOS and Android releases.

There is a genuinely useful warning buried in that section. Only the FMV files from the original Steam release are supported, while the video files from the mobile and Origins versions do not work. Anyone who has tried to assemble a working install from a modern re-release will recognize the problem: the code is portable, the data is not, and a project like this can only promise compatibility with the specific packages its authors tested. The repository is careful about the boundary between code and content, which keeps it on the right side of the line that separates preservation from distribution.

A feature list that reads like a remaster patch

The advantages section is where the project stops being an academic exercise. Compared with the official PC version, the decompilation offers a sharp, pixel perfect display, fully remappable controls through a settings.ini file, window shortcuts that behave like normal desktop software, and support for the mobile and updated scripts, which means content and fixes that never reached the PC release can run there. Compared with the mobile versions, the rendering backend comes from the PC version by default, so palette effects such as the Tidal Tempest water work as intended.

Then there are the additions that no commercial remaster shipped: a built in mod loader with an API, save file redirection, XML game configuration data, and a dev menu reachable from anywhere with the escape key when enabled. The debug keys from Sonic Mania are ported over and extended, with F1 loading the first scene in the presentation list, F2 and F3 stepping through scenes, F5 reloading the current scene and its assets, F8 and F9 visualizing touch screen and object hitboxes, and F10 overlaying the game's eight internal palettes in real time. None of that is required to play Sonic CD. All of it is what makes the project useful to people who want to study or modify it.

Six years, seven open issues

The repository was created on April 15, 2020, and the newest commit is dated October 26, 2026, a one line sounding fix titled Check renderType in CALLBACK_GETWINDOWINFO. Seven issues are open, which for a project of this age is close to a clean bill of health: nothing structural is pending, and the remaining work is the long tail of platform quirks. Thirty six contributors have touched the tree, and 203 forks suggest a modest but real modding population working from it.

The build itself is conventional modern C++ rather than the period accurate compiler gymnastics of a console decompilation. CMake drives the build, dependencies come from vcpkg on Windows or the system package manager on Linux, and the repository has to be cloned recursively because the engine lives in submodules. That is a deliberate design choice: because Retro Engine v3 already shipped on Windows, the decompilation can target ordinary desktop toolchains and spend its effort on correctness and features instead of on reproducing a 1990s compiler. The result is a project that behaves like a maintained open source game rather than an artifact, which is exactly what the Sonic CD modding scene needed.

Project card

FAQ

What is RSDKv3-Decompilation?
A source reconstruction of Retro Engine version 3, the framework used by the 2011 Sonic CD remaster, built so the game can be compiled and modified on modern systems.

Does it include Sonic CD?
No. It contains code only, and the README requires assets from an official release. It also states that only the original Steam release's FMV files are supported.

Do I need the original game?
Yes, for the assets. The project does not distribute game data, and it points buyers toward Steam, Epic through Sonic Origins, Switch, iOS and Android.

What can the mod loader do?
It supports mods with save file redirection and XML game configuration, and the dev menu adds scene loading, hitbox visualization and palette inspection.

Is it hard to build?
It uses CMake with submodules, so the repository must be cloned recursively. Dependencies are standard graphics and audio libraries available through vcpkg or a Linux package manager.

Is the project active?
Yes, a commit landed on October 26, 2026, and only seven issues remain open.

Bottom Line

Sonic CD is one of the few games where a fan decompilation can legitimately claim to be better than the version most people own, and the feature list backs that up: pixel perfect scaling, remappable controls, mobile script support, Steam save loading and a debug menu that exposes the engine's internals. The discipline around assets is the other half of the story, because a project that tells you exactly which release to buy and which video files will not work has thought harder about legality than most. Six years in, with 36 contributors and seven open issues, this is a mature piece of preservation software.

Sources

• GitHub RSDKModding/RSDKv3-Decompilation README, asset requirements, feature list, build instructions, accessed October 28, 2026
• GitHub API metadata for RSDKv3-Decompilation, stars, forks, contributors, issues and latest commit, accessed October 28, 2026

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