RSDKv3-Decompilation: building the Sonic CD retro engine from source

A decompilation that only runs with assets you already bought

RSDKv3-Decompilation is a full decompilation of Retro Engine v3, the engine behind the 2011 Sonic CD release. The important caveat comes first: without assets from the official release, the decompilation will not run. The project is explicit that you must buy or officially download the game, and you do not need to run the official release, only its assets. The README lists where those releases can be obtained, including Steam (either the original release or the one included with Sonic Origins), the Epic Games Store, the Nintendo Switch eShop, the App Store and Google Play, and it notes that the mobile releases have been delisted while remaining redownloadable from a store purchase history. A guide linked from the project explains how to find the required assets from a copy you own. Only FMV video files from the original Steam release are supported, and video files from the mobile or Origins versions will not work.

What the decompilation adds over the official PC build

The stated advantages over the PC version of Sonic CD are specific rather than generic. Display is sharp and pixel-perfect. Controls are fully remappable through a settings.ini file, which the project says works in a way similar to Sonic Mania, and the window lets you use Windows shortcuts. Mobile and updated scripts are supported completely, which means features the official PC release never received can be played on a desktop. Native Windows x64 and x86 builds are both provided, and over the mobile versions the rendering backend is based on the PC version by default, so palettes are fully supported, with Tidal Tempest water called out as the case that matters. The extras layer on top: a built in mod loader and API with save file redirection and XML GameConfig data, a dev menu reachable from anywhere with the ESC key when enabled in the config, and the F12 pause plus F11 step over and fast forward debug features ported from Sonic Mania.

The dev menu and the config flags behind it

The debug features are gated on a config entry, so they are opt-in rather than always on. The README states that the F12 pause and F11 step over and fast forward options are enabled if devMenu is enabled in the config. The dev menu also gained scene navigation: F1 loads the first scene in the Presentation stage list, which is usually the title screen, F2 and F3 move to the previous and next scene in the current stage list, and F5 reloads the current scene along with all its assets and scripts. F8 and F9 visualise touch screen and object hitboxes, and F10 activates a palette overlay showing the game's eight internal palettes in real time. The build system exposes its own switches through cmake -D arguments, and one of them is RETRO_DISABLE_PLUS, a boolean that disables the Plus DLC and defaults to off, with the README recommending on for distribution builds. Another flag, RETRO_FORCE_CASE_INSENSITIVE, defaults to off as well.

Building on Windows, Linux, Mac and Android

The build uses CMake, and the project insists on a recursive clone, warning that the ZIP archive from GitHub does not include the submodules needed to build. The clone command given in the README is `git clone --recursive https://github.com/RSDKModding/RSDKv3-Decompilation`, and if you have already cloned, the README asks you to run a submodule update command inside the repository before continuing. On Windows you need Visual Studio Community with the Desktop development with C++ package, plus vcpkg, where the README says only the setup step is required, followed by a vcpkg install of glew, sdl2, libogg, libtheora and libvorbis with the x64-windows-static triplet, and a cmake invocation carrying the vcpkg toolchain file and target triplet as arguments. Linux packages are listed per distribution for Arch, Debian and Ubuntu, Fedora, and Alpine or PostmarketOS, and Mac and Android have their own build instructions under the dependencies directory. The top level of the repository shows how broad the target set is, with Android.mk, an iOS Xcode project, a Vita project, a UWP solution, a flatpak directory and a props directory alongside the main RSDKv3 source tree.

Two cmake commands produce the executable

Once the dependencies are in place, the compile step is short, and the README states it is run from the root of the repository:

cmake -B build
cmake --build build --config release

The resulting build is located somewhere under build/ depending on the system, which is worth keeping in mind when you go looking for the output. The build system is CMake rather than a hand written Makefile, and the build definition lives in CMakeLists.txt at the repository root, with a .clang-format file for code style. Development on the Linux, Mac and Android sides is described in the dependencies folder, and the CI configuration sits in .github. The whole point of a decompilation build, as opposed to patching a shipped binary, is that you get a source tree that a modern compiler accepts, which is what makes the mod loader and the debug features in the previous section possible at all.

Where this approach falls short

The hard dependency on owned assets is the first constraint, and it is not a technical one. If you do not have a legitimate copy, the engine has nothing to load and the build will not get you a running game. The video file restriction is the second, and it bites people who bought the wrong edition: only FMV files from the original Steam release are supported, and mobile and Origins video files do not work, so a purchase through the Epic Games Store or the eShop may not supply the files the engine expects. Third, the platform coverage in the README is uneven. Windows and Linux get full dependency instructions, while Mac and Android defer to separate documents under dependencies, which means the first build on those platforms is where you will hit missing instructions. The project also depends on submodules being present, so a plain ZIP download is a guaranteed dead end, and a build that appears to succeed can still fail at runtime for the asset reason above.

Compared with running the official release

The obvious alternative is to just play the official 2011 build that Steam, the Epic Games Store or a console provides. The difference in approach is what you can do with it. The official release is a fixed binary with a fixed rendering path, the resolution and the input handling it shipped with, and on some editions the video files differ in ways this engine does not accept. The decompilation replaces that with source you can compile, a pixel-perfect display, remappable controls, a mod loader and API, a dev menu with scene navigation and hitbox visualisation, and a settings.ini that centralises configuration. If your goal is to play the game as released, the official version is simpler and needs no toolchain. If your goal is to change the game, add a mod, inspect a scene or debug a script, the decompilation is the only one of the two that makes those possible, and it accepts the original Steam FMV files that the console and mobile releases do not provide.

Editorial conclusion

RSDKv3-Decompilation suits people who already own a legitimate copy of Sonic CD and want a sharp, moddable, debuggable build of the 2011 engine on a modern toolchain. It is the wrong choice for anyone without the assets, since the engine will not run without them, and it will not work with the video files from the mobile or Sonic Origins releases. Before you start, confirm your platform's dependency list in the README, clone recursively rather than downloading the ZIP archive, and read LICENSE.md, because the project uses a custom licence rather than a standard one. The last push was on 2026-10-10 and the newest tagged release is 1.3.3 from 2025-11-02.

Frequently asked questions

Official sources

1. Issues
2. README
3. Releases
4. RSDKModding/RSDKv3-Decompilation on GitHub