RSDKv5 Decomp: The Retro Engine Behind Sonic Mania, Rebuilt

By Indie Kings | October 28, 2026

Updated October 28, 2026: RSDKModding/RSDKv5-Decompilation, a complete decompilation of Retro Engine version 5 and its Ultimate revision, now builds on Windows, Linux, Android and Nintendo Switch, and its newest default branch commit, dated October 3, 2026, repairs the Android setup action that pulls the platform tools package. The repository was created on June 6, 2022 and has 573 stars, 241 forks and 23 contributors.

Image: a Nintendo Switch in its dock, one of the targets the decompilation builds for, via Wikimedia Commons.

An engine, not a game

Most decompilations are named after the game they rebuild. This one is named after the framework. Retro Engine v5 and v5Ultimate are the software layer that runs a family of games, most famously Sonic Mania, and the README is explicit that the project does not own the engine, that Retro Engine is now owned by Evening Star, and that users should support the studio's work. The framing matters because the repository is not a game preservation project in the usual sense. It is a reusable implementation of a runtime, which is why the Sonic Mania decompilation can include it as a submodule instead of duplicating it.

That separation explains the structure of the RSDKModding organization. RSDKv5-Decompilation provides the engine, RSDKv3-Decompilation provides the older engine used by Sonic CD, and Sonic-Mania-Decompilation provides the game logic and asset loading that sits on top. The README even routes Mania users to the combined repository, noting that they can build v5 alongside the game there. For anyone trying to understand how modern Sonic fangames and mods are assembled, this repository is the foundation layer, and the mod loader built into it is the API those projects actually call.

The platform list is the story

The build documentation covers Windows through Visual Studio and vcpkg, Linux through the usual package managers, Android through a dedicated guide, and Nintendo Switch through devkitPro with the console's SDL2, libogg, libtheora and glad packages. A decompilation that targets a current console is a different kind of project from one that stops at desktop operating systems, and the Switch path is the clearest evidence that the codebase is portable rather than merely compilable. The Linux instructions also include a note to install GL shaders, with a pointer to the FAQ explaining why videos and filters fail without them, which is the sort of detail that only gets written down after users hit it.

The feature list follows the same logic. The mod loader and API support save file redirection and XML asset loading across all sub-versions of v5Ultimate, a built in shader compiler serves backends that can use it, and Windows gained additional rendering backends beyond the usual DirectX 9 path. These are engine level features, not game level content, and they are what a modding community needs before it can build anything: a stable loader, a way to redirect saves so experiments do not destroy progress, and rendering paths that work on hardware DirectX 9 never anticipated.

A small team with a wide target

Twenty three contributors is small for a project with four platform targets and 30 open issues, and the activity pattern shows it. The repository was created in June 2022, most recently had a default branch commit on October 3, 2026 fixing continuous integration for Android, and GitHub records a push to the repository on October 23. The gap between those dates is normal for a project maintained in bursts around platform work: the code is stable, the surrounding automation and packaging need attention, and the people with the relevant hardware or toolchains are a subset of the contributor list.

Thirty open issues for an engine decompilation is not a backlog of broken features so much as a map of the long tail. Rendering differences across backends, platform specific input handling, and build system friction on newer toolchains all live in that list, and none of them threaten the core claim that the engine's code has been reconstructed. The practical takeaway for a reader is that this repository is infrastructure. It will never have the drama of a game decompilation reaching a matching hash, because its output is a library and a set of platform builds, but every Mania mod and every Retro Engine project that wants a readable base depends on it working.

Project card

FAQ

What does RSDKv5-Decompilation rebuild?
Retro Engine version 5 and its Ultimate revision, the runtime that powers Sonic Mania and other games built on the same framework.

Is it a game?
No. It is the engine layer. Game logic and assets come from separate repositories such as the Sonic Mania decompilation, which can include this project as a submodule.

Which platforms can it build for?
Windows, Linux, Android and Nintendo Switch, with the Switch path documented through devkitPro packages.

Does it support mods?
Yes. A built in mod loader and API handle save file redirection and XML asset loading, and they work across all v5Ultimate sub-versions.

Why does the README talk about Evening Star?
Because Evening Star owns Retro Engine. The project credits the studio and asks users to support its games rather than treating the decompilation as a replacement.

How active is it?
Reasonably. A commit landed on October 3, 2026, the repository was pushed to on October 23, and 30 issues remain open.

Bottom Line

Engine decompilations are thankless in a way game decompilations are not: nobody celebrates a matching hash for a runtime, and the output is a library most players never see. But the platform list here, current console included, is the real achievement, and the mod loader is the reason the Retro Engine scene has a stable foundation to build on. Twenty three contributors keeping four targets alive with 30 open long tail issues is a thin margin, and the project deserves more attention than its star count suggests.

Sources

• GitHub RSDKModding/RSDKv5-Decompilation README, engine ownership notice, platform build instructions, feature list, accessed October 28, 2026
• GitHub API metadata for RSDKv5-Decompilation, stars, forks, contributors, issues and latest commit, accessed October 28, 2026

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