C# and native code
Choose how to implement game logic and distinguish scripts, shaders and engine source.
Game logic: C#
The practical Reckfell guides use C#. The distribution provides .NET 10, Reckfell.NET.Sdk and types in the Reckfell namespace. C# is a .NET language; entity behavior, [Export] and [Signal] come from the engine integration.
A script extends an engine class. Player : CharacterBody3D, for example, controls a physics character, while Menu : Control implements UI. The base class must suit the object carrying the script. A file on disk does not create an object or attach behavior to a level.
Start with project setup, your first script and C# basics. C++ knowledge is not required.
When native code is needed
Changing engine internals or integrating a native library is separate C++ work, with builds for the target platforms. It does not mean attaching an ordinary .cpp file to an entity. You need suitable headers, build tools and binary compatibility checks against your Reckfell build.
Do not move game code to C++ simply because a level is large. Measure whether time is spent in scripts, physics, rendering, resource loading or allocations first. A language choice alone does not remove those limits.
Other kinds of code
A shader defines rendering computations and does not replace a C# character controller. JSON and .rdata files store data rather than executable behavior. An editor script performs a tooling task; enable editor execution deliberately, accounting for changes to project resources.
Check the target platform
.NET support in the editor does not prove that a C# game can export to every platform. Check the actual export templates, target support and dependencies on a device. See exporting.