LittleSim/CLAUDE.md

LittleSim

A god-game: minimal graphics, deep simulation. Built on the mrgameeng engine (MonoGame + Friflo ECS), vendored as the git submodule engine/ so the game and the engine are developed side by side in one editor window.

This game is also the engine's showcase: mrgameeng has no sample project, so every new engine feature gets demonstrated here (a scene, a console command, or a system using it) as part of landing the feature.

Game design docs live in docs/ and are written in Russian. Engine rules live in engine/CLAUDE.md — read it before touching engine code; both rule sets apply here.

Layout

engine/        mrgameeng git submodule (own repo, own CLAUDE.md)
src/LittleSim  the game (net8.0); references engine projects directly
Mods/Core      the game's own content as a mod: About, Defs, Languages, Textures
Cache/         runtime-built atlases (gitignored)
docs/          концепт, симуляция, моды, roadmap (Russian)
LittleSim.sln  game + engine sources + engine tests — one window for everything

Commands

git submodule update --init             # after fresh clone
dotnet build LittleSim.sln
dotnet run --project src/LittleSim -c Release   # measure perf in Release only
dotnet test LittleSim.sln                        # runs the engine test suites

Content and mods

All game content is data in mods (MrGameEng.Mods): the game itself ships as the Core mod. Mods/Core/Defs holds JSON defs (terrain, plants, pawns — see docs/mods.md), Mods/Core/Languages/{ru,en} holds UI strings (default language is ru), Mods/Core/Textures holds source images. New mechanics get defs + localization keys, not hardcoded arrays; UI strings go through LanguageManager, never inline.

Atlases are built at game start from the merged texture tree of all active mods into Cache/Atlases (incremental: unchanged groups are skipped, a clean first run takes ~20 s). Region keys are paths relative to Textures/ without extension: atlases.GetRegion(device, "things/plant/treeoak/TreeOakA"). Console commands: mods, lang [code], defs [type], atlas [name].

Submodule workflow

Engine changes are committed inside engine/ first (engine repo, its commit style), pushed to the engine remote, then the submodule pointer bump is committed here. Never commit a pointer to an unpushed engine commit.

Game rules

• Simulation first: depth of behavior over visuals. Graphics stay primitive (tinted quads are fine); complexity budget goes to simulation systems.
• Determinism: the whole world derives from one integer seed. Systems that need randomness own a seeded Random; never use Random.Shared inside simulation.
• Simulation/presentation split: simulation systems mutate components only; rendering reads them. No draw calls or UI from simulation systems.
• ECS-first per the engine: plain struct : IComponent data, logic in systems.
• Content as data: numbers, textures and balance live in Mods/Core/Defs, user-facing strings in Mods/Core/Languages — code only defines systems and def classes.
• Every new mechanic gets a dev-console command for testing (regen, timescale, …).
• Formatting: all C# code is formatted with CSharpier (editor.defaultFormatter is csharpier.csharpier-vscode, format-on-save is on). Match CSharpier's output — run csharpier format . (or let format-on-save handle it) before committing; never hand-format against it.