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
docs/          концепт, симуляция, 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

Texture atlases

Source images live in textures/ (committed); the game only loads packed atlases from src/LittleSim/Assets/Atlases (also committed — the asset generator emits GameAssets.Atlases.* handles for them). After changing textures/, rebuild with:

dotnet run --project engine/tools/MrGameEng.AtlasTool -c Release -- textures src/LittleSim/Assets/Atlases --group-depth 2

Rebuilds are incremental (unchanged groups are skipped). Region keys are paths relative to textures/ without extension: atlas.GetRegion("things/plant/treeoak/TreeOakA").

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.
• Every new mechanic gets a dev-console command for testing (regen, timescale, …).