mrgameeng/CLAUDE.md

# mrgameeng

2D game engine built on MonoGame 3.8.4 (DesktopGL), .NET 8, C#.
ECS-first: Friflo.Engine.ECS 3.6 is tightly integrated into the core — all gameplay
state lives in components, all logic in systems.

Design docs and developer documentation live in `docs/` and are written in **Russian**.
Keep them up to date when architecture or conventions change.

## Solution layout

```
src/      MrGameEng.* engine libraries (grouped by role, not one-per-feature)
tests/    xUnit test projects, one per engine library
tools/    CLI tools (atlas packer)
docs/     architecture, conventions, roadmap (Russian)
```

Libraries are grouped by architectural role rather than split per feature, to avoid a
sprawl of two-file projects. A feature lives in a subfolder of its host library and
keeps its own `MrGameEng.<Feature>` namespace (namespaces are independent of the
assembly), so `using MrGameEng.Tilemaps;` etc. still resolve after a merge.

The engine has no sample project: the **LittleSim** game
(https://gitea.hsrv.site/mrleo1nid/LittleSim, this repo as the `engine/` submodule)
is the living showcase — new engine features are demonstrated there.

Engine libraries (each feature is a namespaced subfolder of its host):

- **`Core`** — game loop, ECS world, scenes, time, plus **Input** (`MrGameEng.Input`:
  `InputManager`, `ActionMap`, `InputSystem`, in `Core/Input/`). Depends only on
  MonoGame and Friflo.Engine.ECS.
- **`Graphics`** — custom batched renderer, camera, sprites, plus **Tilemaps**
  (`MrGameEng.Tilemaps`: code-built tile grids rendered through the batcher,
  `scene.UseTilemaps()` after `UseRenderer2D()`, in `Graphics/Tilemaps/`). → `Core`.
- **`Audio`** — ogg playback (NVorbis). → `Core`.
- **`Content`** — the asset/content pipeline: **Assets** (`MrGameEng.Assets`: runtime
  loading, no MGCB pipeline; FontStash), **Atlases** (`MrGameEng.Atlases`: texture-atlas
  builder + runtime loader, CLI wrapper in `tools/MrGameEng.AtlasTool`; StbImage), and
  **Mods** (`MrGameEng.Mods`: mod discovery + load order from `About/About.json`, JSON
  `Defs/` with parent inheritance and later-mod override, `Languages/<code>/`
  localization, merged texture content trees; the game ships its content as the `Core`
  mod). → `Core`, `Graphics` (Atlases needs `Texture2DRegion`).
- **`Simulation`** — deterministic gameplay primitives that own no world data:
  **Pathfinding** (`MrGameEng.Pathfinding`: grid A*/Dijkstra/BFS and flow fields over a
  game-implemented `IPathGrid`), **AI** (`MrGameEng.AI`: utility-AI primitives —
  `ResponseCurve`, `Consideration<TContext>`, `UtilityAction<TContext>`,
  `UtilityAi<TContext>` selector, `Blackboard`; generic over a game context), and
  **Collisions** (`MrGameEng.Collisions`: `Collider` component, spatial hash rebuilt per
  tick, pairs/queries/raycast, `scene.UseCollisions()` after movement systems).
  → `Core`, `Graphics` (Collisions needs `Transform2D`, `RectF`).
- **`UI`** — Myra integration (`scene.UseUI()` after `UseRenderer2D()`) plus
  **DevConsole** (`MrGameEng.DevConsole`: in-game console capturing `Core.Log`,
  `scene.UseDevConsole()` last in OnLoad). → `Core` (Myra renders with its own
  SpriteBatch internally).
- **`Assets.Generator`** — Roslyn source generator for typed asset handles; standalone
  netstandard2.0 analyzer.

Dependency rule: a library may depend only on `Core` and `Graphics`; `Core` depends only
on MonoGame and Friflo.Engine.ECS. Features grouped into one library share its package
set (e.g. `Content` carries both FontStash and StbImage) — keep optional/heavy deps
(Myra, NVorbis) in their own library so the rest of the engine stays free of them.

## Commands

```
dotnet build MrGameEng.sln
dotnet test MrGameEng.sln
```

Building requires the .NET 10+ SDK (Roslyn 5.3 packages used by the asset-handles
generator do not load under the SDK 8 compiler); the target framework stays net8.0.

## Architecture rules

- ECS-first: components are plain data (`struct` implementing `IComponent`),
  behavior goes into Friflo systems (`QuerySystem`), wired through `SystemRoot`.
  No `Update()` methods on game objects, no inheritance-based entities.
- Hot paths (per-frame systems) must be allocation-free below the renderer's parallel
  threshold; above it Parallel.For scheduler overhead is the accepted trade.
  A Friflo chunk holds a whole archetype — parallelize by slicing chunks into segments,
  never by chunk alone. Measure in Release only, using the Renderer2D phase timings.
- Rendering: custom batcher in `Graphics` (vertex buffers, layer→depth→texture sort,
  atlas support); `SpriteBatch` is not used in engine code. Draw systems write vertices
  directly from Friflo chunk iteration. Orthographic camera (one active per scene),
  registered render layers (World or Screen space, optional Y-sort), AABB culling
  against the camera rect before vertices are written.
- No MGCB content pipeline. Assets are raw files under `Assets/`, loaded at runtime
  (textures via `Texture2D.FromFile`, fonts via FontStashSharp, ogg via NVorbis,
  shaders precompiled by `dotnet-mgfxc` at build time). Game code references assets
  only through generated typed handles (`AssetRef<T>`), never string paths.
- New engine functionality goes into the host library for its role (a namespaced
  subfolder, e.g. a new render feature under `Graphics/`), not a fresh project. Add a
  new `MrGameEng.<Area>` library only when the area is a genuinely new role or needs an
  isolated heavy/optional dependency — never into `Core` by default, never a
  two-file project per feature.
- Every public engine feature must be covered by tests where logic is testable
  without a GPU, and demonstrated in the LittleSim game (the engine's showcase).

## Code conventions

- Nullable reference types enabled, warnings as errors, file-scoped namespaces.
- Public engine API requires XML doc comments (English).
- Tests: xUnit, named `Method_Scenario_Expectation`.
- Formatting: all C# code is formatted with **CSharpier**. Match its output —
  run `csharpier format .` (or let the editor's format-on-save handle it) before
  committing; never hand-format against it.

## Memory (echovault MCP)

- At session start, call `memory_context` to load prior decisions for this project;
  call `memory_search` before working on a topic that may have prior context
  (e.g. "renderer", "transitions", "generator").
- Before ending a session where you decided, fixed or learned something, save it with
  `memory_save`: decisions (X over Y + why), bug root causes, non-obvious gotchas
  (e.g. Friflo/Myra API traps). Write for a future agent with zero context.
- Don't save what the repo already records (code, docs/, git history) or trivia.