acdream/docs/architecture/acdream-architecture.md

# acdream — Comprehensive Architecture Plan

## Vision

A modern C# .NET 10 Asheron's Call client that:
- **Behaves identically to the retail client** — same physics, same
  animations, same terrain, same collision, same network protocol
- **Looks identical to the retail client** — same meshes, same textures,
  same lighting, same blending, rendered via modern Silk.NET OpenGL
- **Adds a plugin API** the retail client never had — native C# plugins
  + Lua macro scripting for player automation
- **Is NOT a 1:1 C++ port** — uses modern C# patterns (composition over
  inheritance, interfaces, dependency injection) while matching retail
  behavior exactly

## Guiding Principle

**The code is modern. The behavior is retail.**

Every AC-specific algorithm is ported faithfully from the **named retail
decomp** at `docs/research/named-retail/` — Sept 2013 EoR build PDB
(18,366 named functions, 5,371 named struct types) + Binary Ninja
pseudo-C with 99.6% function-name recovery + verbatim retail header
struct definitions. The older Ghidra `FUN_xxx` chunks at
`docs/research/decompiled/` (688K lines) remain a fallback for the
obfuscated/packed minority. The code AROUND those algorithms is modern
C# with clean architecture. The plugin API exposes game state through
well-defined interfaces that the retail client never had.

---

## Layer Architecture

```
┌──────────────────────────────────────────────────────────────┐
│  LAYER 5: Plugin API                                        │
│  IGameState, IEvents, IActions, IPacketPipeline, IOverlay   │
│  Plugin host (ALC), Lua macro engine (MoonSharp)            │
│  ► acdream-unique — not in retail client                    │
├──────────────────────────────────────────────────────────────┤
│  LAYER 4: Game Objects                                      │
│  GameEntity (one per world object)                          │
│    ├── PhysicsBody      (ported from decompiled)            │
│    ├── AnimSequencer     (ported from decompiled)            │
│    ├── CellTracker      (ported from decompiled)            │
│    ├── AppearanceState  (ObjDesc: palettes, textures, parts)│
│    └── MotionState      (ported from decompiled)            │
│  ► behavior matches retail, code is modern C# composition   │
├──────────────────────────────────────────────────────────────┤
│  LAYER 3: World Systems                                     │
│  TerrainSystem   (heightmap, blending, scenery)             │
│  CellSystem      (LandCells, EnvCells, portals, BSP)        │
│  StreamingSystem (background loading, LOD, frustum cull)    │
│  ► behavior matches retail, streaming is acdream-unique     │
├──────────────────────────────────────────────────────────────┤
│  LAYER 2: Network                                           │
│  WorldSession (ISAAC, fragments, game messages)             │
│  MessageRouter (opcode dispatch, sequence tracking)         │
│  ► wire-format identical to retail                          │
├──────────────────────────────────────────────────────────────┤
│  LAYER 1: Renderer                                          │
│  Silk.NET OpenGL 4.3 core profile                           │
│  TerrainRenderer, StaticMeshRenderer, TextureCache          │
│  Shaders (terrain blending, mesh lighting, translucency)    │
│  ► completely different from retail (D3D7), same visual     │
│    output                                                   │
├──────────────────────────────────────────────────────────────┤
│  LAYER 0: Platform                                          │
│  .NET 10, Silk.NET window/input, DatReaderWriter            │
│  ► acdream-unique infrastructure                            │
└──────────────────────────────────────────────────────────────┘
```

### UI Architecture (companion stack, spans Layers 1 & 5)

The UI is split into its own three-layer stack with a swappable backend,
designed 2026-04-24. Full design: `docs/plans/2026-04-24-ui-framework.md`.

```
┌─────────────────────────────────────────────────────────────┐
│  UI BACKEND (swappable)                                     │
│  ImGui.NET + Silk.NET.OpenGL.Extensions.ImGui               │
│    (Phase D.2a, short-term)                                 │
│   or custom retail-look toolkit (Phase D.2b, later)         │
├─────────────────────────────────────────────────────────────┤
│  AcDream.UI.Abstractions (stable contract)                  │
│  ViewModels, Commands, IPanel, IPanelHost, IPanelRenderer   │
│  ► plugin-facing UI API lives HERE, not in the backend      │
├─────────────────────────────────────────────────────────────┤
│  Game state + events (unchanged)                            │
│  IGameState / IEvents / WorldSession — UI only reads        │
└─────────────────────────────────────────────────────────────┘
```

The backend is pluggable; ViewModels / Commands / `IPanelRenderer` are
stable across the swap. ImGui persists forever as the
`ACDREAM_DEVTOOLS=1` devtools overlay regardless of which backend owns
the game UI. The full UI design lives in
`docs/plans/2026-04-24-ui-framework.md`.

---

## Project Structure (current + target)

```
src/
  AcDream.Core/              Layer 2-4: no GL, no Silk.NET, pure logic
    Physics/
      PhysicsBody.cs          -> body state / integration foundation (done)
      CollisionPrimitives.cs  -> retail primitive helpers (partial, active)
      MotionInterpreter.cs    -> motion state machine (done, still L.1 polish)
      AnimationSequencer.cs   -> animation playback + root-motion data (done, L.1 active)
      TerrainSurface.cs       -> triangle-aware terrain contact (done)
      BSPQuery.cs             -> partial retail BSP dispatcher (active in L.2)
      TransitionTypes.cs      -> SpherePath / CollisionInfo / transition helpers (active in L.2)
      PhysicsDataCache.cs     -> GfxObj / Setup / CellStruct collision data (done, active)
      ShadowObjectRegistry.cs -> broadphase for nearby physics objects (active)
      PhysicsEngine.cs        -> ResolveWithTransition active player path
      CellBsp.cs              -> not a first-class runtime owner yet (L.2e)
    World/
      GameEntity.cs           -> target unified entity, not current reality
      WorldState.cs           -> target entity owner
      CellTracker.cs          -> target per-entity cell management
      SceneryGenerator.cs     -> verified against decompiled (done)
      LandblockLoader.cs      -> done
    Terrain/
      LandblockMesh.cs        -> verified against ACME (done)
      TerrainBlending.cs      -> verified against ACME (done)
    Meshing/
      GfxObjMesh.cs           -> cross-checked against ACME (done)
      SetupMesh.cs            -> cross-checked (done)
    Textures/
      SurfaceDecoder.cs       -> done
    Dat/
      MotionResolver.cs       -> done (target move from Meshing/)
  
  AcDream.Core.Net/          Layer 2: networking
    WorldSession.cs           -> done (wire-compatible with ACE)
    NetClient.cs              -> done
    Messages/                 -> done (CreateObject, MoveToState, etc.)
  
  AcDream.Plugin.Abstractions/  Layer 5: plugin interfaces
    IAcDreamPlugin.cs         -> done
    IPluginHost.cs            -> done
    IGameState.cs             -> done
    IEvents.cs                -> done
  
  AcDream.App/               Layer 1 + Layer 4 wiring
    Rendering/
      GameWindow.cs           -> still owns too much runtime wiring
      TerrainRenderer.cs      -> done
      StaticMeshRenderer.cs   -> done
      TextureCache.cs         -> done
      ChaseCamera.cs          -> done
      FlyCamera.cs            -> done
    Streaming/
      StreamingController.cs  -> done
      GpuWorldState.cs        -> done
    Input/
      PlayerMovementController.cs  -> active movement driver
    Plugins/
      AppPluginHost.cs        -> done
```

---

## Movement And Collision Architecture

Phase L.2 is the current organizing program for physics, collision,
boundaries, buildings, sliding, cell ownership, movement packets, and server
authority. Detailed plan: `docs/plans/2026-04-29-movement-collision-conformance.md`.

The active player movement spine is:

```text
InputDispatcher / PlayerMovementController
  -> MotionInterpreter + local body prediction
  -> PhysicsEngine.ResolveWithTransition
  -> TransitionTypes + BSPQuery + ShadowObjectRegistry
  -> ResolveResult contact/cell state
  -> MoveToState / AutonomousPosition outbound messages
  -> WorldSession server echo or correction handling
```

What exists and is active:

- `PhysicsEngine.ResolveWithTransition` is the path used for local player
  collision resolution.
- `BSPQuery` contains the partial retail-style BSP collision dispatcher used by
  the transition path.
- `TransitionTypes` carries `SpherePath`, `CollisionInfo`, `ObjectInfo`,
  transition validation, step-up/down, contact-plane handling, and partial
  slide behavior.
- `PhysicsDataCache` loads GfxObj, Setup, and CellStruct physics data from DATs.
- `ShadowObjectRegistry` gives movement a broadphase over nearby objects and
  buildings.
- `TerrainSurface` uses triangle-aware terrain contact; older "bilinear terrain
  Z" descriptions are historical B.3 language, not current architecture.

What remains incomplete:

- `CELLARRAY`, `CObjCell::find_cell_list`, adjacent-cell checks, and low outdoor
  cell id updates across 24m seams.
- `cell_bsp` / `CellBSP` as the authoritative runtime owner for indoor and
  building collision.
- Building portal transit and normal walking through building entry/exit
  boundaries.
- Full retail `edge_slide`, `cliff_slide`, `precipice_slide`, and `NegPolyHit`
  dispatch behavior.
- Exact `CSphere` / `CCylSphere` object-shape parity, especially for live
  entities that currently collapse to a simplified cylinder fallback.
- Routine local/server correction diagnostics. ACE accepting a position is a
  compatibility signal, not proof of fine retail collision parity.

Ownership by phase:

- B.3 is shipped MVP history: first resolver foundation and tests.
- L.1 owns animation/motion parity, including root-motion coupling.
- L.2 owns the movement/collision conformance stack listed above.
- G.3 owns dungeon streaming and portal-space delivery after L.2e gives it
  trustworthy cell/building boundaries.

---

## GameEntity: The Unified Entity (target refactor)

Currently, entity state is scattered across:
- `WorldEntity` (position, rotation, mesh refs)
- `AnimatedEntity` (animation frame, setup, sequencer)
- `_entitiesByServerGuid` dict (server GUID lookup)
- `GpuWorldState._loaded[lb].Entities` (per-landblock lists)
- `_playerController` (player-specific movement)

This should become ONE class:

```csharp
public sealed class GameEntity
{
    // Identity
    public uint ServerGuid { get; }
    public uint SetupId { get; }
    public string? Name { get; }

    // Spatial (ported from CPhysicsObj)
    public PhysicsBody Physics { get; }      // position, velocity, gravity
    public CellTracker Cell { get; }         // which cell we're in
    
    // Appearance (ported from CPartArray)
    public AnimationSequencer Animation { get; }  // frame playback
    public AppearanceState Appearance { get; }     // ObjDesc overrides
    
    // Motion (ported from CMotionInterp)
    public MotionInterpreter Motion { get; }  // walk/run/turn state
    
    // Render output (consumed by StaticMeshRenderer)
    public IReadOnlyList<MeshRef> MeshRefs { get; }
    
    // Per-frame update (matches retail update_object)
    public void Update(float dt)
    {
        Motion.ApplyCurrentMovement();     // set velocity from motion state
        Physics.UpdateObject(dt);          // integrate position
        PhysicsEngine.ResolveWithTransition(); // current L.2 collision spine
        Cell.UpdateCell(Physics.Position); // target: retail cell ownership
        Animation.Advance(dt);            // advance animation frames
        RebuildMeshRefs();                // compute per-part transforms
    }
}
```

Target state: every entity in the world — player, NPC, monster, lifestone,
door, chest — becomes a `GameEntity`. The renderer iterates them and draws.
The plugin API exposes them as `WorldEntitySnapshot`. GameWindow becomes thin.

---

## Per-Frame Update Order (current runtime)

```
1. Network tick
   └── Drain inbound queue → process CreateObject, UpdateMotion,
       UpdatePosition, PlayerTeleport → create/update GameEntities

2. Streaming tick
   └── Compute observer position → load/unload landblocks →
       create terrain + scenery GameEntities

3. Input tick (player mode only)
   └── InputDispatcher scopes → PlayerMovementController →
       MotionInterpreter/body prediction → ResolveWithTransition →
       send MoveToState/AutonomousPosition to server

4. Entity / animation tick
   └── Current code still has scattered world/entity state. L.1 owns
       animation parity; L.2 owns movement/collision conformance.

5. Render tick
   └── Read current entity mesh refs, draw
       TerrainRenderer.Draw, StaticMeshRenderer.Draw
       (frustum cull, translucency pass, etc.)

6. Plugin tick
   └── Fire IEvents, drain IActions queue

6a. UI tick
    IPanelHost.Draw → iterate registered IPanel instances, build
    ViewModels from IGameState, dispatch user Commands via ICommandBus.
    Backend-agnostic — ImGui or custom retail-look draws here depending
    on which is compiled in. See docs/plans/2026-04-24-ui-framework.md.
```

---

## Roadmap Model

The old R1-R8 architecture sequence was a useful early refactor sketch, but it
is no longer the execution plan. The strategic source of truth is now
`docs/plans/2026-04-11-roadmap.md`, with per-phase details in `docs/plans/`
and `docs/superpowers/specs/`.

Current movement/collision ownership:

- **B.3** is shipped MVP history: first collision resolver foundation.
- **L.1** owns animation/motion parity, including root-motion coupling.
- **L.2** owns movement and collision conformance:
  `docs/plans/2026-04-29-movement-collision-conformance.md`.
- **G.3** owns dungeon streaming and portal-space delivery after L.2e lands
  trustworthy `cell_bsp`, `CELLARRAY`, adjacent-cell checks, and building
  entry/exit boundaries.

The GameEntity / thin GameWindow refactor remains a valid target architecture,
but it is not a prerequisite for L.2. Do not resurrect old R1-R8 phase numbers
for new work; add or update roadmap phases instead.

---

## Development Workflow (mandatory for ALL work)

```
For every AC-specific behavior:

0. GREP NAMED   → Search docs/research/named-retail/ by class::method
1. FALLBACK     → Use older docs/research/decompiled/ chunks only if needed
2. CROSS-CHECK  → Verify against ACE + ACME + holtburger where relevant
3. PSEUDOCODE   → Translate to readable pseudocode
4. PORT         → Faithful C# translation
5. TEST         → Conformance test against retail/decomp golden values
6. INTEGRATE    → Surgical wiring into the existing system
7. VERIFY       → Visual + functional test
```

For acdream-specific code (renderer, plugin API, streaming):
- Design for clean interfaces
- Test independently
- No AC-specific magic — those live in the ported layer

---

## Reference Hierarchy

| Domain | Primary Oracle | Secondary |
|--------|---------------|-----------|
| Physics/collision | `docs/research/named-retail/` | ACE Physics/ + older decompiled chunks |
| Animation | `docs/research/named-retail/` + ACE Animation/ | — |
| Terrain | ACME ClientReference.cs | named retail / older decompiled chunks |
| Rendering | WorldBuilder (Silk.NET) | ACViewer |
| Protocol | holtburger | AC2D |
| Server behavior | ACE | — |

---

## Success Criteria

The client is "done" when:
1. You can log in to an ACE server
2. Walk around the entire world (streaming loads new areas)
3. Enter and exit buildings through doorways
4. See all NPCs, monsters, and players animated correctly
5. Open doors, talk to NPCs, pick up items
6. Send and receive chat
7. A Lua macro can automate gameplay
8. Side-by-side with the retail client, the world looks the same