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 decompiled retail client (docs/research/decompiled/, 688K lines). 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.

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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. See memory/project_ui_architecture.md for the session crib-sheet version.

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Project Structure (target)

src/
  AcDream.Core/              Layer 2-4: no GL, no Silk.NET, pure logic
    Physics/
      PhysicsBody.cs          ← ported from decompiled (done)
      CollisionPrimitives.cs  ← ported from decompiled (done)
      MotionInterpreter.cs    ← ported from decompiled (done)
      AnimationSequencer.cs   ← ported from decompiled (done)
      CellBsp.cs              ← TODO: port from decompiled
      Transition.cs           ← TODO: port from decompiled
      TerrainSurface.cs       ← verified against ACME (done)
    World/
      GameEntity.cs           ← TODO: unified entity (replaces scattered state)
      WorldState.cs           ← TODO: owns all entities
      CellTracker.cs          ← TODO: 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 (move here 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           ← TODO: thin down to GL calls only
      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  ← done (uses ported physics)
    Plugins/
      AppPluginHost.cs        ← done

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GameEntity: The Unified Entity (TODO — the big 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:

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
        // TODO: Transition.FindValidPosition  // collision resolve
        Cell.UpdateCell(Physics.Position); // check cell transitions
        Animation.Advance(dt);            // advance animation frames
        RebuildMeshRefs();                // compute per-part transforms
    }
}

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

---

Per-Frame Update Order (matches retail)

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)
   └── Read WASD/mouse → MotionInterpreter.DoMotion →
       send MoveToState/AutonomousPosition to server

4. Entity tick (ALL entities, 30Hz fixed step)
   └── For each GameEntity: entity.Update(dt)
       This runs: motion → physics → collision → cell → animation

5. Render tick
   └── For each GameEntity: read MeshRefs, 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.

---

Execution Plan: How to Get There

Phase R1: GameEntity Refactor (the foundation)

Goal: Replace the scattered entity state with unified GameEntity.

1. Create GameEntity class in AcDream.Core/World/
2. Move AnimatedEntity fields into GameEntity.Animation
3. Move WorldEntity fields into GameEntity.Physics + position
4. Move _entitiesByServerGuid into WorldState
5. Move animation tick from GameWindow.TickAnimations into GameEntity.Update
6. GameWindow.OnRender reads GameEntity.MeshRefs instead of WorldEntity.MeshRefs

Test: Everything looks the same as before. No visual change.

Phase R2: Thin GameWindow

Goal: GameWindow does only GL calls + input dispatch.

1. Extract entity creation from OnLiveEntitySpawned into WorldState.SpawnEntity
2. Extract motion updates from OnLiveMotionUpdated into WorldState.UpdateMotion
3. Extract player movement from the giant OnUpdate block into PlayerController
4. GameWindow.OnUpdate calls: network.Tick → streaming.Tick → input.Tick → worldState.Tick → render

Test: Everything works the same. GameWindow.cs drops from 2000+ to ~500 lines.

Phase R3: CellBSP + Wall Collision

Goal: Entities can't walk through walls.

1. Port CellBSP from decompiled code (sphere_intersects_cell)
2. Port Transition.FindValidPosition (swept sphere collision)
3. Wire into GameEntity.Update between physics and cell tracking
4. Indoor transitions become correct (wall stops you, doorway lets you through)

Test: Walk into building wall → stopped. Walk through doorway → enter.

Phase R4: Complete Animation State Machine

Goal: Every animation works for every entity type.

1. Port full MotionInterp.PerformMovement from decompiled (all 5 movement types)
2. Port Links table resolution for smooth transitions
3. Port idle modifiers (fidgets)
4. Jump animation (wire jump motion command through the pipeline)

Test: All entity types animate correctly. Transitions are smooth.

Phase R5: Lighting from Retail

Goal: Sun, ambient, per-vertex lighting match retail.

1. Port AdjustPlanes (FUN_00532440) — face normals + per-vertex lighting
2. Extract global lighting constants from decompiled DAT addresses
3. Replace hardcoded shader constants with ported values

Test: Side-by-side with retail client shows matching lighting.

Phase R6: Server Compliance

Goal: ACE accepts all movement, no rubber-banding.

1. Server-authoritative Z (trust server position, local is cosmetic)
2. Proper MoveToState with full RawMotionState packing
3. Keepalive ping (5s idle)
4. Graceful session management

Test: Walk around, other clients see smooth movement. No ACE errors.

Phase R7: Interaction

Goal: Click NPCs, open doors, pick up items, chat.

1. Use/UseWithTarget game actions
2. Door open animation (server sends UpdateMotion → animate)
3. Chat send/receive
4. Basic inventory (pickup/drop)

Test: Open a door, talk to an NPC, send a chat message.

Phase R8: Plugin API Completion

Goal: Plugins can observe and control everything.

1. IGameState exposes all GameEntity fields
2. IEvents fires for all world changes
3. IActions covers: Move, Cast, Use, Say, Pickup, Drop
4. IPacketPipeline hooks all 4 stages
5. Lua macro engine (MoonSharp) ships as a built-in plugin

Test: A Lua script auto-loots gems. A C# plugin displays an overlay.

---

Development Workflow (mandatory for ALL work)

For every AC-specific behavior:

1. DECOMPILE    → Find the function in docs/research/decompiled/
2. CROSS-CHECK  → Verify against ACE + ACME + holtburger
3. PSEUDOCODE   → Translate to readable pseudocode
4. PORT         → Faithful C# translation
5. TEST         → Conformance test against decompiled 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

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Reference Hierarchy

Domain	Primary Oracle	Secondary
Physics/collision	Decompiled acclient.exe	ACE Physics/
Animation	Decompiled + ACE Animation/	—
Terrain	ACME ClientReference.cs	Decompiled
Rendering	WorldBuilder (Silk.NET)	ACViewer
Protocol	holtburger	AC2D
Server behavior	ACE	—

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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