openDecal/docs/PLAN.md

Plan: Open-Source Decal Rebuild

Context

Decal is a plugin framework for Asheron's Call. The game's official servers shut down, but the community runs it via ACEmulator. The modern Decal installer (v2.9.8.3) is closed-source. We have old C++ source code (partial match) and have decompiled all .NET assemblies. Goal: produce a fully open-source Decal that works with the original AC client, buildable from a single Visual Studio 2022 solution.

Architecture Decision

• Rewrite native C++ DLLs as C# COM servers — same GUIDs, same interfaces, different implementation language
• Keep only 2 components in C++: Inject.DLL (D3D hooking, ~500-800 lines) and LauncherHook.DLL (~200 lines)
• Use Vortice.DirectX for D3D9 rendering in C# (DecalRender, D3DService)
• Preserve plugin compatibility by matching all COM CLSIDs/IIDs exactly

Project Structure

reconstructed/
├── Managed/                          # 25 C# projects
│   ├── Decal.sln                     # Solution file (25 projects, 0 errors)
│   ├── Directory.Build.props         # Shared: net472, x86, LangVersion 12
│   ├── Decal.Interop.*/              # 11 COM interface assemblies (decompiled)
│   ├── Decal.Adapter/                # Plugin adapter (decompiled)
│   ├── Decal.FileService/            # File service (decompiled)
│   ├── DecalUtil/                    # Utility exe (decompiled)
│   ├── Decal.DecalDat/               # DAT file I/O (COM server)
│   ├── Decal.DHS/                    # Hotkey system (COM server)
│   ├── Decal.SpellFilter/            # Spell data (COM server)
│   ├── Decal.DecalInput/             # Input handling (COM server)
│   ├── Decal.DecalNet/               # Network packets (COM server)
│   ├── Decal.DecalFilters/           # Game data/world objects (COM server)
│   ├── Decal.Core/                   # Plugin manager/lifecycle (COM server)
│   ├── Decal.DecalControls/          # UI widgets (COM server)
│   ├── Decal.DecalRender/            # HUD rendering (COM server)
│   ├── Decal.D3DService/             # 3D markers (COM server)
│   └── Decal.DenAgent/               # System tray app (WinForms)
├── Native/
│   ├── InjectModern/                 # Inject.DLL - D3D9 vtable hooking (C++)
│   ├── LauncherHookModern/           # LauncherHook.DLL - process injection (C++)
│   ├── CMakeLists.txt                # Top-level CMake for native builds
│   ├── Inject/                       # Old C++ source (reference only)
│   ├── LobbyHook/                    # Old C++ source (reference only)
│   ├── Decal/                        # Old C++ source (reference only)
│   └── ...                           # Other old native source (reference)
├── Installer/
│   ├── Package.wxs                   # WiX v5 MSI package definition
│   └── Decal.Installer.wixproj      # WiX project file
├── build.cmd                         # Top-level build script
└── docs/
    └── PLAN.md                       # This file

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Status: Phases 1-5 Complete (Skeleton)

All 5 phases are structurally complete. The solution compiles with 0 errors. Most COM server methods are stubs — they implement the correct interfaces and preserve GUIDs, but many methods are no-ops that need real logic.

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Phase 1: Build Existing .NET Layer ✅ COMPLETE

• 14 decompiled .NET projects building from Decal.sln
• Directory.Build.props centralizes build settings
• All Interop projects use ProjectReference

Phase 2: Rewrite Native DLLs as C# COM Servers ✅ COMPLETE (stubs)

#	Component	CLSID	Status
1	DecalDat	IDatService, IDatReader	Stub
2	DHS	IHotkeySystem, IHotkey	Stub
3	SpellFilter	ISpells, ISpell	Stub
4	DecalInput	IInputService, IKeyboard, IMouse	Stub
5	DecalNet	INetService, IMessage2, INetworkFilter2	Stub
6	DecalFilters	IWorld, IWorldObject, ICharacterStats	Stub
7	Decal.Core	IDecalCore, IPluginSite2, IACHooks, IDecalEnum	Stub
8	DecalControls	16 control types	Stub
9	DecalRender	IRenderService, IHUDView, IHUDBackground	Stub
10	D3DService	ID3DService, ID3DObj	Stub

All preserve original CLSIDs/GUIDs for plugin compatibility.

Phase 3: C++ Shims ✅ COMPLETE

• Native/InjectModern/ — Inject.DLL (~530 lines) — D3D9 vtable hooking, lifecycle
• Native/LauncherHookModern/ — LauncherHook.DLL (~330 lines) — CreateProcess IAT hook
• CMake build: cmake -G "Visual Studio 17 2022" -A Win32

Phase 4: DenAgent ✅ COMPLETE

• Managed/Decal.DenAgent/ — System tray, plugin management, options dialog

Phase 5: Build System & Installer ✅ COMPLETE

• Installer/Package.wxs — WiX v5 MSI
• build.cmd — Top-level build script

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Phase 6: Verification & Implementation (NEXT)

Goal: Pixel-perfect drop-in replacement for the closed-source Decal v2.9.8.3.

Strategy: Bottom-up, one DLL at a time. Replace one original DLL with our C# version while keeping all other original DLLs in place. Test. Move to the next.

Step 1: Build on Windows

# C++ native projects (requires VS 2022 + Windows SDK)
cd Native
cmake -G "Visual Studio 17 2022" -A Win32 -B build
cmake --build build --config Release

# Managed solution
dotnet build Managed\Decal.sln -c Release

Step 2: COM Registration Test

Register all C# COM servers and verify GUIDs match originals:

regasm /codebase Managed\bin\Release\Decal.Core.dll
regasm /codebase Managed\bin\Release\Decal.DecalDat.dll
... (all 10 COM server DLLs)

Then verify in registry: HKCR\CLSID\{GUID}\InprocServer32 points to our DLLs.

Step 3: Smoke Test — DenAgent

Run Decal.DenAgent.exe and verify:

• Tray icon appears
• Configure dialog opens
• Plugin list populates from registry

Step 4: Integration Test (one DLL at a time)

Install original Decal v2.9.8.3, then swap one DLL at a time:

1. Replace DecalDat.DLL → test DAT file reading
2. Replace DHS.dll → test hotkeys
3. Replace SpellFilter.dll → test spell data
4. Continue through all 10... Each swap that fails tells us exactly which stubs need real implementations.

Step 5: Plugin Compatibility Test

Load community Decal plugins and verify they work:

• VTank
• Mag-Tools
• Other popular plugins

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Known Pitfalls

• record types need IsExternalInit, unavailable in net472 → use class instead
• CollectionsMarshal.AsSpan unavailable in net472
• LongValueKey enum: correct names are keyStackCount, keyContainer
• tagPOINT defined in Interop.Inject, needed by Interop.Render → add ProjectReference
• ICommandEvents delegates ambiguous between Interop.Controls and Interop.Inject → use using aliases

Build Requirements

• .NET SDK 8.0+ (targets net472 via NuGet reference assemblies)
• Visual Studio 2022 with C++ Desktop workload (for native DLLs)
• Windows SDK (for d3d9.h, Win32 APIs)
• WiX Toolset v5 (optional, for MSI installer)