BT412/README.md

BattleTech 4.12 (bt412) — the Steamification

BattleTech is VWE's arcade mech-combat game (Tesla platform, release 4.10, ~1995–96), originally played from inside Virtual World cockpit pods. This repo is the consumer line of that reconstruction:

Generation	What it was
BattleTech 4.10	The original pod game — DOS-era MUNGA engine, serial RIO cockpit I/O, 7-monitor cockpit, operator console
BattleTech 4.11	The Win32 port — the BT game logic reconstructed from BTL4OPT.EXE on the shared RP411 Windows engine; DirectX 9, full single-player combat loop, two-instance LAN multiplayer
BattleTech 4.12	This repo: the Steamification of 4.11 — the same engine, missions, and wire protocol, made distributable on Steam and playable over the internet with no pod hardware

The plan and workstreams live in docs/BT412-ROADMAP.md. The sister project RP412 (Red Planet's steamification, shipped end-to-end: lobby → Steam-sockets mesh → marshaled race → results on every machine) is the proven recipe this repo follows — each pod-era dependency replaced by a consumer equivalent behind the engine's existing seams.

License: the game content (content/) and the original binary are proprietary to Virtual World / the pod owner. This repository is private; do not redistribute.

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Layout

CMakeLists.txt      one build: munga_engine lib + bt410_l4 game lib + btl4.exe
engine/
  MUNGA/            shared 2007 sim/render engine (149 .cpp + headers)
  MUNGA_L4/         Win32/D3D9 HAL + renderer + asset loaders (44 .cpp), incl.
                    our BT work: bgfload / L4D3D / L4VIDEO + the image codec
  shim/             minimal ATL shim (USES_CONVERSION/W2A)
  lib/              OpenAL32 / libsndfile import libs + runtime DLLs
game/
  reconstructed/    the reconstructed BT game logic (mech, subsystems, HUD, app; ~47 .cpp)
  original/BT,BT_L4 surviving original BT source + all BT headers
  fwd/              header shims forwarding <NAME.hpp> -> the engine's NAME.h
  btl4main.cpp      WinMain launcher / entry point
content/            runtime data: BTL4.RES, VIDEO/, GAUGE/, AUDIO/, *.EGG, BTDPL.INI
context/            progressive knowledge graph — 18 on-demand topic files (routed by CLAUDE.md)
docs/               format specs + reconstruction ledgers + PROGRESS_LOG.md (full history)
reference/
  decomp/           raw Ghidra pseudocode — source-of-truth for ongoing recon
  ghidra_scripts/   the headless decomp exporter
  glossary.yaml     term / acronym definitions
phases/             restructuring / investigation logs
tools/              btconsole.py (MP console emulator), map/resource scanners
run/                run.cmd helper
CLAUDE.md           knowledge-base ROUTER — identity, protocols, quick-lookup, conventions

Prerequisites

• Visual Studio 2022 BuildTools (MSVC v143, x86) — the BT412 toolchain of record (moved from the 2019/v142 line at the 4.12 fork; v142 still builds if you swap the generator back). The explicit BuildTools instance in the configure line below matches the dev box; adjust to your install.
• CMake ≥ 3.20.
• Legacy DirectX SDK (June 2010) — the engine uses d3dx9/dinput/dxerr, removed from the modern Windows SDK. Default path C:/Program Files (x86)/Microsoft DirectX SDK (June 2010); override with -DDXSDK=<path>. (The installer may throw a harmless S1023 error — dismiss it; the SDK headers/libs install before the failing redist step.)

OpenAL/libsndfile import libs + DLLs are vendored under engine/lib/; the DLLs are copied next to the exe automatically at build time.

Build (32-bit / Win32)

cmake -S . -B build -G "Visual Studio 17 2022" -A Win32 ^
      -DCMAKE_GENERATOR_INSTANCE="C:/Program Files (x86)/Microsoft Visual Studio/2022/BuildTools"
cmake --build build --config Debug

Must be Win32 — the DirectX SDK link libs are Lib/x86. The link uses /FORCE:MULTIPLE: the 1995 headers define free functions/globals without inline/extern, so identical symbols appear in many translation units (~124 LNK2005); MULTIPLE keeps the first. UNRESOLVED is gone as of 4.12 — the v143 linker refuses to emit an image with unresolved externals even under /FORCE, so the dead offline-tool factory in mech3.cpp is neutralized behind BT412_OFFLINE_TOOLS (default off) and a genuinely unresolved symbol is now a hard link error instead of a hidden runtime AV. (Remaining cleanup task: move the multiply-defined globals to single TUs, then drop /FORCE entirely.)

Run

run\run.cmd            REM boots DEV.EGG (grass / day)
run\run.cmd DBASE.EGG  REM any egg in content/

The working directory must be content/ (the engine resolves BTL4.RES, VIDEO\, BTDPL.INI, and eggs relative to cwd); run.cmd handles that. Maps available in BTL4.RES: cavern grass rav polar3 polar4 arena1 arena2 dbase — switch via a copied egg's map= field.

Useful env-var flags (default OFF unless noted)

The authentic stack (gait, collision, real controls) is default-on; set =0 to fall back. Debug/harness flags: BT_FORCE_THROTTLE=1 (auto-walk), BT_SPAWN_ENEMY=1 (spawn a target dummy), BT_FORCE_FIRE=1 (auto-fire), BT_HEAPCHECK=1 (whole-heap validation — slow), BT_BSL=0 (legacy texture decode), BT_DEV_GAUGES=1 (render the cockpit MFDs in a dev window), BT_LOG=<file>. Interactive: WASD drive, Space/Ctrl fire, X all-stop. The complete env-gate table is in context/decomp-reference.md §6 (routed from CLAUDE.md).

Multiplayer (two instances, one box)

instance A:  btl4.exe -egg MP.EGG -net 1501   (BT_LOG=mp_a.log)
instance B:  btl4.exe -net 1601               (BT_LOG=mp_b.log)
console:     python tools/btconsole.py MP.EGG 127.0.0.1:1501 127.0.0.1:1601

-net <port> enables networked mode; the console emulator delivers the mission egg and the launch command. Entity + movement replication works; cross-pod combat is in progress.

Status & continuing the work

The engine, renderer, audio, HAL, build, locomotion, collision, damage, render fidelity, the full cockpit gauge / MFD system (every config binding resolves + every widget builds), and the projectile / missile weapon families are done. Active fronts: per-subsystem polish (the gyroscope integrator; the 0xBD3 message manager that gates the valve / status-message control routes) and cross-pod MP combat. reference/decomp/ holds the raw pseudocode every reconstruction is verified against.

Start with CLAUDE.md — it is the router into the progressive knowledge base: a quick-lookup table pointing to the context/*.md topic files (loaded on demand), the evidence-tier and convention rules, and context/open-questions.md for what's deferred / next. The complete pre-restructure history is preserved verbatim in docs/PROGRESS_LOG.md; docs/*.md holds the detailed running ledgers.