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CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

What This Is

FRIK (Fallout 4 VR Body) is a Fallout 4 VR mod that adds full-body IK, weapon repositioning, an in-VR Pipboy, and hand-pose / finger control. It builds as an F4SE plugin DLL (FRIK.dll).

The project is built on top of F4VR-CommonFramework, which is included as a git submodule and provides the plugin lifecycle (ModBase), config base (ConfigBase), VR controller framework (vrcf), VR UI widgets (vrui), and game/skeleton helpers (f4vr, f4sevr). Reading the framework's CLAUDE.md is the fastest way to understand the namespaces (f4cf::, f4cf::f4vr, f4cf::vrcf, f4cf::vrui, f4cf::common) and the ModBase lifecycle hooks.

Build

Prerequisites:

  • VCPKG_ROOT environment variable must point to a vcpkg installation
  • Visual Studio 2022 (v143) or 2026 (v145), x64
  • CMake 4.2+
  • Init submodules: git submodule update --init --recursive

Generate solution:

cmake --preset default        # uses vs2026 by default

For local development, copy CMakeUserPresets.json.template → CMakeUserPresets.json and set:

  • POST_BUILD_COPY_PLUGIN: true and COPY_PLUGIN_BASE_PATH to your MO2 mod folder(s) (semicolon-separated for multiple) — this auto-copies FRIK.dll + .pdb to <path>/F4SE/Plugins/ after every build.
  • F4VR_COMMON_FRAMEWORK_PATH to point to a sibling checkout of F4VR-CommonFramework if you want to develop against it instead of the submodule.

Build (and ALWAYS check the output before reporting done):

cmake --build build 2>&1 | tee build_output.txt

Then read build_output.txt. Release builds also produce a versioned .7z package in build/package/.

Architecture

Entry point and global

src/FRIK.cpp defines F4SEPlugin_Query/F4SEPlugin_Load, which delegate to f4cf::g_mod. The mod itself is the frik::FRIK class in src/FRIK.h, instantiated as the global singleton frik::g_frik. It extends f4cf::ModBase and overrides:

  • onModLoaded — installs game hooks via frik::hook::patchAll() / hookMain() (src/GameHooks.h)
  • onGameLoaded — registers Papyrus natives, detects Fallout London VR / BetterScopesVR, adds embedded flashlight keyword
  • onGameSessionLoaded — fires on new game and every save load; releases skeleton and reconfigures game INI vars
  • onFrameUpdate — drives the per-frame update of every subsystem

FRIK owns the lifetimes of Skeleton, Pipboy, ConfigurationMode, and WeaponPositionAdjuster. They are created lazily in initSkeleton() once the game's player + camera + bone-tree nodes are all available (isGameReadyForSkeletonInitialization), and destroyed/recreated on power-armor change, root-node release, or loading-screen transitions (releaseSkeleton).

Frame update flow (every frame)

FRIK::onFrameUpdate() runs in this order — order matters because later subsystems read state set by earlier ones:

  1. Validate root node and power-armor state (rebuild skeleton if either changed)
  2. Skeleton::onFrameUpdate — IK, body posture, walking, hand pose (src/skeleton/Skeleton.cpp)
  3. BoneSpheresHandler::onFrameUpdate — interaction-sphere collision/events
  4. PlayerControlsHandler::onFrameUpdate — enable/disable player movement based on UI state
  5. WeaponPositionAdjuster::onFrameUpdate — weapon offsets, offhand grip, reposition mode
  6. Pipboy::onFrameUpdate — wrist Pipboy logic, finger interaction, flashlight
  7. vrui::g_uiManager->onFrameUpdate — VR UI widgets (driven by FrameUpdateContext adapter that exposes the offhand index-finger tip and hand-pointing pose)
  8. MainConfigMode + ConfigurationMode — config UI rendering
  9. updateWorldFinal — three engine-level scene-graph updates (BSFadeNode_MergeWorldBounds, BSFlattenedBoneTree_UpdateBoneArray, BSFadeNode_UpdateGeomArray) needed for cull geometry, finger position, and Pipboy interaction to work correctly

FRIK::smoothMovement is invoked from a separate hook (not from onFrameUpdate).

Subsystem map

Subsystem Location Responsibility
Skeleton/IK src/skeleton/ Body IK, leg walking, head/neck posture, arm solver, fingers via HandPose
Hand pose src/skeleton/HandPose.cpp, HandPoseData.cpp Tagged hand-pose override stack with priority; supports Dynamic, Override, and PrimaryWeaponPose sources
Pipboy src/pipboy/ Wrist & holo Pipboy, physical (finger-touch) interaction, flashlight
Weapon positioning src/weapon-position/ Per-weapon offsets, offhand-grip two-handed mode, in-game reposition tool
Smooth movement src/smooth-movement/ Reduce VR motion sickness on locomotion
Config UI src/config-mode/ In-VR config menus (MainConfigMode, ConfigurationMode, BodyAdjustmentSubConfigMode)
Reload src/reload/ Two-handed gun reload interaction
Public API src/api/FRIKApi.h C ABI exposed to other mods (loaded via GetProcAddress on FRIKAPI_GetApi)
Papyrus API src/PapyrusApi.h Native functions for in-game scripts

Config

src/Config.h / src/Config.cpp extends f4cf::ConfigBase. Files live under %USERPROFILE%\Documents\My Games\Fallout4VR\FRIK_Config\:

  • FRIK.ini — main settings (also embedded as RCDATA IDR_FRIK_INI, extracted on first run)
  • FRIK_FOLVR.ini — Fallout London VR overrides, merged on top when that mod is detected
  • Mesh_Hide/face.ini, skins.ini, slots.ini — geometry hide lists
  • Pipboy_Offsets/*.json — per-Pipboy-style world offsets
  • Weapons_Offsets/*.json — per-weapon offsets, by mode (WeaponOffsetsMode: Weapon / PrimaryHand / OffHand / Throwable / BackOfHandUI) with _PA and _left suffix variants

g_config.fEqual() and friends — see "Conventions" below for float comparisons. The base class auto-reloads on file change via the file watcher.

Public C API for other mods

frik::api::FRIKApi (src/api/FRIKApi.h) is a struct of C function pointers exposed via the exported FRIKAPI_GetApi (src/exports.def). Other mods copy the header into their project, call FRIKApi::initialize(), and use inst->setHandPose(...), inst->getIndexFingerTipPosition(...), inst->blockOffHandWeaponGripping(...), etc. Bump FRIK_API_VERSION whenever you change the struct layout — clients version-check against it. Hand poses use a string tag so multiple systems can layer overrides without clobbering each other.

For mods that want a button in FRIK's main config menu: they call registerOpenModSettingButtonToMainConfig; FRIK dispatches an F4SE message back to them when the button is clicked. Sender name is F4VRBody (also exposed as BETTER_SCOPES_VR_MOD_NAME/FRIK_F4SE_MOD_NAME).

External mod integrations

  • BetterScopesVR — registers as a message listener at startup; messages of type 15 update _isLookingThroughScope, which gates dampening behavior.
  • Fallout London VR — detected via isFalloutLondonVRModLoaded(); loads FRIK_FOLVR.ini overrides and switches Pipboy to "Attaboy" mode. Can be force-disabled with ignoreFalloutLondonVR.
  • Immersive Flashlight VR — if loaded, FRIK skips its embedded flashlight to avoid conflict.

Conventions

  • Build verification: Always build via cmake --build build 2>&1 | tee build_output.txt and read build_output.txt before reporting a change as done. Don't skip this step.
  • Float comparisons: Use common::fEqual() (from F4VR-CommonFramework's common/CommonUtils.h) instead of == / != 0.0f against floats.
  • Code style: clang-format enforced (LLVM-based, 180-col, 4-space indent, CRLF, pointer-left, namespace indentation). C++23, MSVC /W4 /WX (linker), _UNICODE, /permissive-, all common /Zc: conformance flags.
  • PCH: src/PCH.h is precompiled — F4SE/F4SE.h, RE/Fallout.h, REL/Relocation.h, Logger.h, Version.h, and using namespace f4cf are implicit in every TU.
  • Logging: Use logger::trace/debug/info/warn/error (spdlog wrappers). logger::sample(ms, ...) rate-limits noisy logs to once per ms.
  • No in-source builds: CMake hard-fails if you try.