# Gauge / MFD render pipeline — map + dev-composite plan

**Status:** pipeline MAPPED (workflow `gauge-pipeline-map`, 2026-07); the dev composite is **planned, not
yet built**. This is the execute-ready plan for making the pod's gauges/MFDs render + be VISUALLY testable
on a dev box — the "MFD compositing on dev" follow-up the platform profile gates (see §8 / the PLATFORM
PROFILE entry in CLAUDE.md). Companion: the platform-profile scaffold (`-platform pod|dev`).

## The draw model — CONFIRMED (the good news)

**CPU-raster → texture-upload, DEVICE-INDEPENDENT.** Every gauge widget (the radar included) is a *software
rasterizer* that writes 16-bit R5G6B5 pixels into ONE shared CPU buffer (`Video16BitBuffered::pixelBuffer`,
a `PixelMap16`, `L4VB16.h:140`). Logical surfaces are packed by **BIT-PLANE** into that one 640×480×16 buffer
(each MFD = one bit mask; the radar/secondary = the low byte, palette-indexed). D3D is touched **ONLY** in
`SVGA16::Update` (`L4VB16.cpp:4041`): LockRect a `D3DPOOL_SYSTEMMEM` staging texture → a CPU expand loop
(palette-LUT for the radar, case 0; bit-plane→RGB-channel demux for the MFDs, case 1/2) → UnlockRect →
`UpdateTexture` staging→`D3DPOOL_DEFAULT` → ONE fullscreen textured quad (`TRIANGLEFAN`) → `Present`, **per
surface on its own per-adapter device**. So redirecting the content to a texture on the MAIN device is a
small change: the entire raster stays byte-identical; only the upload target + the final blit move.

## The 3 gotchas (why it's a multi-step build, not a one-liner)

1. **DORMANT in BT.** `BTL4GaugeRenderer` passes `L4GaugeRenderer(false, NULL,NULL,NULL)` (`btl4grnd.cpp:151`)
   → `NUMGAUGEWINDOWS=0`; and `MakeGaugeRenderer` only builds anything if `getenv("L4GAUGE")` (`btl4app.cpp:353`).
   Both must change to wake it. With 0 surfaces, `SVGA16::Update` may index an empty `mSurfaces[]` → guard needed.
2. **RP↔BT PORT-NAME MISMATCH.** `SVGA16::Update` hardcodes the Red-Planet MFD port names
   `auxUL2/auxC/auxUR2/auxLL/auxLR` (`L4VB16.cpp:4056-4061`), but BT's `content/GAUGE/L4GAUGE.CFG` names them
   `Heat/Comm/Mfd1/Mfd2/Mfd3` (:4395-4410). `GetGraphicsPort` returns NULL for the RP names → the MFD branch
   early-outs ("No MFDs to draw"). **ONLY the `sec`/radar surface matches today** — the 5 MFDs render nothing
   until the names are reconciled.
3. **CROSS-DEVICE + STATE.** Folding onto the main device means the gauge blit shares the main render state
   (save/restore around it) + an ORDERING concern: is `l4_application->GetVideoRenderer()->GetDevice()` valid
   when the gauge renderer builds during `Application::Initialize`? Verify build order or defer texture creation.

## Architecture options (dev)

- **(A) `SVGA16` dev-composite branch.** In `SVGA16::BuildWindows`/`Update`, when a dev-composite flag is set,
  use the MAIN device for the staging/default textures, skip the per-adapter device/window/`Present`; the main
  renderer composites the DEFAULT textures as insets. Reuses the expand loops verbatim; **branches the pod
  code** (guard on the flag → inert on pod).
- **(B) Bypass `SVGA16`.** Leave the `SVGA16` pod path untouched; add a composite pass in the main renderer
  that reads the shared `pixelBuffer` + palette directly and runs the expand + inset blit itself. **Best
  protects the pod path**; re-implements the expand + needs `pixelBuffer`/palette accessors on
  `Video16BitBuffered`/`SVGA16`.
- **RECOMMEND (B)** for the beachhead (pod path untouched); fall back to (A) if reusing the expand loops
  wholesale is preferred. Decide this with the operator before building — it's the main design fork.

## Beachhead (Step 1) — one surface visible on dev

Goal: the **secondary/radar** surface composited as an **INSET** in the existing 800×600 window (no 2nd
window yet). It's the one surface that works WITHOUT the port-name fix, so it proves the whole chain end-to-end.
1. **Wake** it via a dev-composite opt-in (e.g. `BT_DEV_GAUGES` env, default OFF so DEV/pod defaults are
   unaffected; or gate on `-platform pod` on a dev box). When on: set `L4GAUGE` (so `MakeGaugeRenderer` builds)
   + set the composite flag. Guard `SVGA16::Update` for 0 surfaces (no crash).
2. **Raster**: the widgets already raster into `pixelBuffer` (driven by `GaugeRenderer::ProcessOneActiveGauge`).
3. **Composite**: each frame, in the main renderer's present, upload the secondary-expanded pixels to a
   main-device texture + draw an inset quad (`XYZRHW|TEX1`), main render state saved/restored. Reach the buffer
   via `GetGaugeRenderer()`.
- **Verify**: the radar/secondary inset appears; DEV default (no `BT_DEV_GAUGES`) un-regressed; pod path
  untouched; 0 crashes / 0 heap.

## Follow-ups (after the beachhead)

- **Step 2** — reconcile the MFD port names (rename in `L4GAUGE.CFG` or in `SVGA16::Update`) → the 5 MFDs render.
- **Step 3** — the 2-window layout (3D-view window + an instrument-panel window tiling radar + the 5 MFDs).
- Confirm the MFD widget CONTENT is actually fed each frame (entity→gauge routing
  `BTL4GaugeRenderer::NotifyOfNewInterestingEntity` → the `L4Warehouse` gauge-image bin).

## Key files / hooks

- `engine/MUNGA_L4/L4VB16.cpp`: `SVGA16::Update:4041` (the CPU→texture→blit crux; expand loops :4124-4191),
  `SVGA16::BuildWindows:101` (per-surface device/window/texture — the pod path), `Video16BitBuffered::Draw*`
  (:761/847/1607/1839, the software raster into `pixelBuffer`), `pixelBuffer` `L4VB16.h:140`, RP port names :4056-4061.
- `engine/MUNGA_L4/L4GREND.cpp`: `L4GaugeRenderer` ctor:57 (builds `SVGA16` from `L4GAUGE.INI`),
  `ExecuteBackgroundDisplayUpdate:369` (calls `graphicsDisplay->Update`), `BuildGraphicsPort:485` (every port
  shares ONE `pixelBuffer`, bit-plane per port).
- `engine/MUNGA/GAUGREND.cpp`: `ExecuteForeground:3556` / `ProcessOneActiveGauge:3836` (draw-all-gauges into `pixelBuffer`).
- `game/reconstructed/btl4grnd.cpp`: ctor:151 (the un-dormant point — NULL indices),
  `NotifyOfNewInterestingEntity:250` (routes `GaugeImageStream` type-0x12 entities to moving/static bins).
- `game/reconstructed/btl4rdr.cpp`: `MapDisplay` (the radar; draws into the secondary surface).
- Main device: `l4_application->GetVideoRenderer()->GetDevice()` (`L4VIDEO.h:376`).
- Config: `content/GAUGE/L4GAUGE.CFG` (port→bitmask map, MechInit :4395-4410), `L4GAUGE.INI` (640×480×16 page).

## Surface → content map (for the 2-window layout)

- **Surface 0 = SECONDARY / radar** (640×480, palette-indexed low byte `sec` 0x003F + `overlay` 0x00C0):
  the radar `MapDisplay` + secondary instruments (message board / heading / speed arc / armor-critical-heat maps).
- **Surface 1(+2) = the 5 MFDs** (bit-planes 0x0100–0x8000 of the shared buffer, demuxed to R/G/B channels;
  pod spans them as one 1280×480): `Mfd1`=LL, `Mfd2`=UC, `Mfd3`=LR, `Heat`=UL, `Comm`=UR (+ `Eng1-3`).
- `Plasma` (CFG port 10, `L4PLASMA=com2`) is an EXTERNAL serial annunciator — not a D3D surface.

## Progress log

**Milestone A DONE (2026-07) — the gauge renderer is woken + boots STABLY on a dev box** (opt-in
`BT_DEV_GAUGES`, default OFF; default DEV + pod paths verified un-regressed — DEV combat DESTROYED,
0 crashes). Option **B** chosen. `BT_DEV_GAUGES` sets `L4GAUGE` (so `MakeGaugeRenderer` builds the
renderer) and `SVGA16` does NO per-surface D3D (a file-static `DevGaugeComposite()` gate forces the
no-surface path in `BuildWindows` + short-circuits `Update`/`Refresh`). ⚠ Reality-check: `FindBestAdapterIndices`
hands the gauge renderer **3 non-null indices even on a dev box** (all the primary adapter), so the earlier
"passes NULL → 0 surfaces" assumption was wrong — the gate is keyed on `BT_DEV_GAUGES`, not the count.

Waking the (never-exercised) gauge subsystem exposed a **cascade of 4 dormant-path bugs**, each guarded:
1. `SVGA16::Update` (L4VB16.cpp) — indexed empty `mSurfaces[]`; guarded `DevGaugeComposite()||NUM<=0`.
2. `SVGA16::Refresh` — same; guarded.
3. `LBE4ControlsManager::MakeLinkedLamp` (L4CTRL.cpp:2057) — `GetGaugeRenderer()->GetLampManager()`
   returns NULL (recon gap in `BTL4GaugeRenderer`); guarded (skip the linked lamp when null).
4. `L4GaugeRenderer::NotifyOfNewInterestingEntity` (L4GREND.cpp:440) — `warehousePointer->gaugeImageBin`
   has a garbage internal chain (recon shadow of the warehouse); guarded (skip the per-mech gauge-IMAGE
   cache under `BT_DEV_GAUGES`).

⚠ **KEY FINDING: the gauge subsystem's RECONSTRUCTION IS INCOMPLETE.** It was dormant/never-exercised, so
these latent recon bugs (lamp-manager offset, warehouse init) only surfaced on waking it. It now BOOTS
stably, but whether the widgets raster MEANINGFUL content into `pixelBuffer` is UNVERIFIED until the
composite (Milestone B) draws it. The per-mech gauge IMAGES (armor diagrams via the warehouse) are
currently skipped; the radar/secondary map + instruments read the mech directly and *may* render partially.
So the beachhead's real question shifted from "composite a working buffer" to "how complete is the gauge
recon." FAITHFUL FOLLOW-UPS: fix the `BTL4GaugeRenderer` lamp-manager + warehouse reconstruction (shadowed
members) so per-mech gauges + lamps work (needed for real MFD content anyway).

**Milestone B DONE (2026-07) — THE SECONDARY/RADAR SURFACE COMPOSITES LIVE ON A DEV BOX** (opt-in
`BT_DEV_GAUGES`; default DEV + pod paths verified un-regressed). The inset in the bottom-left of the 800×600
window renders the authentic BT cockpit secondary MFD: the **radar/tactical grid** (SCALE/SECTOR + crosshair),
the **SPEED / HEADING / MAGNETIC / PROP dials**, and the color-coded **ARMOR DAMAGE mech schematic**
(green intact / red damaged) — real content (`nzSec=27247` non-zero secondary-plane pixels), not garbage.
The composite chain: `SVGA16::DrawDevInset(device, secMask, paletteID)` (L4VB16.cpp) lazily creates a MANAGED
R5G6B5 640×480 texture on the MAIN device, palette-expands the secondary plane into it (mirrors
`SVGA16::Update` case 0), and draws an `XYZRHW|TEX1` inset quad; the free entry `BTDrawGaugeInset(mDevice)`
reaches `application->GetGaugeRenderer()->GetGraphicsPort("sec")->graphicsDisplay` and is called from
`DPLRenderer::ExecuteImplementation` as the LAST draw before `EndScene` (no state save/restore needed).

**THREE reconstruction bugs had to be fixed to get from "woken but empty" to "real content" (each a genuine
faithful fix or a clearly-gated dev accommodation):**
1. **⭐ `MakeGaugeRenderer` OVERRIDE SIGNATURE MISMATCH (real bug — FIXED).** The reconstructed
   `BTL4Application::MakeGaugeRenderer()` took NO args, but the 2007 WinTesla engine had WIDENED the base
   virtual to `MakeGaugeRenderer(int* secondaryIndex, int* aux1, int* aux2)` (called from `Application::
   Initialize`, APP.cpp:382).  A no-arg method only HIDES the virtual — it never overrides it — so the engine
   ran `L4Application::MakeGaugeRenderer` instead and built a **base `L4GaugeRenderer`** whose ctor never
   calls `BuildConfigurationFile` → `gauge\l4gauge.cfg` was NEVER PARSED → empty symbol table → the observed
   `GaugeInterpreter: undefined label 'bhk1Init'` → no ports, no gauges.  FIX: match the 3-arg signature so
   it truly overrides (args ignored — BT is fullscreen/no-aux, the `BTL4GaugeRenderer` ctor hardcodes
   `false,NULL,NULL,NULL`).  Same class of bug as the `BTL4GaugeRenderer(false,NULL,NULL,NULL)` ctor fix:
   reconstruction written against the ORIGINAL signature, compiled against the WIDER 2007 engine virtual.
   (btl4app.cpp / btl4app.hpp.)  **Label facts:** the label = `mission->GetGameModel()` + `"Init"` = `bhk1Init`
   (lowercase, no capitalization — the binary `FUN_0046ff64` does a plain copy + `Str_Cat`); the CFG defines
   `Bhk1Init` but the symbol-table lookup is `stricmp` (case-insensitive), so the case doesn't matter — the
   only reason it was "undefined" was the empty table.  `MechInit` (CFG:4390) is the shared macro every
   `<Mech>Init` calls that builds the `sec`/overlay/Mfd*/Heat/Comm PORTS via the base `configure` primitive.
2. **Gauge-config parse HUNG on undefined primitives (dev accommodation, gated).** The BT-specific gauge
   primitive table `BTL4MethodDescription` (btl4grnd.cpp) is still a STUB (only the chain-to-base link; the
   BT gauge widget classes like `PlayerStatus` aren't reconstructed), so `GaugeInterpreter::GetProcedureBody`
   hits an unknown primitive → `ReportParsingError` → `Fail()` → a MODAL assert dialog that FREEZES the game
   mid-parse (cdb confirmed: `MessageBoxW` ← `abort` ← `ReportParsingError` ← `GetProcedureBody`).  FIX
   (GAUGREND.cpp, gated `BT_DEV_GAUGES`): when a primitive doesn't resolve, SKIP its parameter list (paren
   depth walk + `UngetPreviousToken`) and continue — the parse then registers ALL labels (`Bhk1Init`→
   `MechInit`) and runs the base `configure` primitives that build the PORTS.  The base `configure`
   (`MakeConfigMethodDescription`) IS in `L4MethodDescription`, so the `sec`/radar SURFACE builds even though
   the BT widgets are skipped.  Pod keeps the strict `Fail` (it needs a complete real table).
3. **Gauge widgets AV on NULL data bindings (dev accommodation, gated).** Two flavors: (a) value-bound gauges
   (`NumericDisplayScalar`) get `value_pointer = parameterList[8].data.attributePointer` = NULL (the mech data
   binding isn't reconstructed; the source even comments "(Scalar *) is VERY dangerous!") → the
   `GaugeConnectionDirectOf<float>` ctor derefs NULL (gauge.h:198).  FIX: the ctor binds a NULL source to a
   static zero (gated).  (b) game-state gauges (`RankAndScore::Execute`) directly deref unreconstructed
   mission/player data.  FIX: `Gauge::Update` runs `Execute()` under a SEH wrapper `Gauge::GuardedExecute()`
   (a separate fn — `__try/__except` can't share a frame with the `ChainIteratorOf` unwinding local); a gauge
   that faults once is `Disable(True)`d (rate=0) so it never retries.  Both gated `BT_DEV_GAUGES`.

**⚠ KEY TAKEAWAY:** the gauge subsystem is now PROVEN end-to-end on dev (renderer→parse→port config→raster→
palette-expand→composite), and the gauges whose data binds correctly (radar/armor/dials) show REAL content.
The remaining work is the **BT gauge WIDGET reconstruction** — the `BTL4MethodDescription` method table (the
BT gauge classes: `PlayerStatus` + the ~16 recovered `methodDescription` entries) AND the gauge→game-state
DATA BINDINGS (why `RankAndScore` / some `NumericDisplayScalar` resolve NULL).  Those are what the dev
accommodations (skip/guard) stand in for.  Files touched: `L4VB16.{h,cpp}` (DrawDevInset/BTDrawGaugeInset),
`L4VIDEO.cpp` (the EndScene hook), `btl4app.{cpp,hpp}` (the override fix), `GAUGREND.cpp` (tolerant skip),
`gauge.h` + `GAUGE.{h,cpp}` (NULL-source + SEH guards).

## Milestone C DONE (2026-07) — ALL SIX instrument surfaces in a SEPARATE dev window

The beachhead's single-`sec`-inset is now a full **6-surface compositor in its own top-level window** (the
default under `BT_DEV_GAUGES`; `BT_DEV_GAUGES_DOCK=1` docks the panel into the main window instead). The
960×384 gauge window tiles all six pod instrument screens with authentic content: **Heat** (COOLANT/BALANCE/
RES + condenser & temp-leak gauges), **Comm** (KILLS/DEATHS/SELECT TARGET scoreboard), **Mfd1/Mfd2/Mfd3**
(DISPLAY/PROGRAM/NEAREST/TEMP-STATUS frames), and the color **radar** (SCALE grid + speed/heading dials +
ARMOR DAMAGE schematic). Verified live: gauge window renders all 6; main 800×600 3D view is un-occluded;
default DEV (no gauges) un-regressed (TARGET DESTROYED after 8 hits, 0 crashes).

**Architecture (mapped by the `mfd-multisurface-map` workflow, then implemented):**
- **One buffer, six bit-plane views.** All gauge ports share ONE `SVGA16`/`pixelBuffer`; a "surface" is a
  MASK over that one 640×480×16 buffer. The compositor reaches the `SVGA16` once (via any port) and extracts
  each surface by its own plane mask. BT plane map (`L4GAUGE.CFG` MechInit @4395): `sec`=radar (palette,
  low byte) · `Heat`=UL (0x4000) · `Mfd2`=UC (0x0400) · `Comm`=UR (0x8000) · `Mfd1`=LL (0x0100) ·
  `Mfd3`=LR (0x1000). `Eng1/2/3` are the engineering-mode alt planes of UC/LL/LR, not extra monitors.
- **No port-name reconcile needed on the dev path.** The RP names `auxUL2/auxC/…` hardcoded in
  `SVGA16::Update` only matter to the POD demux (a deferred pod-only follow-up); our compositor fetches the
  BT names (`Heat/Comm/Mfd1/Mfd2/Mfd3`) directly via `GetGraphicsPort` (`stricmp`).
- **Two extract kernels** in `SVGA16::DrawDevSurface`: palette-LUT (sec/radar, == `Update` case 0) and mono
  bit-plane → tint (`(word & mask) ? tint : 0`, the reduced core of `Update` cases 1/2; MFD masks are single
  bits so no DWORD SIMD/pack). `BTDrawGaugeSurfaces` iterates a `{name,tint,cellRect}` table over all 6.
- **Separate window = one ADDITIONAL SWAP CHAIN on the existing device** (no 2nd D3D device — textures/verts
  are shared). `BTGaugeWindowRenderAndPresent` (called AFTER the main `EndScene`, before the main Present):
  `GetBackBuffer` → `SetRenderTarget` → **`SetDepthStencilSurface(NULL)`** → Clear → BeginScene → 6 tiles →
  EndScene → restore RT+DS → `swap->Present`. The pod's own per-surface `BuildWindows`/`Update` path is
  byte-unchanged (dev mode already NULLs those objects).
- **⚠ THE KEY BUG (cost a cycle): depth-stencil size mismatch.** The main 800×600 depth surface stays bound
  when you `SetRenderTarget` to the 960×384 gauge backbuffer; a bound depth surface SMALLER than the render
  target is INVALID → every draw silently fails (window showed the Clear color but no tiles). Fix:
  `SetDepthStencilSurface(NULL)` before the gauge draws (Z is disabled anyway), restore after. Symptom to
  remember: render-to-a-second-swap-chain shows the clear color but no geometry ⇒ check the bound depth size.

**Content reality (unchanged from Milestone B):** the surfaces show the authored cockpit FRAME art + a few
base-table gauges (heat numerics, radar) — the live animated MFD widgets are BT-specific gauge classes not
yet reconstructed (parse-skipped). The separate window is now the **live viewer** for that widget-recon work.

## Follow-ups (after Milestone C)

- **Widget recon (the real fix, the big remaining workstream):** populate `BTL4MethodDescription` (give each
  BT gauge class a `methodDescription`) + wire the gauge→game-state `Execute()` data bindings, so the
  skipped/guarded widgets (`map`/`GeneratorCluster`/`vehicleSubSystems`/`pilotList`/`cmArmor`/heat clusters)
  render live data. The Milestone-C window shows them coming online as they're reconstructed.
- **Pod MFD port-name reconcile (pod-only):** a ~5-line positional dual-name fallback in `SVGA16::Update`
  (`UL = GetGraphicsPort("auxUL2"); if(!UL) UL = GetGraphicsPort("Heat"); …`) so BT MFDs reach the pod's real
  monitors. NOT a CFG rename (the CFG uses BT names pervasively + `MUNGA_L4` is shared with RP's aux names).
- **Polish:** overlay-plane compositing over `sec`; a pod-accurate RGB-packing toggle; texture atlas
  (one lock/upload); device-reset recreate hardening for the additional swap chain.