Skip to content
Programming Bible

26 — How to program Terra Firma (Demo)

Audience: Engineers shipping the Demo · Multiplayer Ladder vertical slice first.
Engine: Unreal Engine 5.8 · Lyra host · same “no LyraGame fork” rule as Full game.
Authority: 22-demo.md · 02b-plugin-dependencies.md · Demo kanban · FS AC pack for the slice.
Sibling: Full-game programming → 25-howto-program-full-game.md.

Demo is a cut of the same architecture, not a second codebase. Same GFP packing; smaller enable list; art/systems marked Blocked where needed.

0. Demo product lock (read once)

Section titled “0. Demo product lock (read once)”
In Demo Out of Demo
Ladder (then Regular MP stretch) Campaign / story spine
One-weapon kits (no mesh modularity) Full Refit / modular parts as product
Demo Mod O tuner (team-only; strip external) External players with Mod ON
Hard-coded specials / parkour slice Full skill trees / monetary platform product
Hybrid FPP/TPP + Melee Drive + guns + Flow Perfect final art (placeholders OK)

Single Demo authority: 22-demo.md. GDD: demo-multiplayer-ladder.

1. Same Lyra 5.8 rules as Full game

Section titled “1. Same Lyra 5.8 rules as Full game”
  • Experiences + GFPs; OnExperienceLoaded before gameplay.
  • Do not edit Epic Lyra .uassets — duplicate into ADDON / TFA*.
  • Do not put lasting combat / HUD / economy into ADDON (FS-ARCH-011).
  • Remake TFACore · TFACombat · TFAWeapons on 5.8_terra_demo (old test project is not this host).

If a Demo shortcut fights Lyra updates, it is wrong — use a GFP.

2. What you reuse from Lyra on day one

Section titled “2. What you reuse from Lyra on day one”
Keep from Lyra Demo use
Crouch + default move/look Already works — leave HeroComponent alone
GAS / ASC on Lyra character Grant Demo AbilitySets onto TF hero
Enhanced Input stack Add TF IMC for WallRun/Jump family via Game Feature Action (no Vault — FS-MOV-003 WILL NOT USE)
CommonUI / net / EOS hooks Ladder session + future Online cards
ShooterCore as reference only Do not ship Demo as “Lyra Shooter experience” forever

3. Demo plugin enable picture

Section titled “3. Demo plugin enable picture”
Boot Active:     ADDON (+ remake TFACore when ready)
Experience:      TFACombat (spine) · TFAMelee · TFASingularity · TFAWeapons · TFAOmniVisor
                 (omit any Plugify GFP to lab without it — e.g. no Singularity)
Optional later:  TFAOnline slice · TFAAI sandbox C · TFAModular
Not in Demo:     full Monetary product · Crafting · Vision fog · Campaign maps
Vendor:          AimAssist (on) · SKG (register + glue via ADDON)

Plugify in Demo: same as Full game — one GFP per surface (02-gfp-cookbook.md). Demo Experience just enables a shorter list.

Tick (Lyra 5.8): leave Actor/Component Tick off unless justified (FS-ARCH-014). Server owns combat/economy loops; no melee Tick magnet; no client Tick applying Flow / damage.

Host hygiene first (P0):

  1. Persist ADDON (+ SKG) in Lyra_5p8.uproject.
  2. Point Experience / DefaultPawnData at TF hero (DA_HeroPawnData / BP_Hero_TerraFirma) — stop living on DefaultPawnData_EmptyPawn for Demo maps.
  3. Register IMC_TFA_Default (TFAInput plugin, built) via GameFeatureAction_AddInputContextMapping — not the old IMC_Default_TerraFirma, which duplicated Lyra’s IMC_Default and is deleted.
  4. Grant parkour AbilitySet on that pawn (assets already under ADDON).

Until 1–4 are done, “movement in ADDON” is mostly inert — see 02b §8.

4. Movement: Lyra vs custom (Demo)

Section titled “4. Movement: Lyra vs custom (Demo)”
Verb Owner How to program
Crouch Lyra Use stock path; do not reimplement
Move / Look / Jump baseline Lyra Stock
Roll / Slide / WallRun (current assets) ADDON GAs (temporary host) Wire grant + IMC; server-sim custom modes (FS-MOV-005)
Wall Run completeness (Vault WILL NOT USE) Demo card demo-movement-input Still GFP / ADDON — never LyraGame/*.cpp
Camera director / stance / vitality TFACombat spine (remake) ADDON stays SKG glue
Lasting Melee Drive TFAMelee (Plugify remake) Message-coupled to Singularity
Flow + Singularity TFASingularity (Plugify remake) Subscribes to kill/Flow credit messages

Pattern: new input → new IA in TF content → map in TF IMC → bind via Ability or TF input component on ATerraFirmaCharacter / Hero inject — not a LyraHeroComponent edit.

5. Demo program order (practical)

Section titled “5. Demo program order (practical)”

Kanban: Demo board · Gantt: Demo Gantt.

Phase Do this Exit
A Host uproject persist; Experience; TF default pawn; map /ADDON/Maps/L_TestMap loads clean Two machines / listen server boots
B Glue ADDON character + SKG register; parkour GAs playable Roll/Slide/WallRun on TF pawn
C Remake Core TFACore tags/messages Boot Active Combat can depend
D Camera UTFACameraDirector in TFACombat spine — leave pure FPS (demo-hybrid-camera). Same skeletal mesh: dual components + TPP OwnerNoSee + local TrueFPP bone-hide head/torso/legs/feet (arms+gun only) — no arms-only asset (FS-CAM-002) Gun TrueFPP · melee WideTPP · Shift-Out; remotes always full TPP
E Melee + Singularity Remake TFAMelee + TFASingularity (message-coupled; Plugify) Melee Drive foundation → Flow → Singularity
F Weapons Remake TFAWeapons; one-weapon kits; Firehand; Demo Mod O Mag → OmniVisor ammo; cadence RO
G HUD TFAOmniVisor placeholders (OV locks) Visor seats match GDD
H Ladder Match flow / results stubs per Demo cards Ladder match completes Mod OFF
I Strip bDemoModEnabled false external O does nothing

Motion Matching (Demo + Full): full tutorial tutorials/motion-matching-demo-and-full.md — Pose Search on lower body only; keep Lyra upper/lower Linked Layers; Full adds strike choosers. Kanban Demo demo-motion-matching · Full combat / melee. (Stub: demo-motion-matching-lyra.md.) Wall Run MM: L/R cycle mid-stint; MM enter/exit edges only — 2026-11-07-wall-run-motion-matching-design.md · tutorial §11.3.

Melee Drive / Singularity implementer path (self-contained Bible tutorial — tag gates → GAS · Motion Warp · Counter · gun matrix · Singularity bridge): tutorials/melee-drive-guns-singularity.md. Status deferred until Melee Drive foundation; design lock 2026-10-26-singularity-one-flow-two-verbs-design.md.

6. Demo Mod & promote (team only)

Section titled “6. Demo Mod & promote (team only)”
  1. Implement W_TFA_DemoMod against FS-GUN-012 + Lab dials (mock: tfa_gdd_html/figures/demo_mod_mock.html).
  2. Export split JSON (tfa-demo-mod/v1) — demo-mod-export.md.
  3. python promote_demo_mod.py <exports> → cooked DT/CSV under data/promoted/.
  4. Never ship live Mod RPCs as balance truth.

Kanban: demo-modkit · demo-mod-export-promote.

7. Day-to-day Demo workflow

Section titled “7. Day-to-day Demo workflow”
  1. Pull Demo kanban card — check Blocked reason ([art], [feat], …).
  2. Confirm dependency GFP Exit gate (Core before Combat before Weapons).
  3. Implement in GFP, not LyraGame.
  4. Run Demo AC from FS §23 acceptance pack that apply to the slice.
  5. External build: Mod gated OFF; Ladder still plays.

8. Demo anti-patterns

Section titled “8. Demo anti-patterns”
Anti-pattern Fix
“Demo is temporary → edit LyraHeroComponent” Additive IMC / TF character instead
Grow ADDON into full combat + HUD Remake TFACombat / TFAOmniVisor
Copy old test-project TFAWeapons as Done Remake on this host
Modular gun mesh work for Demo exit One-weapon kits only
Melee Drive Counter before Melee Drive Keep deferred kanban card
Full-body Pose Search wiping Lyra Linked upper/lower Lower-body MM only — motion-matching-demo-and-full.md

9. After Demo

Section titled “9. After Demo”

Promote patterns into Full game enable list (25): same GFPs, more Experiences, MonetaryPlatform, trees, Vision, World, Pose Search / Motion Matching (loco + Melee Drive choosers — motion-matching-full). Demo code should already live in the right plugins so Full game is enable + content + MM DBs, not a rewrite.

10. Pointers

Section titled “10. Pointers”
Doc Use
22-demo.md Product lock
02b-plugin-dependencies.md Deps / hierarchy / conflicts MASTER
08-camera-input-movement.md Camera / move Needs
20-critical-path.md Shared plugin A–E
Demo kanban / gantt Living board