Design Pillars & Lifted Constraints¶
Gameplay Design Pillars¶
These are the non-negotiable design values that resolve every ambiguous feature decision.
- Arcade-to-sim balance: Closer to Ace Combat / Project Wingman than DCS World. Physics are simplified but feel consequential. Stalls, G-effects, and energy management matter; startup checklists, instrument-only navigation, and systems management do not. See prior-art.md for the competitive landscape that motivates this choice.
- Depth through variety, not complexity: Replayability comes from varied missions, wingman decisions, loadout tradeoffs, and campaign outcomes — not from the number of cockpit buttons or procedures.
- Direct, action-mapped controls: Many key bindings, each with a clear and immediate effect. Players can be effective with a keyboard; HOTAS rewards precision without being required.
- Approachable by default: New players should be in the air and shooting within minutes of first launch. Every simulation-leaning feature has a difficulty toggle that makes it optional. Approachability includes accessibility: colorblind-safe presentation (friend/foe and team colours distinguishable under CVD), subtitles for all radio traffic (human and synthetic alike), and scalable UI are baseline courtesies, not backlog extras.
- Single-player first, multiplayer co-equal: A rich solo experience (campaign, instant action, training) is a first-class foundation — and large-scale multiplayer is a co-equal product pillar, not a secondary extension. PvP (squadron/team battles), co-op PvE (shared strike/campaign missions), and persistent-world play are all in scope. The architectural target is 128+ simultaneous players, which makes scalability, server-side identity, and anti-cheat first-class concerns from the engine layer up — not late-phase afterthoughts.
- Tools, not rules: The engine exposes capabilities; players decide what to do with them. No content is locked behind progression in sandbox mode. The campaign layer is an optional narrative experience layered on top of a fundamentally open simulation — not the foundation it depends on. Players can ignore the campaign entirely and still have a complete game.
- Platform for community: Mission editor, open asset formats, mod system, and a Lua scripting API make Fighters Legacy a platform people build content on, not just a game they consume. The tools developers use to build the game are the same tools players and modders use. There is no privileged content pipeline.
- Dynamic world, optional intelligence: Agentic AI — a campaign director, conversational crew, self-operating servers — runs local-first through a pluggable provider and always degrades to scripted behaviour. Intelligence is an amplifier, never a dependency: the game is complete with no model configured.
Engine Capabilities¶
Design choices that explicitly avoid constraints common in older games of this genre.
| Area | Engine Design |
|---|---|
| Theater size | Arbitrary; streaming terrain chunks |
| Object pool | Dynamic allocation; soft limits tunable per server |
| Multiplayer topology | Dedicated fl-server; optional fl-lobby matchmaking |
| Multiplayer players | 128+ architectural target (server-authoritative); 32 is the near-term acceptance floor |
| Campaign structure | Arbitrary YAML graph; branching, nested objectives, any count |
| AI scripting | Lua 5.5; full scripting API; multiple concurrent behaviors |
| Score / rank tiers | Data-driven; TOML-defined rank tables |
| Aircraft count | Unlimited; all content pack entries |
| Weapon hardpoints | Configurable per aircraft TOML |
| Audio sample rates | OGG at any rate; arbitrary sample rate |
| Render resolution | Any resolution; windowed or fullscreen |
Multiplayer at Scale¶
The 128+ player target turns several engine choices into non-negotiables. These are first-class concerns, designed in from the engine layer rather than retrofitted:
- Server-authoritative and cheat-resistant. The client never owns physics or state. Live input validation rejects impossible states in-tick; heavier statistical detection runs offline against logs/replays. No kernel anti-cheat — server authority plus offline review is the right posture for a GPL, self-hostable game.
- Bounded per-client bandwidth. Quantized/bit-packed wire state plus per-client priority/budget snapshot scheduling and 3D interest management keep bandwidth flat as player count grows, rather than scaling with the square of the population.
- Parallel simulation. The authoritative tick parallelizes per-entity integration and AI across cores (data-parallel job system) so 128 players + AI + projectiles hold 60 Hz.
- Server-side identity. Players authenticate against a pluggable identity provider (offline-verifiable signed tokens); persistent stats, ranking, and bans key on a verified account, not a spoofable client GUID. Self-hostable; no first-party hosted infra required.
- Live-ops observability. Servers export metrics and structured logs; clustered fleets are managed by a Kubernetes/OpenShift operator with health, autoscaling, and graceful session draining.
Self-hosting is the default: communities run their own servers and identity. The project ships the software; it does not operate central infrastructure.
Dynamic World & Agentic AI¶
A second cross-cutting initiative (Epics M–P, decision record 2026-07-01) layers modern agentic-AI patterns onto the deterministic core — in ways the genre has not shipped — under five non-negotiable principles:
- LLMs never run in the 60 Hz tick. Agents act at human timescale against a ~1 Hz world-state snapshot and event stream, assembled off the sim thread.
- Validated paths only. Agents act through the same surfaces humans use — the allowlisted
admin/MCP command surface, mission YAML gated by
validate-mission, and the AI behaviour grammar. No direct state mutation, ever. - Graceful degradation. Every AI feature has a scripted fallback that is the CI-tested path; CI never requires a model.
- Tiered ops autonomy. observe → recommend → act-with-allowlist for server operations.
- Untrusted player text. Chat and names entering a prompt are data, not instructions.
What this buys: a campaign director that generates and narrates missions from live theater state; wingmen and GCI you can talk to; servers that triage their own incidents. The provider is pluggable and local-first (Ollama / llama.cpp reference; any OpenAI-compatible endpoint) — consistent with the self-host pillar. Full design in docs/developer/ai-architecture.md.
Settings Philosophy¶
These principles govern what appears in the settings UI and how settings are stored.
Approachable over exhaustive. Only settings a non-technical player can act on meaningfully without reading a manual belong in the primary settings screen. Settings that require understanding of rendering techniques or hardware internals are deferred to an "Advanced" section in a future phase.
Quality preset, with individual overrides. Phase 1 controlled shadow quality, particle density, and anti-aliasing solely through a single quality preset, deferring per-feature controls to keep the screen approachable. As the Vulkan render graph matured these returned as individual settings: shadow quality, particle density, and AA mode (Phase 2, #235), then ambient-occlusion and sky quality (Phase 3, #437). The quality preset remains the high-level convenience knob; the per-feature rows live alongside it for players who want them.
Draw distance is an exception. It is gameplay-critical in a flight sim — seeing a radar contact or a bandit at distance affects situational awareness directly. It is exposed as a primary setting regardless of the quality preset.
Anti-aliasing is a named choice: Off / FXAA / TAA. Phase 1 exposed AA as a simple on/off toggle. The render graph now offers explicit modes; MSAA was dropped in favour of TAA (it resolves shading/specular aliasing MSAA cannot and is the on-ramp to temporal upscaling), so the modes are Off, FXAA, and TAA, with TAA the default.
Audio sliders store integers. Volumes are stored as integers 0–100 in config/user.toml, matching the "0–100%" range in the UI spec, and converted to float 0.0–1.0 at runtime for IAudio::setGain(). This avoids float serialization precision issues and keeps the file human-readable and hand-editable.