Iron Curtain — Design Documentation

Red Alert Experience Recreation Strategy

Making IC feel like Red Alert requires more than loading the right files. The graphics, sounds, menu flow, unit selection, cursor behavior, and click feedback must recreate the experience that players remember — verified against the actual source code. We have access to four authoritative reference codebases. Each serves a different purpose.

Reference Source Strategy

The principle: Original RA tells us what the values ARE. Remastered tells us what a modern version SHOULD feel like. OpenRA tells us what the community EXPECTS. Bevy tells us how to BUILD it.

Visual Fidelity Checklist

These are the specific visual elements that make Red Alert look like Red Alert. Each must be verified against original source code constants, not guessed from screenshots.

Sprite Rendering Pipeline

Z-Order (Draw Order)

The draw order determines what renders on top of what. Getting this wrong makes the game look subtly broken — units clipping through buildings, shadows on top of vehicles, overlays behind walls. The canonical order (verified from original source and OpenRA):

Layer 0: Terrain tiles (ground)
Layer 1: Smudges (craters, scorch marks, oil stains)
Layer 2: Building bibs (paved foundations)
Layer 3: Building shadows + unit shadows
Layer 4: Buildings (sorted by Y position — southern buildings render on top)
Layer 5: Infantry (sub-cell positioned)
Layer 6: Vehicles / Ships (sorted by Y position)
Layer 7: Aircraft shadows (on ground)
Layer 8: Low-flying aircraft (sorted by Y position)
Layer 9: High-flying aircraft
Layer 10: Projectiles
Layer 11: Explosions / visual effects
Layer 12: Shroud / fog-of-war overlay
Layer 13: UI overlays (health bars, selection boxes, waypoint lines)

Within each layer, entities sort by Y-coordinate (south = higher draw order = renders on top). This is the standard isometric sort that prevents visual overlapping artifacts. Bevy’s sprite z-ordering maps to this layer system via Transform.translation.z.

Audio Fidelity Checklist

Red Alert’s audio is iconic — the EVA voice, unit responses, Hell March, the tesla coil zap. Audio fidelity requires matching the original game’s mixing behavior, not just playing the right files.

Sound Categories and Mixing

Original RA music system: The original game’s music was a straightforward sequential playlist. THEME.CPP manages a track list with per-theme attributes — each theme has a scenario owner (some tracks only play in certain missions) and a duration. In skirmish, the full soundtrack is available. In campaign, the scenario INI can specify a starting theme, but once playing, tracks advance sequentially and the player can pick from the jukebox in the options menu. There is no combat-detection system, no crossfades, and no dynamic intensity shifting. The Remastered Collection and OpenRA both preserve this simple jukebox model.

IC enhancement — dynamic situational music: While the original RA’s engine didn’t support dynamic music, IC’s engine and SDK treat dynamic situational music as a first-class capability. Frank Klepacki designed the RA soundtrack with gameplay tempo in mind — high-energy industrial during combat, ambient tension during build-up (see 13-PHILOSOPHY.md § Principle #11) — but the original engine didn’t act on this intent. IC closes that gap at the engine level.

ic-audio provides three music playback modes, selectable per game module, per mission, or per mod:

# audio/music_config.yaml
music_mode: dynamic               # "jukebox" | "sequential" | "dynamic"

# Jukebox mode (classic RA behavior):
jukebox:
  tracks: [BIGF226M, GRNDWIRE, HELLMARCH, MUDRA, JBURN_RG, TRENCHES, CC_THANG, WORKX_RG]
  order: sequential               # or "shuffle"
  loop: true

# Dynamic mode (IC engine feature — mood-tagged tracks with state-driven selection):
dynamic_playlist:
  ambient:
    tracks: [BIGF226M, MUDRA, JBURN_RG]
  build:
    tracks: [GRNDWIRE, WORKX_RG]
  combat:
    tracks: [HELLMARCH, TRENCHES, CC_THANG]
  tension:
    tracks: [RADIO2, FACE_THE_ENEMY]
  victory:
    tracks: [RREPORT]
  defeat:
    tracks: [SMSH_RG]
  crossfade_ms: 2000              # default crossfade between mood transitions
  combat_linger_s: 5              # stay in combat music 5s after last engagement

In dynamic mode, the engine monitors game state — active combat, base threat level, unit losses, objective progress — and crossfades between mood categories automatically. Designers tag tracks by mood; the engine handles transitions. No scripting required for basic dynamic music.

Three layers of control for mission/mod creators:

The scenario editor’s Music Playlist module (see decisions/09f/D038-scenario-editor.md “Dynamic Music”) exposes the full dynamic system visually — a designer drags tracks into mood buckets and previews transitions without writing code. The Music Trigger module handles scripted one-shot moments (“play Hell March when the tanks breach the wall”). Both emit standard Lua that modders can extend.

The music_mode setting defaults to dynamic under the iron_curtain experience profile and jukebox under the vanilla profile for RA1’s built-in soundtrack. Game modules and total conversions define their own default mode and mood-tagged playlists. This is Tier 1 YAML configuration — no recompilation, no Lua required for basic use.

Unit Voice System

Unit voice responses follow a specific pattern from the original game:

Implementation: Unit voice definitions live in mods/ra/rules/units/*.yaml alongside other unit data:

# In rules/units/vehicles.yaml
medium_tank:
  voices:
    select: [VEHIC1, REPORT1, YESSIR1]
    move: [ACKNO, AFFIRM1, MOVOUT1]
    attack: [AFFIRM1, YESSIR1]
    deny: [NEGAT1, CANTDO1]
  voice_interval: 200     # minimum ticks between voice responses (prevents spam)

UX Fidelity Checklist

These are the interaction patterns that make RA play like RA. Each is a combination of input handling, visual feedback, and audio feedback.

Core Interaction Loop

Sidebar System

The sidebar is the player’s primary interface and the most recognizable visual element of Red Alert’s UI. Three reference implementations exist:

IC’s sidebar is YAML-driven (D032 themes), supporting all three styles as switchable presets. The Classic theme recreates the 1996 layout. The Remastered theme matches the modernized layout. The default IC theme takes the best elements of both.

Credit counter animation: The original RA doesn’t jump to the new credit value — it counts up or down smoothly ($5000 → $4200 ticks down digit by digit). This is a small detail that contributes significantly to the game feel. IC replicates this with an interpolated counter in ic-ui.

Build queue clock-wipe: The clock-wipe animation (circular reveal showing build progress on the unit icon) is one of RA’s most distinctive UI elements. ic-render implements this as a shader that masks the icon with a circular wipe driven by build progress percentage.

Verification Method

How we know the recreation is accurate — not “it looks about right” but “we verified against source”:

Community verification: Phase 3 exit criteria include “feels like Red Alert to someone who’s played it before.” This is subjective but critical — IC will release builds to the community for feel testing well before feature-completeness. The community IS the verification instrument for subjective fidelity.

What Each Phase Delivers