Iron Curtain — Design Documentation

D075: Remastered Collection Format Compatibility

Decision Capsule (LLM/RAG Summary)

• Status: Accepted
• Phase: Phase 2 (format parsers), Phase 6a (Asset Studio import wizard)
• Canonical for: Loading and converting assets from the C&C Remastered Collection (EA, 2020) into IC’s native pipeline
• Scope: cnc-formats (MEG/PGM archive parser, clean-room, meg feature flag), ic-cnc-content (TGA+META, DDS, MTD, WAV, config/import-index integration), ic-editor (Asset Studio import wizard and BK2→WebM import pipeline), 05-FORMATS.md
• Decision: IC imports and reads the Remastered Collection’s asset families into IC’s native pipeline — MEG archives, TGA+META sprite sheets, WAV audio, XML config, and BK2 cutscenes normalized to WebM at import time — enabling users who own the Remastered Collection to use those assets directly without redistributing them.
• Why: (1) The Remastered Collection’s C++ DLL source is GPL v3 — format definitions are legally referenceable. (2) Players who own the Remastered Collection expect their HD assets to work. (3) The Remastered formats are well-documented by the modding community (PPM, CnCNet). (4) IC already supports the classic formats these are derived from — HD support is an incremental extension.
• Non-goals: Binary compatibility with Petroglyph’s C# GlyphX layer; redistributing EA’s proprietary HD art, music, or video; running Remastered mods that depend on GlyphX-specific APIs; replacing the Remastered Collection as a product.
• Invariants preserved: ic-cnc-content remains a pure parsing library with no I/O side effects. All imported assets convert to IC-native representations (PNG sprites, OGG/WAV audio, WebM video). Sim determinism unaffected — asset formats are presentation-only.
• Defaults / UX behavior: “Import Remastered Installation” wizard in Asset Studio auto-detects a Remastered install folder, inventories available assets, and offers selective import. Users choose which asset categories to import. Imported assets land in a mod-ready directory structure.
• Compatibility / Export impact: Imported Remastered assets are usable in IC mods but NOT publishable to Workshop (proprietary EA content). Asset Studio marks provenance as source: remastered_collection and Publish Readiness (D038) blocks Workshop upload of EA-sourced assets.
• Security / Trust impact: MEG archive parser in cnc-formats must handle malformed archives safely (fuzzing required). MEG entry extraction uses strict-path PathBoundary to sandbox output to the mod directory — same Zip Slip defense as .oramap and .icpkg (see 06-SECURITY.md § Path Security Infrastructure). TGA/DDS parsers use established Rust crates (image, ddsfile) — no custom decoder needed.
• Public interfaces / types / commands: MegArchive, MegEntry, RemasteredSpriteSheet, MetaFrame, RemasteredImportManifest, ic asset import-remastered
• Affected docs: src/05-FORMATS.md, src/decisions/09f/D040-asset-studio.md, src/architecture/ra-experience.md, src/decisions/09c-modding.md
• Revision note summary: Clarified in March 2026 that BK2 is not part of the baseline runtime decoder set; Remastered cutscenes are normalized to WebM at import time, and IC package/import metadata remains the canonical layer for language/variant/fallback behavior above the raw media container.
• Keywords: remastered, remaster, MEG, TGA, META, BK2, Bink2, HD sprites, megasheet, GlyphX, Petroglyph, EA GPL, import wizard

Context

The C&C Remastered Collection (EA / Petroglyph, 2020) modernized Red Alert and Tiberian Dawn with HD assets while preserving the original gameplay via a C++ DLL (released under GPL v3). The DLL source gives us legal access to format definitions. The HD assets themselves are proprietary EA content — IC never redistributes them, but players who own the Remastered Collection should be able to use their purchased assets in IC.

IC already reads every classic C&C format (.mix, .shp, .pal, .aud, .vqa). The Remastered Collection introduced a parallel set of HD formats that wrap or replace the classics. This decision covers reading those HD formats and converting them into IC’s native pipeline.

Clarification (March 2026): For video, the canonical runtime target stays normalized WebM rather than native BK2 playback. Any track/language metadata discovered during BK2 import can inform IC’s import index, but cutscene variant selection, language capability, and fallback behavior remain governed by IC package/import metadata as defined by D068/D049, not by the raw container alone.

Remastered Format Inventory

The Remastered Collection uses Petroglyph’s format family (from Empire at War / Grey Goo lineage), not Westwood’s original formats. The C++ DLL still reads classic formats internally, but the C# GlyphX layer loads HD replacements from Petroglyph containers.

Archives

Sprites & Textures

Audio

Note: The Remastered Collection’s audio is standard WAV, not a proprietary format. IC already plays WAV natively. The only work is reading them out of MEG archives.

Video

Bink2 strategy: Unlike classic .vqa (which IC decodes natively), Bink2 is a proprietary codec. IC does NOT ship a Bink2 runtime decoder. Instead, the Asset Studio converts BK2 → WebM at import time. This is a one-time operation per cutscene. The converted WebM plays through IC’s standard video pipeline. Users who want the Remastered cutscenes in IC import them once; the originals remain untouched in the Remastered install folder.

Configuration & Metadata

Formats IC Skips

HD Sprite Import Pipeline

The most complex part of Remastered format support is converting HD megasheets into IC’s per-frame sprite representation. This is the core technical contribution of D075.

How Remastered Sprites Work

In the original game, each unit has a .shp file containing N indexed frames (e.g., 32 facings × M animation frames). The Remastered Collection replaces each .shp with:

1. One large TGA — all frames composited into a single atlas image (the “megasheet”)
2. One META JSON — per-frame geometry: canvas size and crop rectangle within the TGA
3. Chroma-key player colors — instead of palette indices 80–95, player-colored pixels use a bright green band (HSV hue ~110–111) with varying saturation/brightness for shading

The frame ordering in the TGA matches the original .shp frame ordering — frame 0 in the META corresponds to frame 0 in the original .shp. This is critical: it means the XML sequence definitions from the original game (facing counts, animation delays) apply directly to the HD frames.

Import Algorithm

Input:  <unit>.tga + <unit>.meta (from Remastered MEG archive)
Output: Vec<RgbaImage> (individual frames) + SequenceMap (frame→animation mapping)

1. Load TGA → full RGBA image
2. Parse META JSON → Vec<MetaFrame { size: [w,h], crop: [x,y,w,h] }>
3. For each MetaFrame:
   a. Extract crop rectangle from the TGA → individual frame image
   b. Detect chroma-key green pixels (hue 110±5, saturation > 0.5)
   c. Replace green band with IC remap marker:
      - Option A: Write palette index 80–95 equivalent into a separate remap mask
      - Option B: Store as a shader-compatible "remap UV" channel
   d. Emit frame as RGBA PNG (IC native) or palette-quantized indexed PNG (classic mode)
4. Map frame indices to animation sequences using original sequence definitions
5. Write IC sprite sheet (PNG atlas + YAML sequence metadata)

Player Color Remapping

The Remastered Collection’s chroma-key approach is more flexible than the original’s palette-index approach — it allows smooth gradients and anti-aliasing in player-colored areas. IC’s import pipeline preserves this:

Rust Types

#![allow(unused)]
fn main() {
/// Petroglyph MEG archive reader.
pub struct MegArchive {
    pub entries: Vec<MegEntry>,
}

pub struct MegEntry {
    pub name: String,
    pub offset: u64,
    pub size: u64,
}

/// A single frame's geometry within a Remastered megasheet TGA.
pub struct MetaFrame {
    /// Canvas dimensions (logical frame size including padding).
    pub size: [u32; 2],
    /// Crop rectangle [x, y, width, height] within the TGA.
    pub crop: [u32; 4],
}

/// Parsed Remastered sprite sheet: TGA image + frame geometry.
pub struct RemasteredSpriteSheet {
    pub image: RgbaImage,
    pub frames: Vec<MetaFrame>,
    /// Original asset name (e.g., "4tnk" for Mammoth Tank).
    pub asset_name: String,
}

/// Import manifest tracking what was imported from a Remastered installation.
pub struct RemasteredImportManifest {
    pub source_path: PathBuf,        // Remastered install dir (trusted, user-provided)
    pub output_boundary: PathBoundary, // `mods/remastered-hd/` — all extraction sandboxed here
    pub imported_at: String,         // RFC 3339 UTC
    pub assets: Vec<ImportedAsset>,
}

pub struct ImportedAsset {
    pub original_path: String,       // Path within MEG archive (untrusted — validated via PathBoundary)
    pub ic_path: PathBuf,            // Where it landed in IC mod structure (within output_boundary)
    pub asset_type: ImportedAssetType,
    pub provenance: AssetProvenance, // From D040 — source: remastered_collection
}

pub enum ImportedAssetType {
    Sprite,
    Terrain,
    Audio,
    Video,
    UiChrome,
    Config,
}
}

Asset Studio Integration — “Import Remastered Installation” Wizard

The Asset Studio (D040) gains a dedicated import workflow for Remastered Collection assets.

UX Flow

1. Detect installation — The wizard checks standard install locations:
   • Steam: <steam_library>/steamapps/common/CnC_Remastered_Collection/
   • EA App: <ea_library>/Command & Conquer Remastered Collection/
   • Custom: user browses to folder
2. Inventory — Scan MEG archives, list available asset categories with counts:
   • Sprites: ~2,400 TGA+META pairs (units, buildings, infantry, terrain, effects)
   • Audio: ~800 WAV files (SFX, EVA, music)
   • Video: ~40 BK2 files (cutscenes, briefings)
   • UI: ~200 DDS/TGA files (sidebar, buttons, icons)
3. Select — User picks categories and optionally individual assets. Presets:
   • “Everything” — imports all categories
   • “Gameplay assets only” — sprites + audio (no video, no UI chrome)
   • “Audio only” — just the remixed sound effects and music
   • “Custom” — pick individual categories
4. Convert — Background processing:
   • TGA+META → IC sprite sheets (PNG atlas + YAML sequences)
   • BK2 → WebM (VP9, preserving original resolution)
   • WAV → passthrough (already IC-compatible)
   • DDS → PNG or KTX2
5. Output — Assets land in a mod directory: mods/remastered-hd/
   • Standard IC mod structure (YAML manifest, asset directories)
   • Provenance metadata set to source: remastered_collection
   • Publish Readiness blocks Workshop upload (proprietary EA content)
6. Activate — User enables the remastered-hd mod in IC. HD assets override classic assets via the standard mod layering system (D062 Virtual Namespace).

Import Performance Estimate

Total: ~10 minutes for a full import. One-time operation. Progress bar with per-category status.

Legal Model

This is the same legal model that OpenRA, CnCNet, and every other community project uses: format compatibility is legal; redistributing proprietary assets is not.

Alternatives Considered

1. Runtime Bink2 decoding — Ship a BK2 decoder in IC so Remastered cutscenes play directly without conversion. Rejected: Bink2 is proprietary (RAD Game Tools). Licensing adds cost and legal complexity. Converting to WebM at import time is simpler, produces better integration with IC’s standard video pipeline, and the one-time conversion cost is negligible.

2. Direct MEG mounting (no conversion) — Mount Remastered MEG archives as a virtual filesystem and read TGA/META at runtime. Rejected: adds runtime complexity, requires Remastered Collection to be installed at all times, and prevents IC from applying its own sprite pipeline optimizations (atlas packing, KTX2 GPU compression). One-time import-and-convert is cleaner.

3. Only support classic formats from Remastered — The Remastered Collection ships classic .mix/.shp/.aud/.vqa alongside HD assets. IC could just read those. Rejected: the whole point of Remastered is the HD assets. Users expect HD. Classic formats are already supported; this decision adds HD on top.

4. Reverse-engineer GlyphX C# layer — The proprietary C# GlyphX engine handles HD rendering, UI, and networking. We could study its asset loading for complete compatibility. Rejected: GlyphX is proprietary (not GPL). The C++ DLL source plus community documentation provides everything needed for format parsing without touching proprietary code.

Phase

• Phase 2: cnc-formats gains clean-room MEG/PGM archive parser (behind meg feature flag). ic-cnc-content gains TGA+META sprite sheet splitter and DDS reader (these reference GPL DLL source). All are pure parsing — no UI.
• Phase 6a: Asset Studio “Import Remastered Installation” wizard ships. BK2→WebM conversion pipeline. Full import workflow with provenance tracking.
• CLI fallback (Phase 2): ic asset import-remastered <path> provides headless import for CI/automation/power users before Asset Studio ships. The output directory (mods/remastered-hd/) is enforced via strict-path PathBoundary — MEG archive entry names (potentially user-modified in modded installs) cannot escape the output mod directory.

Cross-References

• D040 (Asset Studio) — Import wizard lives in Asset Studio Layer 2
• D048 (Render Modes) — HD sprites activate in modern render mode; classic render mode uses palette-quantized versions
• D019 (Balance Presets) — remastered preset already captures Remastered gameplay values
• D045 (Pathfinding Presets) — RemastersPathfinder already reproduces Remastered pathfinding
• D062 (Mod Profiles) — Imported Remastered assets live in a mod namespace (remastered-hd)
• D068 (Selective Installation) — Remastered HD assets are an optional content tier, not required
• research/remastered-collection-netcode-analysis.md — Deep dive on the Remastered C++ DLL architecture
• research/pathfinding-remastered-analysis.md — Remastered pathfinding algorithm analysis
• src/architecture/ra-experience.md — Reference source strategy (Remastered as UX gold standard)