Crimsonland 1.9.93 — reverse engineering + rewrite

A high-fidelity reimplementation of Crimsonland v1.9.93 (2003, GOG "Crimsonland Classic") in Python + raylib, paired with deep reverse engineering of the original Windows binary.

The aim of the project is behavioral parity: timings, RNG sequences, float32 math, UI layout quirks, asset decoding, and gameplay rules should match the original as closely as practical.

We go great lengths to achieve this goal, including a headless differential testing harness to verify runs recorded in the original game versus our reimplementation.

Read the full story — reverse engineering workflow, custom asset formats, AI-assisted decompilation, and game preservation philosophy.

Browse the docs — 100+ pages of analysis, struct layouts, format specs, and parity tracking.

Current state

The rewrite is a playable full game: boot, menus, Survival, Rush, Quests (5 tiers), Tutorial, and Typ-o-Shooter, with full weapon/creature/perk content, terrain/sprite/decal rendering, music, gameplay SFX, and even secrets. The simulation is fully deterministic, supporting seeded runs and headless verifiable replays.

Quick start

Install uv, then:

uvx crimsonland@latest

# or run from source
gh repo clone banteg/crimson && cd crimson
uv run crimson

Wayland on Linux: current PyPI raylib wheels are X11-oriented on x86_64, so you may need xwayland + libX11. See electronstudio/raylib-python-cffi#199.

Runtime files

By default, saves, config, logs, and replays live in your per-user data directory. To keep everything local to the checkout:

export CRIMSON_RUNTIME_DIR="$PWD/artifacts/runtime"
uv run crimson

Assets

The rewrite can load the assets from original PAQ archives (crimson.paq et al). No original assets or binaries are included in this repository.

Point to them explicitly if needed:

uv run crimson --assets-dir path/to/game_dir

Extract PAQs into a filesystem tree for inspection. JAZ textures are automatically converted to PNG with alpha:

uv run crimson extract path/to/game_dir artifacts/assets

CLI

Everything is exposed via the crimson CLI (alias: crimsonland):

crimson                           run the game (default)
crimson view <name>               debug views / sandboxes
crimson quests <level>            print quest spawn script
crimson config                    inspect crimson.cfg
crimson extract <src> <dst>       extract PAQ archives
crimson replay list               list replay files under runtime replays dir
crimson replay play <file>        play back a recorded demo
crimson replay verify <file>      headlessly simulate replay stats / score claims
crimson replay benchmark <file>   benchmark replay throughput (headless or render, + optional profiling)
crimson replay render <file>      render replay to high-quality 60fps video via ffmpeg
crimson replay verify-checkpoints <file>  compare replay output to checkpoint sidecar

Useful flags: --seed N (deterministic runs), --demo (shareware teaser), --no-intro (skip logos), --base-dir PATH / CRIMSON_RUNTIME_DIR (runtime file location), --assets-dir PATH (PAQ / extracted asset location).

Project layout

src/
  crimson/          game logic — modes, weapons, perks, creatures, UI, replay
  grim/             engine layer — raylib wrapper, PAQ/JAZ decoders, audio, fonts
analysis/
  ghidra/           name/type maps (source of truth) and raw decompile exports
  frida/            runtime capture evidence (state snapshots, RNG traces)
  windbg/           debugger session logs
docs/               100+ pages: formats, structs, algorithms, parity tracking
scripts/            40+ analysis and utility tools
tests/              200+ tests: gameplay, perks, physics, replay, parity

Reverse engineering

Static analysis is the source of truth. Names and types live in analysis/ghidra/maps/; raw decompiles in analysis/ghidra/raw/ are regenerated output.

Runtime tooling (Frida, WinDbg) validates ambiguous behavior and captures ground truth. Evidence summaries live under analysis/frida/.

Differential testing captures original execution via Frida, replays the same inputs through the rewrite's headless oracle, and compares state checkpoints field-by-field.

See docs/contributor/project-tracking/provenance.md for exact binary hashes of the target build.

Development

uv run pytest              # test suite
uv run ruff check .        # lint
uv run ty check src        # type check
sg scan                    # ast-grep code scan
sg test                    # ast-grep rule tests
just check                 # all of the above

Docs

Docs are authored in docs/ and built as a static site with zensical:

uv tool install zensical
zensical serve

Parity workflow

1. Recover structure and intent from static analysis (analysis/ghidra/maps/ as source-of-truth maps).
2. Validate ambiguous behavior with runtime evidence (Frida/WinDbg captures under analysis/frida/).
3. Port behavior into src/ with deterministic simulation contracts.
4. Verify against captures/replays with headless differential tools.

For deterministic gameplay code, float behavior is part of the contract.
See docs/rewrite/float-parity-policy.md.

Contributing

• Keep changes small and reviewable — one subsystem at a time.
• Prefer measured parity (captures, logs, deterministic tests) over "looks right".
• Preserve native float32 math behavior in deterministic simulation paths. See float parity policy.
• Run just check before committing.

Tech stack

Python 3.13+ · raylib (pyray) · Construct · msgspec · Typer · Ghidra · Frida · WinDbg · pytest · uv

Legal

This project is an independent reverse engineering and reimplementation effort for preservation, research, and compatibility. No original assets or binaries are included. Use your own legally obtained copy.