reincarnate

Appearance

GameMaker (GML) ​

Status: Active — GMS1 and GMS2/GMS2.3+ frontends are functional. Test projects: Bounty (GMS1) and Dead Estate (GMS2.3+, 0 errors).

Format ​

GameMaker games ship as data.win files (Windows), with platform variants for other targets. The format contains:

  • GML bytecode — a stack-based VM with typed operands
  • Asset tables — sprites (SPRT), sounds (SOND), objects (OBJT), rooms (ROOM), fonts (FONT), scripts (SCPT), and more
  • String pool — all strings referenced by bytecode
  • Texture pages — atlas images for sprites/backgrounds/fonts

The format is partially documented through community reverse-engineering (UndertaleModTool, GameMaker Data Reader). GMS2.3+ introduced significant changes (anonymous functions as closures, structs, sequences, animation curves).

Lifting Strategy ​

Full recompilation. The reincarnate-frontend-gamemaker crate (backed by the datawin crate for format parsing):

  1. Parses data.win using the datawin crate
  2. Decodes GML bytecode per object/event/script
  3. Emits IR per function, with instance variable access modeled as field reads/writes
  4. Identifies GameMaker.* system call boundaries

The replacement runtime in runtime/gamemaker/ts/ implements GML object instances, room management, drawing, input, and audio stubs.

Implementation Status ​

Frontend completeness — GMS1 ​

  • ✅ All standard opcodes (push, pop, call, branch, comparison, arithmetic)
  • ✅ VARI scope dispatch (self, global, local, builtin, stacked instances)
  • ✅ 2D array access (ref_type==0 with instance field as scope owner, not target)
  • ✅ Object event handlers (Create, Destroy, Step, Draw, Alarm, Keyboard, Mouse, Collision, User)
  • ✅ argument variable mapping to function parameters
  • ✅ hasNext2/pushenvv/popenvv (for-in loop lowering)
  • ✅ Object inheritance via event_inherited
  • ✅ Object properties (persistent, visible) emitted as class fields when non-default

Frontend completeness — GMS2.3+ ​

  • ✅ Dup(N) byte-based semantics (duplicates N+1 type-sized chunks, not items)
  • ✅ DupExtra swap mode (high byte of N, reorders stack without duplicating)
  • ✅ Break signals: pushref (-11), chknullish (-10), isstaticok (-6), setstatic/savearef/restorearef (-9/-8/-7)
  • ✅ Shared blob child function length computation (gap-based from sorted offsets)
  • ✅ Anonymous functions as closures (pushref → GlobalRef)
  • ⚠️ Struct literal construction — basic support, edge cases possible
  • ⚠️ Sequences API — not yet extracted from data.win
  • ⚠️ Animation curves API — not yet extracted

Transform pass completeness ​

All standard passes run. GML-specific:

  • ✅ GameMaker.* system calls resolved to runtime function imports
  • ✅ int/uint/real/string casts mapped to gamemaker/math.ts
  • ✅ Global variable reads mapped to GameMaker.Global.get
  • ⚠️ No GML-specific boolean detection pass yet (see below)

Output quality ​

Key remaining issues:

  • Numeric booleans — GML compiles if (self.active) as push; pushi 1; cmp.eq; bf. Output is === 1 / === 0 instead of bare boolean tests. Requires heuristic: identify fields only assigned 0/1/true/false across all functions.
  • Enum detection — Many GML games use string or numeric constants as enums. Could extract into const objects. Reference code uses Advantages.none, MouseButtons.pressed, etc.
  • Type inference gaps — GML is dynamically typed; some field/return types remain : any without cross-function analysis.

Runtime coverage ​

See API-COVERAGE-GML.md for full per-function tracking.

High-level gaps:

CategoryCoverage
Variable functions (struct, instance reflection)⚠️ Partial — global done, instance/struct not started
Sprites⚠️ Partial — basic get_* done, add/replace/delete not started
Audio⚠️ Type sigs only — full Web Audio integration pending
Paths / Timelines❌ Not started
Cameras & Views❌ Not started
Physics (Box2D)❌ Not started
Particles❌ Not started
Surfaces⚠️ Type sigs only
GPU / Shaders❌ Not started
Buffers❌ Not started
Networking❌ Not started
Date/Time functions❌ Not started
Data Structures (ds_list, ds_map, ds_grid)⚠️ Type sigs only
Async functions❌ Not started (mostly irrelevant for offline lifting)
Gamepad input❌ Not started
Time Sources (GMS2.3+)❌ Not started
Sequences / Animation Curves (GMS2.3+)❌ Not started

Platform abstraction gaps ​

  • Audio — no platform module; no Web Audio integration
  • Persistence/Save — INI uses localStorage directly, not abstracted
  • Networking — no platform module
  • Dialog/Modal — no platform module

Known Limitations ​

  • GMS2.3+ structs — Anonymous structs and method binding are partially supported
  • Room transitions — room_goto / room_restart modeled but room initialization order may differ from original
  • Instance deactivation — instance_deactivate_* / instance_activate_* (for off-screen culling) not implemented
  • Paths — The path following system (path_start/path_end + built-in path vars) has field stubs but no path execution logic
  • Collision system — Collision events dispatched but spatial queries (place_meeting, collision_rectangle, etc.) are type-sig stubs only

References ​