GameMaker GML Rules

Code Organization

  • Keep object event code short and move reusable behavior into scripts or functions.
  • Use clear prefixes or naming conventions for scripts, objects, sprites, rooms, and globals.
  • Prefer functions over copy-pasted event blocks.
  • Keep create-step-draw responsibilities separate.
  • Put initialization in Create, simulation in Step, and rendering-only work in Draw.

GML Style

  • Use descriptive variable names and avoid one-letter names outside small loops.
  • Prefer local variables with var or function-scoped declarations over unnecessary instance variables.
  • Use constants, enums, and macros for repeated identifiers, layer names, states, and collision groups.
  • Guard optional instance references with instance_exists.
  • Keep global state minimal and document it.

Gameplay Architecture

  • Use finite state machines for player, enemy, UI, and game-flow states.
  • Keep collision logic explicit and deterministic.
  • Separate input collection from action execution.
  • Use alarms, timelines, or explicit timers consistently; do not mix patterns without reason.
  • Store save data through structured maps/structs and version the save format.

Performance

  • Avoid expensive searches such as broad instance_find or repeated collision scans in every Step event.
  • Cache frequently used asset IDs, layer IDs, and object references when safe.
  • Destroy data structures when no longer needed.
  • Use object pooling for frequent projectiles, particles, or short-lived effects when allocation becomes costly.
  • Profile before optimizing and keep hot-path code simple.

Debugging and Testing

  • Add debug overlays for collision boxes, state, velocity, and AI decisions when useful.
  • Use assertions or explicit guard clauses for impossible states.
  • Test room transitions, pause/resume, save/load, and controller/keyboard input separately.
  • Keep reproducible test rooms for complex mechanics.

Common Mistakes

  • Do not put game logic in Draw events.
  • Do not create data structures without destroying them.
  • Do not rely on room editor instance order for critical behavior.
  • Do not hardcode magic numeric state IDs.