Contents
Engine-independent guidance
Decouple systems through events, not direct references
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The principle
Let systems communicate by broadcasting events through a mediator, rather than holding direct references to one another. A sender announces "this happened" without knowing who listens; listeners subscribe without knowing who sent it. This keeps systems independent — new listeners can be added without touching the sender.
Applies when
Cross-cutting reactions to game events (audio, UI, VFX, analytics, progression), and any system that must observe many others without coupling to them.
Does not apply / Exceptions
Events are not free. Indirection makes control flow harder to trace, hides ordering dependencies, and — overused — produces "event spaghetti" where no one can tell what happens when. For tight, direct, one-to-one relationships a plain function call is clearer and more debuggable than an event. Use events to decouple across system boundaries; don't event-ify everything inside a system.
Rationale
Direct references make systems mutually dependent: the combat system calling the audio system, the UI, the achievement tracker, and the particle system directly becomes a knot where nothing can change in isolation [S-nystrom-gpp]. An event/observer boundary cuts the knot — the combat system fires "enemy died" and is done; any number of systems react, each ignorant of the others. An event queue goes further, decoupling when a message is sent from when it's processed, which smooths frame spikes and ordering. This is the architecture that lets a system like a behavior-observing skill engine watch everything the player does without every other system having to know it exists.
Implementation
Define a clear, typed event vocabulary (a fixed set of well-named events beats ad-hoc strings). Fire events at meaningful moments; let systems subscribe. Consider an event queue when timing/ordering or frame-spikes matter. Guard debuggability: log/inspect the event stream, and keep the vocabulary small and documented (this is where ARCH meets SYS-0006, legibility — events can hurt traceability, so invest in tooling that restores it).
Disagreement
Event-driven decoupling vs. direct calls is a real tradeoff: decoupling and extensibility vs. traceability and simplicity. The synthesis: use events at seams where decoupling pays (many independent reactors, or a system that must not know its observers), and direct calls where the relationship is tight and clarity matters more than flexibility.
Notes
Confidence 4.
Connected principles
Source trail
Evidence strength describes support for this guidance, not a probability that it is right for your situation.
Citation and record details
GDC-L1-ARCH-0003 · contextual guidance · canonical
Recorded verification date: 2026-07-14. This is not a claim of an engine test.