Events & Messaging

Direct method calls couple systems too tightly. Events decouple.

Producer:

Consumer:

Frame:

Order matters: producer before consumer in the same frame.

Otherwise: events deferred to next frame (one-frame delay; usually fine).

Persistent events:

• Game events for save/load.
• Replay system: log all events, replay from saved state.
• Used by deterministic networking (lockstep).

UI events:

• Button click → event.
• UI system fires.
• Game system listens, takes action.

Modern engines:

• Unity: SendMessage (slow), UnityEvents, signals.
• Unreal: Delegates, Game Events.
• Bevy: native events via Events<T> resource.

Events keep code modular. Scale: hundreds of event types per game.

Anti-patterns:

• Event spaghetti: many systems firing/listening, hard to trace.
• Event chains: A fires B fires C fires D. Debugging nightmare.

Best practice: name events descriptively, document data flow, profile hot paths.