Subsystems: Services and events (Blueprint)

What/Why: Centralize cross-cutting logic in Subsystems with clean APIs and events.

Prereqs

• Understand GameInstanceSubsystem vs WorldSubsystem lifecycles

Steps

1. Choose scope

• Global service (saves, audio, telemetry) → GameInstanceSubsystem
• Per-level (encounters, time of day) → WorldSubsystem

2. API and events

• Expose functions (Request*, Get*) and dispatchers (On*)
• Avoid hard refs to heavy assets; use soft refs

3. Access

• Get Game Instance Subsystem or Get World Subsystem from BP

4. Examples

• SaveService queues saves (see page)
• TimeOfDay updates sky via curve and tick at low rate (or timer)

Data

• DataAssets configure rates, paths, and soft references

Networking

• Subsystems don’t replicate; replicate data on actors/components instead

Performance

• Avoid doing work every frame; use timers or events

Testing

• Unit-like BP tests that call API and observe events

Suggested prompts

• “Create a BP_TimeOfDaySubsystem with a curve and timer updating sky light.”
• “Design a clean API for AudioService with play/stop and category volumes.”
• “Show safe access patterns to subsystems from Pawns/Widgets.”

Prompts for this example

• “Write nodes to get BP_SaveService from any Blueprint and call RequestSave(ProfileId).”