Probability Director Architecture
Probability Director separates gameplay randomness from analysis tools. Runtime streams belong to a UGameInstance Probability Director subsystem. The Editor Inspector reads a copied view of a selected context; Runtime Controls can change diagnostic state; the Lab runs isolated experiments.
Streams and determinism
Section titled “Streams and determinism”Create a named stream for a gameplay responsibility and retain its identity for as long as that responsibility exists. A Fixed stream provides reproducible deterministic behavior when its inputs and call sequence are the same. Sequential operations advance that stream’s deterministic state. Keyed operations derive a result from a stable Decision Key and occurrence, so unrelated sequential calls do not shift the keyed result.
Treat stream IDs and Decision Keys as durable gameplay identities. Renaming or reusing them changes which decisions are being addressed. Use one stream per responsibility rather than sharing one stream across unrelated systems.
Secure and deterministic boundaries
Section titled “Secure and deterministic boundaries”Fixed streams are intended for repeatable gameplay simulation. Secure streams use the platform-backed secure randomness path and do not promise deterministic replay from a seed. Choose the source based on the product requirement; Secure randomness does not make game state secret if the result is later exposed to a client or stored without protection.
Persistence
Section titled “Persistence”Probability Director owns its stream state and persistence payload. The host save system owns save slots, storage, encryption, and save/restore orchestration. Persisted streams can continue supported deterministic state across a save/load cycle; Ephemeral streams are not restored. See Persistence and anti-save-scumming guidance.
Resolution Rules
Section titled “Resolution Rules”Resolution Rules are reusable authored descriptions of numeric dice resolution. The consuming gameplay system supplies its own meaning and routing while Probability Director resolves the configured operation through its supported APIs. See the API reference and Data Assets.
Lab boundary
Section titled “Lab boundary”Probability Director Lab performs interactive probability, dice, distribution, stream, RNG-health, and name experiments using local experiment state. Its simulations do not advance a gameplay Runtime Stream. Use the Editor Tools guide for the exact menu paths and the Lab guides for feature workflows.
Extension and integration boundaries
Section titled “Extension and integration boundaries”Public runtime APIs and supported extension points are documented in API Reference. Probability Director remains standalone. Communication between Probability Director and another Director product is routed through the optional DirectorBridge integration.