Zhi Kang Shao (NL)

Senior Software Engineer, Developer Relations @Epic Games

The Player Was Here: Persisting World State and Actor LOD Systems

When players return to an area, they expect the world to be in the same state as they left it. Reloading the world state needs to happen when loading a save file, when changing maps, and even within the same map when the player returns to a location that World Partition has streamed out. Keeping expensive faraway gameplay actors alive also leads to bad performance in a large, dense world.

Persistence and hydration are two closely related aspects of level loading. Persistence refers to reloading map sections while restoring the modified world state and player data. Hydration refers to switching the representation of gameplay entities when they are far away from the player from fully featured actors to more lightweight representations, like simpler actors or instanced static meshes.

Key learnings:

In this talk, we will cover the state of relevant systems in Unreal Engine that help you implement persistence and hydration. We’ll cover both production-ready and experimental UE systems. UE provides solutions like the Instanced Actors plugin, the Mass Entity framework, the Level Streaming Persistence plugin, and the Save Game system. We’ll go over what their features and limitations are, the ways you can use them, and how Epic uses them. We’ll also show some examples of how to restore gameplay state like the Gameplay Ability System (GAS) and State Tree.