Building a 40,000 Entity Deterministic Simulation @ Project 'Outbreak'
Simulation programming; pedestrian AI, traffic systems, and debug tooling
| Studio | RedKite Games (Sumo Digital) |
| Team | Population Simulation & AI |
| Role | Gameplay Programmer |
| Engine | Unreal Engine 5 |
Contributed to a networked, multi-threaded, deterministic ECS-based population simulation running 40,000+ entities. Worked in a 2-person team under a principal engineer with 25 years of experience, primarily at Rockstar Games.
Traffic & pedestrian systems
Multithreaded ECS · ISPC / SPMD · Server-authoritative FSMTraffic signal scheduling
Designed and implemented traffic signal scheduling and dynamic crosswalk crossing behaviour within the ECS-based FSM. This enabled coordinated interaction between vehicles and pedestrians.
Crosswalk Queueing while managing over crowding
Built queuing logic and dynamic overcrowding avoidance, validated state transitions carefully, and monitored agent behaviour at crossings given the rollback cost of any divergence.
Pedestrian distribution system
Designed a pedestrian distribution system to achieve realistic population flow across zones, ensuring agents were spread plausibly at scale without clustering artefacts.
Tooling & debugging
Simulation debugger · Rewind to Snapshot · Resimulate from SnapshotEntity inspection tools
Built debugging and inspection tooling enabling deep per-entity analysis across frames — exposing internal simulation state in a system where bugs were otherwise invisible. The tooling was recognised across teams for unblocking bugs that could not be diagnosed any other way.
Sparse Snapshots
Implemented a record, rewind & resimulate from snapshot functionality, storing ECS state efficiently to allow full playback and frame-by-frame debugging of the simulation.
- This paired with the entity inspection tool proved critical for diagnosing determinism failures.
Cross-team Recognition
| Impact | Bugs unblocked that were only possible with the tools I created |
| Sim scale | 30,000+ pedestrian agents |
Memory Management
Working within an ECS architecture constrained by Intel’s ISPC for SPMD execution made memory layout critical.
Any divergence between clients triggered rollbacks, and beyond a stored-frame ceiling the simulation simply broke.
This made correctness non-negotiable and demanded rigorous debugging discipline across every state transition.
Navigate to objective
Top-down GTA1-style game · Pathfinding · HUDDesigned and implemented a navigate to objective feature — combining pathfinding to guide the player toward their target with a HUD overlay communicating direction and progress.