Easel built a custom physics engine that snapshots only changed objects per frame, enabling rollback netcode for large multiplayer worlds.
Key Takeaways
Incremental rollback targets ~30 changed objects per frame instead of thousands, achieving 30-50x fewer snapshots than whole-world approaches.
Aggressive sleep logic puts bodies to sleep immediately at zero velocity and tracks force balance across stacks to avoid gravity keeping the world perpetually awake.
A lazy BVH with category-aware indexing minimizes unnecessary rebalancing and speeds up common queries like nearest-enemy lookups.
ForcefulStep uses position-correction (not velocity) to implement non-bouncy character stepping without bypassing the physics solver or killing knockback.
Continuous collision detection resolves collisions before sweeping for time-of-impact, avoiding the direction error seen in Rapier and the dynamic-dynamic gap in Box2D 3.0.
Hacker News Comment Review
The author confirms itch.io export works via an HTML iframe embedding the hosted easel.games version, keeping multiplayer and leaderboards intact.
No broader technical debate on the rollback architecture or physics solver tradeoffs has emerged yet.
Notable Comments
@BSTRhino: Author states no existing physics engine supports incremental rollback, framing the custom build as filling a real gap for large-world rollback netcode.
