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8 Frames in 16ms: Rollback Networking in 'Mortal Kombat' and 'Injustice 2'


Michael Stallone (Lead Software Engineer, Engine, Netherrealm Games)

Location: Room 25, North Hall

Date: Wednesday, March 21

Time: 2:00pm - 3:00pm

Pass Type: All Access, GDC Conference + Summits, GDC Conference - Get your pass now!

Topic: Programming

Format: Session

Vault Recording: Video

Audience Level: All

Network latency is an ever present hurdle to overcome when trying to create a compelling multiplayer experience in any game, but can be especially difficult for fighting games. Rollback/re-simulate networking models remove the (often infuriating) local input delay typically associated with a traditional lockstep model. This is achieved by allowing the game simulation to take place without having received input from the remote player(s). This presentation will describe the journey of implementing the rollback/re-simulate model used in 'Mortal Kombat X' and 'Injustice 2'. This lecture will describe the drastic engine changes, optimizations, and tools that are involved in rolling back and simulating up to 8 game frames in 16ms.


Attendees will have an understanding of how the Netherrealm team tackled the challenge of hugely increased simulation costs associated with the rollback networking model for 'Mortal Kombat X' and 'Injustice 2' using aggressive caching, parallelization, CPU optimizations and essential tools.

Intended Audience

This talk would be most interesting to those who are looking to reduce the impact of network latency on the user's experience of input lag. A general familiarity with deterministic lockstep network simulation would be helpful, though not required as a brief overview will be provided.