物理同步

Challenge

• same input, different output on different clients.

• network latency & jitter.

Determinism

what is 'determinism'

Given same input, the final state is always the same, on any device, any platform, any time.

By https://www.ggpo.net/

how to achieve 'determinism'

• use fixed point math

• do not rely on local time or local framerate, but tick

• ensure iteration order (e.g., dictionary iter order is not guaranteed)

why common physics engines are not deterministic?

• they use floating point math rather than fixed point, because

  • floating point math is fast enough on morden computers

  • floating point math has much larger range of values

• the tool chains dealing with collider data, mesh… does not support fixed math.

• even with determinism (including your gameplay framework), we still have big problem to solve: latency.

Latency & jitter

The basic idea against network latency and jitter is

• interpolation

• extrapolation

• client simulation + rollback

NO one-fit-all solution.

Real world solutions

• UE4/UE5

• Rocket League

• WatchDog 2

• CSGO

Other learning materials

• Gaffer on Games