How to Fix Rollback Netcode Desync From Nondeterministic Float Math

Rollback netcode re-simulates frames and only works if both clients compute identical state. Hardware-dependent float rounding means two machines drift apart, and a single bit difference cascades into a full desync.

How to fix it

1. Move simulation to fixed point

Represent positions, velocities, and physics in fixed-point integers (e.g. 16.16) for all gameplay state. Reserve floats strictly for rendering, which never feeds back into the simulation.

2. Use a deterministic math library

If you cannot fully convert, adopt a library with cross-platform deterministic trig and sqrt, and avoid System.Math functions whose results vary by platform.

3. Add rolling state checksums

Hash the full simulation state each frame and exchange checksums. When they diverge, you get the exact frame of desync, making the offending nondeterministic operation easy to find.

Catching the ones you can't reproduce

The hardest version of this to fix is the one you can't reproduce — it only happens on a player's hardware, OS, driver, or save state, under conditions that simply aren't present on your machine. A report that says “it crashed” or “it froze” gives you nothing to act on, so the bug survives release after release while quietly costing you players.

Automatic error capture closes that gap. Each failure arrives with its full stack trace, the device and OS, the build number, and a breadcrumb trail of what the player did right before it broke, so even a failure you have never seen becomes a specific, reproducible issue. Fold identical failures into one signature ranked by how many players each hits, and your worklist sorts itself worst-first instead of arriving as a stream of vague complaints.

This is where a tool like Bugnet earns its place. Its SDK captures every error automatically with the full stack trace plus device, OS, memory, build, and game-state context, folds duplicates into one grouped issue with an occurrence count, and ties each to the build it first appeared on — so you fix the problem that hurts the most players first and confirm it is gone when its signature disappears from the next release.