2.5 KiB
Context
MovementComponent.SetServerTick(long serverTick) drives input-send cadence by comparing server tick to local client tick. When _currentTickOffset = serverTick - Tick - _startTickOffset is negative, it sets _sendInterval = 0.052f; when positive, _sendInterval = 0.048f. When the offset hovers near zero (e.g., due to minor clock drift or network jitter), the sign flips each call, causing _sendInterval to toggle every frame between 0.048 and 0.052. This send-rate oscillation adds jitter to the input cadence.
Goals / Non-Goals
Goals:
- Prevent send interval oscillation when server tick offset is near zero.
- Preserve meaningful clock correction when real drift exists (offset is consistently positive or negative).
Non-Goals:
- This is not a full clock synchronization protocol — only a local oscillation guard.
- Does not change the underlying tick offset computation.
Decisions
Decision: Dead-band hysteresis for send interval correction
Instead of toggling _sendInterval on every sign change of _currentTickOffset, apply a dead-band threshold. Only correct the send interval when the absolute offset exceeds a meaningful threshold (e.g., 1-2 ticks = 50-100ms of drift).
Current code (problematic):
if (_currentTickOffset < 0)
_sendInterval = 0.052f;
if (_currentTickOffset > 0)
_sendInterval = 0.048f;
Proposed replacement:
private const float kTickOffsetThreshold = 2; // ticks
if (_currentTickOffset < -kTickOffsetThreshold)
_sendInterval = 0.052f;
else if (_currentTickOffset > kTickOffsetThreshold)
_sendInterval = 0.048f;
// else: keep current interval (no correction within dead band)
Alternatives considered:
- Exponential moving average of offset — smooths jitter but adds complexity and latency to correction.
- Remove correction entirely, use fixed 0.05s — simpler but loses adaptive behavior when real drift exists.
The dead-band approach is the simplest that directly solves oscillation without adding state complexity.
Risks / Trade-offs
- Risk: If
kTickOffsetThresholdis too large, real drift may not be corrected fast enough.- Mitigation: Start with a conservative threshold (1-2 ticks). Adjust after measuring.
- Risk: The hysteresis introduces a zone where no correction is applied even when offset is slightly non-zero.
- Accepted: This is the intended behavior — minor fluctuations near zero should not disturb steady-rate sending.