Before: remote characters stutter-hop between UpdatePosition broadcasts
(typical 100-200ms interval), looking lagging-forward during continuous
motion. The retail client hides this gap by integrating velocity forward
each tick — apply_current_movement in chunk_00520000.c L7132-L7189,
mirrored by holtburger's project_pose_by_velocity in spatial/physics.rs.
Strategy:
1. RemoteDeadReckonState per remote entity tracks the last authoritative
server position + rotation, an EMA-smoothed observed velocity from
position deltas, and any server-supplied HasVelocity vector.
2. OnLivePositionUpdated: on each UpdatePosition arrival, snap the entity
to the server position, then update the dead-reckon state. The
observed-velocity is a 50/50 EMA against the running average so a
single jitter sample doesn't blow out the velocity.
3. TickAnimations: each tick, for every remote entity in a locomotion
cycle, integrate Entity.Position += worldVelocity * dt. World velocity
is pulled in priority order:
- Sequencer's MotionData.Velocity rotated by Entity.Rotation (the
primary source; matches MotionData's "world-space on the object"
convention per r03 §1.3)
- Server-supplied HasVelocity from UpdatePosition (already world-space)
- EMA-observed position-delta velocity (fallback for NPC motion
tables with HasVelocity=0)
4. Cap: if the predicted position drifts more than velocity ×
DeadReckonMaxPredictSeconds (1.0s) from the last server position,
clamp back toward the server. This prevents runaway when sequencer
velocity and server reality disagree (e.g. server rubber-banding).
Result: remote chars now move smoothly between position updates,
matching the retail client's visual feel. When UpdatePosition arrives
the entity snaps to the authoritative position and the dead-reckon
origin resets, so there's no accumulating drift.
Tests: CurrentVelocity_ScalesWithSpeedMod — new unit test verifying
that the sequencer's CurrentVelocity accurately reflects speedMod changes
across both SetCycle's rebuild path and its rescale path. Combined with
the existing MultiplyCyclicFramerate tests, this validates the
downstream-visible velocity surface the dead-reckoner reads. 633 tests
green (was 632).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
b7a9322b40