fix: half float delta position dither up port - #4129
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NetworkDeltaPosition carries the half float rounding loss of each update into the next one, which keeps the average transmitted position accurate while a value is moving. The loss alone is enough to change the encoded delta, so once the value stops moving that mechanism keeps changing what is sent even though the position has not moved. The encoded value alternates between neighbouring representable values and a stationary object is transmitted as one that oscillates. The rounding loss is now only carried forward while the value moves by at least one representable step. MaxDeltaBeforeAdjustment also determined the transmitted resolution, since a half float's step size grows with its magnitude. At 64 the coarsest step was 31.25mm, so objects away from their base position were reproduced in ~3cm increments. At 2 it is 0.977mm. Folding the delta into the base more often costs no bandwidth with reliable deltas because both sides apply the same rule to the same value, and the reconstructed position is unchanged by the fold. UseUnreliableDeltas forces a full precision base synchronization per fold, so those projects will send those more often. Measured on 10 settling physics objects with half float enabled: 28-42mm of oscillation before, none after, matching the same scene with half float disabled. Objects in motion improve as well, peak error dropping from 12.5mm to 0.587mm. Sender and receiver must agree on MaxDeltaBeforeAdjustment, so this is not compatible across builds. NetworkConstants.PROTOCOL_VERSION already participates in the connection config hash, so mismatched versions cannot connect. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Two NetcodeIntegrationTest cases, one for an object moving in steps too small for the encoding to represent and one for an object at rest. Both move the authority forwards only and require non-authority instances to follow without ever moving backwards. Interpolation cannot overshoot, so movement opposite to the authority's has to have come from the encoding. That also avoids a tolerance that would need revisiting whenever the resolution changes. Two setup details are needed for these to detect anything. The object has to travel away from the base position established when it spawned, since resolution is fine near the base. It then has to step by an amount the encoding cannot represent before coming to rest, because a position a half float represents exactly leaves no rounding loss and so cannot exhibit the problem: resting on 30.0 produces no backwards movement at all while resting on 30.0007 produces 15.6mm. Verified in both directions. Without the fix all four cases fail on the intended assertion, reporting 7.9mm to 10.1mm of backwards movement. With the fix all four pass. These do not use the time travel harness because the behavior only appears over multiple real state update and interpolation cycles. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Updated the changelog to include issue #4129 regarding the precision of NetworkTransform synchronization.
Fixed jitter issue with NetworkTransform.UseHalfFloatPrecision on non-authority instances.
NoelStephensUnity
marked this pull request as ready for review
August 19, 2026 01:36
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Codecov ReportAll modified and coverable lines are covered by tests ✅ @@ Coverage Diff @@
## develop-3.x.x #4129 +/- ##
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+ Coverage 78.01% 78.14% +0.12%
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Files 153 153
Lines 26260 26273 +13
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+ Hits 20486 20530 +44
+ Misses 5774 5743 -31
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... and 4 files with indirect coverage changes
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Adding better coverage and adjusting some of the test to better leverage from NetcodeIntegrationTest helper methods.
Moving the NetworkDeltaPositionTests into its own file.
Bumping the protocol version to assure legacy clients cannot connect to a session with the fixes. While the fixes aren't technically a "breaking change", any projects using the legacy lerp will end up with an offset from the expected final position. Since motion continually feeds the full position (half float or full precision) as deltas this would prevent from "long term drift". Either case, updating the protocol version only assures that clients of a previous version cannot connect to a session with the newer version.
There is one connected client, so the per instance dictionaries and the loops over m_NetworkManagers only ever held one entry. Resolve the non-authority instance once through GetNonAuthorityNetworkManager and name the two sampling frame counts that were inline literals.
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Purpose of this PR
This is an up-port of #4128.
(Refer to that PR for the details)
Jira ticket
NA
Changelog
Documentation
Testing & QA (How your changes can be verified during release Playtest)
Functional Testing
Manual testing :
Automated tests:
The new tests were verified in both directions. Without the fix all four cases fail on the intended assertion, reporting 7.9mm to 10.1mm of backwards movement. With the fix all four pass.
Does the change require QA team to:
These tests do not use the time travel harness, since the behaviour only appears over multiple real state update and interpolation cycles. Runtime is roughly 3.5s per case.
Up-port
No up-port is required.
Backports
Not needed since this is an up-port.