From c4a0b55948eee232d9d2f3abf180b946410c993a Mon Sep 17 00:00:00 2001 From: Noel Stephens Date: Tue, 18 Aug 2026 15:18:36 -0500 Subject: [PATCH 1/3] fix: half float position encoding manufactures motion on resting objects 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 --- com.unity.netcode.gameobjects/CHANGELOG.md | 4 ++ .../Components/NetworkDeltaPosition.cs | 48 +++++++++++++++++-- 2 files changed, 49 insertions(+), 3 deletions(-) diff --git a/com.unity.netcode.gameobjects/CHANGELOG.md b/com.unity.netcode.gameobjects/CHANGELOG.md index 931ae821f3..6f3369de32 100644 --- a/com.unity.netcode.gameobjects/CHANGELOG.md +++ b/com.unity.netcode.gameobjects/CHANGELOG.md @@ -13,6 +13,8 @@ Additional documentation and release notes are available at [Multiplayer Documen ### Changed +- Changed `NetworkTransform.UseHalfFloatPrecision` to synchronize position with a resolution of approximately 1mm regardless of how far an object has travelled. Previously the resolution could degrade to approximately 3cm. This does not increase bandwidth, but projects using `NetworkTransform.UseUnreliableDeltas` will send full precision position updates more often. (#4126) + ### Deprecated @@ -22,6 +24,8 @@ Additional documentation and release notes are available at [Multiplayer Documen ### Fixed +- Issue where objects using `NetworkTransform.UseHalfFloatPrecision` appeared to jitter on non-authority instances while they were stationary or coming to rest, even though the authority was not moving them. (#4126) + ### Security diff --git a/com.unity.netcode.gameobjects/Runtime/Components/NetworkDeltaPosition.cs b/com.unity.netcode.gameobjects/Runtime/Components/NetworkDeltaPosition.cs index a780a07230..3bae7eded3 100644 --- a/com.unity.netcode.gameobjects/Runtime/Components/NetworkDeltaPosition.cs +++ b/com.unity.netcode.gameobjects/Runtime/Components/NetworkDeltaPosition.cs @@ -11,7 +11,14 @@ namespace Unity.Netcode.Components [Serializable] public struct NetworkDeltaPosition : INetworkSerializable { - internal const float MaxDeltaBeforeAdjustment = 64f; + /// + /// How far the delta may grow before it is folded into the base position. + /// + /// + /// This determines the transmitted position resolution, since a half float's step size grows with its + /// magnitude. Keeping the delta small keeps that step small: at 2 the coarsest step is roughly 1mm. + /// + internal const float MaxDeltaBeforeAdjustment = 2f; /// /// The HalfVector3 used to synchronize the delta in position @@ -138,14 +145,29 @@ public void UpdateFrom(ref Vector3 vector3, int networkTick) { CollapsedDeltaIntoBase = false; NetworkTick = networkTick; - DeltaPosition = (vector3 + PrecisionLossDelta) - CurrentBasePosition; for (int i = 0; i < HalfVector3.Length; i++) { if (HalfVector3.AxisToSynchronize[i]) { + var rawDelta = vector3[i] - CurrentBasePosition[i]; + + // Adding the previous rounding loss back in keeps the average position accurate while the + // value is moving, but it also changes the value being sent. Once the value stops moving + // that is all it does, which makes a stationary object appear to oscillate. + var movedSinceLastSend = Mathf.Abs(vector3[i] - PreviousPosition[i]); + var applyPrecisionLoss = movedSinceLastSend >= HalfPrecisionQuantum(rawDelta); + + DeltaPosition[i] = applyPrecisionLoss ? rawDelta + PrecisionLossDelta[i] : rawDelta; + HalfVector3.Axis[i] = math.half(DeltaPosition[i]); HalfDeltaConvertedBack[i] = Mathf.HalfToFloat(HalfVector3.Axis[i].value); - PrecisionLossDelta[i] = DeltaPosition[i] - HalfDeltaConvertedBack[i]; + + // Left unchanged when skipped so it is still applied once movement resumes. + if (applyPrecisionLoss) + { + PrecisionLossDelta[i] = DeltaPosition[i] - HalfDeltaConvertedBack[i]; + } + if (Mathf.Abs(HalfDeltaConvertedBack[i]) >= MaxDeltaBeforeAdjustment) { CurrentBasePosition[i] += HalfDeltaConvertedBack[i]; @@ -165,6 +187,26 @@ public void UpdateFrom(ref Vector3 vector3, int networkTick) } } + /// + /// The smallest change a half float can represent at the magnitude of the value passed in. + /// + /// The value to get the step size for. + /// The distance to the next representable half float value. + [MethodImpl(MethodImplOptions.AggressiveInlining)] + internal static float HalfPrecisionQuantum(float value) + { + // The step size is symmetric about zero, so the sign is dropped. + var magnitude = (ushort)(math.half(value).value & 0x7FFF); + + // Guard only: stepping past the largest finite half float would give infinity. + if (magnitude >= 0x7BFF) + { + return MaxDeltaBeforeAdjustment; + } + + return Mathf.HalfToFloat((ushort)(magnitude + 1)) - Mathf.HalfToFloat(magnitude); + } + /// /// Constructor /// From facdbe73287a0e37412670dce84c3c09eb0b75ab Mon Sep 17 00:00:00 2001 From: Noel Stephens Date: Tue, 18 Aug 2026 15:18:53 -0500 Subject: [PATCH 2/3] test: integration coverage for half float position encoding 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 --- ...NetworkTransformHalfFloatPrecisionTests.cs | 283 ++++++++++++++++++ ...rkTransformHalfFloatPrecisionTests.cs.meta | 11 + 2 files changed, 294 insertions(+) create mode 100644 com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs create mode 100644 com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs.meta diff --git a/com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs b/com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs new file mode 100644 index 0000000000..5f7adc2319 --- /dev/null +++ b/com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs @@ -0,0 +1,283 @@ +using System.Collections; +using System.Collections.Generic; +using NUnit.Framework; +using Unity.Netcode.Components; +using Unity.Netcode.TestHelpers.Runtime; +using UnityEngine; +using UnityEngine.TestTools; + +namespace Unity.Netcode.RuntimeTests +{ + /// + /// Validates that does not introduce motion of its own. + /// + /// + /// Both tests move the authority in one direction only and require non-authority instances to follow without + /// ever moving backwards. Interpolation cannot overshoot, so any movement opposite to the authority's has to + /// have come from how the position was encoded rather than from the authority. + ///

+ /// These do not use the time travel harness because the behavior only appears over multiple real state update + /// and interpolation cycles. + /// + [TestFixture(HostOrServer.Host)] + [TestFixture(HostOrServer.DAHost)] + internal class NetworkTransformHalfFloatPrecisionTests : IntegrationTestWithApproximation + { + protected override int NumberOfClients => 1; + + /// + /// How far the object travels before the position is checked. + /// + /// + /// Half float resolution gets coarser the further the object is from the base position established when it + /// spawned, so the object has to travel away from that base for the resolution to be worth testing. + /// + private const float k_TravelDistance = 30.0f; + + private const float k_TravelStep = 1.5f; + + // Moves the object off a position that a half float can represent exactly, which is a position that leaves + // no rounding loss behind and so cannot show the problem being tested for. + private const float k_UnrepresentableOffset = 0.0007f; + + // Small enough per update that the encoding cannot represent the change on its own. + private const float k_CreepStep = 0.0005f; + + private const int k_CreepTicks = 60; + + // Tolerated backwards movement, which is float noise only. Well below the roughly 1mm resolution. + private const float k_MonotonicEpsilon = 1e-5f; + + private GameObject m_TestPrefab; + private NetworkManager m_AuthorityNetworkManager; + private NetworkTransform m_AuthorityInstance; + private readonly List m_NonAuthorityInstances = new List(); + + private readonly Dictionary m_WorstRegression = new Dictionary(); + private readonly Dictionary m_LastObserved = new Dictionary(); + + private int m_TicksApplied; + private float m_StepThisPhase; + + public NetworkTransformHalfFloatPrecisionTests(HostOrServer hostOrServer) : base(hostOrServer) + { + } + + // TODO: [CmbServiceTests] Validate this against the service once half float precision is covered there. + protected override bool UseCMBService() + { + return false; + } + + protected override void OnServerAndClientsCreated() + { + m_TestPrefab = CreateNetworkObjectPrefab("HalfFloatObj"); + var networkTransform = m_TestPrefab.AddComponent(); + + networkTransform.UseHalfFloatPrecision = true; + networkTransform.Interpolate = true; + + // Lerp smoothing would filter out the movement being tested for. + networkTransform.PositionInterpolationType = NetworkTransform.InterpolationTypes.Lerp; + networkTransform.PositionLerpSmoothing = false; + + // No threshold, so the very small movements used below are actually sent. + networkTransform.PositionThreshold = 0.0f; + + networkTransform.SyncRotAngleX = false; + networkTransform.SyncRotAngleY = false; + networkTransform.SyncRotAngleZ = false; + networkTransform.SyncScaleX = false; + networkTransform.SyncScaleY = false; + networkTransform.SyncScaleZ = false; + + base.OnServerAndClientsCreated(); + } + + private bool AllInstancesSpawned() + { + m_NonAuthorityInstances.Clear(); + foreach (var networkManager in m_NetworkManagers) + { + if (networkManager == m_AuthorityNetworkManager) + { + continue; + } + + if (!networkManager.SpawnManager.SpawnedObjects.ContainsKey(m_AuthorityInstance.NetworkObjectId)) + { + return false; + } + + m_NonAuthorityInstances.Add(networkManager.SpawnManager.SpawnedObjects[m_AuthorityInstance.NetworkObjectId].GetComponent()); + } + return m_NonAuthorityInstances.Count > 0; + } + + private bool AllInstancesCaughtUp() + { + foreach (var nonAuthority in m_NonAuthorityInstances) + { + if (!Approximately(nonAuthority.transform.position, m_AuthorityInstance.transform.position)) + { + return false; + } + } + return true; + } + + /// + /// Records any movement opposite to the direction the authority is moving. + /// + /// + /// Sampled once per frame rather than once per tick, since the position applied to the transform is what + /// needs to be checked. + /// + private void SampleForRegression() + { + foreach (var nonAuthority in m_NonAuthorityInstances) + { + var current = nonAuthority.transform.position.x; + if (m_LastObserved.TryGetValue(nonAuthority, out var previous)) + { + var regression = previous - current; + if (regression > m_WorstRegression[nonAuthority]) + { + m_WorstRegression[nonAuthority] = regression; + } + } + m_LastObserved[nonAuthority] = current; + } + } + + private void BeginSampling() + { + m_WorstRegression.Clear(); + m_LastObserved.Clear(); + foreach (var nonAuthority in m_NonAuthorityInstances) + { + m_WorstRegression.Add(nonAuthority, 0.0f); + m_LastObserved.Add(nonAuthority, nonAuthority.transform.position.x); + } + } + + private void AssertNoRegression(string phase) + { + foreach (var entry in m_WorstRegression) + { + Assert.LessOrEqual(entry.Value, k_MonotonicEpsilon, + $"[{phase}] {entry.Key.NetworkManager.name} moved {entry.Value} backwards along X while the " + + $"authority only ever moved forwards. Interpolation cannot overshoot, so this motion was " + + $"introduced by the half float position encoding rather than reproduced from the authority."); + } + } + + /// + /// Advances the authority one step per tick along +X. + /// + /// + /// Driven from the tick event so the position written is the one captured for that same tick. + /// + private void OnNetworkTick() + { + m_TicksApplied++; + var position = m_AuthorityInstance.transform.position; + position.x += m_StepThisPhase; + m_AuthorityInstance.transform.position = position; + } + + private IEnumerator DriveAuthority(float stepPerTick, int ticks) + { + m_TicksApplied = 0; + m_StepThisPhase = stepPerTick; + m_AuthorityNetworkManager.NetworkTickSystem.Tick += OnNetworkTick; + yield return WaitForConditionOrTimeOut(() => m_TicksApplied >= ticks); + m_AuthorityNetworkManager.NetworkTickSystem.Tick -= OnNetworkTick; + AssertOnTimeout($"Timed out waiting for {ticks} authority updates (applied {m_TicksApplied})."); + } + + /// + /// Moves an object away from its base position and then moves it forward in very small steps, requiring + /// every non-authority instance to follow without ever moving backwards. + /// + /// An for the test coroutine. + [UnityTest] + public IEnumerator HalfFloatPrecisionDoesNotInvertMotion() + { + m_AuthorityNetworkManager = GetAuthorityNetworkManager(); + m_AuthorityInstance = SpawnObject(m_TestPrefab, m_AuthorityNetworkManager).GetComponent(); + + yield return WaitForConditionOrTimeOut(AllInstancesSpawned); + AssertOnTimeout($"Not all clients spawned {m_AuthorityInstance.name}!"); + + var travelTicks = (int)(k_TravelDistance / k_TravelStep); + yield return DriveAuthority(k_TravelStep, travelTicks); + + yield return WaitForConditionOrTimeOut(AllInstancesCaughtUp); + AssertOnTimeout("Non-authority instances did not catch up to the authority after the travel phase."); + + BeginSampling(); + m_TicksApplied = 0; + m_StepThisPhase = k_CreepStep; + m_AuthorityNetworkManager.NetworkTickSystem.Tick += OnNetworkTick; + while (m_TicksApplied < k_CreepTicks) + { + SampleForRegression(); + yield return null; + } + m_AuthorityNetworkManager.NetworkTickSystem.Tick -= OnNetworkTick; + + // Keep sampling while the last sent states are still being interpolated. + for (var i = 0; i < 30; i++) + { + SampleForRegression(); + yield return null; + } + + AssertNoRegression("creep"); + + // Small movements still have to arrive rather than be discarded. + yield return WaitForConditionOrTimeOut(AllInstancesCaughtUp); + AssertOnTimeout($"Non-authority instances did not converge on the authority position " + + $"{m_AuthorityInstance.transform.position} after creeping, which means slow motion is being " + + $"discarded rather than transmitted."); + } + + /// + /// Requires a stationary authority to produce a stationary non-authority. + /// + /// An for the test coroutine. + [UnityTest] + public IEnumerator HalfFloatPrecisionHoldsStillWhenStationary() + { + m_AuthorityNetworkManager = GetAuthorityNetworkManager(); + m_AuthorityInstance = SpawnObject(m_TestPrefab, m_AuthorityNetworkManager).GetComponent(); + + yield return WaitForConditionOrTimeOut(AllInstancesSpawned); + AssertOnTimeout($"Not all clients spawned {m_AuthorityInstance.name}!"); + + var travelTicks = (int)(k_TravelDistance / k_TravelStep); + yield return DriveAuthority(k_TravelStep, travelTicks); + + // A position that a half float happens to represent exactly leaves no rounding loss behind, and with + // no rounding loss there is nothing that could move the object. Offsetting by less than the encoding + // can represent guarantees there is some, which is the state a settling object is normally left in. + yield return DriveAuthority(k_UnrepresentableOffset, 1); + + yield return WaitForConditionOrTimeOut(AllInstancesCaughtUp); + AssertOnTimeout("Non-authority instances did not catch up to the authority after the travel phase."); + + // Nothing moves for the rest of the test, so the authority's last direction was forwards. Checking for + // backwards movement rather than for drift from a starting point means the instances are still free to + // finish interpolating towards the authority without that counting against them. + BeginSampling(); + for (var i = 0; i < 120; i++) + { + SampleForRegression(); + yield return null; + } + + AssertNoRegression("stationary"); + } + } +} diff --git a/com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs.meta b/com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs.meta new file mode 100644 index 0000000000..b380ca173d --- /dev/null +++ b/com.unity.netcode.gameobjects/Tests/Runtime/NetworkTransform/NetworkTransformHalfFloatPrecisionTests.cs.meta @@ -0,0 +1,11 @@ +fileFormatVersion: 2 +guid: 9130626724ce4dddcfcd533d630aa6b3 +MonoImporter: + externalObjects: {} + serializedVersion: 2 + defaultReferences: [] + executionOrder: 0 + icon: {instanceID: 0} + userData: + assetBundleName: + assetBundleVariant: From 68d620128f3a15d51ab687fde12ed234f4d0ee41 Mon Sep 17 00:00:00 2001 From: Noel Stephens Date: Tue, 18 Aug 2026 15:27:55 -0500 Subject: [PATCH 3/3] Update CHANGELOG for NetworkTransform precision changes Updated changelog entries for NetworkTransform.UseHalfFloatPrecision to reflect changes in issue tracking numbers. --- com.unity.netcode.gameobjects/CHANGELOG.md | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/com.unity.netcode.gameobjects/CHANGELOG.md b/com.unity.netcode.gameobjects/CHANGELOG.md index 6f3369de32..41e7c96198 100644 --- a/com.unity.netcode.gameobjects/CHANGELOG.md +++ b/com.unity.netcode.gameobjects/CHANGELOG.md @@ -13,7 +13,7 @@ Additional documentation and release notes are available at [Multiplayer Documen ### Changed -- Changed `NetworkTransform.UseHalfFloatPrecision` to synchronize position with a resolution of approximately 1mm regardless of how far an object has travelled. Previously the resolution could degrade to approximately 3cm. This does not increase bandwidth, but projects using `NetworkTransform.UseUnreliableDeltas` will send full precision position updates more often. (#4126) +- Changed `NetworkTransform.UseHalfFloatPrecision` to synchronize position with a resolution of approximately 1mm regardless of how far an object has travelled. Previously the resolution could degrade to approximately 3cm. This does not increase bandwidth, but projects using `NetworkTransform.UseUnreliableDeltas` will send full precision position updates more often. (#4128) ### Deprecated @@ -24,7 +24,7 @@ Additional documentation and release notes are available at [Multiplayer Documen ### Fixed -- Issue where objects using `NetworkTransform.UseHalfFloatPrecision` appeared to jitter on non-authority instances while they were stationary or coming to rest, even though the authority was not moving them. (#4126) +- Issue where objects using `NetworkTransform.UseHalfFloatPrecision` appeared to jitter on non-authority instances while they were stationary or coming to rest, even though the authority was not moving them. (#4128) ### Security