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2026-07-07T13:17:18Z

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= OpenSimulator Internals/Code Map/ScenePresence =

== Overview ==

OpenSim/Region/Framework/Scenes/ScenePresence.cs

One ScenePresence instance exists per agent per region. It represents the avatar -- whether root (avatar is here) or child (avatar is elsewhere, this is a listening post for interest management). ScenePresence implements IScenePresence and EntityBase.

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== Lifecycle States ==

Governed by ScenePresenceStateMachine. The critical flag for most code paths is IsChildAgent (bool).

{| class="wikitable"
! State !! IsChildAgent !! Description
|-
| Child || true || Pre-seeded in neighbouring region. Tracks position updates, no physics, no full scene state.
|-
| Root || false || Avatar is present in this region. Full physics, full scene state, heartbeat participation.
|-
| Deleted || -- || IsDeleted set. Dispose() called.
|}

Transition from child to root happens in MakeRootAgent(), called from CompleteMovement(). Transition from root to child happens in MakeChildAgent(), called by EntityTransferModule on departure.

See [[OpenSimulator Internals/Walkthroughs/Avatar Rez In Region]] for the full transition sequence on login.

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== Constructor ==

ScenePresence(IClientAPI client, Scene world, AvatarAppearance appearance, PresenceType type)

# Sets IsChildAgent = true.
# Sets draw distance from client.StartFar, clamped to region MaxDrawDistance / DefaultDrawDistance.
# Sets RegionHandle, ControllingClient, name fields, UUID, LocalId.
# Fetches UserAccount -- sets m_userFlags and GodController god level. If no account found, god level 0.
# Initialises ScenePresenceAnimator and MovementAnimationOverrides.
# Sets AbsolutePosition from ControllingClient.StartPos.
# Disables child updates and reprioritization (m_childUpdatesBusy = true, m_reprioritizationBusy = true) -- re-enabled after CompleteMovement.
# Calls AdjustKnownSeeds() -- initialises m_knownChildRegions from CapsModule.
# Calls RegisterToClientEvents() -- see Event Wiring below.
# Sets Appearance from passed AvatarAppearance.
# Constructs ScenePresenceStateMachine.
# Calls ControllingClient.RefreshGroupMembership().

----

== Event Wiring ==

RegisterToClientEvents() hooks the following on ControllingClient:

{| class="wikitable"
! Event !! Handler
|-
| OnCompleteMovementToRegion || CompleteMovement()
|-
| OnAgentUpdate || HandleAgentUpdate()
|-
| OnAgentCameraUpdate || HandleAgentCamerasUpdate()
|-
| OnAgentRequestSit || HandleAgentRequestSit()
|-
| OnAgentSit || HandleAgentSit()
|-
| OnSetAlwaysRun || HandleSetAlwaysRun()
|-
| OnStartAnim || HandleStartAnim()
|-
| OnStopAnim || HandleStopAnim()
|-
| OnChangeAnim || avnHandleChangeAnim()
|-
| OnForceReleaseControls || HandleForceReleaseControls()
|-
| OnAutoPilotGo || MoveToTargetHandle()
|-
| OnRegionHandShakeReply || RegionHandShakeReply()
|}

All removed in RemoveClientEvents() on disposal.

----

== MakeRootAgent() ==

private bool MakeRootAgent(Vector3 pos, bool isFlying, ref Vector3 lookat)

Called only from CompleteMovement(). Returns false if already root.

# Acquires m_completeMovementLock.
# Handles pending sit (ParentUUID set): resolves prim, re-seats avatar.
# Sets IsChildAgent = false.
# Updates RegionHandle.
# Fires EventManager.TriggerSetRootAgentScene().
# If not sitting:
#* Calls CheckAndAdjustLandingPoint_OS() or _SL() -- adjusts position for telehubs, parcel landing points, ban lines.
#* Clamps position to region bounds.
#* Raises Z to ground height + avatar half-height.
#* If ViaLogin or ViaLocation flags: raycasts downward from PhysSearchHeight (300f) using RayFilterFlags.PrimsNonPhantomAgents to find surface, avoids placing avatar inside objects.
#* Sets AbsolutePosition.
#* Calls AddToPhysicalScene(isFlying).
# Calls m_scene.SwapRootAgentCount(false, IsNPC).
# Resets MovementFlags = 0.
# Updates circuit: AuthenticateHandler.UpdateAgentChildStatus(circuitCode, false).
# Fires EventManager.TriggerOnMakeRootAgent(this).

Physics position search constants:
* PhysSearchHeight = 300f
* PhysMinSkipGap = 20f
* PhysSkipGapDelta = 30f
* PhysNumberCollisions = 30

----

== MakeChildAgent() ==

public void MakeChildAgent(ulong newRegionHandle)

Called by EntityTransferModule when avatar departs.

# Resets m_updateAgentReceivedAfterTransferEvent.
# Clears group information and cross-update flags.
# Unhooks RegionHeartbeatEnd.
# Sets IsChildAgent = true.
# Calls m_scene.SwapRootAgentCount(true, IsNPC).
# Calls RemoveFromPhysicalScene().
# Clears parcel tracking.
# Sends kill packets to root presences that don't know the new region (won't receive the avatar as child).
# Updates circuit: AuthenticateHandler.UpdateAgentChildStatus(circuitCode, true).
# Fires EventManager.TriggerOnMakeChildAgent(this).

----

== CompleteMovement() ==

public void CompleteMovement(IClientAPI client, bool openChildAgents)

Triggered by OnCompleteMovementToRegion event from viewer.

* For teleports/crossings: calls WaitForUpdateAgent() -- waits up to 10 seconds for source region's UpdateAgent to arrive (sets m_originRegionID via CopyFrom()).
* For real login (IsRealLogin() true): skips WaitForUpdateAgent().
* Calls MakeRootAgent().
* Sends RegionHandshake if not a crossing.
* Calls ControllingClient.MoveAgentIntoRegion().
* Validates baked texture cache (AvatarFactory.ValidateBakedTextureCache()); queues appearance save if invalid.
* Sends initial avatar data to all presences.
* Sends appearance and animations to self and others.
* For real login: calls Scene.AttachmentsModule.RezAttachments(this).
* For crossing with carried attachments: restarts scripts, sends attachment updates.
* For login: calls IFriendsModule.SendFriendsOnlineIfNeeded().
* Hooks RegionHeartbeatEnd for per-frame processing.

IsRealLogin() check:

(teleportFlags & (ViaLogin | ViaHGLogin)) == ViaLogin

----

== RegionHandShakeReply() / SendInitialData() ==

public void RegionHandShakeReply(IClientAPI client)
private void SendInitialData()

RegionHandShakeReply() sets NeedInitialData = 2 on receipt of viewer handshake reply.

SendInitialData() is called from Update() when NeedInitialData > 0. It waits for:
* ViewerFlags.SentSeeds to be set (caps seeds sent to viewer).
* NeedInitialData incremented to 6 (several heartbeat frames for viewer to process seeds).

Then fires async (Util.FireAndForget):
* Releases source region via SimulationService.ReleaseAgent() if callback URI present.
* Calls IEntityTransferModule.CloseOldChildAgents().
* Sends terrain layer data if not a teleport.
* Sends parcel info.
* Sends full avatar updates for all other root presences (SendOtherAgentsAvatarFullToMe()).
* Sends ObjectUpdate packets for all scene objects -- full updates or cache probes depending on ViewerFlags.
* Calls IEntityTransferModule.EnableChildAgents() -- seeds neighbouring regions.
* Sets m_childUpdatesBusy = false.

----

== Update() ==

Called each heartbeat frame from Scene.Update() for every ScenePresence.

* If NeedInitialData > 0: calls SendInitialData() and returns.
* If IsChildAgent or IsInTransit: returns.
* Calls CheckForBorderCrossing().
* Handles MoveToTarget autopilot updates.
* Handles delayed stop.
* If avatar size changed: sends avatar data to all agents.
* If position, velocity, rotation, or collision plane changed beyond tolerance: calls SendTerseUpdateToAllClients().
* Calls CheckForSignificantMovement().

----

== Physical Scene ==

AddToPhysicalScene(bool isFlying):
* Calls PhysicsScene.AddAvatar() -- creates PhysicsActor.
* Wires pa.OnCollisionUpdate → PhysicsCollisionUpdate().
* Wires pa.OnOutOfBounds → OutOfBoundsCall().
* Sets PhysicsActor = pa.

RemoveFromPhysicalScene():
* Interlocked.Exchange to null (thread-safe).
* Unwires collision and OOB events.
* Calls PhysicsScene.RemoveAvatar().

----

== Neighbour Region Tracking ==

m_knownChildRegions: Dictionary<ulong, string> -- regionHandle → seed cap URL.
m_knownChildRegionsSizeInfo: Dictionary<ulong, spRegionSizeInfo> -- regionHandle → (sizeX, sizeY).

Key methods:
* AddNeighbourRegion() / RemoveNeighbourRegion()
* GetChildAgentsToClose() -- computes which neighbours to close on departure, based on IsOutsideView() distance check (currently hardcoded 255 rather than RegionViewDistance).
* CloseChildAgents() -- sends CloseChildAgentConnections to computed list, drops cap seeds.

----

== Sitting ==

HandleAgentRequestSit() → SendSitResponse() → HandleAgentSit() / PhysicsSit().

PhysicsSit() delegates to PhysicsScene.SitAvatar() with callback PhysicsSitResponse(). Falls back to legacy sit if physics engine doesn't support it.

On sit:
* RemoveFromPhysicalScene().
* ParentID = part.LocalId, ParentPart = part.
* part.AddSittingAvatar(this).
* Animator.SetMovementAnimations("SIT").

StandUp():
* Computes world position from sit offset and prim rotation.
* Clears ParentID, ParentPart.
* Calls AddToPhysicalScene() if addPhys true.
* part.RemoveSittingAvatar(this).
* Animator.SetMovementAnimations("STAND").

SIT_TARGET_ADJUSTMENT = (0, 0, 0.4f) -- empirically derived fudge factor matching SL behaviour (Mantis 1716).

----

== Parcel Visibility ==

ParcelHideThisAvatar: true if current parcel has SeeAVs = false.

On parcel crossing (currentParcelUUID setter → ParcelCrossCheck()):
* Computes which presences need kill packets (now hidden from them or they from us).
* Computes which presences need view packets (now visible).
* Sends kills and views accordingly.

----

== Child Agent Data Transfer ==

CopyTo(AgentData, isCrossUpdate): serialises full avatar state for transfer to destination region -- position, velocity, camera, appearance, animations, attachments, script controls, group info, friends online cache.

CopyFrom(AgentData): deserialises on destination side. Sets m_originRegionID, which signals WaitForUpdateAgent() to unblock CompleteMovement().

UpdateChildAgent(AgentData): called on destination when source fires UpdateAgent. Calls CopyFrom() then sets m_updateAgentReceivedAfterTransferEvent.

UpdateChildAgent(AgentPosition): lightweight position-only update for child agent interest management. Adjusts position by region offset, updates throttles with distance-based scaling factor.

----

== Movement ==

HandleAgentUpdate(): main movement handler. Processes AgentUpdateArgs from viewer each packet.
* Drops updates where IsChildAgent or IsInTransit.
* Updates DrawDistance, HideTitle, MuteCollisions, mouse state, State byte.
* Computes movement vector from control flags.
* Calls AddNewMovement() → sets PhysicsActor.TargetVelocity.
* Calls Animator.UpdateMovementAnimations().
* Calls SendControlsToScripts() -- fires EventManager.TriggerControlEvent for scripted control listeners.

Autopilot: MoveToTarget() / HandleMoveToTargetUpdate() -- PID-style movement toward a target position, used by llMoveToTarget() and parcel enforcement.

Border crossing detection: CheckForBorderCrossing() -- projects position by velocity * FrameTime, if outside region bounds calls CrossToNewRegion() → Scene.CrossAgentToNewRegion().

----

== Attachment Management ==

m_attachments: List<SceneObjectGroup>, locked on AttachmentsSyncLock.

AddAttachment() / RemoveAttachment() / GetAttachments() / ClearAttachments().

SendAttachmentsToAgentNF(): sends terse update then full updates for all attachments to a specific presence.
SendAttachmentScheduleUpdate(): sends pending flagged updates to self and all visible presences.

----

== Animation ==

Animator: ScenePresenceAnimator -- manages animation state machine.
Overrides: MovementAnimationOverrides -- server-side animation override pairs.

HandleStartAnim() / HandleStopAnim() / avnHandleChangeAnim(): viewer-initiated animation control.
RegionHeartbeatEnd hook: calls Animator.UpdateMovementAnimations() every 2 frames when root and not sitting.

----

== Significant Movement ==

CheckForSignificantMovement():
* MOVEMENT (0.25f sq) threshold: fires EventManager.TriggerOnClientMovement().
* SIGNIFICANT_MOVEMENT (16.0f sq) threshold: fires EventManager.TriggerSignificantClientMovement().
* CHILDAGENTSCHECK_MOVEMENT (1024f sq / 32m) threshold: calls IEntityTransferModule.EnableChildAgents() to update neighbour seeds.
* CHILDUPDATES_MOVEMENT (100f sq): sends AgentPosition updates to known child regions.

----

== Key Constants ==

{| class="wikitable"
! Constant !! Value !! Purpose
|-
| MOVEMENT || 0.25f || Minimum movement to trigger client movement event (sq distance)
|-
| SIGNIFICANT_MOVEMENT || 16.0f || Minimum movement to trigger significant movement event (sq distance)
|-
| CHILDUPDATES_MOVEMENT || 100.0f || Minimum movement to send child agent position update (sq distance)
|-
| CHILDAGENTSCHECK_MOVEMENT || 1024.0f || Minimum movement to recheck neighbour child agents (sq distance, ~32m)
|-
| CHILDUPDATES_TIME || 2000f || Minimum ms between child agent updates
|-
| SIT_TARGET_ADJUSTMENT || (0,0,0.4f) || Sit target fudge factor matching SL (Mantis 1716)
|-
| PhysSearchHeight || 300f || Ray cast start height for spawn position search
|-
| PhysMinSkipGap || 20f || Minimum gap between surfaces in spawn position search
|-
| AgentControlNormalVel || 4.096f || Normal walk speed multiplier
|-
| AgentControlMidVel || 0.6 * 4.096f || Slow walk speed multiplier
|}

----

== Known Issues ==

* IncomingAttechments() typo in Scene.cs line 2976 and AttachmentsModule.cs line 384 (Mantis pending).
* GetChildAgentsToClose() uses hardcoded 255 for view distance rather than RegionViewDistance -- comment in source acknowledges this.

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== See Also ==

* [[OpenSimulator Internals/Code Map/Scene]]
* [[OpenSimulator Internals/Code Map/LLClientView]]
* [[OpenSimulator Internals/Code Map/LLUDP]]
* [[OpenSimulator Internals/Walkthroughs/Avatar Rez In Region]]
* [[OpenSimulator Internals/Walkthroughs/Avatar Transfer Between Regions]]
* [[OpenSimulator Internals/Walkthroughs/Avatar Logs Out]]

OpenSimulator Internals/Code Map/ScenePresence - Revision history

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