AMjArticulation

Represents a MuJoCo articulation (robot or multibody system).

This actor parses its hierarchy of MuJoCo-related components (MjBody, MjJoint, etc.) and compiles them into the MuJoCo mjSpec. It also handles runtime synchronization between MuJoCo physics and Unreal SceneComponents.

Attribute	Value
Kind	Class
UE Macro	UCLASS
Inherits	APawn

Properties Functions

Properties

Public Properties

Property	Type	Description
bValidateOnBlueprintCompile	bool	If true, automatically validates spec when the Blueprint is compiled.
bShowGroup3	bool	Toggle to show/hide Group 3 visualization (often used for collision meshes).
bDrawDebugCollision	bool	Toggles debug drawing of MuJoCo collision convex hulls for this articulation.
bDrawDebugJoints	bool	Toggles debug drawing of joint axes and range arcs for this articulation.
bDrawDebugSites	bool	Toggles debug drawing of site markers for this articulation.
PossessCameraDistance	float	Spring arm length when possessed (cm).
PossessCameraPitch	float	Camera pitch angle when possessed (degrees, negative = look down).
PossessCameraLagSpeed	float	Camera position lag speed. Lower = smoother, higher = snappier.
PossessCameraRotationLagSpeed	float	Camera rotation lag speed. Lower = smoother.
PossessCameraOffset	FVector	Vertical offset above body center (cm). Reduces vertical bounce from walking/trotting.
ControlSource	uint8	Determines whether this specific articulation is controlled by ZMQ or UI/Blueprints.
OnCollision	FOnMjCollision	Fires when a collision occurs involving geoms of this articulation.
bAttachFailed	bool	True if mjs_attach failed during Setup. This articulation has no compiled representation.
MuJoCoXMLFile	FFilePath	Optional: Path to an existing MuJoCo XML to import.
SimOptions	FMuJoCoOptions	Simulation options for this articulation's child spec.
DefaultSceneRoot	class USceneComponent*

bValidateOnBlueprintCompile

If true, automatically validates spec when the Blueprint is compiled.

• Type: bool
• Editor: ✏️ EditAnywhere
• Category: MuJoCo|Validation

bShowGroup3

Toggle to show/hide Group 3 visualization (often used for collision meshes).

• Type: bool
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Visuals

bDrawDebugCollision

Toggles debug drawing of MuJoCo collision convex hulls for this articulation.

• Type: bool
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Debug

bDrawDebugJoints

Toggles debug drawing of joint axes and range arcs for this articulation.

• Type: bool
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Debug

bDrawDebugSites

Toggles debug drawing of site markers for this articulation.

• Type: bool
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Debug

PossessCameraDistance

Spring arm length when possessed (cm).

• Type: float
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Camera

PossessCameraPitch

Camera pitch angle when possessed (degrees, negative = look down).

• Type: float
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Camera

PossessCameraLagSpeed

Camera position lag speed. Lower = smoother, higher = snappier.

• Type: float
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Camera

PossessCameraRotationLagSpeed

Camera rotation lag speed. Lower = smoother.

• Type: float
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Camera

PossessCameraOffset

Vertical offset above body center (cm). Reduces vertical bounce from walking/trotting.

• Type: FVector
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Camera

ControlSource

Determines whether this specific articulation is controlled by ZMQ or UI/Blueprints.

• Type: uint8
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Runtime

OnCollision

Fires when a collision occurs involving geoms of this articulation.

• Type: FOnMjCollision
• Category: MuJoCo|Events

bAttachFailed

True if mjs_attach failed during Setup. This articulation has no compiled representation.

• Type: bool
• Blueprint: 🟢 ReadOnly
• Category: MuJoCo|Status

MuJoCoXMLFile

Optional: Path to an existing MuJoCo XML to import.

• Type: FFilePath
• Editor: ✏️ EditAnywhere
• Category: MuJoCo Import

SimOptions

Simulation options for this articulation's child spec.

• Type: FMuJoCoOptions
• Editor: ✏️ EditAnywhere
• Blueprint: 🔵 ReadWrite
• Category: MuJoCo|Options

DefaultSceneRoot

• Type: class USceneComponent*
• Editor: 👁 VisibleAnywhere
• Blueprint: 🟢 ReadOnly
• Category: MjArticulation

Functions

Public Functions

General

Function	Returns	Description
ShouldTickIfViewportsOnly()	bool	Allow ticking in editor viewports when debug drawing is enabled.
UpdateGroup3Visibility()	void	Updates the visibility of all Group 3 geoms based on bShowGroup3.
GetRuntimeComponents()	template<typename T> void	Templated helper to find all components of type T belonging to this articulation
GetComponentByMjId()	UMjComponent*	Gets any UMjComponent by its MuJoCo objective type and ID.
PossessedBy()	void	Adds twist mapping context on possession.
UnPossessed()	void	Removes twist mapping context and zeros twist state on release.
Setup()	void	Initializes the articulation, adding its components to the provided mjSpec.
PostSetup()	void	Finalizes setup after compilation, resolving indices and bindings.
DrawDebugCollision()	void	draws debug lines for collision geoms.
DrawDebugJoints()	void	draws joint axis lines and range arcs.
DrawDebugSites()	void	draws site location markers.

ShouldTickIfViewportsOnly

Allow ticking in editor viewports when debug drawing is enabled.

• Signature: ShouldTickIfViewportsOnly()
• Returns: bool

UpdateGroup3Visibility

Updates the visibility of all Group 3 geoms based on bShowGroup3.

• Signature: UpdateGroup3Visibility()

GetRuntimeComponents

Templated helper to find all components of type T belonging to this articulation

• Signature: GetRuntimeComponents(TArray<T*>& OutComponents)
• Returns: template void

GetComponentByMjId

Gets any UMjComponent by its MuJoCo objective type and ID.

• Signature: GetComponentByMjId(mjtObj type, int32 id)
• Returns: UMjComponent*

PossessedBy

Adds twist mapping context on possession.

• Signature: PossessedBy(AController* NewController)

UnPossessed

Removes twist mapping context and zeros twist state on release.

• Signature: UnPossessed()

Setup

Initializes the articulation, adding its components to the provided mjSpec.

• Signature: Setup(mjSpec* Spec, mjVFS* VFS)

PostSetup

Finalizes setup after compilation, resolving indices and bindings.

• Signature: PostSetup(mjModel* Model, mjData* Data)

DrawDebugCollision

draws debug lines for collision geoms.

• Signature: DrawDebugCollision()

DrawDebugJoints

draws joint axis lines and range arcs.

• Signature: DrawDebugJoints()

DrawDebugSites

draws site location markers.

• Signature: DrawDebugSites()

MuJoCo|Discovery

Function	Returns	Description
GetRuntimeComponentsOfClass()	TArray<USceneComponent*>	Returns all components of a specific class that are not marked as 'bIsDefault'.

GetRuntimeComponentsOfClass

Returns all components of a specific class that are not marked as 'bIsDefault'.

• Signature: GetRuntimeComponentsOfClass(TSubclassOf<USceneComponent> ComponentClass)
• Blueprint: 🔵 Callable
• Returns: TArray

MuJoCo|Keyframes

Function	Returns	Description
GetKeyframeNames()	TArray<FString>	Returns the names of all keyframes on this articulation.
ResetToKeyframe()	bool	Resets simulation state to a named keyframe (one-shot teleport).
HoldKeyframe()	bool	Starts continuously driving actuators to hold a keyframe's joint positions.
StopHoldKeyframe()	void	Stops holding a keyframe. Actuators return to normal control source.
IsHoldingKeyframe()	bool	Returns true if currently holding a keyframe pose.

GetKeyframeNames

Returns the names of all keyframes on this articulation.

• Signature: GetKeyframeNames()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray

ResetToKeyframe

Resets simulation state to a named keyframe (one-shot teleport).

• Signature: ResetToKeyframe(const FString& KeyframeName)
• Blueprint: 🔵 Callable
• Returns: bool

HoldKeyframe

Starts continuously driving actuators to hold a keyframe's joint positions.

• Signature: HoldKeyframe(const FString& KeyframeName)
• Blueprint: 🔵 Callable
• Returns: bool

StopHoldKeyframe

Stops holding a keyframe. Actuators return to normal control source.

• Signature: StopHoldKeyframe()
• Blueprint: 🔵 Callable

IsHoldingKeyframe

Returns true if currently holding a keyframe pose.

• Signature: IsHoldingKeyframe()
• Blueprint: 💎 Pure
• Returns: bool

MuJoCo|Runtime

Function	Returns	Description
ApplyControls()	void	Applies values from ActuatorControls map to the running m_data->ctrl buffer.
GetActuators()	TArray<UMjActuator*>	Returns an array of all UMjActuator components on this articulation.
GetJoints()	TArray<UMjJoint*>	Returns an array of all UMjJoint components on this articulation.
GetSensors()	TArray<UMjSensor*>	Returns an array of all UMjSensor components on this articulation.
GetBodies()	TArray<UMjBody*>	Returns an array of all UMjBody components on this articulation.
GetFrames()	TArray<UMjFrame*>	Returns an array of all UMjFrame components on this articulation.
GetGeoms()	TArray<UMjGeom*>	Returns an array of all UMjGeom components on this articulation.
GetActuatorNames()	TArray<FString>	Returns the UE component names of all actuators on this articulation.
GetJointNames()	TArray<FString>	Returns the UE component names of all joints on this articulation.
GetSensorNames()	TArray<FString>	Returns the UE component names of all sensors on this articulation.
GetBodyNames()	TArray<FString>	Returns the UE component names of all MjBody components on this articulation.
GetActuator()	UMjActuator*	Gets the UMjActuator component by its UE component name. Returns nullptr if not found.
GetJoint()	UMjJoint*	Gets the UMjJoint component by its UE component name. Returns nullptr if not found.
GetSensor()	UMjSensor*	Gets the UMjSensor component by its UE component name. Returns nullptr if not found.
GetBody()	UMjBody*	Gets the UMjBody component by its UE component name. Returns nullptr if not found.
GetTendons()	TArray<UMjTendon*>	Returns an array of all UMjTendon components on this articulation.
GetTendonNames()	TArray<FString>	Returns the UE component names of all tendons on this articulation.
GetTendon()	UMjTendon*	Gets the UMjTendon component by its UE component name. Returns nullptr if not found.
GetEqualities()	TArray<UMjEquality*>	Returns an array of all UMjEquality components on this articulation.
GetKeyframes()	TArray<UMjKeyframe*>	Returns an array of all UMjKeyframe components on this articulation.
GetBodyByMjId()	UMjBody*	Gets a UMjBody component by its MuJoCo Body ID.
GetGeomByMjId()	UMjGeom*	Gets a UMjGeom component by its MuJoCo Geom ID.

ApplyControls

Applies values from ActuatorControls map to the running m_data->ctrl buffer.

• Signature: ApplyControls()
• Blueprint: 🔵 Callable

GetActuators

Returns an array of all UMjActuator components on this articulation.

• Signature: GetActuators()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjActuator*>

GetJoints

Returns an array of all UMjJoint components on this articulation.

• Signature: GetJoints()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjJoint*>

GetSensors

Returns an array of all UMjSensor components on this articulation.

• Signature: GetSensors()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjSensor*>

GetBodies

Returns an array of all UMjBody components on this articulation.

• Signature: GetBodies()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjBody*>

GetFrames

Returns an array of all UMjFrame components on this articulation.

• Signature: GetFrames()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjFrame*>

GetGeoms

Returns an array of all UMjGeom components on this articulation.

• Signature: GetGeoms()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjGeom*>

GetActuatorNames

Returns the UE component names of all actuators on this articulation.

• Signature: GetActuatorNames()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray

GetJointNames

Returns the UE component names of all joints on this articulation.

• Signature: GetJointNames()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray

GetSensorNames

Returns the UE component names of all sensors on this articulation.

• Signature: GetSensorNames()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray

GetBodyNames

Returns the UE component names of all MjBody components on this articulation.

• Signature: GetBodyNames()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray

GetActuator

Gets the UMjActuator component by its UE component name. Returns nullptr if not found.

• Signature: GetActuator(const FString& Name)
• Blueprint: 🔵 Callable
• Returns: UMjActuator*

GetJoint

Gets the UMjJoint component by its UE component name. Returns nullptr if not found.

• Signature: GetJoint(const FString& Name)
• Blueprint: 🔵 Callable
• Returns: UMjJoint*

GetSensor

Gets the UMjSensor component by its UE component name. Returns nullptr if not found.

• Signature: GetSensor(const FString& Name)
• Blueprint: 🔵 Callable
• Returns: UMjSensor*

GetBody

Gets the UMjBody component by its UE component name. Returns nullptr if not found.

• Signature: GetBody(const FString& Name)
• Blueprint: 🔵 Callable
• Returns: UMjBody*

GetTendons

Returns an array of all UMjTendon components on this articulation.

• Signature: GetTendons()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjTendon*>

GetTendonNames

Returns the UE component names of all tendons on this articulation.

• Signature: GetTendonNames()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray

GetTendon

Gets the UMjTendon component by its UE component name. Returns nullptr if not found.

• Signature: GetTendon(const FString& Name)
• Blueprint: 🔵 Callable
• Returns: UMjTendon*

GetEqualities

Returns an array of all UMjEquality components on this articulation.

• Signature: GetEqualities()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjEquality*>

GetKeyframes

Returns an array of all UMjKeyframe components on this articulation.

• Signature: GetKeyframes()
• Blueprint: 🔵 Callable 💎 Pure
• Returns: TArray<UMjKeyframe*>

GetBodyByMjId

Gets a UMjBody component by its MuJoCo Body ID.

• Signature: GetBodyByMjId(int32 id)
• Blueprint: 🔵 Callable
• Returns: UMjBody*

GetGeomByMjId

Gets a UMjGeom component by its MuJoCo Geom ID.

• Signature: GetGeomByMjId(int32 id)
• Blueprint: 🔵 Callable
• Returns: UMjGeom*

MuJoCo|Runtime|Actuators

Function	Returns	Description
SetActuatorControl()	bool	Sets a single actuator's control value by component name. Returns false if not found.
GetActuatorRange()	FVector2D	Gets an actuator's control range [min, max] by component name.

SetActuatorControl

Sets a single actuator's control value by component name. Returns false if not found.

• Signature: SetActuatorControl(const FString& ActuatorName, float Value)
• Blueprint: 🔵 Callable
• Returns: bool

GetActuatorRange

Gets an actuator's control range [min, max] by component name.

• Signature: GetActuatorRange(const FString& ActuatorName)
• Blueprint: 🔵 Callable
• Returns: FVector2D

MuJoCo|Runtime|Joints

Function	Returns	Description
GetJointAngle()	float	Gets a joint's position (qpos) by component name. Returns 0 if not found.

GetJointAngle

Gets a joint's position (qpos) by component name. Returns 0 if not found.

• Signature: GetJointAngle(const FString& JointName)
• Blueprint: 🔵 Callable
• Returns: float

MuJoCo|Runtime|Sensors

Function	Returns	Description
GetSensorScalar()	float	Gets a sensor's scalar reading by component name. Returns 0 if not found.
GetSensorReading()	TArray<float>	Gets a sensor's full reading array by component name. Returns empty if not found.

GetSensorScalar

Gets a sensor's scalar reading by component name. Returns 0 if not found.

• Signature: GetSensorScalar(const FString& SensorName)
• Blueprint: 🔵 Callable
• Returns: float

GetSensorReading

Gets a sensor's full reading array by component name. Returns empty if not found.

• Signature: GetSensorReading(const FString& SensorName)
• Blueprint: 🔵 Callable
• Returns: TArray

MuJoCo|Sleep

Function	Returns	Description
WakeAll()	void	Wakes all bodies in this articulation (MuJoCo 3.4+).
SleepAll()	void	Forces all bodies in this articulation to sleep (MuJoCo 3.4+).

WakeAll

Wakes all bodies in this articulation (MuJoCo 3.4+).

• Signature: WakeAll()
• Blueprint: 🔵 Callable

SleepAll

Forces all bodies in this articulation to sleep (MuJoCo 3.4+).

• Signature: SleepAll()
• Blueprint: 🔵 Callable

MuJoCo|Validation

Function	Returns	Description
ValidateSpec()	void	Validates the articulation's MuJoCo spec by attempting a temporary compile.

ValidateSpec

Validates the articulation's MuJoCo spec by attempting a temporary compile.

• Signature: ValidateSpec()
• Blueprint: 🔵 Callable 🔧 CallInEditor

MuJoCo|Visuals

Function	Returns	Description
ToggleGroup3Visibility()	void	Editor button to toggle Group 3 visibility.

ToggleGroup3Visibility

Editor button to toggle Group 3 visibility.

• Signature: ToggleGroup3Visibility()
• Blueprint: 🔧 CallInEditor

Protected Functions

General

Function	Returns	Description
EndPlay()	void	Called when the game ends or actor is destroyed.
SetupPlayerInputComponent()	void	Binds twist controller input when possessed.

EndPlay

Called when the game ends or actor is destroyed.

• Signature: EndPlay(const EEndPlayReason::Type EndPlayReason)

SetupPlayerInputComponent

Binds twist controller input when possessed.

• Signature: SetupPlayerInputComponent(UInputComponent* PlayerInputComponent)