UMjPerturbation

Mouse-driven body perturbation matching MuJoCo simulate's behaviour.

Input gestures (mirrored from upstream simulate): - Double-click LMB on a body → select (no force applied). - Ctrl + RMB drag with selection → translate (virtual position spring). - Ctrl + LMB drag with selection → rotate (virtual orientation spring). - Release button → stop drag; selection persists. Uses MuJoCo's own mjv_applyPerturbForce every physics pre-step to convert refpos/refquat/refselpos into xfrc_applied — identical spring feel to simulate. The plugin-side code only has to manage the reference positions/orientations from UE mouse input.

Attribute	Value
Kind	Class
UE Macro	UCLASS
Inherits	UActorComponent
Blueprint Spawnable	✅ Yes

Properties Functions

Properties

Private Properties

Property	Type	Description
Manager	AAMjManager*	Cached manager (owner).
ClickHitWorldUE	FVector	Click-time state used to re-derive refpos each frame.

Manager

Cached manager (owner).

• Type: AAMjManager*

ClickHitWorldUE

Click-time state used to re-derive refpos each frame.

• Type: FVector

Functions

Public Functions

General

Function	Returns	Description
HandleSelect()	void	Line-trace from the cursor and, if a body is hit, latch selection.
StartTranslate()	void	Begin a translate drag (Ctrl+RMB press with a body selected).
StartRotate()	void	Begin a rotate drag (Ctrl+LMB press with a body selected).
UpdateDrag()	void	Update drag refpos/refselpos/refquat from current cursor + per-frame
StopDrag()	void	Stop the current drag (mouse release). Selection persists.
HasSelection()	bool	Is a body currently latched (pert.select > 0)?
IsDragging()	bool	Is a drag currently active (LMB/RMB held)?

HandleSelect

Line-trace from the cursor and, if a body is hit, latch selection.

• Signature: HandleSelect(const FVector& CursorOrigin, const FVector& CursorDirection)

StartTranslate

Begin a translate drag (Ctrl+RMB press with a body selected).

• Signature: StartTranslate(const FVector& CursorOrigin, const FVector& CursorDirection)

StartRotate

Begin a rotate drag (Ctrl+LMB press with a body selected).

• Signature: StartRotate()

UpdateDrag

Update drag refpos/refselpos/refquat from current cursor + per-frame

• Signature: UpdateDrag(const FVector& CursorOrigin, const FVector& CursorDirection, float MouseDx, float MouseDy)

StopDrag

Stop the current drag (mouse release). Selection persists.

• Signature: StopDrag()

HasSelection

Is a body currently latched (pert.select > 0)?

• Signature: HasSelection()
• Returns: bool

IsDragging

Is a drag currently active (LMB/RMB held)?

• Signature: IsDragging()
• Returns: bool

Private Functions

General

Function	Returns	Description
ResolveBodyIdFromActor()	int32	Resolve a hit actor to a MuJoCo body_id. Returns <=0 if no match.
DrawDebugSpring()	void	Draw a debug line from the world selection point to the ref target.

ResolveBodyIdFromActor

Resolve a hit actor to a MuJoCo body_id. Returns <=0 if no match.

• Signature: ResolveBodyIdFromActor(const class AActor* Actor, const FVector& HitWorldUE)
• Returns: int32

DrawDebugSpring

Draw a debug line from the world selection point to the ref target.

• Signature: DrawDebugSpring()