UKismetAnimationLibrary::K2_TwoBoneIK

function AnimGraphRuntime Blueprint Since 4.0

#include "KismetAnimationLibrary.h"

Access: public Specifiers: staticUFUNCTIONBlueprintPure

Description

Computes the joint and end positions for a two-bone IK chain (like an arm or leg) so it reaches toward an effector target, given an optional joint/pole target to control bend direction.

Caveats & Gotchas

• This is the pure math version of the Animation Blueprint "Two Bone IK" node — it computes positions only and does not itself modify a skeleton; you still need to feed OutJointPos/OutEndPos into a Transform (Modify) Bone node or equivalent.
• When bAllowStretching is false (the default), the chain simply clamps to its natural reach and will not extend to touch an effector that's further away than RootPos-to-EndPos length.
• JointTarget only influences bend direction (which side the elbow points), not the final joint position when the chain is fully stretched or fully compressed.

Signature

static void K2_TwoBoneIK(const FVector& RootPos, const FVector& JointPos, const FVector& EndPos, const FVector& JointTarget, const FVector& Effector, FVector& OutJointPos, FVector& OutEndPos, bool bAllowStretching, float StartStretchRatio, float MaxStretchScale)

Parameters

Name	Type	Description	Default
RootPos	const FVector&	Input root position of the two-bone chain.	—
JointPos	const FVector&	Input center (elbow) position of the two-bone chain.	—
EndPos	const FVector&	Input end (wrist) position of the two-bone chain.	—
JointTarget	const FVector&	The IK target the joint (elbow) should bend toward.	—
Effector	const FVector&	Position of the target effector for the end of the IK chain.	—
OutJointPos	FVector&	Outputs the resulting position for the center (elbow) joint.	—
OutEndPos	FVector&	Outputs the resulting position for the end (wrist) joint.	—
bAllowStretching	bool	If true, the bones are allowed to stretch beyond their rest length to reach the effector.	false
StartStretchRatio	float	The ratio at which the chain starts to stretch; higher values delay the onset of stretching.	1.0
MaxStretchScale	float	The maximum multiplier the chain's stretch can reach.	1.2

Return Type

void

Example

Compute an arm IK solve C++

FVector OutJointPos, OutEndPos;
UKismetAnimationLibrary::K2_TwoBoneIK(
    ShoulderPos, ElbowPos, WristPos,
    ElbowPoleTarget, HandEffectorTarget,
    OutJointPos, OutEndPos,
    false, 1.0f, 1.2f);

Version History

Introduced in: 4.0

Version	Status	Notes
5.6	stable	—

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