UKismetMathLibrary::Acos

function Engine Blueprint Since 4.0

#include "Kismet/KismetMathLibrary.h"

Access: public Specifiers: staticUFUNCTIONBlueprintPure

Description

Returns the inverse cosine (arc cosine) of A in radians. The result is in the range [0, π].

Caveats & Gotchas

• Input must be clamped to [-1, 1]; passing a value outside this range returns NaN, which silently corrupts downstream calculations.
• The result is in radians — convert with RadiansToDegrees if you need degrees, and be aware that floating-point dot-product values may slightly exceed 1.0 due to precision errors, requiring a manual clamp before calling.

Signature

static UE_INL_API double Acos(double A);

Parameters

Name	Type	Description	Default
A	double	Value in the range [-1, 1] to compute the arc cosine of.	—

Return Type

double

Example

Angle between two unit vectors C++

FVector A = FVector(1, 0, 0);
FVector B = FVector(0, 1, 0);
double Dot = FVector::DotProduct(A, B);
double AngleRad = UKismetMathLibrary::Acos(FMath::Clamp(Dot, -1.0, 1.0));
double AngleDeg = UKismetMathLibrary::RadiansToDegrees(AngleRad); // 90.0

Version History

Introduced in: 4.0

Version	Status	Notes
5.6	stable	—

Feedback

Was this helpful?