Easing functions from easings.net implemented for Unreal Engine

_StevesEaseMath_License.txt

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StevesEaseMath.cpp

#include "StevesEaseMath.h"

float UStevesEaseMath::EaseAlpha(float InAlpha, EStevesEaseFunction Func)
{
	constexpr float BackC1 = 1.70158f;
	constexpr float BackC2 = BackC1 * 1.525f;
	constexpr float BackC3 = BackC1 + 1.f;
	constexpr float ElasticC4 = UE_TWO_PI / 3.f;
	constexpr float ElasticC5 = UE_TWO_PI / 4.5;

	switch(Func)
	{
	default:
	case EStevesEaseFunction::Linear:
		return InAlpha;
	case EStevesEaseFunction::EaseIn_Sine:
		return 1.f - FMath::Cos(InAlpha * UE_HALF_PI);
	case EStevesEaseFunction::EaseOut_Sine:
		return FMath::Sin(InAlpha * UE_HALF_PI);
	case EStevesEaseFunction::EaseInOut_Sine:
		return -(FMath::Cos(UE_PI * InAlpha) - 1.f) / 2.f;
	case EStevesEaseFunction::EaseIn_Quad:
		return InAlpha*InAlpha;
	case EStevesEaseFunction::EaseOut_Quad:
		return 1.f - (1.f - InAlpha) * (1.f - InAlpha);
	case EStevesEaseFunction::EaseInOut_Quad:
		return InAlpha < 0.5f ? 2.f * InAlpha * InAlpha : 1.f - FMath::Pow(-2.f * InAlpha + 2.f, 2.f) / 2.f;
	case EStevesEaseFunction::EaseIn_Cubic:
		return FMath::Pow(InAlpha, 3);
	case EStevesEaseFunction::EaseOut_Cubic:
		return 1.f - FMath::Pow(1.f - InAlpha, 3);
	case EStevesEaseFunction::EaseInOut_Cubic:
		return InAlpha < 0.5f ? 4.f * FMath::Pow(InAlpha, 3) : 1.f - FMath::Pow(-2.f * InAlpha + 2.f, 3) / 2.f;
	case EStevesEaseFunction::EaseIn_Quart:
		return FMath::Pow(InAlpha, 4);
	case EStevesEaseFunction::EaseOut_Quart:
		return 1 - FMath::Pow(1.f - InAlpha, 4.f);
	case EStevesEaseFunction::EaseInOut_Quart:
		return InAlpha < 0.5f ? 8.f * FMath::Pow(InAlpha, 4) : 1.f - FMath::Pow(-2.f * InAlpha + 2.f, 4) / 2.f;
	case EStevesEaseFunction::EaseIn_Quint:
		return FMath::Pow(InAlpha, 5);
	case EStevesEaseFunction::EaseOut_Quint:
		return 1 - FMath::Pow(1.f - InAlpha, 5);
	case EStevesEaseFunction::EaseInOut_Quint:
		return InAlpha < 0.5f ? 16.f * FMath::Pow(InAlpha, 5) : 1.f - FMath::Pow(-2.f * InAlpha + 2.f, 5) / 2.f;
	case EStevesEaseFunction::EaseIn_Expo:
		return InAlpha <= 0 ? 0 : FMath::Pow(2.f, 10.f * InAlpha - 10.f);
	case EStevesEaseFunction::EaseOut_Expo:
		return InAlpha >= 1.f ? 1.f : 1.f - FMath::Pow(2.f, -10.f * InAlpha);
	case EStevesEaseFunction::EaseInOut_Expo:
		if (InAlpha <= 0.f)
			return 0;
		if (InAlpha >= 1.f)
			return 1;
		return InAlpha < 0.5f
			       ? FMath::Pow(2.f, 20.f * InAlpha - 10.f) / 2.f
			       : (2.f - FMath::Pow(2.f, -20.f * InAlpha + 10.f)) / 2.f;
	case EStevesEaseFunction::EaseIn_Circ:
		return 1.f - FMath::Sqrt(1.f - FMath::Pow(InAlpha, 2));
	case EStevesEaseFunction::EaseOut_Circ:
		return FMath::Sqrt(1.f - FMath::Pow(InAlpha - 1.f, 2));
	case EStevesEaseFunction::EaseInOut_Circ:
		return InAlpha < 0.5f
			       ? (1.f - FMath::Sqrt(1.f - FMath::Pow(2.f * InAlpha, 2))) / 2.f
			       : (FMath::Sqrt(1.f - FMath::Pow(-2.f * InAlpha + 2.f, 2)) + 1.f) / 2.f;
	case EStevesEaseFunction::EaseIn_Back:
		return BackC3 * FMath::Pow(InAlpha, 3) - BackC1 * InAlpha * InAlpha;
	case EStevesEaseFunction::EaseOut_Back:
		return 1.f + BackC3 * FMath::Pow(InAlpha - 1.f, 3) + BackC1 * FMath::Pow(InAlpha - 1.f, 2.f);
	case EStevesEaseFunction::EaseInOut_Back:
		return InAlpha < 0.5f
			       ? (FMath::Pow(2.f * InAlpha, 2) * ((BackC2 + 1.f) * 2.f * InAlpha - BackC2)) / 2.f
			       : (FMath::Pow(2.f * InAlpha - 2.f, 2) * ((BackC2 + 1) * (InAlpha * 2.f - 2.f) + BackC2) + 2.f) / 2.f;
	case EStevesEaseFunction::EaseIn_Elastic:
		if (InAlpha <= 0.f)
			return 0;

		if (InAlpha >= 1.f)
			return 1;
		return -FMath::Pow(2.f, 10.f * InAlpha - 10.f) * FMath::Sin((InAlpha * 10.f - 10.75f) * ElasticC4);
	case EStevesEaseFunction::EaseOut_Elastic:
		if (InAlpha <= 0.f)
			return 0;
		if (InAlpha >= 1.f)
			return 1;
		return FMath::Pow(2.f, -10.f * InAlpha) * FMath::Sin((InAlpha * 10.f - 0.75f) * ElasticC4) + 1.f;
	case EStevesEaseFunction::EaseInOut_Elastic:
		if (InAlpha <= 0.f)
			return 0;
		if (InAlpha >= 1.f)
			return 1;
		return InAlpha < 0.5f
			       ? -(FMath::Pow(2.f, 20.f * InAlpha - 10.f) * FMath::Sin((20.f * InAlpha - 11.125f) * ElasticC5)) /
			       2.f
			       : (FMath::Pow(2.f, -20.f * InAlpha + 10.f) * FMath::Sin((20.f * InAlpha - 11.125f) * ElasticC5)) /
			       2.f + 1.f;
	case EStevesEaseFunction::EaseIn_Bounce:
		return 1 - EaseAlpha(1 - InAlpha, EStevesEaseFunction::EaseOut_Bounce);
	case EStevesEaseFunction::EaseOut_Bounce:
		{
			constexpr float n1 = 7.5625f;
			constexpr float d1 = 2.75f;

			if (InAlpha < 1.f / d1) { return n1 * InAlpha * InAlpha; }
			else if (InAlpha < 2.f / d1) { return n1 * (InAlpha -= 1.5f / d1) * InAlpha + 0.75f; }
			else if (InAlpha < 2.5f / d1) { return n1 * (InAlpha -= 2.25f / d1) * InAlpha + 0.9375f; }
			else { return n1 * (InAlpha -= 2.625f / d1) * InAlpha + 0.984375f; }
		}
	case EStevesEaseFunction::EaseInOut_Bounce:
		return InAlpha < 0.5f
			       ? (1.f - EaseAlpha(1.f - 2.f * InAlpha, EStevesEaseFunction::EaseOut_Bounce)) / 2.f
			       : (1.f + EaseAlpha(2.f * InAlpha - 1.f, EStevesEaseFunction::EaseOut_Bounce)) / 2.f;
	}
}

StevesEaseMath.h

#pragma once

#include "CoreMinimal.h"
#include "StevesEaseMath.generated.h"

/// Easing functions
/// See https://easings.net/
/// Could have used UE EEasingFunc but it's missing some nice options like back/elastic 
UENUM(BlueprintType)
enum class EStevesEaseFunction : uint8
{
	Linear,
	EaseIn_Sine,
	EaseOut_Sine,
	EaseInOut_Sine,
	EaseIn_Quad,
	EaseOut_Quad,
	EaseInOut_Quad,
	EaseIn_Cubic,
	EaseOut_Cubic,
	EaseInOut_Cubic,
	EaseIn_Quart,
	EaseOut_Quart,
	EaseInOut_Quart,
	EaseIn_Quint,
	EaseOut_Quint,
	EaseInOut_Quint,
	EaseIn_Expo,
	EaseOut_Expo,
	EaseInOut_Expo,
	EaseIn_Circ,
	EaseOut_Circ,
	EaseInOut_Circ,
	EaseIn_Back,
	EaseOut_Back,
	EaseInOut_Back,
	EaseIn_Elastic,
	EaseOut_Elastic,
	EaseInOut_Elastic,
	EaseIn_Bounce,
	EaseOut_Bounce,
	EaseInOut_Bounce
};

UCLASS()
class STEVESEASE_API StevesEaseMath : public UBlueprintFunctionLibrary
{
	GENERATED_BODY()

public:

	/**
	 * Convert a linear alpha value into an eased alpha value using an easing function 
	 * @param InAlpha The input linear alpha
	 * @param Func The easing function
	 * @return The eased version of the alpha
	 */
	UFUNCTION(BlueprintCallable, Category="StevesEaseMath")
	static float EaseAlpha(float InAlpha, EStevesEaseFunction Func);

	/**
	 * Interpolate with easing function support 
	 * @param A Input Value from
	 * @param B Input Value to
	 * @param Alpha Value between 0 and 1
	 * @param Func Easing function
	 * @return Interpolated value
	 */
	UFUNCTION(BlueprintCallable, Category="StevesEaseMath")
	static float EaseFloat(float A, float B, float Alpha, EStevesEaseFunction Func)
	{
		return A + EaseAlpha(Alpha, Func) * (B - A);
	}
	/**
	 * Interpolate with easing function support 
	 * @param A Input Value from
	 * @param B Input Value to
	 * @param Alpha Value between 0 and 1
	 * @param Func Easing function
	 * @return Interpolated value
	 */
	UFUNCTION(BlueprintCallable, Category="StevesEaseMath")
	static FVector EaseVector(const FVector& A, const FVector& B, float Alpha, EStevesEaseFunction Func)
	{
		return A + EaseAlpha(Alpha, Func) * (B - A);
	}
	/**
	 * Interpolate with easing function support 
	 * @param A Input Value from
	 * @param B Input Value to
	 * @param Alpha Value between 0 and 1
	 * @param Func Easing function
	 * @return Interpolated value
	 */
	UFUNCTION(BlueprintCallable, Category="StevesEaseMath")
	static FRotator EaseRotator(const FRotator& A, const FRotator& B, float Alpha, EStevesEaseFunction Func, bool bShortest)
	{
		if (bShortest)
			return EaseQuat(FQuat(A), FQuat(B), Alpha, Func).Rotator();

		return A + EaseAlpha(Alpha, Func) * (B - A);
	}
	/**
	 * Interpolate with easing function support 
	 * @param A Input Value from
	 * @param B Input Value to
	 * @param Alpha Value between 0 and 1
	 * @param Func Easing function
	 * @return Interpolated value
	 */
	UFUNCTION(BlueprintCallable, Category="StevesEaseMath")
	static FQuat EaseQuat(const FQuat& A, const FQuat& B, float Alpha, EStevesEaseFunction Func)
	{
		return FQuat::Slerp(A, B, EaseAlpha(Alpha, Func));
	}	
	/**
	 * Interpolate with easing function support 
	 * @param A Input Value from
	 * @param B Input Value to
	 * @param Alpha Value between 0 and 1
	 * @param Func Easing function
	 * @return Interpolated value
	 */
	UFUNCTION(BlueprintCallable, Category="StevesEaseMath")
	static FTransform EaseTransform(const FTransform& A, const FTransform& B, float Alpha, EStevesEaseFunction Func)
	{
		return FTransform(
			EaseQuat(A.GetRotation(), B.GetRotation(), Alpha, Func),
			EaseVector(A.GetLocation(), B.GetLocation(), Alpha, Func),
			EaseVector(A.GetScale3D(), B.GetScale3D(), Alpha, Func));
	}	
	
	
};