Animation Curves Blended by Montage?

Development Character & Animation
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4

It’s really an old post, but I went into this issue recently. Hope my solution can help others.

Using the workaround provided by @SteveProteau can be a bit inconvenient, and it does not support blending values between curves if multiple montages have curves with the same name. For instance, if you have two montages, A and B, active at the same time, and both of them have a curve X, you might want to get a blended result of curve X that respects the values provided by both A and B.

Here is my solution, you need to implement a custom anim instance like this:

UCLASS(Config = Game)
class UMyAnimInstance : public UAnimInstance
{
	GENERATED_BODY()

public:
	UMyAnimInstance(const FObjectInitializer& ObjectInitializer);

	// keep montage curve value when blending in/out
	UFUNCTION(BlueprintCallable, BlueprintPure = false)
	float GetFadelessCurveValue(FName CurveName) const;
	bool GetFadelessCurveValue(FName CurveName, float& OutValue) const;
};

float UMyAnimInstance::GetFadelessCurveValue(FName const CurveName) const
{
	float Value = 0.f;
	GetFadelessCurveValue(CurveName, Value);
	return Value;
}

bool UMyAnimInstance::GetFadelessCurveValue(FName const CurveName, float& OutValue) const
{
	float TotalWeight{};
	TArray<TTuple<float, float>, TInlineAllocator<5>> CurvesWithWeight{};

	for (FAnimMontageInstance const* Instance : MontageInstances)
	{
		if (!Instance->Montage || !Instance->Montage->HasCurveData(CurveName))
		{
			continue;
		}

		float const Weight = Instance->GetWeight();
		float const Position = Instance->GetPosition();
		float const CurveValue = Instance->Montage->EvaluateCurveData(CurveName, Position);
		CurvesWithWeight.Emplace(CurveValue, Weight);
		TotalWeight += Weight;
	}

	if (TotalWeight <= 0 || FMath::IsNearlyZero(TotalWeight))
	{
		return false;
	}

	OutValue = 0.0f;
	for (auto const& [CurveValue, Weight] : CurvesWithWeight)
	{
		OutValue += CurveValue * Weight / TotalWeight;
	}

	return true;
}

Then you can get correct curve values by GetFadelessCurveValue function.

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