How to use InterpEaseIn method?

Development Programming & Scripting
1

I’m familiar with the FMath::FInterpTo method. It works as expected here:

void AMyCharacter::Tick(float DeltaSeconds) {

    Result = FMath::FInterpTo(Result, 0, DeltaSeconds, 20.0f);
    Super::Tick(DeltaSeconds);

}

However, FInterpTo applies an “ease out”.

Instead, I would like an “ease in”. So I want to use FMath::InterpEaseIn which should do just that.

I tried using it like this:

void AMyCharacter::Tick(float DeltaSeconds) {

    Result = FMath::InterpEaseIn<float>(Result, 0, DeltaSeconds, 90.0f);
    Super::Tick(DeltaSeconds);

}

But this literally doesn’t do anything; Result is never changed.

How do I correctly apply an “ease in” interpolation?

2

Your issue here is you are using DeltaSeconds where it should be an alpha. The alpha here is a value between 0 and 1, at 1 the float will be a max, at 0 it will be at the starting value. If you want for example the item to reach the end point in 1 second, rather than passing in Delta seconds pass in a value that is incremented by DaltaSeconds each run of the Tick. For example:

void AMyCharacter::Tick(float DeltaSeconds) {
 
     float secondsToFinish = 1.0f;
     Alpha += (DeltaSeconds / secondsToFinish);

     Result = FMath::InterpEaseIn<float>(Result, 0, Alpha, 90.0f);
     Super::Tick(DeltaSeconds);
 
 }

In the above change the secondsToFinish value to increase the amount of time the Interp will take to get to the end.

3

Robert Penner equations are awesome :

float Elastic::easeOut(float t,float b , float c, float d) {
	if (t==0) return b;  if ((t/=d)==1) return b+c;  
	float p=d*.3f;
	float a=c; 
	float s=p/4;
	return (a*pow(2,-10*t) * sin( (t*d-s)*(2*PI)/p ) + c + b);	
}

t is time, d is duration, c is the offset, b is initial value