Interpolation

Commonly known as tweening, interpolation is useful for generating values between two discrete end points using various curve functions. Often used with key-framed animation, interpolation allows an animator to specify a sparse collection of explicit frames for an animation and then generate a smooth transition between these frames computationally. The simplest form of interpolation is linear interpolation such as that available directly in the Vector2 (code) and Vector3 (code) classes. The Interpolation (code) class provides more interesting results by using non-linear curve functions to interpolate values.

Types of Interpolation

These are the basic built-in types of interpolation:

• Bounce
• Circle
• Elastic
• Exponential
• Fade
• Power
• Sine
• Swing

Code Example

// Written in Kotlin
val easAlpha:Interpolation = Interpolation.fade
val lifeTime:Int = 2
var elapsed:Float = 0f
..
fun update(delta:Float)
{
    elapsed += delta
    val progress = Math.min(1f, elapsed/lifeTime)   // 0 -> 1 
    val alpha = easAlpha.apply(progress)
}

Most types offer three varieties which bias towards one or the other or both ends of the curve creating an easing in or out of the animation.

See InterpolationTest for a visual display of each interpolation.

Visual display of interpolations

bounce	bounceIn	bounceOut	circle
circleIn	circleOut	elastic	elasticIn
elasticOut	exp5	exp5In	exp5Out
exp10	exp10In	exp10Out	fade
fastSlow	linear	pow2	pow2In
pow2InInverse	pow2Out	pow2OutInverse	pow3
pow3In	pow3InInverse	pow3Out	pow3OutInverse
pow4	pow4In	pow4Out	pow5
pow5In	pow5Out	sine	sineIn
sineOut	slowFast	smooth	smooth2
smoother	swing	swingIn	swingOut