Robert Penner's Easing Functions in Kotlin

Kotlin implementation of the well-known easing functions from Robert Penner.

Usage

Include the library in your build:

allprojects {
    repositories {
        ...
        maven { url 'https://jitpack.io' }
    }
}

dependencies {
    implementation 'com.github.imeszaros:easing-kotlin:v0.1'
}

The EasingFunction interface

The EasingFunction interface defines a single abstract function that maps a Double in the range 0..1 to an 'eased' value - usually also closely in the range 0..1 (some styles may map outside, e.g. Back, Elastic):

interface EasingFunction {

    fun ease(time: Double): Double
    fun ease(time: Double, begin: Double, change: Double, duration: Double) = change * ease(time / duration) + begin
}

The second function makes it possible to ease a value specifying an elapsed time, a begin value, a change value and a duration to get an appropriately mapped value back.

The Easing interface

The Easing interface defines three easing functions for each easing style:

sealed interface Easing {

    val easeIn: EasingFunction
    val easeOut: EasingFunction
    val easeInOut: EasingFunction
}

Calling

To call an easing function, simply address it by the easing style, select the easing function and call one of its methods according to your needs:

fun main() {
    val eased1 = Linear.easeIn.ease(.5) // .5
    val eased2 = Linear.easeIn.ease(500.0, 120.0, 120.0, 1000.0) // 180, halfway between 120 and 240
}

Available easing styles

Back
Bounce
Circ
Cubic
Elastic
Expo
Linear
Quad
Quart
Quint
Sine