Games require tweening visual properties in order to be appealing. Korge provides a simple, yet powerful interface for creating tweens.

Simple interface

View has an extension method called View.tween that allows you to do the magic. And has the following definition:

suspend fun View?.tween(vararg vs: V2<*>, time: Int, easing: Easing = Easing.LINEAR, callback: (Double) -> Unit = { })

You have to use bound callable references to define properties that will change. And Korge provides some extension methods to bound callable references to generate tween parameters.

If you want to linearly interpolate view.x from 10.0 to 100.0 in one second you would write:

view.tween(view::x[10.0, 100.0], time = 1000)

Interpolating Colors

Since in KorGE 1.0 (until project valhalla is available), colors are represented as RGBA Integers. Which are not directly interpolable. KorGE provides an extension method V2.color():V2 to decorate interpolation with a color interpolation. You can use it:

view.tween(view::colorMul[Colors.WHITE, Colors.RED].color(), time = 1000)

delay + duration + easing

You can control the start time, duration and easing per interpolated property. Using theesee V2 extensions:

V2.delay(timeMs:Int):V2, V2.duration(timeMs:Int):V2, V2.easing(easing:Easing):V2

  view::y[0.0, 200.0].delay(50),
  time = 1000

Implementation details

The tween execution will be attached as a component to the receiver View that holds the tween method. That means that the view has to be in the stage or be manually updated. Also means that any View.speed changes in that view or ancestors will affect the tween.

PRO Tip: You can even interpolate the View.speed property to get some cool time effects.


Korge provides an Easing class with the most common easings. And allows you to create your own easings.

  • Easings.LINEAR
  • Easings.EASE_IN
  • Easings.EASE_OUT
  • Easings.EASE_IN_OUT
  • Easings.EASE_OUT_IN
  • Easings.EASE_IN_BACK
  • Easings.EASE_OUT_BACK
  • Easings.EASE_IN_OUT_BACK
  • Easings.EASE_OUT_IN_BACK
  • Easings.EASE_IN_BOUNCE
  • Easings.EASE_IN_QUAD
  • Easings.EASE_OUT_QUAD
  • Easings.EASE_IN_OUT_QUAD

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