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wispborne/Easing.kt

Created October 6, 2022 14:44
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Methods for easing.
Raw
Easing.kt
package org.wisp.gatesawakened.jumping
/**
* Taken from <a href="https://github.com/mattdesl/cisc226game/blob/master/SpaceGame/src/space/engine/easing/Easing.java">Github</a>
*
* @author Robert Penner (functions)
* @author davedes (java port)
* @author Wisp (kotlin port)
*/
object Easing {
object Quadratic {
/**
* Quadratic easing in - accelerating from zero velocity.
*/
fun easeIn(time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float): Float {
return flipIfNeeded(time, valueAtStart, valueAtEnd, duration) { thyme, start, end, dur ->
var t = thyme
return@flipIfNeeded end * (run { t /= dur;t }) * t + start
}
}
/**
* Quadratic easing out - decelerating to zero velocity.
*/
fun easeOut(time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float): Float {
return flipIfNeeded(time, valueAtStart, valueAtEnd, duration) { thyme, start, end, dur ->
var t = thyme
return@flipIfNeeded -end * (run { t /= dur;t }) * (t - 2) + start
}
}
/**
* Quadratic easing in/out - acceleration until halfway, then deceleration
*/
fun easeInThenOut(time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float): Float {
return flipIfNeeded(time, valueAtStart, valueAtEnd, duration) { thyme, start, end, dur ->
var t = thyme
return@flipIfNeeded if ((run { t /= dur / 2;t }) < 1)
end / 2 * t * t + start;
else -end / 2 * ((--t) * (t - 2) - 1) + start;
}
}
}
object Linear {
/**
* Simple linear tweening - no easing.
*/
fun tween(time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float): Float {
return flipIfNeeded(time, valueAtStart, valueAtEnd, duration) { thyme, start, end, dur ->
return@flipIfNeeded end * thyme / dur + start
}
}
}
object Cubic {
/**
* Cubic easing in - accelerating from zero velocity.
*/
fun easeIn(time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float): Float {
return flipIfNeeded(time, valueAtStart, valueAtEnd, duration) { thyme, start, end, dur ->
var t = thyme
return@flipIfNeeded end * (run { t /= dur;t }) * t * t + start
}
}
/**
* Cubic easing out - decelerating to zero velocity.
*/
fun easeOut(time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float): Float {
return flipIfNeeded(time, valueAtStart, valueAtEnd, duration) { thyme, start, end, dur ->
var t = thyme
return@flipIfNeeded end * ((run { t = t / dur - 1;t }) * t * t + 1) + start;
}
}
/**
* Cubic easing in/out - acceleration until halfway, then deceleration
*/
fun easeInThenOut(time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float): Float {
return flipIfNeeded(time, valueAtStart, valueAtEnd, duration) { thyme, end, start, dur ->
var t = thyme
return@flipIfNeeded if ((run { t /= dur / 2;t }) < 1)
end / 2 * t * t * t + start
else end / 2 * ((run { t -= 2;t }) * t * t + 2) + start;
}
}
}
private fun flipIfNeeded(
time: Float,
valueAtStart: Float,
valueAtEnd: Float,
duration: Float,
easeFunction: (time: Float, valueAtStart: Float, valueAtEnd: Float, duration: Float) -> Float
): Float {
return if (valueAtStart > valueAtEnd) {
valueAtEnd - easeFunction(time, valueAtEnd, valueAtStart, duration)
} else {
easeFunction(time, valueAtStart, valueAtEnd, duration)
}
}
}
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