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commonMain.io.nacular.doodle.animation.transition.Cubic.kt Maven / Gradle / Ivy
package io.nacular.doodle.animation.transition
import io.nacular.doodle.animation.Moment
import io.nacular.doodle.animation.Velocity
import io.nacular.measured.units.Measure
import io.nacular.measured.units.Time
import io.nacular.measured.units.Units
import io.nacular.measured.units.div
import io.nacular.measured.units.times
import kotlin.math.pow
/**
* Created by Nicholas Eddy on 10/29/18.
*/
public class Cubic(private val duration: Measure, private val endValue: Measure, private val endVelocity: Measure>): Transition {
private val deltaTime = duration * 0.1
override fun value(initial: Moment, timeOffset: Measure): Moment {
val t = timeOffset / duration
val p0 = initial.position
val p1 = p0 + deltaTime * initial.velocity
val p2 = endValue - deltaTime * endVelocity
val p3 = endValue
val points = listOf(p0, p1, p2, p3)
var result = 0 * points[0]
val n = points.size - 1
points.forEachIndexed { i, point ->
val bin = (n choose i) * (1-t).pow(n-i) * t.pow(i)
result += bin * point
}
return Moment(result, endVelocity) // FIXME: Calculate instantaneous velocity
}
override fun duration(initial: Moment): Measure = duration
override fun endState(initial: Moment): Moment = Moment(endValue, endVelocity)
// TODO: Is there a faster way?
private infix fun Int.choose(value: Int): Int {
var coefficient = 1
for (x in this - value + 1..this ) { coefficient *= x }
for (x in 1..value) { coefficient /= x }
return coefficient
}
// fun fromX(x: Double, x1: T, x2: T, y1: T, y2: T): T {
//// if (mX1 == mY1 && mX2 == mY2) return aX // linear
// return calcBezier(tForX(x, x1, x2), y1, y2)
// }
//
// fun A(a1: T, a2: T) = 1 - 3 * a2 + 3 * a1
// fun B(a1: T, a2: T) = 3 * a2 - 6 * a1
// fun C(a1: T ) = 3 * a1
//
// // Returns x(t) given t, x1, and x2, or y(t) given t, y1, and y2.
// fun calcBezier(t: Double, a1: T, a2: T) = ((A(a1, a2)*t + B(a1, a2))*t + C(a1))*t
//
// // Returns dx/dt given t, x1, and x2, or dy/dt given t, y1, and y2.
// fun slope(t: Double, a1: T, a2: T) = 3 * A(a1, a2) * t * t + 2 * B(a1, a2) * t + C(a1)
//
// fun tForX(x: Double, x1: T, x2: T): Double {
// // Newton raphson iteration
// var guessT = x
//
// for (i in 0..4) {
// val currentSlope = slope(guessT, x1, x2)
// if (currentSlope == 0.0) return guessT
// val currentX = calcBezier(guessT, x1, x2) - x
// guessT -= currentX / currentSlope
// }
//
// return guessT
// }
}
