EnvelopeInterpolation.scala

import de.sciss.kollflitz.Vec
import de.sciss.kollflitz.Ops._

case class Segment(numFrames: Int, targetLevel: Double, curve: Curve = Curve.linear) {
  require (numFrames > 0)
}

object Envelope {
  implicit def constant(f: Double): Envelope = Envelope(f, Vector.empty)
}
case class Envelope(startLevel: Double, segments: Vec[Segment]) {
  private[this] val pairs = (Segment(numFrames = 1, targetLevel = startLevel) +: segments).mapPairs { (s1, s2) =>
    s1.targetLevel -> s2
  }

  /* private[this] */ val frameAccum = {
    (0 +: segments.map(_.numFrames)).integrate.toArray
  }

  /* private[this] */ val numFrames   = if (frameAccum.isEmpty) 0           else frameAccum.last
  /* private[this] */ val lastLevel   = if (segments  .isEmpty) startLevel  else segments.last.targetLevel

  def levelAt(frame: Int): Double = {
    if (frame <= 0) startLevel else if (frame >= numFrames) lastLevel
    else {
      val i = java.util.Arrays.binarySearch(frameAccum, frame)
      val j = if (i < 0) -(i + 2) else i
      println(s"i = $i, j = $j, pairs.size = ${pairs.size}, frameAccum.size = ${frameAccum.size}")
      val (startLevel, seg) = pairs(j)
      val pos = (frame - frameAccum(j)).toDouble / seg.numFrames
      seg.curve.levelAt(pos = pos.toFloat, y1 = startLevel.toFloat, y2 = seg.targetLevel.toFloat)
    }
  }
}

val e1 = 3.4: Envelope
e1.levelAt(-1)
e1.levelAt(0)
e1.levelAt(1)

val e2 = Envelope(3.4, Vector(Segment(1000, 4.0)))
e2.levelAt(-1)
e2.levelAt(0)
e2.levelAt(1)
e2.levelAt(999)
e2.levelAt(1000)
e2.levelAt(1001)