class kscroll
{
  float speed=0;
  float start;
  float decay;
  float decay_start;
  int decay_maxmillis=5000;

  // decrease scrolling speed once mouse is released
  float slowdown()
  {
    float d=0;
    // if there is still some scrolling energy
    if(this.decay>0)
    {
      //i tried a few slowing formulas
      this.decay=1-inverse(millis()-this.decay_start,this.decay_maxmillis);
      //this.decay=1-sigmoid(millis()-this.decay_start,this.decay_maxmillis);
      //this.decay=this.decay*.9;
      d=this.speed*this.decay;
    }
    return d;
  } //slowdown

  void begin(int x)
  {
    // the initial scrolling speed is the speed it was being dragged
    this.speed = x-this.start;
    this.start = x;
  } //begin

  void grab(int x)
  {
    // while grabbing is occuring, the scrolling link to mouse movement
    this.start = x;
    this.speed = 0;
  } //grab

  void startslowdown()
  {
    // the mouse has been released and we can start slowing the scroll
    // the speed starts at 100% of the current scroll speed
    // record the time so we can calualte the decay rate
    this.decay=1;
    this.decay_start=millis();
  } //startslodown
}//kdrag