// acc is number between -1 and 1 ( -1 full decelerated, 1 full accelerated, 0 linear, i.e. no acceleration)

dynObj.prototype.slideTo = function (destX,destY,slideDur,acc,endFn) {
  if (!document.getElementById) return;
  this.slideDur = slideDur || .0001; var acc = -acc || 0;
  if (endFn) this.onSlideEnd = endFn;
  if (destX == null) this.destX = this.x;				// hold destination values (check for movement on 1 axis only)
    else this.destX = destX;
  if (destY == null) this.destY = this.y;
    else this.destY = destY;
  this.startX = this.x;
  this.startY = this.y;
  this.st = new Date().getTime();
  this.xc1 = this.x + ( (1+acc) * (this.destX-this.x)/3 );		// control points for bezier-controlled slide
  this.xc2 = this.x + ( (2+acc) * (this.destX-this.x)/3 );
  this.yc1 = this.y + ( (1+acc) * (this.destY-this.y)/3 );
  this.yc2 = this.y + ( (2+acc) * (this.destY-this.y)/3 );
  this.sliding = true;
  this.onSlideStart();
  dw_Animation.add(this.animString + ".doSlide()");
}

dynObj.prototype.doSlide = function() {
  if (!this.sliding) return;
  var elapsed = new Date().getTime() - this.st;
  if (elapsed < this.slideDur) {
    var x = dw_Bezier.getValue(elapsed/this.slideDur, this.startX, this.destX, this.xc1, this.xc2);
    var y = dw_Bezier.getValue(elapsed/this.slideDur, this.startY, this.destY, this.yc1, this.yc2);
    this.shiftTo( Math.round(x) ,Math.round(y) );
    this.onSlide();
  } else {								// if time's up
  dw_Animation.remove(this.animString + ".doSlide()");
  this.shiftTo(this.destX,this.destY);
  this.onSlide();
  this.sliding = false;
  this.onSlideEnd();
}}

dynObj.prototype.slideBy = function(dx,dy,slideDur,acc,endFn) {
  var destX=this.x+dx; var destY=this.y+dy;
  this.slideTo(destX,destY,slideDur,acc,endFn);
}

dynObj.prototype.onSlideStart = function () {}
dynObj.prototype.onSlide = function () {}
dynObj.prototype.onSlideEnd = function () { if (this.el) this.el = null; }