() {
        t.anim_step_forward();
    }, this.interval);
  }

  Animation.prototype.reverse_animation = function()
  {
    this.pause_animation();
    this.direction = -1;
    var t = this;
    if (!this.timer) this.timer = setInterval(function() {
        t.anim_step_reverse();
    }, this.interval);
  }
</script>
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