public MoveAnimation(Vector2 start, Vector2 end)
 {
     _start = start;
     _end   = end;
     _type  = MoveAnimationType.TWO_POINTS;
 }
 public MoveAnimation(Vector2 direction, Func <float, float, Vector2> function = null)
 {
     _direction = direction;
     _function  = function;
     _type      = MoveAnimationType.DIRECTION;
 }