code: func (b *Bound) Extend(point *Point) *Bound {
  
  	// already included, no big deal
  	if b.Contains(point) {
  		return b
  	}
  
  	b.sw.SetX(math.Min(b.sw.X(), point.X()))
  	b.ne.SetX(math.Max(b.ne.X(), point.X()))
  
  	b.sw.SetY(math.Min(b.sw.Y(), point.Y()))
  	b.ne.SetY(math.Max(b.ne.Y(), point.Y()))
  
  	return b
  }
docs: // Extend grows the bound to include the new point.