code: func (v *ViewPort) ValidateViewX() {
  	if v.viewx >= v.limx-v.width {
  		v.viewx = (v.limx - v.width)
  	}
  	if v.viewx < 0 {
  		v.viewx = 0
  	}
  }
docs: // ValidateViewX ensures that the X offset of the view port is limited so that
  // it cannot scroll away from the content.