label.go
func (l *Label) SetText(format string, args ...interface{}) {
	l.text = fmt.Sprintf(format, args...)
}
func (l *Label) SetText(format string, args ...interface{}) {
	l.text = fmt.Sprintf(format, args...)
}
// SetText sets the label caption.  This will not be displayed immediately.
// SetText shall be called from queue context.