code: func (g *Gui) SetRune(x, y int, ch rune, fgColor, bgColor Attribute) error {
  	if x < 0 || y < 0 || x >= g.maxX || y >= g.maxY {
  		return errors.New("invalid point")
  	}
  	termbox.SetCell(x, y, ch, termbox.Attribute(fgColor), termbox.Attribute(bgColor))
  	return nil
  }
docs: // SetRune writes a rune at the given point, relative to the top-left
  // corner of the terminal. It checks if the position is valid and applies
  // the given colors.